Spring Integration Reference Manual


Mark Fisher, Marius Bogoevici, Iwein Fuld, Jonas Partner, Oleg Zhurakousky, Gary Russell, Dave Syer, Josh Long, David Turanski, Gunnar Hillert, Artem Bilan, Amol Nayak


Table of Contents

1. Requirements
1.1. Compatible Java Versions
1.2. Compatible Versions of the Spring Framework
2. Code Conventions
I. What's new?
1. What's new in Spring Integration 3.0?
1.1. New Components
1.1.1. HTTP Request Mapping
1.1.2. Spring Expression Language (SpEL) Configuration
1.1.3. SpEL Functions Support
1.1.4. SpEL PropertyAccessors Support
1.1.5. Redis: New Components
1.1.6. Header Channel Registry
1.1.7. MongoDB support: New ConfigurableMongoDbMessageStore
1.1.8. Syslog Support
1.1.9. 'Tail' Support
1.1.10. JMX Support
1.1.11. TCP/IP Connection Events and Connection Management
1.1.12. Inbound Channel Adapter Script Support
1.1.13. Content Enricher: Headers Enrichment Support
1.2. General Changes
1.2.1. Message ID Generation
1.2.2. <gateway> Changes
1.2.3. HTTP Endpoint Changes
1.2.4. Jackson Support (JSON)
1.2.5. Chain Elements 'id' Attribute
1.2.6. Aggregator 'empty-group-min-timeout' property
1.2.7. Persistent File List Filters (file, (S)FTP)
1.2.8. Scripting Support: Variables Changes
1.2.9. Direct Channel Load Balancing configuration
1.2.10. PublishSubscribeChannel Behavior
1.2.11. FTP, SFTP and FTPS Changes
1.2.12. 'requires-reply' Attribute for Outbound Gateways
1.2.13. AMQP Outbound Gateway Header Mapping
1.2.14. Stored Procedure Components Improvements
1.2.15. Web Service Outbound URI Configuration
1.2.16. Redis Adapter Changes
1.2.17. Advising Filters
1.2.18. Advising Endpoints using Annotations
1.2.19. ObjectToStringTransformer Improvements
1.2.20. JPA Support Changes
1.2.21. Delayer: delay expression
1.2.22. JDBC Message Store Improvements
1.2.23. IMAP Idle Connection Exceptions
1.2.24. Message Headers and TCP
1.2.25. JMS Message Driven Channel Adapter
1.2.26. RMI Inbound Gateway
1.2.27. XsltPayloadTransformer
II. Overview of Spring Integration Framework
2. Spring Integration Overview
2.1. Background
2.2. Goals and Principles
2.3. Main Components
2.3.1. Message
2.3.2. Message Channel
2.3.3. Message Endpoint
2.4. Message Endpoints
2.4.1. Transformer
2.4.2. Filter
2.4.3. Router
2.4.4. Splitter
2.4.5. Aggregator
2.4.6. Service Activator
2.4.7. Channel Adapter
III. Core Messaging
3. Messaging Channels
3.1. Message Channels
3.1.1. The MessageChannel Interface
3.1.2. Message Channel Implementations
Scoped Channel
3.1.3. Channel Interceptors
3.1.4. MessagingTemplate
3.1.5. Configuring Message Channels
DirectChannel Configuration
Datatype Channel Configuration
QueueChannel Configuration
PublishSubscribeChannel Configuration
PriorityChannel Configuration
RendezvousChannel Configuration
Scoped Channel Configuration
Channel Interceptor Configuration
Global Channel Interceptor
Wire Tap
Global Wire Tap Configuration
3.1.6. Special Channels
3.2. Poller (Polling Consumer)
3.3. Channel Adapter
3.3.1. Configuring An Inbound Channel Adapter
3.3.2. Configuring An Outbound Channel Adapter
3.3.3. Channel Adapter Expressions and Scripts
3.4. Messaging Bridge
3.4.1. Introduction
3.4.2. Configuring Bridge
4. Message Construction
4.1. Message
4.1.1. The Message Interface
4.1.2. Message Headers
Message ID Generation
4.1.3. Message Implementations
4.1.4. The MessageBuilder Helper Class
5. Message Routing
5.1. Routers
5.1.1. Overview
5.1.2. Common Router Parameters
Inside and Outside of a Chain
Top-Level (Outside of a Chain)
5.1.3. Router Implementations
XPath Router
Routing and Error handling
5.1.4. Configuring (Generic) Router
Configuring a Content Based Router with XML
Configuring a Router with Annotations
5.1.5. Dynamic Routers
Manage Router Mappings using the Control Bus
Manage Router Mappings using JMX
5.2. Filter
5.2.1. Introduction
5.2.2. Configuring Filter
Configuring a Filter with XML
Configuring a Filter with Annotations
5.3. Splitter
5.3.1. Introduction
5.3.2. Programming model
5.3.3. Configuring Splitter
Configuring a Splitter using XML
Configuring a Splitter with Annotations
5.4. Aggregator
5.4.1. Introduction
5.4.2. Functionality
5.4.3. Programming model
5.4.4. Configuring an Aggregator
Configuring an Aggregator with XML
Configuring an Aggregator with Annotations
5.4.5. Managing State in an Aggregator: MessageGroupStore
5.5. Resequencer
5.5.1. Introduction
5.5.2. Functionality
5.5.3. Configuring a Resequencer
5.6. Message Handler Chain
5.6.1. Introduction
5.6.2. Configuring a Chain
6. Message Transformation
6.1. Transformer
6.1.1. Introduction
6.1.2. Configuring Transformer
Configuring Transformer with XML
Configuring a Transformer with Annotations
6.1.3. Header Filter
6.2. Content Enricher
6.2.1. Introduction
6.2.2. Header Enricher
6.2.3. Payload Enricher
6.3. Claim Check
6.3.1. Introduction
6.3.2. Incoming Claim Check Transformer
6.3.3. Outgoing Claim Check Transformer
6.3.4. A word on Message Store
7. Messaging Endpoints
7.1. Message Endpoints
7.1.1. Message Handler
7.1.2. Event Driven Consumer
7.1.3. Polling Consumer
7.1.4. Namespace Support
7.1.5. Change Polling Rate at Runtime
7.1.6. Payload Type Conversion
7.1.7. Asynchronous polling
7.1.8. Endpoint Inner Beans
7.2. Messaging Gateways
7.2.1. Enter the GatewayProxyFactoryBean
7.2.2. Gateway XML Namespace Support
7.2.3. Setting the Default Reply Channel
7.2.4. Gateway Configuration with Annotations and/or XML
7.2.5. Mapping Method Arguments to a Message
7.2.6. Invoking No-Argument Methods
7.2.7. Error Handling
7.2.8. Asynchronous Gateway
7.2.9. Gateway behavior when no response arrives
7.3. Service Activator
7.3.1. Introduction
7.3.2. Configuring Service Activator
7.4. Delayer
7.4.1. Introduction
7.4.2. Configuring Delayer
7.4.3. Delayer and Message Store
7.5. Scripting support
7.5.1. Script configuration
7.6. Groovy support
7.6.1. Groovy configuration
7.6.2. Control Bus
7.7. Adding Behavior to Endpoints
7.7.1. Provided Advice Classes
Retry Advice
Circuit Breaker Advice
Expression Evaluating Advice
7.7.2. Custom Advice Classes
7.7.3. Other Advice Chain Elements
7.7.4. Advising Filters
7.7.5. Advising Endpoints Using Annotations
7.7.6. Ordering Advices within an Advice Chain
7.8. Logging Channel Adapter
8. System Management
8.1. JMX Support
8.1.1. Notification Listening Channel Adapter
8.1.2. Notification Publishing Channel Adapter
8.1.3. Attribute Polling Channel Adapter
8.1.4. Tree Polling Channel Adapter
8.1.5. Operation Invoking Channel Adapter
8.1.6. Operation Invoking Outbound Gateway
8.1.7. MBean Exporter
MBean ObjectNames
MessageChannel MBean Features
Orderly Shutdown Managed Operation
8.2. Message History
8.2.1. Message History Configuration
8.3. Message Store
8.4. Metadata Store
8.4.1. Idempotent Receiver
8.5. Control Bus
8.6. Orderly Shutdown
IV. Integration Endpoints
9. Endpoint Quick Reference Table
10. AMQP Support
10.1. Introduction
10.2. Inbound Channel Adapter
10.3. Outbound Channel Adapter
10.4. Inbound Gateway
10.5. Outbound Gateway
10.6. AMQP Backed Message Channels
10.7. AMQP Message Headers
10.8. AMQP Samples
11. Spring ApplicationEvent Support
11.1. Receiving Spring ApplicationEvents
11.2. Sending Spring ApplicationEvents
12. Feed Adapter
12.1. Introduction
12.2. Feed Inbound Channel Adapter
13. File Support
13.1. Introduction
13.2. Reading Files
13.2.1. 'Tail'ing Files
13.3. Writing files
13.3.1. Generating Filenames
13.3.2. Specifying the Output Directory
13.3.3. Dealing with Existing Destination Files
13.3.4. File Outbound Channel Adapter
13.3.5. Outbound Gateway
13.4. File Transformers
14. FTP/FTPS Adapters
14.1. Introduction
14.2. FTP Session Factory
14.3. FTP Inbound Channel Adapter
14.4. FTP Outbound Channel Adapter
14.5. FTP Outbound Gateway
14.6. FTP Session Caching
14.7. RemoteFileTemplate
15. GemFire Support
15.1. Introduction
15.2. Inbound Channel Adapter
15.3. Continuous Query Inbound Channel Adapter
15.4. Outbound Channel Adapter
15.5. Gemfire Message Store
16. HTTP Support
16.1. Introduction
16.2. Http Inbound Gateway
16.3. Http Outbound Gateway
16.4. HTTP Namespace Support
16.5. Timeout Handling
16.6. HTTP Proxy configuration
16.7. HTTP Header Mappings
16.8. HTTP Samples
16.8.1. Multipart HTTP request - RestTemplate (client) and Http Inbound Gateway (server)
17. JDBC Support
17.1. Inbound Channel Adapter
17.1.1. Polling and Transactions
17.1.2. Max-rows-per-poll versus Max-messages-per-poll
17.2. Outbound Channel Adapter
17.3. Outbound Gateway
17.4. JDBC Message Store
17.4.1. The Generic JDBC Message Store
17.4.2. Backing Message Channels
17.4.3. Initializing the Database
17.4.4. Partitioning a Message Store
17.5. Stored Procedures
17.5.1. Supported Databases
17.5.2. Configuration
17.5.3. Common Configuration Attributes
17.5.4. Common Configuration Sub-Elements
17.5.5. Defining Parameter Sources
17.5.6. Stored Procedure Inbound Channel Adapter
17.5.7. Stored Procedure Outbound Channel Adapter
17.5.8. Stored Procedure Outbound Gateway
17.5.9. Examples
18. JPA Support
18.1. Supported Persistence Providers
18.2. Java Implementation
18.3. Namespace Support
18.3.1. Common XML Namespace Configuration Attributes
18.3.2. Providing JPA Query Parameters
18.3.3. Transaction Handling
18.4. Inbound Channel Adapter
18.4.1. Configuration Parameter Reference
18.5. Outbound Channel Adapter
18.5.1. Using an Entity Class
18.5.2. Using JPA Query Language (JPA QL)
18.5.3. Using Native Queries
18.5.4. Using Named Queries
18.5.5. Configuration Parameter Reference
18.6. Outbound Gateways
18.6.1. Common Configuration Parameters
18.6.2. Updating Outbound Gateway
18.6.3. Retrieving Outbound Gateway
18.6.4. JPA Outbound Gateway Samples
19. JMS Support
19.1. Inbound Channel Adapter
19.2. Message-Driven Channel Adapter
19.3. Outbound Channel Adapter
19.4. Inbound Gateway
19.5. Outbound Gateway
19.5.1. Attribute Reference
19.6. Mapping Message Headers to/from JMS Message
19.7. Message Conversion, Marshalling and Unmarshalling
19.8. JMS Backed Message Channels
19.9. Using JMS Message Selectors
19.10. JMS Samples
20. Mail Support
20.1. Mail-Sending Channel Adapter
20.2. Mail-Receiving Channel Adapter
20.3. Mail Namespace Support
20.4. Email Message Filtering
20.5. Transaction Synchronization
21. MongoDb Support
21.1. Introduction
21.2. Connecting to MongoDb
21.3. MongoDB Message Store
21.4. MongoDB Inbound Channel Adapter
21.5. MongoDB Outbound Channel Adapter
22. Redis Support
22.1. Introduction
22.2. Connecting to Redis
22.3. Messaging with Redis
22.3.1. Redis Publish/Subscribe channel
22.3.2. Redis Inbound Channel Adapter
22.3.3. Redis Outbound Channel Adapter
22.3.4. Redis Queue Inbound Channel Adapter
22.3.5. Redis Queue Outbound Channel Adapter
22.3.6. Redis Application Events
22.4. Redis Message Store
22.5. Redis Metadata Store
22.6. RedisStore Inbound Channel Adapter
22.7. RedisStore Outbound Channel Adapter
23. Resource Support
23.1. Introduction
23.2. Resource Inbound Channel Adapter
24. RMI Support
24.1. Introduction
24.2. Outbound RMI
24.3. Inbound RMI
24.4. RMI namespace support
25. SFTP Adapters
25.1. Introduction
25.2. SFTP Session Factory
25.2.1. Configuration Properties
25.3. SFTP Session Caching
25.4. RemoteFileTemplate
25.5. SFTP Inbound Channel Adapter
25.6. SFTP Outbound Channel Adapter
25.7. SFTP Outbound Gateway
25.8. SFTP/JSCH Logging
26. Stream Support
26.1. Introduction
26.2. Reading from streams
26.3. Writing to streams
26.4. Stream namespace support
27. Syslog Support
27.1. Introduction
27.2. Syslog <inbound-channel-adapter>
27.2.1. Example Configuration
28. TCP and UDP Support
28.1. Introduction
28.2. UDP Adapters
28.3. TCP Connection Factories
28.3.1. TCP Caching Client Connection Factory
28.3.2. TCP Failover Client Connection Factory
28.4. TCP Connection Interceptors
28.5. TCP Connection Events
28.6. TCP Adapters
28.7. TCP Gateways
28.8. TCP Message Correlation
28.8.1. Overview
28.8.2. Gateways
28.8.3. Collaborating Outbound and Inbound Channel Adapters
28.8.4. Transferring Headers
28.9. A Note About NIO
28.9.1. Thread Pool Task Executor with CALLER_RUNS Policy
28.10. SSL/TLS Support
28.10.1. Overview
28.10.2. Getting Started
28.10.3. Advanced Techniques
28.11. IP Configuration Attributes
28.12. IP Message Headers
29. Twitter Adapter
29.1. Introduction
29.2. Twitter OAuth Configuration
29.3. Twitter Template
29.4. Twitter Inbound Adapters
29.4.1. Inbound Message Channel Adapter
29.4.2. Direct Inbound Message Channel Adapter
29.4.3. Mentions Inbound Message Channel Adapter
29.4.4. Search Inbound Message Channel Adapter
29.5. Twitter Outbound Adapter
29.5.1. Twitter Outbound Update Channel Adapter
29.5.2. Twitter Outbound Direct Message Channel Adapter
30. Web Services Support
30.1. Outbound Web Service Gateways
30.2. Inbound Web Service Gateways
30.3. Web Service Namespace Support
30.4. Outbound URI Configuration
31. XML Support - Dealing with XML Payloads
31.1. Introduction
31.2. Namespace Support
31.2.1. XPath Expressions
Providing Namespaces (Optional) to XPath Expressions
Using XPath Expressions with Default Namespaces
31.3. Transforming XML Payloads
31.3.1. Configuring Transformers as Beans
31.3.2. Namespace Support for XML Transformers
31.3.3. Namespace Configuration and ResultTransformers
31.4. Transforming XML Messages Using XPath
31.5. Splitting XML Messages
31.6. Routing XML Messages Using XPath
31.6.1. XML Payload Converter
31.7. XPath Header Enricher
31.8. Using the XPath Filter
31.9. #xpath SpEL Function
31.10. XML Validating Filter
32. XMPP Support
32.1. Introduction
32.2. XMPP Connection
32.3. XMPP Messages
32.3.1. Inbound Message Channel Adapter
32.3.2. Outbound Message Channel Adapter
32.4. XMPP Presence
32.4.1. Inbound Presence Message Channel Adapter
32.4.2. Outbound Presence Message Channel Adapter
32.5. Advanced Configuration
V. Appendices
A. Spring Expression Language (SpEL)
A.1. Introduction
A.2. SpEL Evaluation Context Customization
A.3. SpEL Functions
A.4. PropertyAccessors
B. Message Publishing
B.1. Message Publishing Configuration
B.1.1. Annotation-driven approach via @Publisher annotation
B.1.2. XML-based approach via the <publishing-interceptor> element
B.1.3. Producing and publishing messages based on a scheduled trigger
C. Transaction Support
C.1. Understanding Transactions in Message flows
C.1.1. Poller Transaction Support
C.2. Transaction Boundaries
C.3. Transaction Synchronization
C.4. Pseudo Transactions
D. Security in Spring Integration
D.1. Introduction
D.2. Securing channels
E. Spring Integration Samples
E.1. Introduction
E.2. Where to get Samples
E.3. Submitting Samples or Sample Requests
E.4. Samples Structure
E.5. Samples
E.5.1. Loan Broker
E.5.2. The Cafe Sample
E.5.3. The XML Messaging Sample
F. Configuration
F.1. Introduction
F.2. Namespace Support
F.3. Configuring the Task Scheduler
F.4. Error Handling
F.5. Annotation Support
F.6. Message Mapping rules and conventions
F.6.1. Simple Scenarios
F.6.2. Complex Scenarios
G. Additional Resources
G.1. Spring Integration Home
H. Change History
H.1. Changes between 1.0 and 2.0
H.1.1. Spring 3 support
Support for the Spring Expression Language (SpEL)
ConversionService and Converter
TaskScheduler and Trigger
RestTemplate and HttpMessageConverter
H.1.2. Enterprise Integration Pattern Additions
Message History
Message Store
Claim Check
Control Bus
H.1.3. New Channel Adapters and Gateways
TCP/UDP Adapters
Twitter Adapters
XMPP Adapters
FTP/FTPS Adapters
SFTP Adapters
Feed Adapters
H.1.4. Other Additions
Groovy Support
Map Transformers
JSON Transformers
Serialization Transformers
H.1.5. Framework Refactoring
H.1.6. New Source Control Management and Build Infrastructure
H.1.7. New Spring Integration Samples
H.1.8. SpringSource Tool Suite Visual Editor for Spring Integration
H.2. Changes between 2.0 and 2.1
H.2.1. New Components
JSR-223 Scripting Support
GemFire Support
AMQP Support
MongoDB Support
Redis Support
Support for Spring's Resource abstraction
Stored Procedure Components
XPath and XML Validating Filter
Payload Enricher
FTP and SFTP Outbound Gateways
FTP Session Caching
H.2.2. Framework Refactoring
Standardizing Router Configuration
XML Schemas updated to 2.1
H.2.3. Source Control Management and Build Infrastructure
Source Code now hosted on Github
Improved Source Code Visibility with Sonar
H.2.4. New Samples
H.3. Changes between 2.1 and 2.2
H.3.1. New Components
RedisStore Inbound and Outbound Channel Adapters
MongoDB Inbound and Outbound Channel Adapters
JPA Endpoints
H.3.2. General Changes
Spring 3.1 Used by Default
Adding Behavior to Endpoints
Transaction Synchronization and Pseudo Transactions
File Adapter - Improved File Overwrite/Append Handling
Reply-Timeout added to more Outbound Gateways
Spring-AMQP 1.1
JDBC Support - Stored Procedures Components
JDBC Support - Outbound Gateway
JDBC Support - Channel-specific Message Store Implementation
Orderly Shutdown
JMS Oubound Gateway Improvements
HTTP Support


1 Requirements

This section details the compatible Java and Spring Framework versions.

1.1 Compatible Java Versions

For Spring Integration 3.0.x, the minimum compatible Java version is Java SE 6. Older versions of Java will not be supported any longer.

Spring Integration 3.0.x is also compatible with Java SE 7 as well as Java SE 8.

Spring Integration 2.2.x is the last version that is compatible with Java 5 (J2SE 5.0).

1.2 Compatible Versions of the Spring Framework

The default dependency used by Spring Integration 3.0.0.RELEASE is Spring Framework 3.2.x.

Generally, Spring Integration 3.0.x is compatible with the following Spring Framework releases:

  • Spring Framework 3.1.x
  • Spring Framework 3.2.x
  • Spring Framework 4.0.x
Spring Integration 2.2.x is the last version that is compatible with Spring Framework 3.0.x.

2 Code Conventions

The Spring Framework 2.0 introduced support for namespaces, which simplifies the Xml configuration of the application context, and consequently Spring Integration provides broad namespace support. This reference guide applies the following conventions for all code examples that use namespace support:

The int namespace prefix will be used for Spring Integration's core namespace support. Each Spring Integration adapter type (module) will provide its own namespace, which is configured using the following convention:

int- followed by the name of the module, e.g. int-twitter, int-stream, …

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"

For a detailed explanation regarding Spring Integration's namespace support see Section F.2, “Namespace Support”.

Please note that the namespace prefix can be freely chosen. You may even choose not to use any namespace prefixes at all. Therefore, apply the convention that suits your application needs best. Be aware, though, that SpringSource Tool Suite™ (STS) uses the same namespace conventions for Spring Integration as used in this reference guide.

Part I. What's new?

For those who are already familiar with Spring Integration, this chapter provides a brief overview of the new features of version 3.0. If you are interested in the changes and features, that were introduced in earlier versions, please see chapter: Appendix H, Change History

1. What's new in Spring Integration 3.0?

This chapter provides an overview of the new features and improvements that have been introduced with Spring Integration 3.0. If you are interested in more details, please see the Issue Tracker tickets that were resolved as part of the 3.0 development process.

1.1 New Components

1.1.1 HTTP Request Mapping

The HTTP module now provides powerful Request Mapping support for Inbound Endpoints. Class UriPathHandlerMapping was replaced by IntegrationRequestMappingHandlerMapping, which is registered under the bean name integrationRequestMappingHandlerMapping in the application context. Upon parsing of the HTTP Inbound Endpoint, a new IntegrationRequestMappingHandlerMapping bean is either registered or an existing bean is being reused. To achieve flexible Request Mapping configuration, Spring Integration provides the <request-mapping/> sub-element for the <http:inbound-channel-adapter/> and the <http:inbound-gateway/>. Both HTTP Inbound Endpoints are now fully based on the Request Mapping infrastructure that was introduced with Spring MVC 3.1. For example, multiple paths are supported on a single inbound endpoint. For more information see Section 16.4, “HTTP Namespace Support”.

1.1.2 Spring Expression Language (SpEL) Configuration

A new IntegrationEvaluationContextFactoryBean is provided to allow configuration of custom PropertyAccessors and functions for use in SpEL expressions throughout the framework. For more information see Appendix A, Spring Expression Language (SpEL).

1.1.3 SpEL Functions Support

To customize the SpEL EvaluationContext with static Method functions, the new <spel-function/> component is introduced. Two built-in functions are also provided (#jsonPath and #xpath). For more information see Section A.3, “SpEL Functions”.

1.1.4 SpEL PropertyAccessors Support

To customize the SpEL EvaluationContext with PropertyAccessor implementations the new <spel-property-accessors/> component is introduced. For more information see Section A.4, “PropertyAccessors”.

1.1.5 Redis: New Components

A new Redis-based MetadataStore implementation has been added. The RedisMetadataStore can be used to maintain state of a MetadataStore across application restarts. This new MetadataStore implementation can be used with adapters such as:

  • Twitter Inbound Adapters
  • Feed Inbound Channel Adapter

New queue-based components have been added. The <int-redis:queue-inbound-channel-adapter/> and the <int-redis:queue-outbound-channel-adapter/> components are provided to perform 'right pop' and 'left push' operations on a Redis List, respectively.

For more information see Chapter 22, Redis Support.

1.1.6 Header Channel Registry

It is now possible to instruct the framework to store reply and error channels in a registry for later resolution. This is useful for cases where the replyChannel or errorChannel might be lost; for example when serializing a message. See Section 6.2.2, “Header Enricher” for more information.

1.1.7 MongoDB support: New ConfigurableMongoDbMessageStore

In addition to the existing eMongoDbMessageStore, a new ConfigurableMongoDbMessageStore has been introduced. This provides a more robust and flexible implementation of MessageStore for MongoDB. It does not have backward compatibility, with the existing store, but it is recommended to use it for new applications. Existing applications can use it, but messages in the old store will not be available. See Chapter 21, MongoDb Support for more information.

1.1.8 Syslog Support

Building on the 2.2 SyslogToMapTransformer Spring Integration 3.0 now introduces UDP and TCP inbound channel adapters especially tailored for receiving SYSLOG messages. For more information, see Chapter 27, Syslog Support.

1.1.9 'Tail' Support

File 'tail'ing inbound channel adapters are now provided to generate messages when lines are added to the end of text files; see Section 13.2.1, “'Tail'ing Files”.

1.1.10 JMX Support

  • A new <int-jmx:tree-polling-channel-adapter/> is provided; this adapter queries the JMX MBean tree and sends a message with a payload that is the graph of objects that matches the query. By default the MBeans are mapped to primitives and simple Objects like Map, List and arrays - permitting simple transformation, for example, to JSON.
  • The IntegrationMBeanExporter now allows the configuration of a custom ObjectNamingStrategy using the naming-strategy attribute.

For more information, see Section 8.1, “JMX Support”.

1.1.11 TCP/IP Connection Events and Connection Management

TcpConnections now emit ApplicationEvents (specifically TcpConnectionEvents) when connections are opened, closed, or an exception occurs. This allows applications to be informed of changes to TCP connections using the normal Spring ApplicationListener mechanism.

AbstractTcpConnection has been renamed TcpConnectionSupport; custom connections that are subclasses of this class, can use its methods to publish events. Similarly, AbstractTcpConnectionInterceptor has been renamed to TcpConnectionInterceptorSupport.

In addition, a new <int-ip:tcp-connection-event-inbound-channel-adapter/> is provided; by default, this adapter sends all TcpConnectionEvents to a Channel.

Further, the TCP Connection Factories, now provide a new method getOpenConnectionIds(), which returns a list of identifiers for all open connections; this allows applications, for example, to broadcast to all open connections.

Finally, the connection factories also provide a new method closeConnection(String connectionId) which allows applications to explicitly close a connection using its ID.

For more information see Section 28.5, “TCP Connection Events”.

1.1.12 Inbound Channel Adapter Script Support

The <int:inbound-channel-adapter/> now supports <expression/> and <script/> sub-elements to create a MessageSource; see Section 3.3.3, “Channel Adapter Expressions and Scripts”.

1.1.13 Content Enricher: Headers Enrichment Support

The Content Enricher now provides configuration for <header/> sub-elements, to enrich the outbound Message with headers based on the reply Message from the underlying message flow. For more information see Section 6.2.3, “Payload Enricher”.

1.2 General Changes

1.2.1 Message ID Generation

Previously, message ids were generated using the JDK UUID.randomUUID() method. With this release, the default mechanism has been changed to use a more efficient algorithm which is significantly faster. In addition, the ability to change the strategy used to generate message ids has been added. For more information see the section called “Message ID Generation”.

1.2.2 <gateway> Changes

  • It is now possible to set common headers across all gateway methods, and more options are provided for adding, to the message, information about which method was invoked.
  • It is now possible to entirely customize the way that gateway method calls are mapped to messages.
  • The GatewayMethodMetadata is now public class and it makes possible flexibly to configure the GatewayProxyFactoryBean programmatically from Java code.

For more information see Section 7.2, “Messaging Gateways”.

1.2.3 HTTP Endpoint Changes

  • Outbound Endpoint 'encode-uri' - <http:outbound-gateway/> and <http:outbound-channel-adapter/> now provide an encode-uri attribute to allow disabling the encoding of the URI object before sending the request.
  • Inbound Endpoint 'merge-with-default-converters' - <http:inbound-gateway/> and <http:inbound-channel-adapter/> now have a merge-with-default-converters attribute to include the list of default HttpMessageConverters after the custom message converters.
  • 'If-(Un)Modified-Since' HTTP Headers - previously, 'If-Modified-Since' and 'If-Unmodified-Since' HTTP headers were incorrectly processed within from/to HTTP headers mapping in the DefaultHttpHeaderMapper. Now, in addition correcting that issue, DefaultHttpHeaderMapper provides date parsing from formatted strings for any HTTP headers that accept date-time values.
  • Inbound Endpoint Expression Variables - In addition to the existing #requestParams and #pathVariables, the <http:inbound-gateway/> and <http:inbound-channel-adapter/> now support additional useful variables: #matrixVariables, #requestAttributes, #requestHeaders and #cookies. These variables are available in both payload and header expressions.
  • Outbound Endpoint 'uri-variables-expression' - HTTP Outbound Endpoints now support the uri-variables-expression attribute to specify an Expression to evaluate a Map for all URI variable placeholders within URL template. This allows selection of a different map of expressions based on the outgoing message.

For more information see Chapter 16, HTTP Support.

1.2.4 Jackson Support (JSON)

  • A new abstraction for JSON conversion has been introduced. Implementations for Jackson 1.x and Jackson 2 are currently provided, with the version being determined by presence on the classpath. Previously, only Jackson 1.x was supported.
  • The ObjectToJsonTransformer and JsonToObjectTransformer now emit/consume headers containing type information.

For more information, see 'JSON Transformers' in Section 6.1, “Transformer”.

1.2.5 Chain Elements 'id' Attribute

Previously, the id attribute for elements within a <chain> was ignored and, in some cases, disallowed. Now, the id attribute is allowed for all elements within a <chain>. The bean names of chain elements is a combination of the surrounding chain's id and the id of the element itself. For example: 'fooChain$child.fooTransformer.handler'. For more information see Section 5.6, “Message Handler Chain”.

1.2.6 Aggregator 'empty-group-min-timeout' property

The AbstractCorrelatingMessageHandler provides a new property empty-group-min-timeout to allow empty group expiry to run on a longer schedule than expiring partial groups. Empty groups will not be removed from the MessageStore until they have not been modified for at least this number of milliseconds. For more information see Section 5.4.4, “Configuring an Aggregator”.

1.2.7 Persistent File List Filters (file, (S)FTP)

New FileListFilters that use a persistent MetadataStore are now available. These can be used to prevent duplicate files after a system restart. See Section 13.2, “Reading Files”, Section 14.3, “FTP Inbound Channel Adapter”, and Section 25.5, “SFTP Inbound Channel Adapter” for more information.

1.2.8 Scripting Support: Variables Changes

A new variables attribute has been introduced for scripting components. In addition, variable bindings are now allowed for inline scripts. See Section 7.6, “Groovy support” and Section 7.5, “Scripting support” for more information.

1.2.9 Direct Channel Load Balancing configuration

Previously, when configuring LoadBalancingStrategy on the channel's 'dispatcher' sub-element, the only available option was to use a pre-defined enumeration of values which did not allow one to set a custom implementation of the LoadBalancingStrategy. You can now use load-balancer-ref to provide a reference to a custom implementation of the LoadBalancingStrategy. For more information see the section called “DirectChannel”.

1.2.10 PublishSubscribeChannel Behavior

Previously, sending to a <publish-subscribe-channel/> that had no subscribers would return a false result. If used in conjunction with a MessagingTemplate, this would result in an exception being thrown. Now, the PublishSubscribeChannel has a property minSubscribers (default 0). If the message is sent to at least the minimum number of subscribers, the send is deemed to be successful (even if zero). If an application is expecting to get an exception under these conditions, set the minimum subscribers to at least 1.

1.2.11 FTP, SFTP and FTPS Changes

The FTP, SFTP and FTPS endpoints no longer cache sessions by default

The deprecated cached-sessions attribute has been removed from all endpoints. Previously, the embedded caching mechanism controlled by this attribute's value didn't provide a way to limit the size of the cache, which could grow indefinitely. The CachingConnectionFactory was introduced in release 2.1 and it became the preferred (and is now the only) way to cache sessions.

The CachingConnectionFactory now provides a new method resetCache(). This immediately closes idle sessions and causes in-use sessions to be closed as and when they are returned to the cache.

The DefaultSftpSessionFactory (in conjunction with a CachingSessionFactory) now supports multiplexing channels over a single SSH connection (SFTP Only).

FTP, SFTP and FTPS Inbound Adapters

Previously, there was no way to override the default filter used to process files retrieved from a remote server. The filter attribute determines which files are retrieved but the FileReadingMessageSource uses an AcceptOnceFileListFilter. This means that if a new copy of a file is retrieved, with the same name as a previously copied file, no message was sent from the adapter.

With this release, a new attribute local-filter allows you to override the default filter, for example with an AcceptAllFileListFilter, or some other custom filter.

For users that wish the behavior of the AcceptOnceFileListFilter to be maintained across JVM executions, a custom filter that retains state, perhaps on the file system, can now be configured.

Inbound Channel Adapters now support the preserve-timestamp attribute, which sets the local file modified timestamp to the timestamp from the server (default false).

FTP, SFTP and FTPS Gateways

  • The gateways now support the mv command, enabling the renaming of remote files.
  • The gateways now support recursive ls and mget commands, enabling the retrieval of a remote file tree.
  • The gateways now support put and mput commands, enabling sending file(s) to the remote server.
  • The local-filename-generator-expression attribute is now supported, enabling the naming of local files during retrieval. By default, the same name as the remote file is used.
  • The local-directory-expression attribute is now supported, enabling the naming of local directories during retrieval based on the remote directory.

Remote File Template

A new higher-level abstraction (RemoteFileTemplate) is provided over the Session implementations used by the FTP and SFTP modules. While it is used internally by endpoints, this abstraction can also be used programmatically and, like all Spring *Template implementations, reliably closes the underlying session while allowing low level access to the session when needed.

For more information, see Chapter 14, FTP/FTPS Adapters and Chapter 25, SFTP Adapters.

1.2.12 'requires-reply' Attribute for Outbound Gateways

All Outbound Gateways (e.g. <jdbc:outbound-gateway/> or <jms:outbound-gateway/>) are designed for 'request-reply' scenarios. A response is expected from the external service and will be published to the reply-channel, or the replyChannel message header. However, there are some cases where the external system might not always return a result, e.g. a <jdbc:outbound-gateway/>, when a SELECT ends with an empty ResultSet or, say, a Web Service is One-Way. An option is therefore needed to configure whether or not a reply is required. For this purpose, the requires-reply attribute has been introduced for Outbound Gateway components. In most cases, the default value for requires-reply is true and, if there is not any result, a ReplyRequiredException will be thrown. Changing the value to false means that, if an external service doesn't return anything, the message-flow will end at that point, similar to an Outbound Channel Adapter.

The WebService outbound gateway has an additional attribute ignore-empty-responses; this is used to treat an empty String response as if no response was received. It is true by default but can be set to false to allow the application to receive an empty String in the reply message payload. When the attribute is true an empty string is treated as no response for the purposes of the requires-reply attribute. requires-reply is false by default for the WebService outbound gateway.

Note, the requiresReply property was previously present in the AbstractReplyProducingMessageHandler but set to false, and there wasn't any way to configure it on Outbound Gateways using the XML namespace.

Previously, a gateway receiving no reply would silently end the flow (with a DEBUG log message); with this change an exception will now be thrown by default by most gateways. To revert to the previous behavior, set requires-reply to false.

1.2.13 AMQP Outbound Gateway Header Mapping

Previously, the <int-amqp:outbound-gateway/> mapped headers before invoking the message converter, and the converter could overwrite headers such as content-type. The outbound adapter maps the headers after the conversion, which means headers like content-type from the outbound Message (if present) are used.

Starting with this release, the gateway now maps the headers after the message conversion, consistent with the adapter. If your application relies on the previous behavior (where the converter's headers overrode the mapped headers), you either need to filter those headers (before the message reaches the gateway) or set them appropriately. The headers affected by the SimpleMessageConverter are content-type and content-encoding. Custom message converters may set other headers.

1.2.14 Stored Procedure Components Improvements

For more complex database-specific types, not supported by the standard CallableStatement.getObject method, 2 new additional attributes were introduced to the <sql-parameter-definition/> element with OUT-direction:

  • type-name
  • return-type

The row-mapper attribute of the Stored Procedure Inbound Channel Adapter <returning-resultset/> sub-element now supports a reference to a RowMapper bean definition. Previously, it contained just a class name (which is still supported).

For more information see Section 17.5, “Stored Procedures”.

1.2.15 Web Service Outbound URI Configuration

Web Service Outbound Gateway 'uri' attribute now supports <uri-variable/> substitution for all URI-schemes supported by Spring Web Services. For more information see Section 30.4, “Outbound URI Configuration”.

1.2.16 Redis Adapter Changes

  • The Redis Inbound Channel Adapter can now use a null value for serializer property, with the raw data being the message payload.
  • The Redis Outbound Channel Adapter now has the topic-expression property to determine the Redis topic against the Message at runtime.
  • The Redis Inbound Channel Adapter, in addition to the existing topics attribute, now has the topic-patterns attribute.

For more information, see Chapter 22, Redis Support.

1.2.17 Advising Filters

Previously, when a <filter/> had a <request-handler-advice-chain/>, the discard action was all performed within the scope of the advice chain (including any downstream flow on the discard-channel). The filter element now has an attribute discard-within-advice (default true), to allow the discard action to be performed after the advice chain completes. See Section 7.7.4, “Advising Filters”.

1.2.18 Advising Endpoints using Annotations

Request Handler Advice Chains can now be configured using annotations. See Section 7.7.5, “Advising Endpoints Using Annotations”.

1.2.19 ObjectToStringTransformer Improvements

This transformer now correctly transforms byte[] and char[] payloads to String. For more information see Section 6.1, “Transformer”.

1.2.20 JPA Support Changes

Payloads to persist or merge can now be of type java.lang.Iterable.

In that case, each object returned by the Iterable is treated as an entity and persisted or merged using the underlying EntityManager. NULL values returned by the iterator are ignored.

The JPA adapters now have additional attributes to optionally 'flush' and 'clear' entities from the associated persistence context after performing persistence operations.

Retrieving gateways had no mechanism to specify the first record to be retrieved which is a common use case. The retrieving gateways now support specifying this parameter using a first-result and first-result-expression attributes to the gateway definition. Section 18.6.3, “Retrieving Outbound Gateway”.

The JPA retrieving gateway and inbound adapter now have an attribute to specify the maximum number of results in a result set as an expression. In addition, the max-results attribute has been introduced to replace max-number-of-results, which has been deprecated. max-results and max-results-expression are used to provide the maximum number of results, or an expression to compute the maximum number of results, respectively, in the result set.

For more information see Chapter 18, JPA Support.

1.2.21 Delayer: delay expression

Previously, the <delayer> provided a delay-header-name attribute to determine the delay value at runtime. In complex cases it was necessary to precede the <delayer> with a <header-enricher>. Spring Integration 3.0 introduced the expression attribute and expression sub-element for dynamic delay determination. The delay-header-name attribute is now deprecated because the header evaluation can be specified in the expression. In addition, the ignore-expression-failures was introduced to control the behavior when an expression evaluation fails. For more information see Section 7.4, “Delayer”.

1.2.22 JDBC Message Store Improvements

Spring Integration 3.0 adds a new set of DDL scripts for MySQL version 5.6.4 and higher. Now MySQL supports fractional seconds and is thus improving the FIFO ordering when polling from a MySQL-based Message Store. For more information, please see Section 17.4.1, “The Generic JDBC Message Store”.

1.2.23 IMAP Idle Connection Exceptions

Previously, if an IMAP idle connection failed, it was logged but there was no mechanism to inform an application. Such exceptions now generate ApplicationEvents. Applications can obtain these events using an <int-event:inbound-channel-adapter> or any ApplicationListener configured to receive an ImapIdleExceptionEvent or one of its super classes.

1.2.24 Message Headers and TCP

The TCP connection factories now enable the configuration of a flexible mechanism to transfer selected headers (as well as the payload) over TCP. A new TcpMessageMapper enables the selection of the headers, and an appropriate (de)serializer needs to be configured to write the resulting Map to the TCP stream. A MapJsonSerializer is provided as a convenient mechanism to transfer headers and payload over TCP. For more information see Section 28.8.4, “Transferring Headers”.

1.2.25 JMS Message Driven Channel Adapter

Previously, when configuring a <message-driven-channel-adapter/>, if you wished to use a specific TaskExecutor, it was necessary to declare a container bean and provide it to the adapter using the container attribute. The task-executor is now provided, allowing it to be set directly on the adapter. This is in addition to several other container attributes that were already available.

1.2.26 RMI Inbound Gateway

The RMI Inbound Gateway now supports an error-channel attribute. See Section 24.3, “Inbound RMI”.

1.2.27 XsltPayloadTransformer

You can now specify the transformer factory class name using the transformer-factory-class attribute. See the section called “XsltPayloadTransformer”

Part II. Overview of Spring Integration Framework

Spring Integration provides an extension of the Spring programming model to support the well-known Enterprise Integration Patterns. It enables lightweight messaging within Spring-based applications and supports integration with external systems via declarative adapters. Those adapters provide a higher-level of abstraction over Spring's support for remoting, messaging, and scheduling. Spring Integration's primary goal is to provide a simple model for building enterprise integration solutions while maintaining the separation of concerns that is essential for producing maintainable, testable code.

2. Spring Integration Overview

2.1 Background

One of the key themes of the Spring Framework is inversion of control. In its broadest sense, this means that the framework handles responsibilities on behalf of the components that are managed within its context. The components themselves are simplified since they are relieved of those responsibilities. For example, dependency injection relieves the components of the responsibility of locating or creating their dependencies. Likewise, aspect-oriented programming relieves business components of generic cross-cutting concerns by modularizing them into reusable aspects. In each case, the end result is a system that is easier to test, understand, maintain, and extend.

Furthermore, the Spring framework and portfolio provide a comprehensive programming model for building enterprise applications. Developers benefit from the consistency of this model and especially the fact that it is based upon well-established best practices such as programming to interfaces and favoring composition over inheritance. Spring's simplified abstractions and powerful support libraries boost developer productivity while simultaneously increasing the level of testability and portability.

Spring Integration is motivated by these same goals and principles. It extends the Spring programming model into the messaging domain and builds upon Spring's existing enterprise integration support to provide an even higher level of abstraction. It supports message-driven architectures where inversion of control applies to runtime concerns, such as when certain business logic should execute and where the response should be sent. It supports routing and transformation of messages so that different transports and different data formats can be integrated without impacting testability. In other words, the messaging and integration concerns are handled by the framework, so business components are further isolated from the infrastructure and developers are relieved of complex integration responsibilities.

As an extension of the Spring programming model, Spring Integration provides a wide variety of configuration options including annotations, XML with namespace support, XML with generic "bean" elements, and of course direct usage of the underlying API. That API is based upon well-defined strategy interfaces and non-invasive, delegating adapters. Spring Integration's design is inspired by the recognition of a strong affinity between common patterns within Spring and the well-known Enterprise Integration Patterns as described in the book of the same name by Gregor Hohpe and Bobby Woolf (Addison Wesley, 2004). Developers who have read that book should be immediately comfortable with the Spring Integration concepts and terminology.

2.2 Goals and Principles

Spring Integration is motivated by the following goals:

  • Provide a simple model for implementing complex enterprise integration solutions.

  • Facilitate asynchronous, message-driven behavior within a Spring-based application.

  • Promote intuitive, incremental adoption for existing Spring users.

Spring Integration is guided by the following principles:

  • Components should be loosely coupled for modularity and testability.

  • The framework should enforce separation of concerns between business logic and integration logic.

  • Extension points should be abstract in nature but within well-defined boundaries to promote reuse and portability.

2.3 Main Components

From the vertical perspective, a layered architecture facilitates separation of concerns, and interface-based contracts between layers promote loose coupling. Spring-based applications are typically designed this way, and the Spring framework and portfolio provide a strong foundation for following this best practice for the full-stack of an enterprise application. Message-driven architectures add a horizontal perspective, yet these same goals are still relevant. Just as "layered architecture" is an extremely generic and abstract paradigm, messaging systems typically follow the similarly abstract "pipes-and-filters" model. The "filters" represent any component that is capable of producing and/or consuming messages, and the "pipes" transport the messages between filters so that the components themselves remain loosely-coupled. It is important to note that these two high-level paradigms are not mutually exclusive. The underlying messaging infrastructure that supports the "pipes" should still be encapsulated in a layer whose contracts are defined as interfaces. Likewise, the "filters" themselves would typically be managed within a layer that is logically above the application's service layer, interacting with those services through interfaces much in the same way that a web-tier would.

2.3.1 Message

In Spring Integration, a Message is a generic wrapper for any Java object combined with metadata used by the framework while handling that object. It consists of a payload and headers. The payload can be of any type and the headers hold commonly required information such as id, timestamp, correlation id, and return address. Headers are also used for passing values to and from connected transports. For example, when creating a Message from a received File, the file name may be stored in a header to be accessed by downstream components. Likewise, if a Message's content is ultimately going to be sent by an outbound Mail adapter, the various properties (to, from, cc, subject, etc.) may be configured as Message header values by an upstream component. Developers can also store any arbitrary key-value pairs in the headers.

2.3.2 Message Channel

A Message Channel represents the "pipe" of a pipes-and-filters architecture. Producers send Messages to a channel, and consumers receive Messages from a channel. The Message Channel therefore decouples the messaging components, and also provides a convenient point for interception and monitoring of Messages.

A Message Channel may follow either Point-to-Point or Publish/Subscribe semantics. With a Point-to-Point channel, at most one consumer can receive each Message sent to the channel. Publish/Subscribe channels, on the other hand, will attempt to broadcast each Message to all of its subscribers. Spring Integration supports both of these.

Whereas "Point-to-Point" and "Publish/Subscribe" define the two options for how many consumers will ultimately receive each Message, there is another important consideration: should the channel buffer messages? In Spring Integration, Pollable Channels are capable of buffering Messages within a queue. The advantage of buffering is that it allows for throttling the inbound Messages and thereby prevents overloading a consumer. However, as the name suggests, this also adds some complexity, since a consumer can only receive the Messages from such a channel if a poller is configured. On the other hand, a consumer connected to a Subscribable Channel is simply Message-driven. The variety of channel implementations available in Spring Integration will be discussed in detail in Section 3.1.2, “Message Channel Implementations”.

2.3.3 Message Endpoint

One of the primary goals of Spring Integration is to simplify the development of enterprise integration solutions through inversion of control. This means that you should not have to implement consumers and producers directly, and you should not even have to build Messages and invoke send or receive operations on a Message Channel. Instead, you should be able to focus on your specific domain model with an implementation based on plain Objects. Then, by providing declarative configuration, you can "connect" your domain-specific code to the messaging infrastructure provided by Spring Integration. The components responsible for these connections are Message Endpoints. This does not mean that you will necessarily connect your existing application code directly. Any real-world enterprise integration solution will require some amount of code focused upon integration concerns such as routing and transformation. The important thing is to achieve separation of concerns between such integration logic and business logic. In other words, as with the Model-View-Controller paradigm for web applications, the goal should be to provide a thin but dedicated layer that translates inbound requests into service layer invocations, and then translates service layer return values into outbound replies. The next section will provide an overview of the Message Endpoint types that handle these responsibilities, and in upcoming chapters, you will see how Spring Integration's declarative configuration options provide a non-invasive way to use each of these.

2.4 Message Endpoints

A Message Endpoint represents the "filter" of a pipes-and-filters architecture. As mentioned above, the endpoint's primary role is to connect application code to the messaging framework and to do so in a non-invasive manner. In other words, the application code should ideally have no awareness of the Message objects or the Message Channels. This is similar to the role of a Controller in the MVC paradigm. Just as a Controller handles HTTP requests, the Message Endpoint handles Messages. Just as Controllers are mapped to URL patterns, Message Endpoints are mapped to Message Channels. The goal is the same in both cases: isolate application code from the infrastructure. These concepts are discussed at length along with all of the patterns that follow in the Enterprise Integration Patterns book. Here, we provide only a high-level description of the main endpoint types supported by Spring Integration and their roles. The chapters that follow will elaborate and provide sample code as well as configuration examples.

2.4.1 Transformer

A Message Transformer is responsible for converting a Message's content or structure and returning the modified Message. Probably the most common type of transformer is one that converts the payload of the Message from one format to another (e.g. from XML Document to java.lang.String). Similarly, a transformer may be used to add, remove, or modify the Message's header values.

2.4.2 Filter

A Message Filter determines whether a Message should be passed to an output channel at all. This simply requires a boolean test method that may check for a particular payload content type, a property value, the presence of a header, etc. If the Message is accepted, it is sent to the output channel, but if not it will be dropped (or for a more severe implementation, an Exception could be thrown). Message Filters are often used in conjunction with a Publish Subscribe channel, where multiple consumers may receive the same Message and use the filter to narrow down the set of Messages to be processed based on some criteria.

Be careful not to confuse the generic use of "filter" within the Pipes-and-Filters architectural pattern with this specific endpoint type that selectively narrows down the Messages flowing between two channels. The Pipes-and-Filters concept of "filter" matches more closely with Spring Integration's Message Endpoint: any component that can be connected to Message Channel(s) in order to send and/or receive Messages.

2.4.3 Router

A Message Router is responsible for deciding what channel or channels should receive the Message next (if any). Typically the decision is based upon the Message's content and/or metadata available in the Message Headers. A Message Router is often used as a dynamic alternative to a statically configured output channel on a Service Activator or other endpoint capable of sending reply Messages. Likewise, a Message Router provides a proactive alternative to the reactive Message Filters used by multiple subscribers as described above.

2.4.4 Splitter

A Splitter is another type of Message Endpoint whose responsibility is to accept a Message from its input channel, split that Message into multiple Messages, and then send each of those to its output channel. This is typically used for dividing a "composite" payload object into a group of Messages containing the sub-divided payloads.

2.4.5 Aggregator

Basically a mirror-image of the Splitter, the Aggregator is a type of Message Endpoint that receives multiple Messages and combines them into a single Message. In fact, Aggregators are often downstream consumers in a pipeline that includes a Splitter. Technically, the Aggregator is more complex than a Splitter, because it is required to maintain state (the Messages to-be-aggregated), to decide when the complete group of Messages is available, and to timeout if necessary. Furthermore, in case of a timeout, the Aggregator needs to know whether to send the partial results or to discard them to a separate channel. Spring Integration provides a CompletionStrategy as well as configurable settings for timeout, whether to send partial results upon timeout, and the discard channel.

2.4.6 Service Activator

A Service Activator is a generic endpoint for connecting a service instance to the messaging system. The input Message Channel must be configured, and if the service method to be invoked is capable of returning a value, an output Message Channel may also be provided.

The output channel is optional, since each Message may also provide its own 'Return Address' header. This same rule applies for all consumer endpoints.

The Service Activator invokes an operation on some service object to process the request Message, extracting the request Message's payload and converting if necessary (if the method does not expect a Message-typed parameter). Whenever the service object's method returns a value, that return value will likewise be converted to a reply Message if necessary (if it's not already a Message). That reply Message is sent to the output channel. If no output channel has been configured, then the reply will be sent to the channel specified in the Message's "return address" if available.

A request-reply "Service Activator" endpoint connects a target object's method to input and output Message Channels.

2.4.7 Channel Adapter

A Channel Adapter is an endpoint that connects a Message Channel to some other system or transport. Channel Adapters may be either inbound or outbound. Typically, the Channel Adapter will do some mapping between the Message and whatever object or resource is received-from or sent-to the other system (File, HTTP Request, JMS Message, etc). Depending on the transport, the Channel Adapter may also populate or extract Message header values. Spring Integration provides a number of Channel Adapters, and they will be described in upcoming chapters.

An inbound "Channel Adapter" endpoint connects a source system to a MessageChannel.

An outbound "Channel Adapter" endpoint connects a MessageChannel to a target system.

Part III. Core Messaging

This section covers all aspects of the core messaging API in Spring Integration. Here you will learn about Messages, Message Channels, and Message Endpoints. Many of the Enterprise Integration Patterns are covered here as well, such as Filters, Routers, Transformers, Service-Activators, Splitters, and Aggregators. The section also contains material about System Management, including the Control Bus and Message History support.

3. Messaging Channels

3.1 Message Channels

While the Message plays the crucial role of encapsulating data, it is the MessageChannel that decouples message producers from message consumers.

3.1.1 The MessageChannel Interface

Spring Integration's top-level MessageChannel interface is defined as follows.

public interface MessageChannel {

    boolean send(Message message);

    boolean send(Message message, long timeout);

When sending a message, the return value will be true if the message is sent successfully. If the send call times out or is interrupted, then it will return false.


Since Message Channels may or may not buffer Messages (as discussed in the overview), there are two sub-interfaces defining the buffering (pollable) and non-buffering (subscribable) channel behavior. Here is the definition of PollableChannel.

public interface PollableChannel extends MessageChannel {

    Message<?> receive();

    Message<?> receive(long timeout);


Similar to the send methods, when receiving a message, the return value will be null in the case of a timeout or interrupt.


The SubscribableChannel base interface is implemented by channels that send Messages directly to their subscribed MessageHandlers. Therefore, they do not provide receive methods for polling, but instead define methods for managing those subscribers:

public interface SubscribableChannel extends MessageChannel {

    boolean subscribe(MessageHandler handler);

    boolean unsubscribe(MessageHandler handler);


3.1.2 Message Channel Implementations

Spring Integration provides several different Message Channel implementations. Each is briefly described in the sections below.


The PublishSubscribeChannel implementation broadcasts any Message sent to it to all of its subscribed handlers. This is most often used for sending Event Messages whose primary role is notification as opposed to Document Messages which are generally intended to be processed by a single handler. Note that the PublishSubscribeChannel is intended for sending only. Since it broadcasts to its subscribers directly when its send(Message) method is invoked, consumers cannot poll for Messages (it does not implement PollableChannel and therefore has no receive() method). Instead, any subscriber must be a MessageHandler itself, and the subscriber's handleMessage(Message) method will be invoked in turn.

Prior to version 3.0, invoking the send method on a PublishSubscribeChannel that had no subscribers returned false. When used in conjunction with a MessagingTemplate, a MessageDeliveryException was thrown. Starting with version 3.0, the behavior has changed such that a send is always considered successful if at least the minimum subscribers are present (and successfully handle the message). This behavior can be modified by setting the minSubscribers property, which defaults to 0.

If a TaskExecutor is used, only the presence of the correct number of subscribers is used for this determination, because the actual handling of the message is performed asynchronously.


The QueueChannel implementation wraps a queue. Unlike the PublishSubscribeChannel, the QueueChannel has point-to-point semantics. In other words, even if the channel has multiple consumers, only one of them should receive any Message sent to that channel. It provides a default no-argument constructor (providing an essentially unbounded capacity of Integer.MAX_VALUE) as well as a constructor that accepts the queue capacity:

public QueueChannel(int capacity)

A channel that has not reached its capacity limit will store messages in its internal queue, and the send() method will return immediately even if no receiver is ready to handle the message. If the queue has reached capacity, then the sender will block until room is available. Or, if using the send call that accepts a timeout, it will block until either room is available or the timeout period elapses, whichever occurs first. Likewise, a receive call will return immediately if a message is available on the queue, but if the queue is empty, then a receive call may block until either a message is available or the timeout elapses. In either case, it is possible to force an immediate return regardless of the queue's state by passing a timeout value of 0. Note however, that calls to the no-arg versions of send() and receive() will block indefinitely.


Whereas the QueueChannel enforces first-in/first-out (FIFO) ordering, the PriorityChannel is an alternative implementation that allows for messages to be ordered within the channel based upon a priority. By default the priority is determined by the 'priority' header within each message. However, for custom priority determination logic, a comparator of type Comparator<Message<?>> can be provided to the PriorityChannel's constructor.


The RendezvousChannel enables a "direct-handoff" scenario where a sender will block until another party invokes the channel's receive() method or vice-versa. Internally, this implementation is quite similar to the QueueChannel except that it uses a SynchronousQueue (a zero-capacity implementation of BlockingQueue). This works well in situations where the sender and receiver are operating in different threads but simply dropping the message in a queue asynchronously is not appropriate. In other words, with a RendezvousChannel at least the sender knows that some receiver has accepted the message, whereas with a QueueChannel, the message would have been stored to the internal queue and potentially never received.


Keep in mind that all of these queue-based channels are storing messages in-memory only by default. When persistence is required, you can either provide a 'message-store' attribute within the 'queue' element to reference a persistent MessageStore implementation, or you can replace the local channel with one that is backed by a persistent broker, such as a JMS-backed channel or Channel Adapter. The latter option allows you to take advantage of any JMS provider's implementation for message persistence, and it will be discussed in Chapter 19, JMS Support. However, when buffering in a queue is not necessary, the simplest approach is to rely upon the DirectChannel discussed next.

The RendezvousChannel is also useful for implementing request-reply operations. The sender can create a temporary, anonymous instance of RendezvousChannel which it then sets as the 'replyChannel' header when building a Message. After sending that Message, the sender can immediately call receive (optionally providing a timeout value) in order to block while waiting for a reply Message. This is very similar to the implementation used internally by many of Spring Integration's request-reply components.


The DirectChannel has point-to-point semantics but otherwise is more similar to the PublishSubscribeChannel than any of the queue-based channel implementations described above. It implements the SubscribableChannel interface instead of the PollableChannel interface, so it dispatches Messages directly to a subscriber. As a point-to-point channel, however, it differs from the PublishSubscribeChannel in that it will only send each Message to a single subscribed MessageHandler.

In addition to being the simplest point-to-point channel option, one of its most important features is that it enables a single thread to perform the operations on "both sides" of the channel. For example, if a handler is subscribed to a DirectChannel, then sending a Message to that channel will trigger invocation of that handler's handleMessage(Message) method directly in the sender's thread, before the send() method invocation can return.

The key motivation for providing a channel implementation with this behavior is to support transactions that must span across the channel while still benefiting from the abstraction and loose coupling that the channel provides. If the send call is invoked within the scope of a transaction, then the outcome of the handler's invocation (e.g. updating a database record) will play a role in determining the ultimate result of that transaction (commit or rollback).

Since the DirectChannel is the simplest option and does not add any additional overhead that would be required for scheduling and managing the threads of a poller, it is the default channel type within Spring Integration. The general idea is to define the channels for an application and then to consider which of those need to provide buffering or to throttle input, and then modify those to be queue-based PollableChannels. Likewise, if a channel needs to broadcast messages, it should not be a DirectChannel but rather a PublishSubscribeChannel. Below you will see how each of these can be configured.

The DirectChannel internally delegates to a Message Dispatcher to invoke its subscribed Message Handlers, and that dispatcher can have a load-balancing strategy exposed via load-balancer or load-balancer-ref attributes (mutually exclusive). The load balancing strategy is used by the Message Dispatcher to help determine how Messages are distributed amongst Message Handlers in the case that there are multiple Message Handlers subscribed to the same channel. As a convinience the load-balancer attribute exposes enumeration of values pointing to pre-existing implementations of LoadBalancingStrategy. The "round-robin" (load-balances across the handlers in rotation) and "none" (for the cases where one wants to explicitely disable load balancing) are the only available values. Other strategy implementations may be added in future versions. However, since version 3.0 you can provide your own implementation of the LoadBalancingStrategy and inject it using load-balancer-ref attribute which should point to a bean that implements LoadBalancingStrategy.

<int:channel id="lbRefChannel">
  <int:dispatcher load-balancer-ref="lb"/>
<bean id="lb" class="foo.bar.SampleLoadBalancingStrategy"/>

Note that load-balancer or load-balancer-ref attributes are mutually exclusive.

The load-balancing also works in combination with a boolean failover property. If the "failover" value is true (the default), then the dispatcher will fall back to any subsequent handlers as necessary when preceding handlers throw Exceptions. The order is determined by an optional order value defined on the handlers themselves or, if no such value exists, the order in which the handlers are subscribed.

If a certain situation requires that the dispatcher always try to invoke the first handler, then fallback in the same fixed order sequence every time an error occurs, no load-balancing strategy should be provided. In other words, the dispatcher still supports the failover boolean property even when no load-balancing is enabled. Without load-balancing, however, the invocation of handlers will always begin with the first according to their order. For example, this approach works well when there is a clear definition of primary, secondary, tertiary, and so on. When using the namespace support, the "order" attribute on any endpoint will determine that order.

Keep in mind that load-balancing and failover only apply when a channel has more than one subscribed Message Handler. When using the namespace support, this means that more than one endpoint shares the same channel reference in the "input-channel" attribute.


The ExecutorChannel is a point-to-point channel that supports the same dispatcher configuration as DirectChannel (load-balancing strategy and the failover boolean property). The key difference between these two dispatching channel types is that the ExecutorChannel delegates to an instance of TaskExecutor to perform the dispatch. This means that the send method typically will not block, but it also means that the handler invocation may not occur in the sender's thread. It therefore does not support transactions spanning the sender and receiving handler.

Note that there are occasions where the sender may block. For example, when using a TaskExecutor with a rejection-policy that throttles back on the client (such as the ThreadPoolExecutor.CallerRunsPolicy), the sender's thread will execute the method directly anytime the thread pool is at its maximum capacity and the executor's work queue is full. Since that situation would only occur in a non-predictable way, that obviously cannot be relied upon for transactions.

Scoped Channel

Spring Integration 1.0 provided a ThreadLocalChannel implementation, but that has been removed as of 2.0. Now, there is a more general way for handling the same requirement by simply adding a "scope" attribute to a channel. The value of the attribute can be any name of a Scope that is available within the context. For example, in a web environment, certain Scopes are available, and any custom Scope implementations can be registered with the context. Here's an example of a ThreadLocal-based scope being applied to a channel, including the registration of the Scope itself.

<int:channel id="threadScopedChannel" scope="thread">
     <int:queue />

<bean class="org.springframework.beans.factory.config.CustomScopeConfigurer">
    <property name="scopes">
            <entry key="thread" value="org.springframework.context.support.SimpleThreadScope" />

The channel above also delegates to a queue internally, but the channel is bound to the current thread, so the contents of the queue are as well. That way the thread that sends to the channel will later be able to receive those same Messages, but no other thread would be able to access them. While thread-scoped channels are rarely needed, they can be useful in situations where DirectChannels are being used to enforce a single thread of operation but any reply Messages should be sent to a "terminal" channel. If that terminal channel is thread-scoped, the original sending thread can collect its replies from it.

Now, since any channel can be scoped, you can define your own scopes in addition to Thread Local.

3.1.3 Channel Interceptors

One of the advantages of a messaging architecture is the ability to provide common behavior and capture meaningful information about the messages passing through the system in a non-invasive way. Since the Messages are being sent to and received from MessageChannels, those channels provide an opportunity for intercepting the send and receive operations. The ChannelInterceptor strategy interface provides methods for each of those operations:

public interface ChannelInterceptor {

    Message<?> preSend(Message<?> message, MessageChannel channel);

    void postSend(Message<?> message, MessageChannel channel, boolean sent);

    boolean preReceive(MessageChannel channel);

    Message<?> postReceive(Message<?> message, MessageChannel channel);

After implementing the interface, registering the interceptor with a channel is just a matter of calling:


The methods that return a Message instance can be used for transforming the Message or can return 'null' to prevent further processing (of course, any of the methods can throw a RuntimeException). Also, the preReceive method can return 'false' to prevent the receive operation from proceeding.

Keep in mind that receive() calls are only relevant for PollableChannels. In fact the SubscribableChannel interface does not even define a receive() method. The reason for this is that when a Message is sent to a SubscribableChannel it will be sent directly to one or more subscribers depending on the type of channel (e.g. a PublishSubscribeChannel sends to all of its subscribers). Therefore, the preReceive(..) and postReceive(..) interceptor methods are only invoked when the interceptor is applied to a PollableChannel.

Spring Integration also provides an implementation of the Wire Tap pattern. It is a simple interceptor that sends the Message to another channel without otherwise altering the existing flow. It can be very useful for debugging and monitoring. An example is shown in the section called “Wire Tap”.

Because it is rarely necessary to implement all of the interceptor methods, a ChannelInterceptorAdapter class is also available for sub-classing. It provides no-op methods (the void method is empty, the Message returning methods return the Message as-is, and the boolean method returns true). Therefore, it is often easiest to extend that class and just implement the method(s) that you need as in the following example.

public class CountingChannelInterceptor extends ChannelInterceptorAdapter {

    private final AtomicInteger sendCount = new AtomicInteger();

    public Message<?> preSend(Message<?> message, MessageChannel channel) {
        return message;

The order of invocation for the interceptor methods depends on the type of channel. As described above, the queue-based channels are the only ones where the receive method is intercepted in the first place. Additionally, the relationship between send and receive interception depends on the timing of separate sender and receiver threads. For example, if a receiver is already blocked while waiting for a message the order could be: preSend, preReceive, postReceive, postSend. However, if a receiver polls after the sender has placed a message on the channel and already returned, the order would be: preSend, postSend, (some-time-elapses) preReceive, postReceive. The time that elapses in such a case depends on a number of factors and is therefore generally unpredictable (in fact, the receive may never happen!). Obviously, the type of queue also plays a role (e.g. rendezvous vs. priority). The bottom line is that you cannot rely on the order beyond the fact that preSend will precede postSend and preReceive will precede postReceive.

3.1.4 MessagingTemplate

As you will see when the endpoints and their various configuration options are introduced, Spring Integration provides a foundation for messaging components that enables non-invasive invocation of your application code from the messaging system. However, sometimes it is necessary to invoke the messaging system from your application code. For convenience when implementing such use-cases, Spring Integration provides a MessagingTemplate that supports a variety of operations across the Message Channels, including request/reply scenarios. For example, it is possible to send a request and wait for a reply.

MessagingTemplate template = new MessagingTemplate();

Message reply = template.sendAndReceive(someChannel, new GenericMessage("test"));

In that example, a temporary anonymous channel would be created internally by the template. The 'sendTimeout' and 'receiveTimeout' properties may also be set on the template, and other exchange types are also supported.

public boolean send(final MessageChannel channel, final Message<?> message) { ... }

public Message<?> sendAndReceive(final MessageChannel channel, final Message<?> request) { .. }

public Message<?> receive(final PollableChannel<?> channel) { ... }


A less invasive approach that allows you to invoke simple interfaces with payload and/or header values instead of Message instances is described in Section 7.2.1, “Enter the GatewayProxyFactoryBean”.

3.1.5 Configuring Message Channels

To create a Message Channel instance, you can use the <channel/> element:

<int:channel id="exampleChannel"/>

The default channel type is Point to Point. To create a Publish Subscribe channel, use the <publish-subscribe-channel/> element:

<int:publish-subscribe-channel id="exampleChannel"/>

When using the <channel/> element without any sub-elements, it will create a DirectChannel instance (a SubscribableChannel).

However, you can alternatively provide a variety of <queue/> sub-elements to create any of the pollable channel types (as described in Section 3.1.2, “Message Channel Implementations”). Examples of each are shown below.

DirectChannel Configuration

As mentioned above, DirectChannel is the default type.

<int:channel id="directChannel"/>

A default channel will have a round-robin load-balancer and will also have failover enabled (See the discussion in the section called “DirectChannel” for more detail). To disable one or both of these, add a <dispatcher/> sub-element and configure the attributes:

<int:channel id="failFastChannel">
    <int:dispatcher failover="false"/>

<int:channel id="channelWithFixedOrderSequenceFailover">
    <int:dispatcher load-balancer="none"/>

Datatype Channel Configuration

There are times when a consumer can only process a particular type of payload and you need to therefore ensure the payload type of input Messages. Of course the first thing that comes to mind is Message Filter. However all that Message Filter will do is filter out Messages that are not compliant with the requirements of the consumer. Another way would be to use a Content Based Router and route Messages with non-compliant data-types to specific Transformers to enforce transformation/conversion to the required data-type. This of course would work, but a simpler way of accomplishing the same thing is to apply the Datatype Channel pattern. You can use separate Datatype Channels for each specific payload data-type.

To create a Datatype Channel that only accepts messages containing a certain payload type, provide the fully-qualified class name in the channel element's datatype attribute:

<int:channel id="numberChannel" datatype="java.lang.Number"/>

Note that the type check passes for any type that is assignable to the channel's datatype. In other words, the "numberChannel" above would accept messages whose payload is java.lang.Integer or java.lang.Double. Multiple types can be provided as a comma-delimited list:

<int:channel id="stringOrNumberChannel" datatype="java.lang.String,java.lang.Number"/>

So the 'numberChannel' above will only accept Messages with a data-type of java.lang.Number. But what happens if the payload of the Message is not of the required type? It depends on whether you have defined a bean named "integrationConversionService" that is an instance of Spring's Conversion Service. If not, then an Exception would be thrown immediately, but if you do have an "integrationConversionService" bean defined, it will be used in an attempt to convert the Message's payload to the acceptable type.

You can even register custom converters. For example, let's say you are sending a Message with a String payload to the 'numberChannel' we configured above.

MessageChannel inChannel = context.getBean("numberChannel", MessageChannel.class);
inChannel.send(new GenericMessage<String>("5"));

Typically this would be a perfectly legal operation, however since we are using Datatype Channel the result of such operation would generate an exception:

Exception in thread "main" org.springframework.integration.MessageDeliveryException:
Channel 'numberChannel'
expected one of the following datataypes [class java.lang.Number],
but received [class java.lang.String]

And rightfully so since we are requiring the payload type to be a Number while sending a String. So we need something to convert String to a Number. All we need to do is implement a Converter.

public static class StringToIntegerConverter implements Converter<String, Integer> {
	public Integer convert(String source) {
		return Integer.parseInt(source);

Then, register it as a Converter with the Integration Conversion Service:

<int:converter ref="strToInt"/>

<bean id="strToInt" class="org.springframework.integration.util.Demo.StringToIntegerConverter"/>

When the 'converter' element is parsed, it will create the "integrationConversionService" bean on-demand if one is not already defined. With that Converter in place, the send operation would now be successful since the Datatype Channel will use that Converter to convert the String payload to an Integer.


For more information regarding Payload Type Conversion, please read Section 7.1.6, “Payload Type Conversion”.

QueueChannel Configuration

To create a QueueChannel, use the <queue/> sub-element. You may specify the channel's capacity:

<int:channel id="queueChannel">
    <queue capacity="25"/>

If you do not provide a value for the 'capacity' attribute on this <queue/> sub-element, the resulting queue will be unbounded. To avoid issues such as OutOfMemoryErrors, it is highly recommended to set an explicit value for a bounded queue.

Persistent QueueChannel Configuration

Since a QueueChannel provides the capability to buffer Messages, but does so in-memory only by default, it also introduces a possibility that Messages could be lost in the event of a system failure. To mitigate this risk, a QueueChannel may be backed by a persistent implementation of the MessageGroupStore strategy interface. For more details on MessageGroupStore and MessageStore see Section 8.3, “Message Store”.

When a QueueChannel receives a Message, it will add it to the Message Store, and when a Message is polled from a QueueChannel, it is removed from the Message Store.

By default any QueueChannel only stores its Messages in an in-memory Queue and can therefore lead to the lost message scenario mentioned above. However Spring Integration provides a JdbcMessageStore to allow a QueueChannel to be backed by an RDBMS.

You can configure a Message Store for any QueueChannel by adding the message-store attribute as shown in the next example.

<int:channel id="dbBackedChannel">
    <int:queue message-store="messageStore"/>

<int-jdbc:message-store id="messageStore" data-source="someDataSource"/>

The above example also shows that JdbcMessageStore can be configured with the namespace support provided by the Spring Integration JDBC module. All you need to do is inject any javax.sql.DataSource instance. The Spring Integration JDBC module also provides schema DDL for most popular databases. These schemas are located in the org.springframework.integration.jdbc package of that module (spring-integration-jdbc).

One important feature is that with any transactional persistent store (e.g., JdbcMessageStore), as long as the poller has a transaction configured, a Message removed from the store will only be permanently removed if the transaction completes successfully, otherwise the transaction will roll back and the Message will not be lost.

Many other implementations of the Message Store will be available as the growing number of Spring projects related to "NoSQL" data stores provide the underlying support. Of course, you can always provide your own implementation of the MessageGroupStore interface if you cannot find one that meets your particular needs.

PublishSubscribeChannel Configuration

To create a PublishSubscribeChannel, use the <publish-subscribe-channel/> element. When using this element, you can also specify the task-executor used for publishing Messages (if none is specified it simply publishes in the sender's thread):

<int:publish-subscribe-channel id="pubsubChannel" task-executor="someExecutor"/>

If you are providing a Resequencer or Aggregator downstream from a PublishSubscribeChannel, then you can set the 'apply-sequence' property on the channel to true. That will indicate that the channel should set the sequence-size and sequence-number Message headers as well as the correlation id prior to passing the Messages along. For example, if there are 5 subscribers, the sequence-size would be set to 5, and the Messages would have sequence-number header values ranging from 1 to 5.

<int:publish-subscribe-channel id="pubsubChannel" apply-sequence="true"/>

The apply-sequence value is false by default so that a Publish Subscribe Channel can send the exact same Message instances to multiple outbound channels. Since Spring Integration enforces immutability of the payload and header references, the channel creates new Message instances with the same payload reference but different header values when the flag is set to true.


To create an ExecutorChannel, add the <dispatcher> sub-element along with a task-executor attribute. Its value can reference any TaskExecutor within the context. For example, this enables configuration of a thread-pool for dispatching messages to subscribed handlers. As mentioned above, this does break the "single-threaded" execution context between sender and receiver so that any active transaction context will not be shared by the invocation of the handler (i.e. the handler may throw an Exception, but the send invocation has already returned successfully).

<int:channel id="executorChannel">
    <int:dispatcher task-executor="someExecutor"/>

The load-balancer and failover options are also both available on the <dispatcher/> sub-element as described above in the section called “DirectChannel Configuration”. The same defaults apply as well. So, the channel will have a round-robin load-balancing strategy with failover enabled unless explicit configuration is provided for one or both of those attributes.
<int:channel id="executorChannelWithoutFailover">
    <int:dispatcher task-executor="someExecutor" failover="false"/>

PriorityChannel Configuration

To create a PriorityChannel, use the <priority-queue/> sub-element:

<int:channel id="priorityChannel">
    <int:priority-queue capacity="20"/>

By default, the channel will consult the priority header of the message. However, a custom Comparator reference may be provided instead. Also, note that the PriorityChannel (like the other types) does support the datatype attribute. As with the QueueChannel, it also supports a capacity attribute. The following example demonstrates all of these:

<int:channel id="priorityChannel" datatype="example.Widget">
    <int:priority-queue comparator="widgetComparator"

RendezvousChannel Configuration

A RendezvousChannel is created when the queue sub-element is a <rendezvous-queue>. It does not provide any additional configuration options to those described above, and its queue does not accept any capacity value since it is a 0-capacity direct handoff queue.

<int:channel id="rendezvousChannel"/>

Scoped Channel Configuration

Any channel can be configured with a "scope" attribute.

<int:channel id="threadLocalChannel" scope="thread"/>

Channel Interceptor Configuration

Message channels may also have interceptors as described in Section 3.1.3, “Channel Interceptors”. The <interceptors/> sub-element can be added within <channel/> (or the more specific element types). Provide the ref attribute to reference any Spring-managed object that implements the ChannelInterceptor interface:

<int:channel id="exampleChannel">
        <ref bean="trafficMonitoringInterceptor"/>

In general, it is a good idea to define the interceptor implementations in a separate location since they usually provide common behavior that can be reused across multiple channels.

Global Channel Interceptor Configuration

Channel Interceptors provide a clean and concise way of applying cross-cutting behavior per individual channel. If the same behavior should be applied on multiple channels, configuring the same set of interceptors for each channel would not be the most efficient way. To avoid repeated configuration while also enabling interceptors to apply to multiple channels, Spring Integration provides Global Interceptors. Look at the example below:

<int:channel-interceptor pattern="input*, bar*, foo" order="3">
    <bean class="foo.barSampleInterceptor"/>


<int:channel-interceptor ref="myInterceptor" pattern="input*, bar*, foo" order="3"/>

<bean id="myInterceptor" class="foo.barSampleInterceptor"/>

Each <channel-interceptor/> element allows you to define a global interceptor which will be applied on all channels that match any patterns defined via the pattern attribute. In the above case the global interceptor will be applied on the 'foo' channel and all other channels that begin with 'bar' or 'input'. The order attribute allows you to manage where this interceptor will be injected if there are multiple interceptors on a given channel. For example, channel 'inputChannel' could have individual interceptors configured locally (see below):

<int:channel id="inputChannel"> 
    <int:wire-tap channel="logger"/> 

A reasonable question is how will a global interceptor be injected in relation to other interceptors configured locally or through other global interceptor definitions? The current implementation provides a very simple mechanism for defining the order of interceptor execution. A positive number in the order attribute will ensure interceptor injection after any existing interceptors and a negative number will ensure that the interceptor is injected before existing interceptors. This means that in the above example, the global interceptor will be injected AFTER (since its order is greater than 0) the 'wire-tap' interceptor configured locally. If there were another global interceptor with a matching pattern, its order would be determined by comparing the values of the order attribute. To inject a global interceptor BEFORE the existing interceptors, use a negative value for the order attribute.

Note that both the order and pattern attributes are optional. The default value for order will be 0 and for pattern, the default is '*' (to match all channels).

Wire Tap

As mentioned above, Spring Integration provides a simple Wire Tap interceptor out of the box. You can configure a Wire Tap on any channel within an <interceptors/> element. This is especially useful for debugging, and can be used in conjunction with Spring Integration's logging Channel Adapter as follows:

<int:channel id="in">
        <int:wire-tap channel="logger"/>

<int:logging-channel-adapter id="logger" level="DEBUG"/>

The 'logging-channel-adapter' also accepts an 'expression' attribute so that you can evaluate a SpEL expression against 'payload' and/or 'headers' variables. Alternatively, to simply log the full Message toString() result, provide a value of "true" for the 'log-full-message' attribute. That is false by default so that only the payload is logged. Setting that to true enables logging of all headers in addition to the payload. The 'expression' option does provide the most flexibility, however (e.g. expression="payload.user.name").

A little more on Wire Tap

One of the common misconceptions about the wire tap and other similar components (Section B.1, “Message Publishing Configuration”) is that they are automatically asynchronous in nature. Wire-tap as a component is not invoked asynchronously be default. Instead, Spring Integration focuses on a single unified approach to configuring asynchronous behavior: the Message Channel. What makes certain parts of the message flow sync or async is the type of Message Channel that has been configured within that flow. That is one of the primary benefits of the Message Channel abstraction. From the inception of the framework, we have always emphasized the need and the value of the Message Channel as a first-class citizen of the framework. It is not just an internal, implicit realization of the EIP pattern, it is fully exposed as a configurable component to the end user. So, the Wire-tap component is ONLY responsible for performing the following 3 tasks:

  • intercept a message flow by tapping into a channel (e.g., channelA)

  • grab each message

  • send the message to another channel (e.g., channelB)

It is essentially a variation of the Bridge, but it is encapsulated within a channel definition (and hence easier to enable and disable without disrupting a flow). Also, unlike the bridge, it basically forks another message flow. Is that flow synchronous or asynchronous? The answer simply depends on the type of Message Channel that 'channelB' is. And, now you know that we have: Direct Channel, Pollable Channel, and Executor Channel as options. The last two do break the thread boundary making communication via such channels asynchronous simply because the dispatching of the message from that channel to its subscribed handlers happens on a different thread than the one used to send the message to that channel. That is what is going to make your wire-tap flow sync or async. It is consistent with other components within the framework (e.g., Message Publisher) and actually brings a level of consistency and simplicity by sparing you from worrying in advance (other than writing thread safe code) whether a particular piece of code should be implemented as sync or async. The actual wiring of two pieces of code (component A and component B) via Message Channel is what makes their collaboration sync or async. You may even want to change from sync to async in the future and Message Channel is what's going to allow you to do it swiftly without ever touching the code.

One final point regarding the Wire Tap is that, despite the rationale provided above for not being async be default, one should keep in mind it is usually desirable to hand off the Message as soon as possible. Therefore, it would be quite common to use an asynchronous channel option as the wire-tap's outbound channel. Nonetheless, another reason that we do not enforce asynchronous behavior by default is that you might not want to break a transactional boundary. Perhaps you are using the Wire Tap for auditing purposes, and you DO want the audit Messages to be sent within the original transaction. As an example, you might connect the wire-tap to a JMS outbound-channel-adapter. That way, you get the best of both worlds: 1) the sending of a JMS Message can occur within the transaction while 2) it is still a "fire-and-forget" action thereby preventing any noticeable delay in the main message flow.

Global Wire Tap Configuration

It is possible to configure a global wire tap as a special case of the Global Channel Interceptor. Simply configure a top level wire-tap element. Now, in addition to the normal wire-tap namespace support, the pattern and order attributes are supported and work in exactly the same way as with the channel-interceptor

<int:wire-tap pattern="input*, bar*, foo" order="3" channel="wiretapChannel"/>

A global wire tap provides a convenient way to configure a single channel wire tap externally without modifying the existing channel configuration. Simply set the pattern attribute to the target channel name. For example, This technique may be used to configure a test case to verify messages on a channel.

3.1.6 Special Channels

If namespace support is enabled, there are two special channels defined within the application context by default: errorChannel and nullChannel. The 'nullChannel' acts like /dev/null, simply logging any Message sent to it at DEBUG level and returning immediately. Any time you face channel resolution errors for a reply that you don't care about, you can set the affected component's output-channel attribute to 'nullChannel' (the name 'nullChannel' is reserved within the application context). The 'errorChannel' is used internally for sending error messages and may be overridden with a custom configuration. This is discussed in greater detail in Section F.4, “Error Handling”.

3.2 Poller (Polling Consumer)

When Message Endpoints (Channel Adapters) are connected to channels and instantiated, they produce one of the following 2 instances:

The actual implementation depends on which type of channel these Endpoints are connected to. A channel adapter connected to a channel that implements the org.springframework.integration.core.SubscribableChannel interface will produce an instance of EventDrivenConsumer. On the other hand, a channel adapter connected to a channel that implements the org.springframework.integration.core.PollableChannel interface (e.g. a QueueChannel) will produce an instance of PollingConsumer.

Polling Consumers allow Spring Integration components to actively poll for Messages, rather than to process Messages in an event-driven manner.

They represent a critical cross cutting concern in many messaging scenarios. In Spring Integration, Polling Consumers are based on the pattern with the same name, which is described in the book "Enterprise Integration Patterns" by Gregor Hohpe and Bobby Woolf. You can find a description of the pattern on the book's website at:

Furthermore, in Spring Integration a second variation of the Polling Consumer pattern exists. When Inbound Channel Adapters are being used, these adapters are often wrapped by a SourcePollingChannelAdapter. For example, when retrieving messages from a remote FTP Server location, the adapter described in Section 14.3, “FTP Inbound Channel Adapter” is configured with a poller to retrieve messages periodically. So, when components are configured with Pollers, the resulting instances are of one of the following types:

This means, Pollers are used in both inbound and outbound messaging scenarios. Here are some use-cases that illustrate the scenarios in which Pollers are used:

  • Polling certain external systems such as FTP Servers, Databases, Web Services
  • Polling internal (pollable) Message Channels
  • Polling internal services (E.g. repeatedly execute methods on a Java class)

This chapter is meant to only give a high-level overview regarding Polling Consumers and how they fit into the concept of message channels - Section 3.1, “Message Channels” and channel adapters - Section 3.3, “Channel Adapter”. For more in-depth information regarding Messaging Endpoints in general and Polling Consumers in particular, please see Section 7.1, “Message Endpoints”.

3.3 Channel Adapter

A Channel Adapter is a Message Endpoint that enables connecting a single sender or receiver to a Message Channel. Spring Integration provides a number of adapters out of the box to support various transports, such as JMS, File, HTTP, Web Services, Mail, and more. Those will be discussed in upcoming chapters of this reference guide. However, this chapter focuses on the simple but flexible Method-invoking Channel Adapter support. There are both inbound and outbound adapters, and each may be configured with XML elements provided in the core namespace. These provide an easy way to extend Spring Integration as long as you have a method that can be invoked as either a source or destination.

3.3.1 Configuring An Inbound Channel Adapter

An "inbound-channel-adapter" element can invoke any method on a Spring-managed Object and send a non-null return value to a MessageChannel after converting it to a Message. When the adapter's subscription is activated, a poller will attempt to receive messages from the source. The poller will be scheduled with the TaskScheduler according to the provided configuration. To configure the polling interval or cron expression for an individual channel-adapter, provide a 'poller' element with one of the scheduling attributes, such as 'fixed-rate' or 'cron'.

<int:inbound-channel-adapter ref="source1" method="method1" channel="channel1">
    <int:poller fixed-rate="5000"/>

<int:inbound-channel-adapter ref="source2" method="method2" channel="channel2">
    <int:poller cron="30 * 9-17 * * MON-FRI"/>

Also see Section 3.3.3, “Channel Adapter Expressions and Scripts”.


If no poller is provided, then a single default poller must be registered within the context. See Section 7.1.4, “Namespace Support” for more detail.


Poller Configuration

Some inbound-channel-adapter types are backed by a SourcePollingChannelAdapter which means they contain Poller configuration which will poll the MessageSource (invoke a custom method which produces the value that becomes a Message payload) based on the configuration specified in the Poller.

For example:

<int:poller max-messages-per-poll="1" fixed-rate="1000"/>

<int:poller max-messages-per-poll="10" fixed-rate="1000"/>

In the the first configuration the polling task will be invoked once per poll and during such task (poll) the method (which results in the production of the Message) will be invoked once based on the max-messages-per-poll attribute value. In the second configuration the polling task will be invoked 10 times per poll or until it returns 'null' thus possibly producing 10 Messages per poll while each poll happens at 1 second intervals. However what if the configuration looks like this:

<int:poller fixed-rate="1000"/>

Note there is no max-messages-per-poll specified. As you'll learn later the identical poller configuration in the PollingConsumer (e.g., service-activator, filter, router etc.) would have a default value of -1 for max-messages-per-poll which means "execute poling task non-stop unless polling method returns null (e.g., no more Messages in the QueueChannel)" and then sleep for 1 second.

However in the SourcePollingChannelAdapter it is a bit different. The default value for max-messages-per-poll will be set to 1 by default unless you explicitly set it to a negative value (e.g., -1). It is done so to make sure that poller can react to a LifeCycle events (e.g., start/stop) and prevent it from potentially spinning in the infinite loop if the implementation of the custom method of the MessageSource has a potential to never return null and happened to be non-interruptible.

However if you are sure that your method can return null and you need the behavior where you want to poll for as many sources as available per each poll, then you should explicitly set max-messages-per-poll to negative value.

<int:poller max-messages-per-poll="-1" fixed-rate="1000"/>

3.3.2 Configuring An Outbound Channel Adapter

An "outbound-channel-adapter" element can also connect a MessageChannel to any POJO consumer method that should be invoked with the payload of Messages sent to that channel.

<int:outbound-channel-adapter channel="channel1" ref="target" method="handle"/>

<beans:bean id="target" class="org.Foo"/>

If the channel being adapted is a PollableChannel, provide a poller sub-element:

<int:outbound-channel-adapter channel="channel2" ref="target" method="handle">
    <int:poller fixed-rate="3000"/>

<beans:bean id="target" class="org.Foo"/>

Using a "ref" attribute is generally recommended if the POJO consumer implementation can be reused in other <outbound-channel-adapter> definitions. However if the consumer implementation is only referenced by a single definition of the <outbound-channel-adapter>, you can define it as inner bean:

<int:outbound-channel-adapter channel="channel" method="handle">
    <beans:bean class="org.Foo"/>


Using both the "ref" attribute and an inner handler definition in the same <outbound-channel-adapter> configuration is not allowed as it creates an ambiguous condition. Such a configuration will result in an Exception being thrown.

Any Channel Adapter can be created without a "channel" reference in which case it will implicitly create an instance of DirectChannel. The created channel's name will match the "id" attribute of the <inbound-channel-adapter> or <outbound-channel-adapter> element. Therefore, if the "channel" is not provided, the "id" is required.

3.3.3 Channel Adapter Expressions and Scripts

Like many other Spring Integration components, the <inbound-channel-adapter> and <outbound-channel-adapter> also provide support for SpEL expression evaluation. To use SpEL, provide the expression string via the 'expression' attribute instead of providing the 'ref' and 'method' attributes that are used for method-invocation on a bean. When an Expression is evaluated, it follows the same contract as method-invocation where: the expression for an <inbound-channel-adapter> will generate a message anytime the evaluation result is a non-null value, while the expression for an <outbound-channel-adapter> must be the equivalent of a void returning method invocation.

Starting with Spring Integration 3.0, an <int:inbound-channel-adapter/> can also be configured with a SpEL <expression/> (or even with <script/>) sub-element, for when more sophistication is required than can be achieved with the simple 'expression' attribute. If you provide a script as a Resource using the location attribute, you can also set the refresh-check-delay allowing the resource to be refreshed periodically. If you want the script to be checked on each poll, you would need to coordinate this setting with the poller's trigger:

<int:inbound-channel-adapter ref="source1" method="method1" channel="channel1">
    <int:poller max-messages-per-poll="1" fixed-delay="5000"/>
    <script:script lang="ruby" location="Foo.rb" refresh-check-delay="5000"/>

Also see the cacheSeconds property on the ReloadableResourceBundleExpressionSource when using the <expression/> sub-element. For more information regarding expressions see Appendix A, Spring Expression Language (SpEL), and for scripts - Section 7.6, “Groovy support” and Section 7.5, “Scripting support”.


The <int:inbound-channel-adapter/> is an endpoint that starts a message flow via periodic triggering to poll some underlying MessageSource. Since, at the time of polling, there is not yet a message object, expressions and scripts don't have access to a root Message, so there are no payload or headers properties that are available in most other messaging SpEL expressions. Of course, the script can generate and return a complete Message object with headers and payload, or just a payload, which will be added to a message with basic headers.

3.4 Messaging Bridge

3.4.1 Introduction

A Messaging Bridge is a relatively trivial endpoint that simply connects two Message Channels or Channel Adapters. For example, you may want to connect a PollableChannel to a SubscribableChannel so that the subscribing endpoints do not have to worry about any polling configuration. Instead, the Messaging Bridge provides the polling configuration.

By providing an intermediary poller between two channels, a Messaging Bridge can be used to throttle inbound Messages. The poller's trigger will determine the rate at which messages arrive on the second channel, and the poller's "maxMessagesPerPoll" property will enforce a limit on the throughput.

Another valid use for a Messaging Bridge is to connect two different systems. In such a scenario, Spring Integration's role would be limited to making the connection between these systems and managing a poller if necessary. It is probably more common to have at least a Transformer between the two systems to translate between their formats, and in that case, the channels would be provided as the 'input-channel' and 'output-channel' of a Transformer endpoint. If data format translation is not required, the Messaging Bridge may indeed be sufficient.

3.4.2 Configuring Bridge

The <bridge> element is used to create a Messaging Bridge between two Message Channels or Channel Adapters. Simply provide the "input-channel" and "output-channel" attributes:

<int:bridge input-channel="input" output-channel="output"/>

As mentioned above, a common use case for the Messaging Bridge is to connect a PollableChannel to a SubscribableChannel, and when performing this role, the Messaging Bridge may also serve as a throttler:

<int:bridge input-channel="pollable" output-channel="subscribable">
     <int:poller max-messages-per-poll="10" fixed-rate="5000"/>

Connecting Channel Adapters is just as easy. Here is a simple echo example between the "stdin" and "stdout" adapters from Spring Integration's "stream" namespace.

<int-stream:stdin-channel-adapter id="stdin"/>

 <int-stream:stdout-channel-adapter id="stdout"/>

 <int:bridge id="echo" input-channel="stdin" output-channel="stdout"/>

Of course, the configuration would be similar for other (potentially more useful) Channel Adapter bridges, such as File to JMS, or Mail to File. The various Channel Adapters will be discussed in upcoming chapters.


If no 'output-channel' is defined on a bridge, the reply channel provided by the inbound Message will be used, if available. If neither output or reply channel is available, an Exception will be thrown.

4. Message Construction

4.1 Message

The Spring Integration Message is a generic container for data. Any object can be provided as the payload, and each Message also includes headers containing user-extensible properties as key-value pairs.

4.1.1 The Message Interface

Here is the definition of the Message interface:

public interface Message<T> {

    T getPayload();

    MessageHeaders getHeaders();


The Message is obviously a very important part of the API. By encapsulating the data in a generic wrapper, the messaging system can pass it around without any knowledge of the data's type. As an application evolves to support new types, or when the types themselves are modified and/or extended, the messaging system will not be affected by such changes. On the other hand, when some component in the messaging system does require access to information about the Message, such metadata can typically be stored to and retrieved from the metadata in the Message Headers.

4.1.2 Message Headers

Just as Spring Integration allows any Object to be used as the payload of a Message, it also supports any Object types as header values. In fact, the MessageHeaders class implements the java.util.Map interface:

public final class MessageHeaders implements Map<String, Object>, Serializable {

Even though the MessageHeaders implements Map, it is effectively a read-only implementation. Any attempt to put a value in the Map will result in an UnsupportedOperationException. The same applies for remove and clear. Since Messages may be passed to multiple consumers, the structure of the Map cannot be modified. Likewise, the Message's payload Object can not be set after the initial creation. However, the mutability of the header values themselves (or the payload Object) is intentionally left as a decision for the framework user.

As an implementation of Map, the headers can obviously be retrieved by calling get(..) with the name of the header. Alternatively, you can provide the expected Class as an additional parameter. Even better, when retrieving one of the pre-defined values, convenient getters are available. Here is an example of each of these three options:

 Object someValue = message.getHeaders().get("someKey");

 CustomerId customerId = message.getHeaders().get("customerId", CustomerId.class);

 Long timestamp = message.getHeaders().getTimestamp();

The following Message headers are pre-defined:

Table 4.1. Pre-defined Message Headers

Header NameHeader Type
REPLY_CHANNELjava.lang.Object (can be a String or MessageChannel)
ERROR_CHANNELjava.lang.Object (can be a String or MessageChannel)

Many inbound and outbound adapter implementations will also provide and/or expect certain headers, and additional user-defined headers can also be configured.

Message ID Generation

When a message transitions through an application, each time it is mutated (e.g. by a transformer) a new message id is assigned. The message id is a UUID. Beginning with Spring Integration 3.0, the default strategy used for id generation is more efficient than the previous java.util.UUID.randomUUID() implementation. It uses simple random numbers based on a secure random seed, instead of creating a secure random number each time.

A different UUID generation strategy can be selected by declaring a bean that implements MessageHeaders.IdGenerator in the application context.

Only one UUID generation strategy can be used in a classloader. This means that if two or more application contexts are running in the same classloader, they will share the same strategy. If one of the contexts changes the strategy, it will be used by all contexts. If two or more contexts in the same classloader declare a bean of type MessageHeaders.IdGenerator, they must all be an instance of the same class, otherwise the context attempting to replace a custom strategy will fail to initialize. If the strategy is the same, but parameterized, the strategy in the first context to initialize will be used.

In addition to the default strategy, two additional IdGenerators are provided; MessageHeaders.JdkIdGenerator uses the previous UUID.randomUUID() mechanism; MessageHeaders.SimpleIncrementingIdGenerator can be used in cases where a UUID is not really needed and a simple incrementing value is sufficient.

4.1.3 Message Implementations

The base implementation of the Message interface is GenericMessage<T>, and it provides two constructors:

new GenericMessage<T>(T payload);

new GenericMessage<T>(T payload, Map<String, Object> headers)

When a Message is created, a random unique id will be generated. The constructor that accepts a Map of headers will copy the provided headers to the newly created Message.

There is also a convenient implementation of Message designed to communicate error conditions. This implementation takes Throwable object as its payload:

ErrorMessage message = new ErrorMessage(someThrowable);

Throwable t = message.getPayload();

Notice that this implementation takes advantage of the fact that the GenericMessage base class is parameterized. Therefore, as shown in both examples, no casting is necessary when retrieving the Message payload Object.

4.1.4 The MessageBuilder Helper Class

You may notice that the Message interface defines retrieval methods for its payload and headers but no setters. The reason for this is that a Message cannot be modified after its initial creation. Therefore, when a Message instance is sent to multiple consumers (e.g. through a Publish Subscribe Channel), if one of those consumers needs to send a reply with a different payload type, it will need to create a new Message. As a result, the other consumers are not affected by those changes. Keep in mind, that multiple consumers may access the same payload instance or header value, and whether such an instance is itself immutable is a decision left to the developer. In other words, the contract for Messages is similar to that of an unmodifiable Collection, and the MessageHeaders' map further exemplifies that; even though the MessageHeaders class implements java.util.Map, any attempt to invoke a put operation (or 'remove' or 'clear') on the MessageHeaders will result in an UnsupportedOperationException.

Rather than requiring the creation and population of a Map to pass into the GenericMessage constructor, Spring Integration does provide a far more convenient way to construct Messages: MessageBuilder. The MessageBuilder provides two factory methods for creating Messages from either an existing Message or with a payload Object. When building from an existing Message, the headers and payload of that Message will be copied to the new Message:

Message<String> message1 = MessageBuilder.withPayload("test")
        .setHeader("foo", "bar")

Message<String> message2 = MessageBuilder.fromMessage(message1).build();

assertEquals("test", message2.getPayload());
assertEquals("bar", message2.getHeaders().get("foo"));

If you need to create a Message with a new payload but still want to copy the headers from an existing Message, you can use one of the 'copy' methods.

Message<String> message3 = MessageBuilder.withPayload("test3")

Message<String> message4 = MessageBuilder.withPayload("test4")
        .setHeader("foo", 123)

assertEquals("bar", message3.getHeaders().get("foo"));
assertEquals(123, message4.getHeaders().get("foo"));

Notice that the copyHeadersIfAbsent does not overwrite existing values. Also, in the second example above, you can see how to set any user-defined header with setHeader. Finally, there are set methods available for the predefined headers as well as a non-destructive method for setting any header (MessageHeaders also defines constants for the pre-defined header names).

Message<Integer> importantMessage = MessageBuilder.withPayload(99)

assertEquals(5, importantMessage.getHeaders().getPriority());

Message<Integer> lessImportantMessage = MessageBuilder.fromMessage(importantMessage)
        .setHeaderIfAbsent(MessageHeaders.PRIORITY, 2)

assertEquals(2, lessImportantMessage.getHeaders().getPriority());

The priority header is only considered when using a PriorityChannel (as described in the next chapter). It is defined as java.lang.Integer.

5. Message Routing

5.1 Routers

5.1.1 Overview

Routers are a crucial element in many messaging architectures. They consume Messages from a Message Channel and forward each consumed message to one or more different Message Channel depending on a set of conditions.

Spring Integration provides the following routers out-of-the-box:

Router implementations share many configuration parameters. Yet, certain differences exist between routers. Furthermore, the availability of configuration parameters depends on whether Routers are used inside or outside of a chain. In order to provide a quick overview, all available attributes are listed in the 2 tables below.

Table 5.1. Routers Outside of a Chain

Attributerouterheader value routerxpath routerpayload type routerrecipient list routerexception type router

Table 5.2. Routers Inside of a Chain

Attributerouterheader value routerxpath routerpayload type routerrecipient list routerexception type router


Router parameters have been more standardized across all router implementations with Spring Integration 2.1. Consequently, there are a few minor changes that leave the possibility of breaking older Spring Integration based applications.

Since Spring Integration 2.1 the ignore-channel-name-resolution-failures attribute is removed in favor of consolidating its behavior with the resolution-required attribute. Also, the resolution-required attribute now defaults to true.

Prior to these changes, the resolution-required attribute defaulted to false causing messages to be silently dropped when no channel was resolved and no default-output-channel was set. The new behavior will require at least one resolved channel and by default will throw an MessageDeliveryException if no channel was determined (or an attempt to send was not successful).

If you do desire to drop messages silently simply set default-output-channel="nullChannel".

5.1.2 Common Router Parameters

Inside and Outside of a Chain

The following parameters are valid for all routers inside and outside of chains.


This attribute specifies whether sequence number and size headers should be added to each Message. This optional attribute defaults to false.


If set, this attribute provides a reference to the channel, where Messages should be sent, if channel resolution fails to return any channels. If no default output channel is provided, the router will throw an Exception. If you would like to silently drop those messages instead, add the nullChannel as the default output channel attribute value.


If true this attribute specifies that channel names must always be successfully resolved to channel instances that exist. If set to true, a MessagingException will be raised, in case the channel cannot be resolved. Setting this attribute to false, will cause any unresovable channels to be ignored. This optional attribute will, if not explicitly set, default to true.


If set to true, failures to send to a message channel will be ignored. If set to false, a MessageDeliveryException will be thrown instead, and if the router resolves more than one channel, any subsequent channels will not receive the message.

The exact behavior of this attribute depends on the type of the Channel messages are sent to. For example, when using direct channels (single threaded), send-failures can be caused by exceptions thrown by components much further down-stream. However, when sending messages to a simple queue channel (asynchronous) the likelihood of an exception to be thrown is rather remote.

While most routers will route to a single channel, they are allowed to return more than one channel name. The recipient-list-router, for instance, does exactly that. If you set this attribute to true on a router that only routes to a single channel, any caused exception is simply swallowed, which usually makes little sense to do. In that case it would be better to catch the exception in an error flow at the flow entry point. Therefore, setting the ignore-send-failures attribute to true usually makes more sense when the router implementation returns more than one channel name, because the other channel(s) following the one that fails would still receive the Message.

This attribute defaults to false.


The timeout attribute specifies the maximum amount of time in milliseconds to wait, when sending Messages to the target Message Channels. By default the send operation will block indefinitely.

Top-Level (Outside of a Chain)

The following parameters are valid only across all top-level routers that are ourside of chains.


Identifies the underlying Spring bean definition which in case of Routers is an instance of EventDrivenConsumer or PollingConsumer depending on whether the Router's input-channel is a SubscribableChannel or PollableChannel, respectively. This is an optional attribute.


This Lifecycle attribute signaled if this component should be started during startup of the Application Context. This optional attribute defaults to true.


The receiving Message channel of this endpoint.


This attribute defines the order for invocation when this endpoint is connected as a subscriber to a channel. This is particularly relevant when that channel is using a failover dispatching strategy. It has no effect when this endpoint itself is a Polling Consumer for a channel with a queue.

5.1.3 Router Implementations

Since content-based routing often requires some domain-specific logic, most use-cases will require Spring Integration's options for delegating to POJOs using the XML namespace support and/or Annotations. Both of these are discussed below, but first we present a couple implementations that are available out-of-the-box since they fulfill common requirements.


A PayloadTypeRouter will send Messages to the channel as defined by payload-type mappings.

<bean id="payloadTypeRouter"
    <property name="channelIdentifierMap">
            <entry key="java.lang.String" value-ref="stringChannel"/>
            <entry key="java.lang.Integer" value-ref="integerChannel"/>

Configuration of the PayloadTypeRouter is also supported via the namespace provided by Spring Integration (see Section F.2, “Namespace Support”), which essentially simplifies configuration by combining the <router/> configuration and its corresponding implementation defined using a <bean/> element into a single and more concise configuration element. The example below demonstrates a PayloadTypeRouter configuration which is equivalent to the one above using the namespace support:

<int:payload-type-router input-channel="routingChannel">
    <int:mapping type="java.lang.String" channel="stringChannel" />
    <int:mapping type="java.lang.Integer" channel="integerChannel" />


A HeaderValueRouter will send Messages to the channel based on the individual header value mappings. When a HeaderValueRouter is created it is initialized with the name of the header to be evaluated. The value of the header could be one of two things:

1. Arbitrary value

2. Channel name

If arbitrary then additional mappings for these header values to channel names is required, otherwise no additional configuration is needed.

Spring Integration provides a simple namespace-based XML configuration to configure a HeaderValueRouter. The example below demonstrates two types of namespace-based configuration for the HeaderValueRouter.

1. Configuration where mapping of header values to channels is required

<int:header-value-router input-channel="routingChannel" header-name="testHeader">
    <int:mapping value="someHeaderValue" channel="channelA" />
    <int:mapping value="someOtherHeaderValue" channel="channelB" />

During the resolution process this router may encounter channel resolution failures, causing an exception. If you want to suppress such exceptions and send unresolved messages to the default output channel (identified with the default-output-channel attribute) set resolution-required to false.

Normally, messages for which the header value is not explicitly mapped to a channel will be sent to the default-output-channel. However, in cases where the header value is mapped to a channel name but the channel cannot be resolved, setting the resolution-required attribute to false will result in routing such messages to the default-output-channel.

With Spring Integration 2.1 the attribute was changed from ignore-channel-name-resolution-failures to resolution-required. Attribute resolution-required will default to true.

2. Configuration where mapping of header values to channel names is not required since header values themselves represent channel names

<int:header-value-router input-channel="routingChannel" header-name="testHeader"/>

Since Spring Integration 2.1 the behavior of resolving channels is more explicit. For example, if you ommit the default-output-channel attribute and the Router was unable to resolve at least one valid channel, and any channel name resolution failures were ignored by setting resolution-required to false, then a MessageDeliveryException is thrown.

Basically, by default the Router must be able to route messages successfully to at least one channel. If you really want to drop messages, you must also have default-output-channel set to nullChannel.


A RecipientListRouter will send each received Message to a statically defined list of Message Channels:

<bean id="recipientListRouter"
    <property name="channels">
            <ref bean="channel1"/>
            <ref bean="channel2"/>
            <ref bean="channel3"/>

Spring Integration also provides namespace support for the RecipientListRouter configuration (see Section F.2, “Namespace Support”) as the example below demonstrates.

<int:recipient-list-router id="customRouter" input-channel="routingChannel"
  <int:recipient channel="channel1"/>
  <int:recipient channel="channel2"/>
The 'apply-sequence' flag here has the same effect as it does for a publish-subscribe-channel, and like a publish-subscribe-channel, it is disabled by default on the recipient-list-router. Refer to the section called “PublishSubscribeChannel Configuration” for more information.

Another convenient option when configuring a RecipientListRouter is to use Spring Expression Language (SpEL) support as selectors for individual recipient channels. This is similar to using a Filter at the beginning of 'chain' to act as a "Selective Consumer". However, in this case, it's all combined rather concisely into the router's configuration.

<int:recipient-list-router id="customRouter" input-channel="routingChannel">
    <int:recipient channel="channel1" selector-expression="payload.equals('foo')"/>
    <int:recipient channel="channel2" selector-expression="headers.containsKey('bar')"/>

In the above configuration a SpEL expression identified by the selector-expression attribute will be evaluated to determine if this recipient should be included in the recipient list for a given input Message. The evaluation result of the expression must be a boolean. If this attribute is not defined, the channel will always be among the list of recipients.

XPath Router

The XPath Router is part of the XML Module. As such, please read chapter Routing XML Messages Using XPath

Routing and Error handling

Spring Integration also provides a special type-based router called ErrorMessageExceptionTypeRouter for routing Error Messages (Messages whose payload is a Throwable instance). ErrorMessageExceptionTypeRouter is very similar to the PayloadTypeRouter. In fact they are almost identical. The only difference is that while PayloadTypeRouter navigates the instance hierarchy of a payload instance (e.g., payload.getClass().getSuperclass()) to find the most specific type/channel mappings, the ErrorMessageExceptionTypeRouter navigates the hierarchy of 'exception causes' (e.g., payload.getCause()) to find the most specific Throwable type/channel mappings.

Below is a sample configuration for ErrorMessageExceptionTypeRouter.

<int:exception-type-router input-channel="inputChannel"
    <int:mapping exception-type="java.lang.IllegalArgumentException"
    <int:mapping exception-type="java.lang.NullPointerException"

<int:channel id="illegalChannel" />
<int:channel id="npeChannel" />

5.1.4 Configuring (Generic) Router

Configuring a Content Based Router with XML

The "router" element provides a simple way to connect a router to an input channel and also accepts the optional default-output-channel attribute. The ref attribute references the bean name of a custom Router implementation (extending AbstractMessageRouter):

<int:router ref="payloadTypeRouter" input-channel="input1"

<int:router ref="recipientListRouter" input-channel="input2"

<int:router ref="customRouter" input-channel="input3"

<beans:bean id="customRouterBean class="org.foo.MyCustomRouter"/>

Alternatively, ref may point to a simple POJO that contains the @Router annotation (see below), or the ref may be combined with an explicit method name. Specifying a method applies the same behavior described in the @Router annotation section below.

<int:router input-channel="input" ref="somePojo" method="someMethod"/>

Using a ref attribute is generally recommended if the custom router implementation is referenced in other <router> definitions. However if the custom router implementation should be scoped to a single definition of the <router>, you may provide an inner bean definition:

<int:router method="someMethod" input-channel="input3"
    <beans:bean class="org.foo.MyCustomRouter"/>

Using both the ref attribute and an inner handler definition in the same <router> configuration is not allowed, as it creates an ambiguous condition, and an Exception will be thrown.

Routers and the Spring Expression Language (SpEL)

Sometimes the routing logic may be simple and writing a separate class for it and configuring it as a bean may seem like overkill. As of Spring Integration 2.0 we offer an alternative where you can now use SpEL to implement simple computations that previously required a custom POJO router.


For more information about the Spring Expression Language, please refer to the respective chapter in the Spring Framework Reference Documentation at:


Generally a SpEL expression is evaluated and the result is mapped to a channel:

<int:router input-channel="inChannel" expression="payload.paymentType">
    <int:mapping value="CASH" channel="cashPaymentChannel"/>
    <int:mapping value="CREDIT" channel="authorizePaymentChannel"/>
    <int:mapping value="DEBIT" channel="authorizePaymentChannel"/>

To simplify things even more, the SpEL expression may evaluate to a channel name:

<int:router input-channel="inChannel" expression="payload + 'Channel'"/>

In the above configuration the result channel will be computed by the SpEL expression which simply concatenates the value of the payload with the literal String 'Channel'.

Another value of SpEL for configuring routers is that an expression can actually return a Collection, effectively making every <router> a Recipient List Router. Whenever the expression returns multiple channel values the Message will be forwarded to each channel.

<int:router input-channel="inChannel" expression="headers.channels"/>

In the above configuration, if the Message includes a header with the name 'channels' the value of which is a List of channel names then the Message will be sent to each channel in the list. You may also find Collection Projection and Collection Selection expressions useful to select multiple channels. For further information, please see:

Configuring a Router with Annotations

When using @Router to annotate a method, the method may return either a MessageChannel or String type. In the latter case, the endpoint will resolve the channel name as it does for the default output channel. Additionally, the method may return either a single value or a collection. If a collection is returned, the reply message will be sent to multiple channels. To summarize, the following method signatures are all valid.

public MessageChannel route(Message message) {...}

public List<MessageChannel> route(Message message) {...}

public String route(Foo payload) {...}

public List<String> route(Foo payload) {...}

In addition to payload-based routing, a Message may be routed based on metadata available within the message header as either a property or attribute. In this case, a method annotated with @Router may include a parameter annotated with @Header which is mapped to a header value as illustrated below and documented in Section F.5, “Annotation Support”.

public List<String> route(@Header("orderStatus") OrderStatus status)
For routing of XML-based Messages, including XPath support, see Chapter 31, XML Support - Dealing with XML Payloads.

5.1.5 Dynamic Routers

So as you can see, Spring Integration provides quite a few different router configurations for common content-based routing use cases as well as the option of implementing custom routers as POJOs. For example PayloadTypeRouter provides a simple way to configure a router which computes channels based on the payload type of the incoming Message while HeaderValueRouter provides the same convenience in configuring a router which computes channels by evaluating the value of a particular Message Header. There are also expression-based (SpEL) routers where the channel is determined based on evaluating an expression. Thus, these type of routers exhibit some dynamic characteristics.

However these routers all require static configuration. Even in the case of expression-based routers, the expression itself is defined as part of the router configuration which means that the same expression operating on the same value will always result in the computation of the same channel. This is acceptable in most cases since such routes are well defined and therefore predictable. But there are times when we need to change router configurations dynamically so message flows may be routed to a different channel.


You might want to bring down some part of your system for maintenance and temporarily re-reroute messages to a different message flow. Or you may want to introduce more granularity to your message flow by adding another route to handle a more concrete type of java.lang.Number (in the case of PayloadTypeRouter).

Unfortunately with static router configuration to accomplish this, you would have to bring down your entire application, change the configuration of the router (change routes) and bring it back up. This is obviously not the solution.

The Dynamic Router pattern describes the mechanisms by which one can change/configure routers dynamically without bringing down the system or individual routers. 

Before we get into the specifics of how this is accomplished in Spring Integration, let's quickly summarize the typical flow of the router, which consists of 3 simple steps:

  • Step 1 - Compute channel identifier which is a value calculated by the router once it receives the Message. Typically it is a String or and instance of the actual MessageChannel.

  • Step 2 - Resolve channel identifier to channel name. We'll describe specifics of this process in a moment.

  • Step 3 - Resolve channel name to the actual MessageChannel

There is not much that can be done with regard to dynamic routing if Step 1 results in the actual instance of the MessageChannel, simply because the MessageChannel is the final product of any router's job. However, if Step 1 results in a channel identifier that is not an instance of MessageChannel, then there are quite a few possibilities to influence the process of deriving the Message Channel. Lets look at couple of the examples in the context of the 3 steps mentioned above: 

Payload Type Router

<int:payload-type-router input-channel="routingChannel">
    <int:mapping type="java.lang.String"  channel="channel1" />
    <int:mapping type="java.lang.Integer" channel="channel2" />

Within the context of the Payload Type Router the 3 steps mentioned above would be realized as:

  • Step 1 - Compute channel identifier which is the fully qualified name of the payload type (e.g., java.lang.String).

  • Step 2 - Resolve channel identifier to channel name where the result of the previous step is used to select the appropriate value from the payload type mapping defined via mapping element.

  • Step 3 - Resolve channel name to the actual instance of the MessageChannel as a reference to a bean within the Application Context (which is hopefully a MessageChannel) identified by the result of the previous step.

In other words, each step feeds the next step until the process completes.

Header Value Router

<int:header-value-router input-channel="inputChannel" header-name="testHeader">
    <int:mapping value="foo" channel="fooChannel" />
    <int:mapping value="bar" channel="barChannel" />

Similar to the PayloadTypeRouter:

  • Step 1 - Compute channel identifier which is the value of the header identified by the header-name attribute.

  • Step 2 - Resolve channel identifier to channel name where the result of the previous step is used to select the appropriate value from the general mapping defined via mapping element.

  • Step 3 - Resolve channel name to the actual instance of the MessageChannel as a reference to a bean within the Application Context (which is hopefully a MessageChannel) identified by the result of the previous step.

The above two configurations of two different router types look almost identical. However if we look at the alternate configuration of the HeaderValueRouter we clearly see that there is no mapping sub element:

<int:header-value-router input-channel="inputChannel" header-name="testHeader">

But the configuration is still perfectly valid. So the natural question is what about the mapping in the Step 2?

What this means is that Step 2 is now an optional step. If mapping is not defined then the channel identifier value computed in Step 1 will automatically be treated as the channel name, which will now be resolved to the actual MessageChannel as in Step 3. What it also means is that Step 2 is one of the key steps to provide dynamic characteristics to the routers, since it introduces a process which allows you to change the way 'channel identifier' resolves to 'channel name', thus influencing the process of determining the final instance of the MessageChannel from the initial channel identifier

For Example:

In the above configuration let's assume that the testHeader value is 'kermit' which is now a channel identifier (Step 1). Since there is no mapping in this router, resolving this channel identifier to a channel name (Step 2) is impossible and this channel identifier is now treated as channel name. However what if there was a mapping but for a different value? The end result would still be the same and that is: if a new value cannot be determined through the process of resolving the 'channel identifier' to a 'channel name', such 'channel identifier' becomes 'channel name'.

So all that is left is for Step 3 to resolve the channel name ('kermit') to an actual instance of the MessageChannel identified by this name. That basically involves a bean lookup for the name provided. So now all messages which contain the header/value pair as testHeader=kermit are going to be routed to a MessageChannel whose bean name (id) is 'kermit'.

But what if you want to route these messages to the 'simpson' channel? Obviously changing a static configuration will work, but will also require bringing your system down. However if you had access to the channel identifier map, then you could just introduce a new mapping where the header/value pair is now kermit=simpson, thus allowing Step 2 to treat 'kermit' as a channel identifier while resolving it to 'simpson' as the channel name .

The same obviously applies for PayloadTypeRouter, where you can now remap or remove a particular payload type mapping. In fact, it applies to every other router, including expression-based routers, since their computed values will now have a chance to go through Step 2 to be additionally resolved to the actual channel name.

In Spring Integration 2.0 the router hierarchy underwent significant refactoring, so that now any router that is a subclass of the AbstractMessageRouter (which includes all framework defined routers) is a Dynamic Router simply because the channelIdentiferMap is defined at the AbstractMessageRouter level. That map's setter method is exposed as a public method along with 'setChannelMapping' and 'removeChannelMapping' methods. These allow you to change/add/remove router mappings at runtime as long as you have a reference to the router itself. It also means that you could expose these same configuration options via JMX (see Section 8.1, “JMX Support”) or the Spring Integration ControlBus (see Section 8.5, “Control Bus”) functionality. 

Manage Router Mappings using the Control Bus

One way to manage the router mappings is through the Control Bus pattern which exposes a Control Channel where you can send control messages to manage and monitor Spring Integration components, including routers.


For more information about the Control Bus, please see chapter Section 8.5, “Control Bus”.

Typically you would send a control message asking to invoke a particular operation on a particular managed component (e.g. router). The two managed operations (methods) that are specific to changing the router resolution process are:

  • public void setChannelMapping(String channelIdentifier, String channelName) - will allow you to add a new or modify an existing mapping between channel identifier and channel name

  • public void removeChannelMapping(String channelIdentifier) - will allow you to remove a particular channel mapping, thus disconnecting the relationship between channel identifier and channel name

Manage Router Mappings using JMX

You can also expose a router instance with Spring's JMX support, and then use your favorite JMX client (e.g., JConsole) to manage those operations (methods) for changing the router's configuration.


For more information about Spring Integration's JMX suppor, please see chapter JMX Support.

5.2 Filter

5.2.1 Introduction

Message Filters are used to decide whether a Message should be passed along or dropped based on some criteria such as a Message Header value or Message content itself. Therefore, a Message Filter is similar to a router, except that for each Message received from the filter's input channel, that same Message may or may not be sent to the filter's output channel. Unlike the router, it makes no decision regarding which Message Channel to send the Message to but only decides whether to send.

As you will see momentarily, the Filter also supports a discard channel, so in certain cases it can play the role of a very simple router (or "switch") based on a boolean condition.

In Spring Integration, a Message Filter may be configured as a Message Endpoint that delegates to an implementation of the MessageSelector interface. That interface is itself quite simple:

public interface MessageSelector {

    boolean accept(Message<?> message);


The MessageFilter constructor accepts a selector instance:

MessageFilter filter = new MessageFilter(someSelector);

In combination with the namespace and SpEL, very powerful filters can be configured with very little java code.

5.2.2 Configuring Filter

Configuring a Filter with XML

The <filter> element is used to create a Message-selecting endpoint. In addition to "input-channel and output-channel attributes, it requires a ref. The ref may point to a MessageSelector implementation:

<int:filter input-channel="input" ref="selector" output-channel="output"/>

<bean id="selector" class="example.MessageSelectorImpl"/>

Alternatively, the method attribute can be added at which point the ref may refer to any object. The referenced method may expect either the Message type or the payload type of inbound Messages. The method must return a boolean value. If the method returns 'true', the Message will be sent to the output-channel.

<int:filter input-channel="input" output-channel="output"
    ref="exampleObject" method="someBooleanReturningMethod"/>

<bean id="exampleObject" class="example.SomeObject"/>

If the selector or adapted POJO method returns false, there are a few settings that control the handling of the rejected Message. By default (if configured like the example above), rejected Messages will be silently dropped. If rejection should instead result in an error condition, then set the throw-exception-on-rejection attribute to true:

<int:filter input-channel="input" ref="selector"
    output-channel="output" throw-exception-on-rejection="true"/> 

If you want rejected messages to be routed to a specific channel, provide that reference as the discard-channel:

<int:filter input-channel="input" ref="selector"
    output-channel="output" discard-channel="rejectedMessages"/> 

Message Filters are commonly used in conjunction with a Publish Subscribe Channel. Many filter endpoints may be subscribed to the same channel, and they decide whether or not to pass the Message to the next endpoint which could be any of the supported types (e.g. Service Activator). This provides a reactive alternative to the more proactive approach of using a Message Router with a single Point-to-Point input channel and multiple output channels.

Using a ref attribute is generally recommended if the custom filter implementation is referenced in other <filter> definitions. However if the custom filter implementation is scoped to a single <filter> element, provide an inner bean definition:

<int:filter method="someMethod" input-channel="inChannel" output-channel="outChannel">
  <beans:bean class="org.foo.MyCustomFilter"/>


Using both the ref attribute and an inner handler definition in the same <filter> configuration is not allowed, as it creates an ambiguous condition, and an Exception will be thrown.

With the introduction of SpEL support, Spring Integration added the expression attribute to the filter element. It can be used to avoid Java entirely for simple filters.

<int:filter input-channel="input" expression="payload.equals('nonsense')"/>

The string passed as the expression attribute will be evaluated as a SpEL expression with the Message available in the evaluation context. If it is necessary to include the result of an expression in the scope of the application context you can use the #{} notation as defined in the SpEL reference documentation .

<int:filter input-channel="input"

If the Expression itself needs to be dynamic, then an 'expression' sub-element may be used. That provides a level of indirection for resolving the Expression by its key from an ExpressionSource. That is a strategy interface that you can implement directly, or you can rely upon a version available in Spring Integration that loads Expressions from a "resource bundle" and can check for modifications after a given number of seconds. All of this is demonstrated in the following configuration sample where the Expression could be reloaded within one minute if the underlying file had been modified. If the ExpressionSource bean is named "expressionSource", then it is not necessary to provide the source attribute on the <expression> element, but in this case it's shown for completeness.

<int:filter input-channel="input" output-channel="output">
    <int:expression key="filterPatterns.example" source="myExpressions"/>

<beans:bean id="myExpressions" id="myExpressions"
    <beans:property name="basename" value="config/integration/expressions"/>
    <beans:property name="cacheSeconds" value="60"/>

Then, the 'config/integration/expressions.properties' file (or any more specific version with a locale extension to be resolved in the typical way that resource-bundles are loaded) would contain a key/value pair:

filterPatterns.example=payload > 100

All of these examples that use expression as an attribute or sub-element can also be applied within transformer, router, splitter, service-activator, and header-enricher elements. Of course, the semantics/role of the given component type would affect the interpretation of the evaluation result in the same way that the return value of a method-invocation would be interpreted. For example, an expression can return Strings that are to be treated as Message Channel names by a router component. However, the underlying functionality of evaluating the expression against the Message as the root object, and resolving bean names if prefixed with '@' is consistent across all of the core EIP components within Spring Integration.

Configuring a Filter with Annotations

A filter configured using annotations would look like this.

public class PetFilter {
    @Filter 1
    public boolean dogsOnly(String input) {


An annotation indicating that this method shall be used as a filter. Must be specified if this class will be used as a filter.

All of the configuration options provided by the xml element are also available for the @Filter annotation.

The filter can be either referenced explicitly from XML or, if the @MessageEndpoint annotation is defined on the class, detected automatically through classpath scanning.

Also see Section 7.7.5, “Advising Endpoints Using Annotations”.

5.3 Splitter

5.3.1 Introduction

The Splitter is a component whose role is to partition a message in several parts, and send the resulting messages to be processed independently. Very often, they are upstream producers in a pipeline that includes an Aggregator.

5.3.2 Programming model

The API for performing splitting consists of one base class, AbstractMessageSplitter, which is a MessageHandler implementation, encapsulating features which are common to splitters, such as filling in the appropriate message headers CORRELATION_ID, SEQUENCE_SIZE, and SEQUENCE_NUMBER on the messages that are produced. This enables tracking down the messages and the results of their processing (in a typical scenario, these headers would be copied over to the messages that are produced by the various transforming endpoints), and use them, for example, in a Composed Message Processor scenario.

An excerpt from AbstractMessageSplitter can be seen below:

public abstract class AbstractMessageSplitter
    extends AbstractReplyProducingMessageConsumer {
    protected abstract Object splitMessage(Message<?> message);


To implement a specific Splitter in an application, extend AbstractMessageSplitter and implement the splitMessage method, which contains logic for splitting the messages. The return value may be one of the following:

  • a Collection (or subclass thereof) or an array of Message objects - in this case the messages will be sent as such (after the CORRELATION_ID, SEQUENCE_SIZE and SEQUENCE_NUMBER are populated). Using this approach gives more control to the developer, for example for populating custom message headers as part of the splitting process.

  • a Collection (or subclass thereof) or an array of non-Message objects - works like the prior case, except that each collection element will be used as a Message payload. Using this approach allows developers to focus on the domain objects without having to consider the Messaging system and produces code that is easier to test.

  • a Message or non-Message object (but not a Collection or an Array) - it works like the previous cases, except a single message will be sent out.

In Spring Integration, any POJO can implement the splitting algorithm, provided that it defines a method that accepts a single argument and has a return value. In this case, the return value of the method will be interpreted as described above. The input argument might either be a Message or a simple POJO. In the latter case, the splitter will receive the payload of the incoming message. Since this decouples the code from the Spring Integration API and will typically be easier to test, it is the recommended approach.

5.3.3 Configuring Splitter

Configuring a Splitter using XML

A splitter can be configured through XML as follows:

<int:channel id="inputChannel"/>

<int:splitter id="splitter" 1
  ref="splitterBean" 2
  method="split" 3
  input-channel="inputChannel" 4
  output-channel="outputChannel" 5/>

<int:channel id="outputChannel"/>

<beans:bean id="splitterBean" class="sample.PojoSplitter"/>


The id of the splitter is optional.


A reference to a bean defined in the application context. The bean must implement the splitting logic as described in the section above .Optional. If reference to a bean is not provided, then it is assumed that the payload of the Message that arrived on the input-channel is an implementation of java.util.Collection and the default splitting logic will be applied to the Collection, incorporating each individual element into a Message and sending it to the output-channel.


The method (defined on the bean specified above) that implements the splitting logic. Optional.


The input channel of the splitter. Required.


The channel to which the splitter will send the results of splitting the incoming message. Optional (because incoming messages can specify a reply channel themselves).

Using a ref attribute is generally recommended if the custom splitter implementation may be referenced in other <splitter> definitions. However if the custom splitter handler implementation should be scoped to a single definition of the <splitter>, configure an inner bean definition:

<int:splitter id="testSplitter" input-channel="inChannel" method="split"
  <beans:bean class="org.foo.TestSplitter"/>


Using both a ref attribute and an inner handler definition in the same <int:splitter> configuration is not allowed, as it creates an ambiguous condition and will result in an Exception being thrown.

Configuring a Splitter with Annotations

The @Splitter annotation is applicable to methods that expect either the Message type or the message payload type, and the return values of the method should be a Collection of any type. If the returned values are not actual Message objects, then each item will be wrapped in a Message as its payload. Each message will be sent to the designated output channel for the endpoint on which the @Splitter is defined.

List<LineItem> extractItems(Order order) {
    return order.getItems()

Also see Section 7.7.5, “Advising Endpoints Using Annotations”.

5.4 Aggregator

5.4.1 Introduction

Basically a mirror-image of the Splitter, the Aggregator is a type of Message Handler that receives multiple Messages and combines them into a single Message. In fact, an Aggregator is often a downstream consumer in a pipeline that includes a Splitter.

Technically, the Aggregator is more complex than a Splitter, because it is stateful as it must hold the Messages to be aggregated and determine when the complete group of Messages is ready to be aggregated. In order to do this it requires a MessageStore.

5.4.2 Functionality

The Aggregator combines a group of related messages, by correlating and storing them, until the group is deemed complete. At that point, the Aggregator will create a single message by processing the whole group, and will send the aggregated message as output.

Implementing an Aggregator requires providing the logic to perform the aggregation (i.e., the creation of a single message from many). Two related concepts are correlation and release.

Correlation determines how messages are grouped for aggregation. In Spring Integration correlation is done by default based on the MessageHeaders.CORRELATION_ID message header. Messages with the same MessageHeaders.CORRELATION_ID will be grouped together. However, the correlation strategy may be customized to allow other ways of specifying how the messages should be grouped together by implementing a CorrelationStrategy (see below).

To determine the point at which a group of messages is ready to be processed, a ReleaseStrategy is consulted. The default release strategy for the Aggregator will release a group when all messages included in a sequence are present, based on the MessageHeaders.SEQUENCE_SIZE header. This default strategy may be overridden by providing a reference to a custom ReleaseStrategy implementation.

5.4.3 Programming model

The Aggregation API consists of a number of classes:

  • The interface MessageGroupProcessor, and its subclasses: MethodInvokingAggregatingMessageGroupProcessor and ExpressionEvaluatingMessageGroupProcessor

  • The ReleaseStrategy interface and its default implementation SequenceSizeReleaseStrategy

  • The CorrelationStrategy interface and its default implementation HeaderAttributeCorrelationStrategy


The AggregatingMessageHandler (subclass of AbstractCorrelatingMessageHandler) is a MessageHandler implementation, encapsulating the common functionalities of an Aggregator (and other correlating use cases), which are:

  • correlating messages into a group to be aggregated

  • maintaining those messages in a MessageStore until the group can be released

  • deciding when the group can be released

  • aggregating the released group into a single message

  • recognizing and responding to an expired group

The responsibility of deciding how the messages should be grouped together is delegated to a CorrelationStrategy instance. The responsibility of deciding whether the message group can be released is delegated to a ReleaseStrategy instance.

Here is a brief highlight of the base AbstractAggregatingMessageGroupProcessor (the responsibility of implementing the aggregatePayloads method is left to the developer):

public abstract class AbstractAggregatingMessageGroupProcessor
              implements MessageGroupProcessor {

    protected Map<String, Object> aggregateHeaders(MessageGroup group) {
        // default implementation exists

    protected abstract Object aggregatePayloads(MessageGroup group, Map<String, Object> defaultHeaders);

The CorrelationStrategy is owned by the AbstractCorrelatingMessageHandler and it has a default value based on the MessageHeaders.CORRELATION_ID message header:
public AbstractCorrelatingMessageHandler(MessageGroupProcessor processor, MessageGroupStore store,
        CorrelationStrategy correlationStrategy, ReleaseStrategy releaseStrategy) {
    this.correlationStrategy = correlationStrategy == null ?
        new HeaderAttributeCorrelationStrategy(MessageHeaders.CORRELATION_ID) : correlationStrategy;
    this.releaseStrategy = releaseStrategy == null ? new SequenceSizeReleaseStrategy() : releaseStrategy;

As for actual processing of the message group, the default implementation is the DefaultAggregatingMessageGroupProcessor. It creates a single Message whose payload is a List of the payloads received for a given group. This works well for simple Scatter Gather implementations with either a Splitter, Publish Subscribe Channel, or Recipient List Router upstream.


When using a Publish Subscribe Channel or Recipient List Router in this type of scenario, be sure to enable the flag to apply-sequence. That will add the necessary headers (CORRELATION_ID, SEQUENCE_NUMBER and SEQUENCE_SIZE). That behavior is enabled by default for Splitters in Spring Integration, but it is not enabled for the Publish Subscribe Channel or Recipient List Router because those components may be used in a variety of contexts in which these headers are not necessary.

When implementing a specific aggregator strategy for an application, a developer can extend AbstractAggregatingMessageGroupProcessor and implement the aggregatePayloads method. However, there are better solutions, less coupled to the API, for implementing the aggregation logic which can be configured easily either through XML or through annotations.

In general, any POJO can implement the aggregation algorithm if it provides a method that accepts a single java.util.List as an argument (parameterized lists are supported as well). This method will be invoked for aggregating messages as follows:

  • if the argument is a java.util.List<T>, and the parameter type T is assignable to Message, then the whole list of messages accumulated for aggregation will be sent to the aggregator

  • if the argument is a non-parameterized java.util.List or the parameter type is not assignable to Message, then the method will receive the payloads of the accumulated messages

  • if the return type is not assignable to Message, then it will be treated as the payload for a Message that will be created automatically by the framework.


In the interest of code simplicity, and promoting best practices such as low coupling, testability, etc., the preferred way of implementing the aggregation logic is through a POJO, and using the XML or annotation support for configuring it in the application.


The ReleaseStrategy interface is defined as follows:

public interface ReleaseStrategy {

  boolean canRelease(MessageGroup group);


In general, any POJO can implement the completion decision logic if it provides a method that accepts a single java.util.List as an argument (parameterized lists are supported as well), and returns a boolean value. This method will be invoked after the arrival of each new message, to decide whether the group is complete or not, as follows:

  • if the argument is a java.util.List<T>, and the parameter type T is assignable to Message, then the whole list of messages accumulated in the group will be sent to the method

  • if the argument is a non-parametrized java.util.List or the parameter type is not assignable to Message, then the method will receive the payloads of the accumulated messages

  • the method must return true if the message group is ready for aggregation, and false otherwise.

For example:
public class MyReleaseStrategy {

    public boolean canMessagesBeReleased(List<Message<?>>) {...}
public class MyReleaseStrategy {

    public boolean canMessagesBeReleased(List<String>) {...}

As you can see based on the above signatures, the POJO-based Release Strategy will be passed a Collection of not-yet-released Messages (if you need access to the whole Message) or a Collection of payload objects (if the type parameter is anything other than Message). Typically this would satisfy the majority of use cases. However if, for some reason, you need to access the full MessageGroup then you should simply provide an implementation of the ReleaseStrategy interface.

When the group is released for aggregation, all its not-yet-released messages are processed and removed from the group. If the group is also complete (i.e. if all messages from a sequence have arrived or if there is no sequence defined), then the group is marked as complete. Any new messages for this group will be sent to the discard channel (if defined). Setting expire-groups-upon-completion to true (default is false) removes the entire group and any new messages, with the same correlation id as the removed group, will form a new group. Partial sequences can be released by using a MessageGroupStoreReaper together with send-partial-result-on-expiry being set to true.

To facilitate discarding of late-arriving messages, the aggregator must maintain state about the group after it has been released. This can eventually cause out of memory conditions. To avoid such situations, you should consider configuring a MessageGroupStoreReaper to remove the group metadata; the expiry parameters should be set to expire groups after it is not expected that late messages will arrive. For information about configuring a reaper, see Section 5.4.5, “Managing State in an Aggregator: MessageGroupStore”.

Spring Integration provides an out-of-the box implementation for ReleaseStrategy, the SequenceSizeReleaseStrategy. This implementation consults the SEQUENCE_NUMBER and SEQUENCE_SIZE headers of each arriving message to decide when a message group is complete and ready to be aggregated. As shown above, it is also the default strategy.


The CorrelationStrategy interface is defined as follows:

public interface CorrelationStrategy {

  Object getCorrelationKey(Message<?> message);


The method returns an Object which represents the correlation key used for associating the message with a message group. The key must satisfy the criteria used for a key in a Map with respect to the implementation of equals() and hashCode().

In general, any POJO can implement the correlation logic, and the rules for mapping a message to a method's argument (or arguments) are the same as for a ServiceActivator (including support for @Header annotations). The method must return a value, and the value must not be null.

Spring Integration provides an out-of-the box implementation for CorrelationStrategy, the HeaderAttributeCorrelationStrategy. This implementation returns the value of one of the message headers (whose name is specified by a constructor argument) as the correlation key. By default, the correlation strategy is a HeaderAttributeCorrelationStrategy returning the value of the CORRELATION_ID header attribute. If you have a custom header name you would like to use for correlation, then simply configure that on an instance of HeaderAttributeCorrelationStrategy and provide that as a reference for the Aggregator's correlation-strategy.

5.4.4 Configuring an Aggregator

Configuring an Aggregator with XML

Spring Integration supports the configuration of an aggregator via XML through the <aggregator/> element. Below you can see an example of an aggregator.

<channel id="inputChannel"/>

<int:aggregator id="myAggregator" 1
		auto-startup="true" 2
		input-channel="inputChannel" 3
		output-channel="outputChannel" 4
		discard-channel="throwAwayChannel" 5
		message-store="persistentMessageStore" 6
		order="1" 7
		send-partial-result-on-expiry="false" 8
		send-timeout="1000" 9

		correlation-strategy="correlationStrategyBean" 10
		correlation-strategy-method="correlate" 11
		correlation-strategy-expression="headers['foo']" 12

		ref="aggregatorBean" 13
		method="aggregate" 14

		release-strategy="releaseStrategyBean" 15
		release-strategy-method="release" (16)
		release-strategy-expression="size() == 5" (17)

		expire-groups-upon-completion="false" (18)
		empty-group-min-timeout="60000" /> (19)

<int:channel id="outputChannel"/>

<int:channel id="throwAwayChannel"/>

<bean id="persistentMessageStore" class="org.springframework.integration.jdbc.JdbcMessageStore">
	<constructor-arg ref="dataSource"/>

<bean id="aggregatorBean" class="sample.PojoAggregator"/>

<bean id="releaseStrategyBean" class="sample.PojoReleaseStrategy"/>

<bean id="correlationStrategyBean" class="sample.PojoCorrelationStrategy"/>


The id of the aggregator is 0ptional.


Lifecycle attribute signaling if aggregator should be started during Application Context startup. Optional (default is 'true').


The channel from which where aggregator will receive messages. Required.


The channel to which the aggregator will send the aggregation results. Optional (because incoming messages can specify a reply channel themselves via 'replyChannel' Message Header).


The channel to which the aggregator will send the messages that timed out (if send-partial-result-on-expiry is false). Optional.


A reference to a MessageGroupStore used to store groups of messages under their correlation key until they are complete. Optional, by default a volatile in-memory store.


Order of this aggregator when more than one handle is subscribed to the same DirectChannel (use for load balancing purposes). Optional.


Indicates that expired messages should be aggregated and sent to the 'output-channel' or 'replyChannel' once their containing MessageGroup is expired (see MessageGroupStore.expireMessageGroups(long)). One way of expiring MessageGroups is by configuring a MessageGroupStoreReaper. However MessageGroups can alternatively be expired by simply calling MessageGroupStore.expireMessageGroup(groupId). That could be accomplished via a Control Bus operation or by simply invoking that method if you have a reference to the MessageGroupStore instance. Otherwise by itself this attribute has no behavior. It only serves as an indicator of what to do (discard or send to the output/reply channel) with Messages that are still in the MessageGroup that is about to be expired. Optional.

Default - 'false'.


The timeout interval for sending the aggregated messages to the output or reply channel. Optional.


A reference to a bean that implements the message correlation (grouping) algorithm. The bean can be an implementation of the CorrelationStrategy interface or a POJO. In the latter case the correlation-strategy-method attribute must be defined as well. Optional (by default, the aggregator will use the MessageHeaders.CORRELATION_ID header) .


A method defined on the bean referenced by correlation-strategy, that implements the correlation decision algorithm. Optional, with restrictions (requires correlation-strategy to be present).


A SpEL expression representing the correlation strategy. Example: "headers['foo']". Only one of correlation-strategy or correlation-strategy-expression is allowed.


A reference to a bean defined in the application context. The bean must implement the aggregation logic as described above. Optional (by default the list of aggregated Messages will become a payload of the output message).


A method defined on the bean referenced by ref, that implements the message aggregation algorithm. Optional, depends on ref attribute being defined.


A reference to a bean that implements the release strategy. The bean can be an implementation of the ReleaseStrategy interface or a POJO. In the latter case the release-strategy-method attribute must be defined as well. Optional (by default, the aggregator will use the MessageHeaders.SEQUENCE_SIZE header attribute).


A method defined on the bean referenced by release-strategy, that implements the completion decision algorithm. Optional, with restrictions (requires release-strategy to be present).


A SpEL expression representing the release strategy; the root object for the expression is a Collection of Messages. Example: "size() == 5". Only one of release-strategy or release-strategy-expression is allowed.


When set to true (default false), completed groups are removed from the message store, allowing subsequent messages with the same correlation to form a new group. The default behavior is to send messages with the same correlation as a completed group to the discard-channel.


Only applies if a MessageGroupStoreReaper is configured for the <aggregator>'s MessageStore. By default, when a MessageGroupStoreReaper is configured to expire partial groups, empty groups are also removed. Empty groups exist after a group is released normally. This is to enable the detection and discarding of late-arriving messages. If you wish to expire empty groups on a longer schedule than expiring partial groups, set this property. Empty groups will then not be removed from the MessageStore until they have not been modified for at least this number of milliseconds. Note that the actual time to expire an empty group will also be affected by the reaper's timeout property and it could be as much as this value plus the timeout.

Using a ref attribute is generally recommended if a custom aggregator handler implementation may be referenced in other <aggregator> definitions. However if a custom aggregator implementation is only being used by a single definition of the <aggregator>, you can use an inner bean definition (starting with version 1.0.3) to configure the aggregation POJO within the <aggregator> element:

<aggregator input-channel="input" method="sum" output-channel="output">
    <beans:bean class="org.foo.PojoAggregator"/>

Using both a ref attribute and an inner bean definition in the same <aggregator> configuration is not allowed, as it creates an ambiguous condition. In such cases, an Exception will be thrown.

An example implementation of the aggregator bean looks as follows:

public class PojoAggregator {

  public Long add(List<Long> results) {
    long total = 0l;
    for (long partialResult: results) {
      total += partialResult;
    return total;


An implementation of the completion strategy bean for the example above may be as follows:

public class PojoReleaseStrategy {
  public boolean canRelease(List<Long> numbers) {
    int sum = 0;
    for (long number: numbers) {
      sum += number;
    return sum >= maxValue;


Wherever it makes sense, the release strategy method and the aggregator method can be combined in a single bean.

An implementation of the correlation strategy bean for the example above may be as follows:

public class PojoCorrelationStrategy {
  public Long groupNumbersByLastDigit(Long number) {
    return number % 10;

For example, this aggregator would group numbers by some criterion (in our case the remainder after dividing by 10) and will hold the group until the sum of the numbers provided by the payloads exceeds a certain value.


Wherever it makes sense, the release strategy method, correlation strategy method and the aggregator method can be combined in a single bean (all of them or any two).

Aggregators and Spring Expression Language (SpEL)

Since Spring Integration 2.0, the various strategies (correlation, release, and aggregation) may be handled with SpEL which is recommended if the logic behind such release strategy is relatively simple. Let's say you have a legacy component that was designed to receive an array of objects. We know that the default release strategy will assemble all aggregated messages in the List. So now we have two problems. First we need to extract individual messages from the list, and then we need to extract the payload of each message and assemble the array of objects (see code below).

public String[] processRelease(List<Message<String>> messages){
    List<String> stringList = new ArrayList<String>();
    for (Message<String> message : messages) {
    return stringList.toArray(new String[]{});

However, with SpEL such a requirement could actually be handled relatively easily with a one-line expression, thus sparing you from writing a custom class and configuring it as a bean.

<int:aggregator input-channel="aggChannel"

In the above configuration we are using a Collection Projection expression to assemble a new collection from the payloads of all messages in the list and then transforming it to an Array, thus achieving the same result as the java code above.

The same expression-based approach can be applied when dealing with custom Release and Correlation strategies.

Instead of defining a bean for a custom CorrelationStrategy via the correlation-strategy attribute, you can implement your simple correlation logic via a SpEL expression and configure it via the correlation-strategy-expression attribute.

For example:


In the above example it is assumed that the payload has an attribute person with an id which is going to be used to correlate messages.

Likewise, for the ReleaseStrategy you can implement your release logic as a SpEL expression and configure it via the release-strategy-expression attribute. The only difference is that since ReleaseStrategy is passed the List of Messages, the root object in the SpEL evaluation context is the List itself. That List can be referenced as #this within the expression.

For example:

release-strategy-expression="#this.size() gt 5"

In this example the root object of the SpEL Evaluation Context is the MessageGroup itself, and you are simply stating that as soon as there are more than 5 messages in this group, it should be released.

Configuring an Aggregator with Annotations

An aggregator configured using annotations would look like this.

public class Waiter {

  @Aggregator 1
  public Delivery aggregatingMethod(List<OrderItem> items) {

  @ReleaseStrategy 2
  public boolean releaseChecker(List<Message<?>> messages) {

  @CorrelationStrategy 3
  public String correlateBy(OrderItem item) {



An annotation indicating that this method shall be used as an aggregator. Must be specified if this class will be used as an aggregator.


An annotation indicating that this method shall be used as the release strategy of an aggregator. If not present on any method, the aggregator will use the SequenceSizeReleaseStrategy.


An annotation indicating that this method shall be used as the correlation strategy of an aggregator. If no correlation strategy is indicated, the aggregator will use the HeaderAttributeCorrelationStrategy based on CORRELATION_ID.

All of the configuration options provided by the xml element are also available for the @Aggregator annotation.

The aggregator can be either referenced explicitly from XML or, if the @MessageEndpoint is defined on the class, detected automatically through classpath scanning.

5.4.5 Managing State in an Aggregator: MessageGroupStore

Aggregator (and some other patterns in Spring Integration) is a stateful pattern that requires decisions to be made based on a group of messages that have arrived over a period of time, all with the same correlation key. The design of the interfaces in the stateful patterns (e.g. ReleaseStrategy) is driven by the principle that the components (whether defined by the framework or a user) should be able to remain stateless. All state is carried by the MessageGroup and its management is delegated to the MessageGroupStore.

public interface MessageGroupStore {
    int getMessageCountForAllMessageGroups();

    int getMarkedMessageCountForAllMessageGroups();

    int getMessageGroupCount();

    MessageGroup getMessageGroup(Object groupId);

    MessageGroup addMessageToGroup(Object groupId, Message<?> message);

    MessageGroup markMessageGroup(MessageGroup group);

    MessageGroup removeMessageFromGroup(Object key, Message<?> messageToRemove);

    MessageGroup markMessageFromGroup(Object key, Message<?> messageToMark);

    void removeMessageGroup(Object groupId);

    void registerMessageGroupExpiryCallback(MessageGroupCallback callback);

    int expireMessageGroups(long timeout);

For more information please refer to the JavaDoc.

The MessageGroupStore accumulates state information in MessageGroups while waiting for a release strategy to be triggered, and that event might not ever happen. So to prevent stale messages from lingering, and for volatile stores to provide a hook for cleaning up when the application shuts down, the MessageGroupStore allows the user to register callbacks to apply to its MessageGroups when they expire. The interface is very straightforward:

public interface MessageGroupCallback {

    void execute(MessageGroupStore messageGroupStore, MessageGroup group);


The callback has direct access to the store and the message group so it can manage the persistent state (e.g. by removing the group from the store entirely).

The MessageGroupStore maintains a list of these callbacks which it applies, on demand, to all messages whose timestamp is earlier than a time supplied as a parameter (see the registerMessageGroupExpiryCallback(..) and expireMessageGroups(..) methods above).

The expireMessageGroups method can be called with a timeout value. Any message older than the current time minus this value will be expired, and have the callbacks applied. Thus it is the user of the store that defines what is meant by message group "expiry".

As a convenience for users, Spring Integration provides a wrapper for the message expiry in the form of a MessageGroupStoreReaper:

<bean id="reaper" class="org...MessageGroupStoreReaper">
    <property name="messageGroupStore" ref="messageStore"/>
    <property name="timeout" value="30000"/>

<task:scheduled-tasks scheduler="scheduler">
    <task:scheduled ref="reaper" method="run" fixed-rate="10000"/>

The reaper is a Runnable, and all that is happening in the example above is that the message group store's expire method is being called once every 10 seconds. The timeout itself is 30 seconds.

It is important to understand that the 'timeout' property of the MessageGroupStoreReaper is an approximate value and is impacted by the the rate of the task scheduler since this property will only be checked on the next scheduled execution of the MessageGroupStoreReaper task. For example if the timeout is set for 10 min, but the MessageGroupStoreReaper task is scheduled to run every 60 min and the last execution of the MessageGroupStoreReaper task happened 1 min before the timeout, the MessageGroup will not expire for the next 59 min. So it is recommended to set the rate at least equal to the value of the timeout or shorter.

In addition to the reaper, the expiry callbacks are invoked when the application shuts down via a lifecycle callback in the AbstractCorrelatingMessageHandler.

The AbstractCorrelatingMessageHandler registers its own expiry callback, and this is the link with the boolean flag send-partial-result-on-expiry in the XML configuration of the aggregator. If the flag is set to true, then when the expiry callback is invoked, any unmarked messages in groups that are not yet released can be sent on to the output channel.


When using a MessageGroupStoreReaper, it is generally recommended to use a separate MessageStore for each correlating endpoint. Otherwise, unexpected results may occur because one endpoint may remove another endpoint's groups.

Some MessageStore implementations allow using the same physical resources, by partitioning the data; for example, the JdbcMessageStore has a region property; the MongoDbMessageStore has a collectionName property.

For more information about MessageStore interface and its implementations, please read Section 8.3, “Message Store”.

5.5 Resequencer

5.5.1 Introduction

Related to the Aggregator, albeit different from a functional standpoint, is the Resequencer.

5.5.2 Functionality

The Resequencer works in a similar way to the Aggregator, in the sense that it uses the CORRELATION_ID to store messages in groups, the difference being that the Resequencer does not process the messages in any way. It simply releases them in the order of their SEQUENCE_NUMBER header values.

With respect to that, the user might opt to release all messages at once (after the whole sequence, according to the SEQUENCE_SIZE, has been released), or as soon as a valid sequence is available.

5.5.3 Configuring a Resequencer

Configuring a resequencer requires only including the appropriate element in XML.

A sample resequencer configuration is shown below.

<int:channel id="inputChannel"/>

<int:channel id="outputChannel"/>

<int:resequencer id="completelyDefinedResequencer" 1
  input-channel="inputChannel" 2
  output-channel="outputChannel" 3
  discard-channel="discardChannel" 4
  release-partial-sequences="true" 5
  message-store="messageStore" 6
  send-partial-result-on-expiry="true" 7
  send-timeout="86420000" 8
  correlation-strategy="correlationStrategyBean" 9
  correlation-strategy-method="correlate" 10
  correlation-strategy-expression="headers['foo']" 11
  release-strategy="releaseStrategyBean" 12
  release-strategy-method="release" 13
  release-strategy-expression="size() == 10" 14
  empty-group-min-timeout="60000" />15


The id of the resequencer is optional.


The input channel of the resequencer. Required.


The channel to which the resequencer will send the reordered messages. Optional.


The channel to which the resequencer will send the messages that timed out (if send-partial-result-on-timeout is false). Optional.


Whether to send out ordered sequences as soon as they are available, or only after the whole message group arrives. Optional (false by default).


A reference to a MessageGroupStore that can be used to store groups of messages under their correlation key until they are complete. Optional with default a volatile in-memory store.


Whether, upon the expiration of the group, the ordered group should be sent out (even if some of the messages are missing). Optional (false by default). See Section 5.4.5, “Managing State in an Aggregator: MessageGroupStore”.


The timeout for sending out messages. Optional.


A reference to a bean that implements the message correlation (grouping) algorithm. The bean can be an implementation of the CorrelationStrategy interface or a POJO. In the latter case the correlation-strategy-method attribute must be defined as well. Optional (by default, the aggregator will use the MessageHeaders.CORRELATION_ID header) .


A method defined on the bean referenced by correlation-strategy, that implements the correlation decision algorithm. Optional, with restrictions (requires correlation-strategy to be present).


A SpEL expression representing the correlation strategy. Example: "headers['foo']". Only one of correlation-strategy or correlation-strategy-expression is allowed.


A reference to a bean that implements the release strategy. The bean can be an implementation of the ReleaseStrategy interface or a POJO. In the latter case the release-strategy-method attribute must be defined as well. Optional (by default, the aggregator will use the MessageHeaders.SEQUENCE_SIZE header attribute).


A method defined on the bean referenced by release-strategy, that implements the completion decision algorithm. Optional, with restrictions (requires release-strategy to be present).


A SpEL expression representing the release strategy; the root object for the expression is a Collection of Messages. Example: "size() == 5". Only one of release-strategy or release-strategy-expression is allowed.


Only applies if a MessageGroupStoreReaper is configured for the <resequcencer>'s MessageStore. By default, when a MessageGroupStoreReaper is configured to expire partial groups, empty groups are also removed. Empty groups exist after a group is released normally. This is to enable the detection and discarding of late-arriving messages. If you wish to expire empty groups on a longer schedule than expiring partial groups, set this property. Empty groups will then not be removed from the MessageStore until they have not been modified for at least this number of milliseconds. Note that the actual time to expire an empty group will also be affected by the reaper's timeout property and it could be as much as this value plus the timeout.

Since there is no custom behavior to be implemented in Java classes for resequencers, there is no annotation support for it.

5.6 Message Handler Chain

5.6.1 Introduction

The MessageHandlerChain is an implementation of MessageHandler that can be configured as a single Message Endpoint while actually delegating to a chain of other handlers, such as Filters, Transformers, Splitters, and so on. This can lead to a much simpler configuration when several handlers need to be connected in a fixed, linear progression. For example, it is fairly common to provide a Transformer before other components. Similarly, when providing a Filter before some other component in a chain, you are essentially creating a Selective Consumer. In either case, the chain only requires a single input-channel and a single output-channel eliminating the need to define channels for each individual component.

Spring Integration's Filter provides a boolean property throwExceptionOnRejection. When providing multiple Selective Consumers on the same point-to-point channel with different acceptance criteria, this value should be set to 'true' (the default is false) so that the dispatcher will know that the Message was rejected and as a result will attempt to pass the Message on to other subscribers. If the Exception were not thrown, then it would appear to the dispatcher as if the Message had been passed on successfully even though the Filter had dropped the Message to prevent further processing. If you do indeed want to "drop" the Messages, then the Filter's 'discard-channel' might be useful since it does give you a chance to perform some operation with the dropped message (e.g. send to a JMS queue or simply write to a log).

The handler chain simplifies configuration while internally maintaining the same degree of loose coupling between components, and it is trivial to modify the configuration if at some point a non-linear arrangement is required.

Internally, the chain will be expanded into a linear setup of the listed endpoints, separated by anonymous channels. The reply channel header will not be taken into account within the chain: only after the last handler is invoked will the resulting message be forwarded on to the reply channel or the chain's output channel. Because of this setup all handlers except the last required to implement the MessageProducer interface (which provides a 'setOutputChannel()' method). The last handler only needs an output channel if the outputChannel on the MessageHandlerChain is set.


As with other endpoints, the output-channel is optional. If there is a reply Message at the end of the chain, the output-channel takes precedence, but if not available, the chain handler will check for a reply channel header on the inbound Message as a fallback.

In most cases there is no need to implement MessageHandlers yourself. The next section will focus on namespace support for the chain element. Most Spring Integration endpoints, like Service Activators and Transformers, are suitable for use within a MessageHandlerChain.

5.6.2 Configuring a Chain

The <chain> element provides an input-channel attribute, and if the last element in the chain is capable of producing reply messages (optional), it also supports an output-channel attribute. The sub-elements are then filters, transformers, splitters, and service-activators. The last element may also be a router or an outbound-channel-adapter.

<int:chain input-channel="input" output-channel="output">
    <int:filter ref="someSelector" throw-exception-on-rejection="true"/>
        <int:header name="foo" value="bar"/>
    <int:service-activator ref="someService" method="someMethod"/>

The <header-enricher> element used in the above example will set a message header named "foo" with a value of "bar" on the message. A header enricher is a specialization of Transformer that touches only header values. You could obtain the same result by implementing a MessageHandler that did the header modifications and wiring that as a bean, but the header-enricher is obviously a simpler option.

The <chain> can be configured as the last 'black-box' consumer of the message flow. For this solution it is enough to put at the end of the <chain> some <outbound-channel-adapter>:

<int:chain input-channel="input">
    <si-xml:marshalling-transformer marshaller="marshaller" result-type="StringResult" />
    <int:service-activator ref="someService" method="someMethod"/>
        <int:header name="foo" value="bar"/>
    <int:logging-channel-adapter level="INFO" log-full-message="true"/>

Disallowed Attributes and Elements

It is important to note that certain attributes, such as order and input-channel are not allowed to be specified on components used within a chain. The same is true for the poller sub-element.


For the Spring Integration core components, the XML Schema itself will enforce some of these constraints. However, for non-core components or your own custom components, these constraints are enforced by the XML namespace parser, not by the XML Schema.

These XML namespace parser constraints were added with Spring Integration 2.2. The XML namespace parser will throw an BeanDefinitionParsingException if you try to use disallowed attributes and elements.

'id' Attribute

Beginning with Spring Integration 3.0, if a chain element is given an id, the bean name for the element is a combination of the chain's id and the id of the element itself. Elements without an id are not registered as beans, but they are given componentNames that include the chain id. For example:

<int:chain id="fooChain" input-channel="input">
    <int:service-activator id="fooService" ref="someService" method="someMethod"/>

  • The <chain> root element has an id 'fooChain'. So, the AbstractEndpoint implementation (PollingConsumer or EventDrivenConsumer, depending on the input-channel type) bean takes this value as it's bean name.
  • The MessageHandlerChain bean acquires a bean alias 'fooChain.handler', which allows direct access to this bean from the BeanFactory.
  • The <service-activator> is not a fully-fledged Messaging Endpoint (PollingConsumer or EventDrivenConsumer) - it is simply a MessageHandler within the <chain>. In this case, the bean name registered with the BeanFactory is 'fooChain$child.fooService.handler'.
  • The componentName of this ServiceActivatingHandler takes the same value, but without the '.handler' suffix - 'fooChain$child.fooService'.
  • The last <chain> sub-component, <object-to-json-transformer>, doesn't have an id attribute. Its componentName is based on its position in the <chain>. In this case, it is 'fooChain$child#1'. (The final element of the name is the order within the chain, beginning with '#0'). Note, this transformer isn't registered as a bean within the application context, so, it doesn't get a beanName, however its componentName has a value which is useful for logging etc.

The id attribute for <chain> elements allows them to be eligible for JMX export and they are trackable via Message History. They can also be accessed from the BeanFactory using the appropriate bean name as discussed above.


It is useful to provide an explicit id attribute on <chain>s to simplify the identification of sub-components in logs, and to provide access to them from the BeanFactory etc.

Calling a Chain from within a Chain

Sometimes you need to make a nested call to another chain from within a chain and then come back and continue execution within the original chain. To accomplish this you can utilize a Messaging Gateway by including a <gateway> element. For example:

<int:chain id="main-chain" input-channel="in" output-channel="out">
      <int:header name="name" value="Many" />
      <bean class="org.foo.SampleService" />
    <int:gateway request-channel="inputA"/>  

<int:chain id="nested-chain-a" input-channel="inputA">
        <int:header name="name" value="Moe" />
    <int:gateway request-channel="inputB"/> 
        <bean class="org.foo.SampleService" />

<int:chain id="nested-chain-b" input-channel="inputB">
        <int:header name="name" value="Jack" />
        <bean class="org.foo.SampleService" />

In the above example the nested-chain-a will be called at the end of main-chain processing by the 'gateway' element configured there. While in nested-chain-a a call to a nested-chain-b will be made after header enrichment and then it will come back to finish execution in nested-chain-b. Finally the flow returns to the main-chain. When the nested version of a <gateway> element is defined in the chain, it does not require the service-interface attribute. Instead, it simple takes the message in its current state and places it on the channel defined via the request-channel attribute. When the downstream flow initiated by that gateway completes, a Message will be returned to the gateway and continue its journey within the current chain.

6. Message Transformation

6.1 Transformer

6.1.1 Introduction

Message Transformers play a very important role in enabling the loose-coupling of Message Producers and Message Consumers. Rather than requiring every Message-producing component to know what type is expected by the next consumer, Transformers can be added between those components. Generic transformers, such as one that converts a String to an XML Document, are also highly reusable.

For some systems, it may be best to provide a Canonical Data Model, but Spring Integration's general philosophy is not to require any particular format. Rather, for maximum flexibility, Spring Integration aims to provide the simplest possible model for extension. As with the other endpoint types, the use of declarative configuration in XML and/or Annotations enables simple POJOs to be adapted for the role of Message Transformers. These configuration options will be described below.

For the same reason of maximizing flexibility, Spring does not require XML-based Message payloads. Nevertheless, the framework does provide some convenient Transformers for dealing with XML-based payloads if that is indeed the right choice for your application. For more information on those transformers, see Chapter 31, XML Support - Dealing with XML Payloads.

6.1.2 Configuring Transformer

Configuring Transformer with XML

The <transformer> element is used to create a Message-transforming endpoint. In addition to "input-channel" and "output-channel" attributes, it requires a "ref". The "ref" may either point to an Object that contains the @Transformer annotation on a single method (see below) or it may be combined with an explicit method name value provided via the "method" attribute.

<int:transformer id="testTransformer" ref="testTransformerBean" input-channel="inChannel"
             method="transform" output-channel="outChannel"/>
<beans:bean id="testTransformerBean" class="org.foo.TestTransformer" />

Using a "ref" attribute is generally recommended if the custom transformer handler implementation can be reused in other <transformer> definitions. However if the custom transformer handler implementation should be scoped to a single definition of the <transformer>, you can define an inner bean definition:

<int:transformer id="testTransformer" input-channel="inChannel" method="transform"
  <beans:bean class="org.foo.TestTransformer"/>


Using both the "ref" attribute and an inner handler definition in the same <transformer> configuration is not allowed, as it creates an ambiguous condition and will result in an Exception being thrown.

The method that is used for transformation may expect either the Message type or the payload type of inbound Messages. It may also accept Message header values either individually or as a full map by using the @Header and @Headers parameter annotations respectively. The return value of the method can be any type. If the return value is itself a Message, that will be passed along to the transformer's output channel.

As of Spring Integration 2.0, a Message Transformer's transformation method can no longer return null. Returning null will result in an exception since a Message Transformer should always be expected to transform each source Message into a valid target Message. In other words, a Message Transformer should not be used as a Message Filter since there is a dedicated <filter> option for that. However, if you do need this type of behavior (where a component might return NULL and that should not be considered an error), a service-activator could be used. Its requires-reply value is FALSE by default, but that can be set to TRUE in order to have Exceptions thrown for NULL return values as with the transformer.

Transformers and Spring Expression Language (SpEL)

Just like Routers, Aggregators and other components, as of Spring Integration 2.0 Transformers can also benefit from SpEL support (http://static.springsource.org/spring/docs/3.0.x/spring-framework-reference/html/expressions.html) whenever transformation logic is relatively simple.

<int:transformer input-channel="inChannel"
	expression="payload.toUpperCase() + '- [' + T(java.lang.System).currentTimeMillis() + ']'"/>

In the above configuration we are achieving a simple transformation of the payload with a simple SpEL expression and without writing a custom transformer. Our payload (assuming String) will be upper-cased and concatenated with the current timestamp with some simple formatting.

Common Transformers

There are also a few Transformer implementations available out of the box. Because, it is fairly common to use the toString() representation of an Object, Spring Integration provides an ObjectToStringTransformer whose output is a Message with a String payload. That String is the result of invoking the toString() operation on the inbound Message's payload.

<int:object-to-string-transformer input-channel="in" output-channel="out"/>

A potential example for this would be sending some arbitrary object to the 'outbound-channel-adapter' in the file namespace. Whereas that Channel Adapter only supports String, byte-array, or java.io.File payloads by default, adding this transformer immediately before the adapter will handle the necessary conversion. Of course, that works fine as long as the result of the toString() call is what you want to be written to the File. Otherwise, you can just provide a custom POJO-based Transformer via the generic 'transformer' element shown previously.

When debugging, this transformer is not typically necessary since the 'logging-channel-adapter' is capable of logging the Message payload. Refer to the section called “Wire Tap” for more detail.


The object-to-string-transformer is very simple; it invokes toString() on the inbound payload. There are two exceptions to this (since 3.0): if the payload is a char[], it invokes new String(payload); if the payload is a byte[], it invokes new String(payload, charset), where charset is "UTF-8" by default. The charset can be modified by supplying the charset attribute on the transformer.

For more sophistication (such as selection of the charset dynamically, at runtime), you can use a SpEL expression-based transformer instead; for example:

<int:transformer input-channel="in" output-channel="out"
		 expression="new java.lang.String(payload, headers['myCharset']" />

If you need to serialize an Object to a byte array or deserialize a byte array back into an Object, Spring Integration provides symmetrical serialization transformers. These will use standard Java serialization by default, but you can provide an implementation of Spring 3.0's Serializer or Deserializer strategies via the 'serializer' and 'deserializer' attributes, respectively.

<int:payload-serializing-transformer input-channel="objectsIn" output-channel="bytesOut"/>

<int:payload-deserializing-transformer input-channel="bytesIn" output-channel="objectsOut"/>

Object-to-Map Transformer

Spring Integration also provides Object-to-Map and Map-to-Object transformers which utilize the Spring Expression Language (SpEL) to serialize and de-serialize the object graphs. The object hierarchy is introspected to the most primitive types (String, int, etc.). The path to this type is described via SpEL, which becomes the key in the transformed Map. The primitive type becomes the value.

For example:

public class Parent{
    private Child child;
    private String name; 
    // setters and getters are omitted

public class Child{
   private String name; 
   private List<String> nickNames;
   // setters and getters are omitted

... will be transformed to a Map which looks like this: {person.name=George, person.child.name=Jenna, person.child.nickNames[0]=Bimbo . . . etc}

The SpEL-based Map allows you to describe the object structure without sharing the actual types allowing you to restore/rebuild the object graph into a differently typed Object graph as long as you maintain the structure.

For example: The above structure could be easily restored back to the following Object graph via the Map-to-Object transformer:

public class Father {
    private Kid child;
    private String name; 
    // setters and getters are omitted

public class Kid {
   private String name; 
   private List<String> nickNames;
   // setters and getters are omitted

If you need to create a "structured" map, you can provide the 'flatten' attribute. The default value for this attribute is 'true' meaning the default behavior; if you provide a 'false' value, then the structure will be a map of maps.

For example:

public class Parent {
	private Child child;
	private String name;
	// setters and getters are omitted

public class Child {
	private String name;
	private List<String> nickNames;
	// setters and getters are omitted

... will be transformed to a Map which looks like this: {name=George, child={name=Jenna, nickNames=[Bimbo, ...]}}

To configure these transformers, Spring Integration provides namespace support Object-to-Map:

<int:object-to-map-transformer input-channel="directInput" output-channel="output"/>


<int:object-to-map-transformer input-channel="directInput" output-channel="output" flatten="false"/>


<int:map-to-object-transformer input-channel="input" 


<int:map-to-object-transformer input-channel="inputA" 
<bean id="person" class="org.foo.Person" scope="prototype"/>

NOTE: 'ref' and 'type' attributes are mutually exclusive. You can only use one. Also, if using the 'ref' attribute, you must point to a 'prototype' scoped bean, otherwise a BeanCreationException will be thrown. 

JSON Transformers

Object to JSON and JSON to Object transformers are provided.

<int:object-to-json-transformer input-channel="objectMapperInput"/>

<int:json-to-object-transformer input-channel="objectMapperInput"

These use a vanilla Jackson ObjectMapper by default. If you wish to customize the ObjectMapper (for example, to configure the 'ALLOW_COMMENTS' feature when parsing JSON), you can supply a reference to your custom ObjectMapper bean using the object-mapper attribute.

<int:json-to-object-transformer input-channel="objectMapperInput"
    type="foo.MyDomainObject" object-mapper="customObjectMapper"/>


Beginning with version 3.0, the object-mapper attribute references an instance of a new strategy interface JsonObjectMapper. This abstraction allows multiple implementations of json mappers to be used. Implementations that wrap Jackson 1.x and Jackson 2 are provided, with the version being detected on the classpath. These classes are JacksonJsonObjectMapper and Jackson2JsonObjectMapper.

For backward compatibility, a simple Jackson 1.x ObjectMapper can be provided instead of a JsonObjectMapper. This will be removed in a future release.

If there are requirements to use both Jackson libraries in the same application, keep in mind that before version 3.0, the JSON transformers used only Jackson 1.x and, from 3.0 on, the framework will select Jackson 2 by default, if both are on the classpath. So, to avoid unexpected issues with Jackson's mapping features, when using annotations, there may be a need to apply annotations from both Jacksons on domain classes:
public class Foo {

        public Object bar;


You may wish to consider using a FactoryBean or simple factory method to create the JsonObjectMapper with the required characteristics.

public class ObjectMapperFactory {

    public static Jackson2JsonObjectMapper getMapper() {
        ObjectMapper mapper = new ObjectMapper();
        mapper.configure(JsonParser.Feature.ALLOW_COMMENTS, true);
        return new Jackson2JsonObjectMapper(mapper);

<bean id="customObjectMapper" class="foo.ObjectMapperFactory"


Beginning with version 2.2, the object-to-json-transformer sets the content-type header to application/json, by default, if the input message does not already have that header present.

It you wish to set the content type header to some other value, or explicitly overwrite any existing header with some value (including application/json), use the content-type attribute. If you wish to suppress the setting of the header, set the content-type attribute to an empty string (""). This will result in a message with no content-type header, unless such a header was present on the input message.

Beginning with version 3.0, the ObjectToJsonTransformer adds headers, reflecting the source type, to the message. Similarly, the JsonToObjectTransformer can use those type headers when converting the JSON to an object. These headers are mapped in the AMQP adapters so that they are entirely compatible with the Spring-AMQP JsonMessageConverter.

This enables the following flows to work without any special configuration...



Where the outbound adapter is configured with a JsonMessageConverter and the inbound adapter uses the default SimpleMessageConverter.



Where the outbound adapter is configured with a SimpleMessageConverter and the inbound adapter uses the default JsonMessageConverter.



Where both adapters are configured with a SimpleMessageConverter.

When using the headers to determine the type, you should not provide a class attribute, because it takes precedence over the headers.

In addition to JSON Transformers, Spring Integration provides a built-in #jsonPath SpEL function for use in expressions. For more information see Appendix A, Spring Expression Language (SpEL).

#xpath SpEL Function

Since version 3.0, Spring Integration also provides a built-in #xpath SpEL function for use in expressions. For more information see Section 31.9, “#xpath SpEL Function”.

Configuring a Transformer with Annotations

The @Transformer annotation can also be added to methods that expect either the Message type or the message payload type. The return value will be handled in the exact same way as described above in the section describing the <transformer> element.

Order generateOrder(String productId) {
    return new Order(productId);

Transformer methods may also accept the @Header and @Headers annotations that is documented in Section F.5, “Annotation Support”

Order generateOrder(String productId, @Header("customerName") String customer) {
    return new Order(productId, customer);

Also see Section 7.7.5, “Advising Endpoints Using Annotations”.

6.1.3 Header Filter

Some times your transformation use case might be as simple as removing a few headers. For such a use case, Spring Integration provides a Header Filter which allows you to specify certain header names that should be removed from the output Message (e.g. for security reasons or a value that was only needed temporarily). Basically the Header Filter is the opposite of the Header Enricher. The latter is discussed in Section 6.2.2, “Header Enricher”
<int:header-filter input-channel="inputChannel"
		output-channel="outputChannel" header-names="lastName, state"/>
As you can see, configuration of a Header Filter is quite simple. It is a typical endpoint with input/output channels and a header-names attribute. That attribute accepts the names of the header(s) (delimited by commas if there are multiple) that need to be removed. So, in the above example the headers named 'lastName' and 'state' will not be present on the outbound Message.

6.2 Content Enricher

6.2.1 Introduction

At times you may have a requirement to enhance a request with more information than was provided by the target system. The Content Enricher pattern describes various scenarios as well as the component (Enricher), which allows you to address such requirements.

The Spring Integration Core module includes 2 enrichers:

Furthermore, several Adapter specific Header Enrichers are included as well:

Please go to the adapter specific sections of this reference manual to learn more about those adapters.

For more information regarding expressions support, please see Appendix A, Spring Expression Language (SpEL).

6.2.2 Header Enricher

If you only need to add headers to a Message, and they are not dynamically determined by the Message content, then referencing a custom implementation of a Transformer may be overkill. For that reason, Spring Integration provides support for the Header Enricher pattern. It is exposed via the <header-enricher> element.

<int:header-enricher input-channel="in" output-channel="out">
     <int:header name="foo" value="123"/>
     <int:header name="bar" ref="someBean"/>

The Header Enricher also provides helpful sub-elements to set well-known header names.

<int:header-enricher input-channel="in" output-channel="out">
		<int:error-channel ref="applicationErrorChannel"/>
		<int:reply-channel ref="quoteReplyChannel"/>
		<int:correlation-id value="123"/>
		<int:priority value="HIGHEST"/>
		<int:header name="bar" ref="someBean"/>

In the above configuration you can clearly see that for well-known headers such as errorChannel, correlationId, priority, replyChanneletc., instead of using generic <header> sub-elements where you would have to provide both header 'name' and 'value', you can use convenient sub-elements to set those values directly.

POJO Support

Often a header value cannot be defined statically and has to be determined dynamically based on some content in the Message. That is why Header Enricher allows you to also specify a bean reference using the ref and method attribute. The specified method will calculate the header value. Let's look at the following configuration:

<int:header-enricher input-channel="in" output-channel="out">
    <int:header name="foo" method="computeValue" ref="myBean"/>

<bean id="myBean" class="foo.bar.MyBean"/>
public class MyBean {
    public String computeValue(String payload){
        return payload.toUpperCase() + "_US";


You can also configure your POJO as inner bean:

<int:header-enricher  input-channel="inputChannel" output-channel="outputChannel">
	<int:header name="some_header">
            <bean class="org.MyEnricher"/>

as well as point to a Groovy script:

<int:header-enricher  input-channel="inputChannel" output-channel="outputChannel">
		<int:header name="some_header">
            <int-groovy:script location="org/SampleGroovyHeaderEnricher.groovy"/>

SpEL Support

In Spring Integration 2.0 we have introduced the convenience of the Spring Expression Language (SpEL) to help configure many different components. The Header Enricher is one of them. Looking again at the POJO example above, you can see that the computation logic to determine the header value is actually pretty simple. A natural question would be: "is there a simpler way to accomplish this?". That is where SpEL shows its true power.

<int:header-enricher input-channel="in" output-channel="out">
	<int:header name="foo" expression="payload.toUpperCase() + '_US'"/>

As you can see, by using SpEL for such simple cases, we no longer have to provide a separate class and configure it in the application context. All we need is the expression attribute configured with a valid SpEL expression. The 'payload' and 'headers' variables are bound to the SpEL Evaluation Context, giving you full access to the incoming Message.

Header Channel Registry

Starting with Spring Integration 3.0, a new sub-element <int:header-channels-to-string/> is available; it has no attributes. This converts existing replyChannel and errorChannel headers (when they are a MessageChannel) to a String and stores the channel(s) in a registry for later resolution when it is time to send a reply, or handle an error. This is useful for cases where the headers might be lost; for example when serializing a message into a message store or when transporting the message over JMS. If the header does not already exist, or it is not a MessageChannel, no changes are made.

Use of this functionality requires the presence of a HeaderChannelRegistry bean. By default, the framework creates a DefaultHeaderChannelRegistry with the default expiry (60 seconds). Channels are removed from the registry after this time. To change this, simply define a bean with id integrationHeaderChannelRegistry and configure the required delay using a constructor argument (milliseconds).

The HeaderChannelRegistry has a size() method to determine the current size of the registry. The runReaper() method cancels the current scheduled task and runs the reaper immediately; the task is then scheduled to run again based on the current delay. These methods can be invoked directly by getting a reference to the registry, or you can send a message with, for example, the following content to a control bus:


This sub-element is a convenience only, and is the equivalent of specifying:

For more examples for configuring header enrichers, see Header Enricher Advanced Configuration.

6.2.3 Payload Enricher

In certain situations the Header Enricher, as discussed above, may not be sufficient and payloads themselves may have to be enriched with additional information. For example, order messages that enter the Spring Integration messaging system have to look up the order's customer based on the provided customer number and then enrich the original payload with that information.

Since Spring Integration 2.1, the Payload Enricher is provided. A Payload Enricher defines an endpoint that passes a Message to the exposed request channel and then expects a reply message. The reply message then becomes the root object for evaluation of expressions to enrich the target payload.

The Payload Enricher provides full XML namespace support via the enricher element. In order to send request messages, the payload enricher has a request-channel attribute that allows you to dispatch messages to a request channel.

Basically by defining the request channel, the Payload Enricher acts as a Gateway, waiting for the message that were sent to the request channel to return, and the Enricher then augments the message's payload with the data provided by the reply message.

When sending messages to the request channel you also have the option to only send a subset of the original payload using the request-payload-expression attribute.

The enriching of payloads is configured through SpEL expressions, providing users with a maximum degree of flexibility. Therefore, users are not only able to enrich payloads with direct values from the reply channel's Message, but they can use SpEL expressions to extract a subset from that Message, only, or to apply addtional inline transformations, allowing them to further manipulate the data.

If you only need to enrich payloads with static values, you don't have to provide the request-channel attribute.

Enrichers are a variant of Transformers and in many cases you could use a Payload Enricher or a generic Transformer implementation to add additional data to your messages payloads. Thus, familiarize yourself with all transformation-capable components that are provided by Spring Integration and carefully select the implementation that semantically fits your business case best.


Below, please find an overview of all available configuration options that are available for the payload enricher:

<int:enricher request-channel=""                          1
              auto-startup="true"                         2
              id=""                                       3
              order=""                                    4
              output-channel=""                           5
              request-payload-expression=""               6
              reply-channel=""                            7
              send-timeout=""                             8
              should-clone-payload="false">               9
    <int:poller></int:poller>                             10
    <int:property name="" expression=""/>  11
    <int:property name="" value=""/>
	<int:header name="" expression=""/>  12
    <int:header name="" value="" overwrite="" type=""/>


Channel to which a Message will be sent to get the data to use for enrichment. Optional.


Lifecycle attribute signaling if this component should be started during Application Context startup. Defaults to true. Optional.


Id of the underlying bean definition, which is either an EventDrivenConsumer or a PollingConsumer. Optional.


Specifies the order for invocation when this endpoint is connected as a subscriber to a channel. This is particularly relevant when that channel is using a "failover" dispatching strategy. It has no effect when this endpoint itself is a Polling Consumer for a channel with a queue. Optional.


Identifies the Message channel where a Message will be sent after it is being processed by this endpoint. Optional.


By default the original message's payload will be used as payload that will be send to the request-channel. By specifying a SpEL expression as value for the request-payload-expression attribute, a subset of the original payload, a header value or any other resolvable SpEL expression can be used as the basis for the payload, that will be sent to the request-channel.

For the Expression evaluation the full message is available as the 'root object'.

For instance the following SpEL expressions (among others) are possible:

  • payload.foo
  • headers.foobar
  • new java.util.Date()
  • 'foo' + 'bar'

If more sophisticated logic is required (e.g. changing the message headers etc.) please use additional downstream transformers. Optional.


Channel where a reply Message is expected. This is optional; typically the auto-generated temporary reply channel is sufficient. Optional.


Maximum amount of time in milliseconds to wait when sending a message to the channel, if such channel may block.

For example, a Queue Channel can block until space is available, if its maximum capacity has been reached. Internally the send timeout is set on the MessagingTemplate and ultimately applied when invoking the send operation on the MessageChannel.

By default the send timeout is set to '-1', which may cause the send operation on the MessageChannel, depending on the implementation, to block indefinitely. Optional.


Boolean value indicating whether any payload that implements Cloneable should be cloned prior to sending the Message to the request chanenl for acquiring the enriching data. The cloned version would be used as the target payload for the ultimate reply. Default is false. Optional.


Allows you to configure a Message Poller if this endpoint is a Polling Consumer. Optional.


Each property sub-element provides the name of a property (via the mandatory name attribute). That property should be settable on the target payload instance. Exactly one of the value or expression attributes must be provided as well. The former for a literal value to set, and the latter for a SpEL expression to be evaluated. The root object of the evaluation context is the Message that was returned from the flow initiated by this enricher, the input Message if there is no request channel, or the application context (using the '@<beanName>.<beanProperty>' SpEL syntax).


Each header sub-element provides the name of a Message header (via the mandatory name attribute). Exactly one of the value or expression attributes must be provided as well. The former for a literal value to set, and the latter for a SpEL expression to be evaluated. The root object of the evaluation context is the Message that was returned from the flow initiated by this enricher, the input Message if there is no request channel, or the application context (using the '@<beanName>.<beanProperty>' SpEL syntax). Note, similar to the <header-enricher>, the <enricher>'s header element has type and overwrite attributes. However, a difference is that, with the <enricher>, the overwrite attribute is true by default, to be consistent with <enricher>'s <property> sub-element.


Below, please find several examples of using a Payload Enricher in various situations.

In the following example, a User object is passed as the payload of the Message. The User has several properties but only the username is set initially. The Enricher's request-channel attribute below is configured to pass the User on to the findUserServiceChannel.

Through the implicitly set reply-channel a User object is returned and using the property sub-element, properties from the reply are extracted and used to enrich the original payload.

<int:enricher id="findUserEnricher"
    <int:property name="email"    expression="payload.email"/>
    <int:property name="password" expression="payload.password"/>
The code samples shown here, are part of the Spring Integration Samples project. Please feel free to check it out at: https://github.com/SpringSource/spring-integration-samples

How do I pass only a subset of data to the request channel?

Using a request-payload-expression attribute a single property of the payload can be passed on to the request channel instead of the full message. In the example below on the username property is passed on to the request channel. Keep in mind, that alwhough only the username is passed on, the resulting message send to the request channel will contain the full set of MessageHeaders.

<int:enricher id="findUserByUsernameEnricher"
    <int:property name="email"    expression="payload.email"/>
    <int:property name="password" expression="payload.password"/>

How can I enrich payloads that consist of Collection data?

In the following example, instead of a User object, a Map is passed in. The Map contains the username under the map key username. Only the username is passed on to the request channel. The reply contains a full User object, which is ultimately added to the Map under the user key.

<int:enricher id="findUserWithMapEnricher"
    <int:property name="user"    expression="payload"/>

How can I enrich payloads with static information without using a request channel?

Here is an example that does not use a request channel at all, but solely enriches the message's payload with static values. But please be aware that the word 'static' is used loosly here. You can still use SpEL expressions for setting those values.

<int:enricher id="userEnricher"
    <int:property name="user.updateDate" expression="new java.util.Date()"/>
    <int:property name="user.firstName" value="foo"/>
    <int:property name="user.lastName"  value="bar"/>
    <int:property name="user.age"       value="42"/>

6.3 Claim Check

6.3.1 Introduction

In the earlier sections we've covered several Content Enricher type components that help you deal with situations where a message is missing a piece of data. We also discussed Content Filtering which lets you remove data items from a message. However there are times when we want to hide data temporarily. For example, in a distributed system we may receive a Message with a very large payload. Some intermittent message processing steps may not need access to this payload and some may only need to access certain headers, so carrying the large Message payload through each processing step may cause performance degradation, may produce a security risk, and may make debugging more difficult.

The Claim Check pattern describes a mechanism that allows you to store data in a well known place while only maintaining a pointer (Claim Check) to where that data is located. You can pass that pointer around as a payload of a new Message thereby allowing any component within the message flow to get the actual data as soon as it needs it. This approach is very similar to the Certified Mail process where you'll get a Claim Check in your mailbox and would have to go to the Post Office to claim your actual package. Of course it's also the same idea as baggage-claim on a flight or in a hotel.

Spring Integration provides two types of Claim Check transformers:

  • Incoming Claim Check Transformer
  • Outgoing Claim Check Transformer

Convenient namespace-based mechanisms are available to configure them.

6.3.2 Incoming Claim Check Transformer

An Incoming Claim Check Transformer will transform an incoming Message by storing it in the Message Store identified by its message-store attribute.

<int:claim-check-in id="checkin"

In the above configuration the Message that is received on the input-channel will be persisted to the Message Store identified with the message-store attribute and indexed with generated ID. That ID is the Claim Check for that Message. The Claim Check will also become the payload of the new (transformed) Message that will be sent to the output-channel.

Now, lets assume that at some point you do need access to the actual Message. You can of course access the Message Store manually and get the contents of the Message, or you can use the same approach as before except now you will be transforming the Claim Check to the actual Message by using an Outgoing Claim Check Transformer.

Here is an overview of all available parameters of an Incoming Claim Check Transformer:

<int:claim-check-in auto-startup="true" 1
                    id=""                          2
                    input-channel=""               3
                    message-store="messageStore"   4
                    order=""                       5
                    output-channel=""              6
                    send-timeout="">               7
    <int:poller></int:poller>                      8


Lifecycle attribute signaling if this component should be started during Application Context startup. Defaults to true. Attribute is not available inside a Chain element. Optional.


Id identifying the underlying bean definition (MessageTransformingHandler). Attribute is not available inside a Chain element. Optional.


The receiving Message channel of this endpoint. Attribute is not available inside a Chain element. Optional.


Reference to the MessageStore to be used by this Claim Check transformer. If not specified, the default reference will be to a bean named messageStore. Optional.


Specifies the order for invocation when this endpoint is connected as a subscriber to a channel. This is particularly relevant when that channel is using a failover dispatching strategy. It has no effect when this endpoint itself is a Polling Consumer for a channel with a queue. Attribute is not available inside a Chain element. Optional.


Identifies the Message channel where Message will be sent after its being processed by this endpoint. Attribute is not available inside a Chain element. Optional.


Specify the maximum amount of time in milliseconds to wait when sending a reply Message to the output channel. By default the send will block for one second. Attribute is not available inside a Chain element. Optional.


Defines a poller. Element is not available inside a Chain element. Optional.

6.3.3 Outgoing Claim Check Transformer

An Outgoing Claim Check Transformer allows you to transform a Message with a Claim Check payload into a Message with the original content as its payload.

<int:claim-check-out id="checkout"

In the above configuration, the Message that is received on the input-channel should have a Claim Check as its payload and the Outgoing Claim Check Transformer will transform it into a Message with the original payload by simply querying the Message store for a Message identified by the provided Claim Check. It then sends the newly checked-out Message to the output-channel.

Here is an overview of all available parameters of an Outgoing Claim Check Transformer:

<int:claim-check-out auto-startup="true" 1
                     id=""                          2
                     input-channel=""               3
                     message-store="messageStore"   4
                     order=""                       5
                     output-channel=""              6
                     remove-message="false"         7
                     send-timeout="">               8
    <int:poller></int:poller>                       9


Lifecycle attribute signaling if this component should be started during Application Context startup. Defaults to true. Attribute is not available inside a Chain element. Optional.


Id identifying the underlying bean definition (MessageTransformingHandler). Attribute is not available inside a Chain element. Optional.


The receiving Message channel of this endpoint. Attribute is not available inside a Chain element. Optional.


Reference to the MessageStore to be used by this Claim Check transformer. If not specified, the default reference will be to a bean named messageStore. Optional.


Specifies the order for invocation when this endpoint is connected as a subscriber to a channel. This is particularly relevant when that channel is using a failover dispatching strategy. It has no effect when this endpoint itself is a Polling Consumer for a channel with a queue. Attribute is not available inside a Chain element. Optional.


Identifies the Message channel where Message will be sent after its being processed by this endpoint. Attribute is not available inside a Chain element. Optional.


If set to true the Message will be removed from the MessageStore by this transformer. Useful when Message can be "claimed" only once. Defaults to false. Optional.


Specify the maximum amount of time in milliseconds to wait when sending a reply Message to the output channel. By default the send will block for one second. Attribute is not available inside a Chain element. Optional.


Defines a poller. Element is not available inside a Chain element. Optional.

Claim Once

There are scenarios when a particular message must be claimed only once. As an analogy, consider the airplane luggage check-in/out process. Checking-in your luggage on departure and and then claiming it on arrival is a classic example of such a scenario. Once the luggage has been claimed, it can not be claimed again without first checking it back in. To accommodate such cases, we introduced a remove-message boolean attribute on the claim-check-out transformer. This attribute is set to false by default. However, if set to true, the claimed Message will be removed from the MessageStore, so that it can no longer be claimed again.

This is also something to consider in terms of storage space, especially in the case of the in-memory Map-based SimpleMessageStore, where failing to remove the Messages could ultimately lead to an OutOfMemoryException. Therefore, if you don't expect multiple claims to be made, it's recommended that you set the remove-message attribute's value to true.

<int:claim-check-out id="checkout"

6.3.4 A word on Message Store

Although we rarely care about the details of the claim checks as long as they work, it is still worth knowing that the current implementation of the actual Claim Check (the pointer) in Spring Integration is a UUID to ensure uniqueness.

org.springframework.integration.store.MessageStore is a strategy interface for storing and retrieving messages. Spring Integration provides two convenient implementations of it. SimpleMessageStore: an in-memory, Map-based implementation (the default, good for testing) and JdbcMessageStore: an implementation that uses a relational database via JDBC.

7. Messaging Endpoints

7.1 Message Endpoints

The first part of this chapter covers some background theory and reveals quite a bit about the underlying API that drives Spring Integration's various messaging components. This information can be helpful if you want to really understand what's going on behind the scenes. However, if you want to get up and running with the simplified namespace-based configuration of the various elements, feel free to skip ahead to Section 7.1.4, “Namespace Support” for now.

As mentioned in the overview, Message Endpoints are responsible for connecting the various messaging components to channels. Over the next several chapters, you will see a number of different components that consume Messages. Some of these are also capable of sending reply Messages. Sending Messages is quite straightforward. As shown above in Section 3.1, “Message Channels”, it's easy to send a Message to a Message Channel. However, receiving is a bit more complicated. The main reason is that there are two types of consumers: Polling Consumers and Event Driven Consumers.

Of the two, Event Driven Consumers are much simpler. Without any need to manage and schedule a separate poller thread, they are essentially just listeners with a callback method. When connecting to one of Spring Integration's subscribable Message Channels, this simple option works great. However, when connecting to a buffering, pollable Message Channel, some component has to schedule and manage the polling thread(s). Spring Integration provides two different endpoint implementations to accommodate these two types of consumers. Therefore, the consumers themselves can simply implement the callback interface. When polling is required, the endpoint acts as a container for the consumer instance. The benefit is similar to that of using a container for hosting Message Driven Beans, but since these consumers are simply Spring-managed Objects running within an ApplicationContext, it more closely resembles Spring's own MessageListener containers.

7.1.1 Message Handler

Spring Integration's MessageHandler interface is implemented by many of the components within the framework. In other words, this is not part of the public API, and a developer would not typically implement MessageHandler directly. Nevertheless, it is used by a Message Consumer for actually handling the consumed Messages, and so being aware of this strategy interface does help in terms of understanding the overall role of a consumer. The interface is defined as follows:

public interface MessageHandler {

    void handleMessage(Message<?> message);


Despite its simplicity, this provides the foundation for most of the components that will be covered in the following chapters (Routers, Transformers, Splitters, Aggregators, Service Activators, etc). Those components each perform very different functionality with the Messages they handle, but the requirements for actually receiving a Message are the same, and the choice between polling and event-driven behavior is also the same. Spring Integration provides two endpoint implementations that host these callback-based handlers and allow them to be connected to Message Channels.

7.1.2 Event Driven Consumer

Because it is the simpler of the two, we will cover the Event Driven Consumer endpoint first. You may recall that the SubscribableChannel interface provides a subscribe() method and that the method accepts a MessageHandler parameter (as shown in the section called “SubscribableChannel”):


Since a handler that is subscribed to a channel does not have to actively poll that channel, this is an Event Driven Consumer, and the implementation provided by Spring Integration accepts a a SubscribableChannel and a MessageHandler:

SubscribableChannel channel = context.getBean("subscribableChannel", SubscribableChannel.class);

EventDrivenConsumer consumer = new EventDrivenConsumer(channel, exampleHandler);

7.1.3 Polling Consumer

Spring Integration also provides a PollingConsumer, and it can be instantiated in the same way except that the channel must implement PollableChannel:

PollableChannel channel = context.getBean("pollableChannel", PollableChannel.class);

PollingConsumer consumer = new PollingConsumer(channel, exampleHandler);
For more information regarding Polling Consumers, please also read Section 3.2, “Poller (Polling Consumer)” as well as Section 3.3, “Channel Adapter”.

There are many other configuration options for the Polling Consumer. For example, the trigger is a required property:

PollingConsumer consumer = new PollingConsumer(channel, handler);

consumer.setTrigger(new IntervalTrigger(30, TimeUnit.SECONDS));

Spring Integration currently provides two implementations of the Trigger interface: IntervalTrigger and CronTrigger. The IntervalTrigger is typically defined with a simple interval (in milliseconds), but also supports an initialDelay property and a boolean fixedRate property (the default is false, i.e. fixed delay):

IntervalTrigger trigger = new IntervalTrigger(1000);

The CronTrigger simply requires a valid cron expression (see the Javadoc for details):

CronTrigger trigger = new CronTrigger("*/10 * * * * MON-FRI");

In addition to the trigger, several other polling-related configuration properties may be specified:

PollingConsumer consumer = new PollingConsumer(channel, handler);


The maxMessagesPerPoll property specifies the maximum number of messages to receive within a given poll operation. This means that the poller will continue calling receive() without waiting until either null is returned or that max is reached. For example, if a poller has a 10 second interval trigger and a maxMessagesPerPoll setting of 25, and it is polling a channel that has 100 messages in its queue, all 100 messages can be retrieved within 40 seconds. It grabs 25, waits 10 seconds, grabs the next 25, and so on.

The receiveTimeout property specifies the amount of time the poller should wait if no messages are available when it invokes the receive operation. For example, consider two options that seem similar on the surface but are actually quite different: the first has an interval trigger of 5 seconds and a receive timeout of 50 milliseconds while the second has an interval trigger of 50 milliseconds and a receive timeout of 5 seconds. The first one may receive a message up to 4950 milliseconds later than it arrived on the channel (if that message arrived immediately after one of its poll calls returned). On the other hand, the second configuration will never miss a message by more than 50 milliseconds. The difference is that the second option requires a thread to wait, but as a result it is able to respond much more quickly to arriving messages. This technique, known as long polling, can be used to emulate event-driven behavior on a polled source.

A Polling Consumer may also delegate to a Spring TaskExecutor, as illustrated in the following example:

PollingConsumer consumer = new PollingConsumer(channel, handler);

TaskExecutor taskExecutor = context.getBean("exampleExecutor", TaskExecutor.class);

Furthermore, a PollingConsumer has a property called adviceChain. This property allows you to specify a List of AOP Advices for handling additional cross cutting concerns including transactions. These advices are applied around the doPoll() method. For more in-depth information, please see the sections AOP Advice chains and Transaction Support under Section 7.1.4, “Namespace Support”.

The examples above show dependency lookups, but keep in mind that these consumers will most often be configured as Spring bean definitions. In fact, Spring Integration also provides a FactoryBean called ConsumerEndpointFactoryBean that creates the appropriate consumer type based on the type of channel, and there is full XML namespace support to even further hide those details. The namespace-based configuration will be featured as each component type is introduced.

Many of the MessageHandler implementations are also capable of generating reply Messages. As mentioned above, sending Messages is trivial when compared to the Message reception. Nevertheless, when and how many reply Messages are sent depends on the handler type. For example, an Aggregator waits for a number of Messages to arrive and is often configured as a downstream consumer for a Splitter which may generate multiple replies for each Message it handles. When using the namespace configuration, you do not strictly need to know all of the details, but it still might be worth knowing that several of these components share a common base class, the AbstractReplyProducingMessageHandler, and it provides a setOutputChannel(..) method.

7.1.4 Namespace Support

Throughout the reference manual, you will see specific configuration examples for endpoint elements, such as router, transformer, service-activator, and so on. Most of these will support an input-channel attribute and many will support an output-channel attribute. After being parsed, these endpoint elements produce an instance of either the PollingConsumer or the EventDrivenConsumer depending on the type of the input-channel that is referenced: PollableChannel or SubscribableChannel respectively. When the channel is pollable, then the polling behavior is determined based on the endpoint element's poller sub-element and its attributes.


Below you find a poller with all available configuration options:

<int:poller cron=""                                 1
            default="false"                         2
            error-channel=""                        3
            fixed-delay=""                          4
            fixed-rate=""                           5
            id=""                                   6
            max-messages-per-poll=""                7
            receive-timeout=""                      8
            ref=""                                  9
            task-executor=""                        10
            time-unit="MILLISECONDS"                11
            trigger="">                             12
            <int:advice-chain />                    13
            <int:transactional />                   14


Provides the ability to configure Pollers using Cron expressions. The underlying implementation uses a org.springframework.scheduling.support.CronTrigger. If this attribute is set, none of the following attributes must be specified: fixed-delay, trigger, fixed-rate, ref.


By setting this attribute to true, it is possible to define exactly one (1) global default poller. An exception is raised if more than one default poller is defined in the application context. Any endpoints connected to a PollableChannel (PollingConsumer) or any SourcePollingChannelAdapter that does not have any explicitly configured poller will then use the global default Poller. Optional. Defaults to false.


Identifies the channel which error messages will be sent to if a failure occurs in this poller's invocation. To completely suppress Exceptions, provide a reference to the nullChannel. Optional.


The fixed delay trigger uses a PeriodicTrigger under the covers. If the time-unit attribute is not used, the specified value is represented in milliseconds. If this attribute is set, none of the following attributes must be specified: fixed-rate, trigger, cron, ref.


The fixed rate trigger uses a PeriodicTrigger under the covers. If the time-unit attribute is not used the specified value is represented in milliseconds. If this attribute is set, none of the following attributes must be specified: fixed-delay, trigger, cron, ref.


The Id referring to the Poller's underlying bean-definition, which is of type org.springframework.integration.scheduling.PollerMetadata. The id attribute is required for a top-level poller element unless it is the default poller (default="true").


Please see Section 3.3.1, “Configuring An Inbound Channel Adapter” for more information. Optional. If not specified the default values used depends on the context. If a PollingConsumer is used, this atribute will default to -1. However, if a SourcePollingChannelAdapter is used, then the max-messages-per-poll attribute defaults to 1.


Value is set on the underlying class PollerMetadata Optional. If not specified it defaults to 1000 (milliseconds).


Bean reference to another top-level poller. The ref attribute must not be present on the top-level poller element. However, if this attribute is set, none of the following attributes must be specified: fixed-rate, trigger, cron, fixed-deleay.


Provides the ability to reference a custom task executor. Please see the section below titled TaskExecutor Support for further information. Optional.


This attribute specifies the java.util.concurrent.TimeUnit enum value on the underlying org.springframework.scheduling.support.PeriodicTrigger. Therefore, this attribute can ONLY be used in combination with the fixed-delay or fixed-rate attributes. If combined with either cron or a trigger reference attribute, it will cause a failure.

The minimal supported granularity for a PeriodicTrigger is MILLISECONDS. Therefore, the only available options are MILLISECONDS and SECONDS. If this value is not provided, then any fixed-delay or fixed-rate value will be interpreted as MILLISECONDS by default.

Basically this enum provides a convenience for SECONDS-based interval trigger values. For hourly, daily, and monthly settings, consider using a cron trigger instead.


Reference to any spring configured bean which implements the org.springframework.scheduling.Trigger interface. Optional. However, if this attribute is set, none of the following attributes must be specified: fixed-delay, fixed-rate, cron, ref.


Allows to specify extra AOP Advices to handle additional cross cutting concerns. Please see the section below titled Transaction Support for further information. Optional.


Pollers can be made transactional. Please see the section below titled AOP Advice chains for further information. Optional.


For example, a simple interval-based poller with a 1-second interval would be configured like this:

<int:transformer input-channel="pollable"
    <int:poller fixed-rate="1000"/>

As an alternative to fixed-rate you can also use the fixed-delay attribute.

For a poller based on a Cron expression, use the cron attribute instead:

<int:transformer input-channel="pollable"
    <int:poller cron="*/10 * * * * MON-FRI"/>

If the input channel is a PollableChannel, then the poller configuration is required. Specifically, as mentioned above, the trigger is a required property of the PollingConsumer class. Therefore, if you omit the poller sub-element for a Polling Consumer endpoint's configuration, an Exception may be thrown. The exception will also be thrown if you attempt to configure a poller on the element that is connected to a non-pollable channel.

It is also possible to create top-level pollers in which case only a ref is required:

<int:poller id="weekdayPoller" cron="*/10 * * * * MON-FRI"/>

<int:transformer input-channel="pollable"
    <int:poller ref="weekdayPoller"/>

The ref attribute is only allowed on the inner-poller definitions. Defining this attribute on a top-level poller will result in a configuration exception thrown during initialization of the Application Context.

Global Default Pollers

In fact, to simplify the configuration even further, you can define a global default poller. A single top-level poller within an ApplicationContext may have the default attribute with a value of true. In that case, any endpoint with a PollableChannel for its input-channel that is defined within the same ApplicationContext and has no explicitly configured poller sub-element will use that default.

<int:poller id="defaultPoller" default="true" max-messages-per-poll="5" fixed-rate="3000"/>

<!-- No <poller/> sub-element is necessary since there is a default -->
<int:transformer input-channel="pollable"

Transaction Support

Spring Integration also provides transaction support for the pollers so that each receive-and-forward operation can be performed as an atomic unit-of-work. To configure transactions for a poller, simply add the <transactional/> sub-element. The attributes for this element should be familiar to anyone who has experience with Spring's Transaction management:

<int:poller fixed-delay="1000">
    <int:transactional transaction-manager="txManager"

For more information please refer to Section C.1.1, “Poller Transaction Support”.

AOP Advice chains

Since Spring transaction support depends on the Proxy mechanism  with TransactionInterceptor (AOP Advice) handling transactional behavior of the message flow initiated by the poller, some times there is a need to provide extra Advice(s) to handle other cross cutting behavior associated with the poller. For that poller defines an advice-chain element allowing you to add more advices - class that  implements MethodInterceptor interface.. 

<int:service-activator id="advicedSa" input-channel="goodInputWithAdvice" ref="testBean"
		method="good" output-channel="output">
	<int:poller max-messages-per-poll="1" fixed-rate="10000">
		<int:transactional transaction-manager="txManager" />
			<ref bean="adviceA" />
			<beans:bean class="org.bar.SampleAdvice"/>

For more information on how to implement MethodInterceptor please refer to AOP sections of Spring reference manual (section 8 and 9). Advice chain can also be applied on the poller that does not have any transaction configuration essentially allowing you to enhance the behavior of the message flow initiated by the poller.

TaskExecutor Support

The polling threads may be executed by any instance of Spring's TaskExecutor abstraction. This enables concurrency for an endpoint or group of endpoints. As of Spring 3.0, there is a task namespace in the core Spring Framework, and its <executor/> element supports the creation of a simple thread pool executor. That element accepts attributes for common concurrency settings such as pool-size and queue-capacity. Configuring a thread-pooling executor can make a substantial difference in how the endpoint performs under load. These settings are available per-endpoint since the performance of an endpoint is one of the major factors to consider (the other major factor being the expected volume on the channel to which the endpoint subscribes). To enable concurrency for a polling endpoint that is configured with the XML namespace support, provide the task-executor reference on its <poller/> element and then provide one or more of the properties shown below:

<int:poller task-executor="pool" fixed-rate="1000"/>

<task:executor id="pool"

If no task-executor is provided, the consumer's handler will be invoked in the caller's thread. Note that the caller is usually the default TaskScheduler (see Section F.3, “Configuring the Task Scheduler”). Also, keep in mind that the task-executor attribute can provide a reference to any implementation of Spring's TaskExecutor interface by specifying the bean name. The executor element above is simply provided for convenience.

As mentioned in the background section for Polling Consumers above, you can also configure a Polling Consumer in such a way as to emulate event-driven behavior. With a long receive-timeout and a short interval-trigger, you can ensure a very timely reaction to arriving messages even on a polled message source. Note that this will only apply to sources that have a blocking wait call with a timeout. For example, the File poller does not block, each receive() call returns immediately and either contains new files or not. Therefore, even if a poller contains a long receive-timeout, that value would never be usable in such a scenario. On the other hand when using Spring Integration's own queue-based channels, the timeout value does have a chance to participate. The following example demonstrates how a Polling Consumer will receive Messages nearly instantaneously.

<int:service-activator input-channel="someQueueChannel"
    <int:poller receive-timeout="30000" fixed-rate="10"/>


Using this approach does not carry much overhead since internally it is nothing more then a timed-wait thread which does not require nearly as much CPU resource usage as a thrashing, infinite while loop for example.

7.1.5 Change Polling Rate at Runtime

When configuring Pollers with a fixed-delay or fixed-rate attribute, the default implementation will use a PeriodicTrigger instance. The PeriodicTrigger is part of the Core Spring Framework and it accepts the interval as a constructor argument, only. Therefore it cannot be changed at runtime.

However, you can define your own implementation of the org.springframework.scheduling.Trigger interface. You could even use the PeriodicTrigger as a starting point. Then, you can add a setter for the interval (period), or you could even embed your own throttling logic within the trigger itself if desired. The period property will be used with each call to nextExecutionTime to schedule the next poll. To use this custom trigger within pollers, declare the bean defintion of the custom Trigger in your application context and inject the dependency into your Poller configuration using the trigger attribute, which references the custom Trigger bean instance. You can now obtain a reference to the Trigger bean and the polling interval can be changed between polls.

For an example, please see the Spring Integration Samples project. It contains a sample called dynamic-poller, which uses a custom Trigger and demonstrates the ability to change the polling interval at runtime.

The sample provides a custom Trigger which implements the org.springframework.scheduling.Trigger interface. The sample's Trigger is based on Spring's PeriodicTrigger implementation. However, the fields of the custom trigger are not final and the properties have explicit getters and setters, allowing to dynamically change the polling period at runtime.


It is important to note, though, that because the Trigger method is nextExecutionTime(), any changes to a dynamic trigger will not take effect until the next poll, based on the existing configuration. It is not possible to force a trigger to fire before it's currently configured next execution time.

7.1.6 Payload Type Conversion

Throughout the reference manual, you will also see specific configuration and implementation examples of various endpoints which can accept a Message or any arbitrary Object as an input parameter. In the case of an Object, such a parameter will be mapped to a Message payload or part of the payload or header (when using the Spring Expression Language). However there are times when the type of input parameter of the endpoint method does not match the type of the payload or its part. In this scenario we need to perform type conversion. Spring Integration provides a convenient way for registering type converters (using the Spring 3.x ConversionService) within its own instance of a conversion service bean named integrationConversionService. That bean is automatically created as soon as the first converter is defined using the Spring Integration namespace support. To register a Converter all you need is to implement org.springframework.core.convert.converter.Converter and define it via convenient namespace support:

<int:converter ref="sampleConverter"/>

<bean id="sampleConverter" class="foo.bar.TestConverter"/>

or as an inner bean:

    <bean class="o.s.i.config.xml.ConverterParserTests$TestConverter3"/>


When configuring an Application Context, the Spring Framework allows you to add a conversionService bean (see Configuring a ConversionService chapter). This service is used, when needed, to perform appropriate conversions during bean creation and configuration.

In contrast, the integrationConversionService is used for runtime conversions. These uses are quite different; converters that are intended for use when wiring bean constructor-args and properties may produce unintended results if used at runtime for Spring Integration expression evaluation against Messages within Datatype Channels, Payload Type transformers etc.

However, if you do want to use the Spring conversionService as the Spring Integration integrationConversionService, you can configure an alias in the Application Context:

<alias name="conversionService" alias="integrationConversionService"/>

In this case the conversionService's Converters will be available for Spring Integration runtime conversion.

7.1.7 Asynchronous polling

If you want the polling to be asynchronous, a Poller can optionally specify a task-executor attribute pointing to an existing instance of any TaskExecutor bean (Spring 3.0 provides a convenient namespace configuration via the task namespace). However, there are certain things you must understand when configuring a Poller with a TaskExecutor. 

The problem is that there are two configurations in place. The Poller and the TaskExecutor, and they both have to be in tune with each other otherwise you might end up creating an artificial memory leak.

Let's look at the following configuration provided by one of the users on the Spring Integration forum (http://forum.springsource.org/showthread.php?t=94519):

<int:service-activator input-channel="publishChannel" ref="myService">
	<int:poller receive-timeout="5000" task-executor="taskExecutor" fixed-rate="50"/>

<task:executor id="taskExecutor" pool-size="20" queue-capacity="20"/>

The above configuration demonstrates one of those out of tune configurations.

The poller keeps scheduling new tasks even though all the threads are blocked waiting for either a new message to arrive, or the timeout to expire. Given that there are 20 threads executing tasks with a 5 second timeout, they will be executed at a rate of 4 per second (5000/20 = 250ms). But, new tasks are being scheduled at a rate of 20 per second, so the internal queue in the task executor will grow at a rate of 16 per second (while the process is idle), so we essentially have a memory leak.

One of the ways to handle this is to set the queue-capacity attribute of the Task Executor to 0. You can also manage it by specifying what to do with messages that can not be queued by setting the rejection-policy attribute of the Task Executor (e.g., DISCARD). In other words there are certain details you must understand with regard to configuring the TaskExecutor. Please refer to - Section 25 - Task Execution and Scheduling of the Spring reference manual for more detail on the subject.

7.1.8 Endpoint Inner Beans

Many endpoints are composite beans; this includes all consumers and all polled inbound channel adapters. Consumers (polled or event- driven) delegate to a MessageHandler; polled adapters obtain messages by delegating to a MessageSource. Often, it is useful to obtain a reference to the delegate bean, perhaps to change configuration at runtime, or for testing. These beans can be obtained from the ApplicationContext with well-known names. MessageHandlers are registered with the application context with a bean id someConsumer.handler (where 'consumer' is the endpoint's id attribute). MessageSources are registered with a bean id somePolledAdapter.source, again where 'somePolledAdapter' is the id of the adapter.

7.2 Messaging Gateways

The primary purpose of a Gateway is to hide the messaging API provided by Spring Integration. It allows your application's business logic to be completely unaware of the Spring Integration API and using a generic Gateway, your code interacts instead with a simple interface, only.

7.2.1 Enter the GatewayProxyFactoryBean

As mentioned above, it would be great to have no dependency on the Spring Integration API at all - including the gateway class. For that reason, Spring Integration provides the GatewayProxyFactoryBean that generates a proxy for any interface and internally invokes the gateway methods shown below. Using dependency injection you can then expose the interface to your business methods.

Here is an example of an interface that can be used to interact with Spring Integration:

package org.cafeteria;

public interface Cafe {

    void placeOrder(Order order);


7.2.2 Gateway XML Namespace Support

Namespace support is also provided which allows you to configure such an interface as a service as demonstrated by the following example.

<int:gateway id="cafeService"

With this configuration defined, the "cafeService" can now be injected into other beans, and the code that invokes the methods on that proxied instance of the Cafe interface has no awareness of the Spring Integration API. The general approach is similar to that of Spring Remoting (RMI, HttpInvoker, etc.). See the "Samples" Appendix for an example that uses this "gateway" element (in the Cafe demo).

7.2.3 Setting the Default Reply Channel

Typically you don't have to specify the default-reply-channel, since a Gateway will auto-create a temporary, anonymous reply channel, where it will listen for the reply. However, there are some cases which may prompt you to define a default-reply-channel (or reply-channel with adapter gateways such as HTTP, JMS, etc.).

For some background, we'll quickly discuss some of the inner-workings of the Gateway. A Gateway will create a temporary point-to-point reply channel which is anonymous and is added to the Message Headers with the name replyChannel. When providing an explicit default-reply-channel (reply-channel with remote adapter gateways), you have the option to point to a publish-subscribe channel, which is so named because you can add more than one subscriber to it. Internally Spring Integration will create a Bridge between the temporary replyChannel and the explicitly defined default-reply-channel.

So let's say you want your reply to go not only to the gateway, but also to some other consumer. In this case you would want two things: a) a named channel you can subscribe to and b) that channel is a publish-subscribe-channel. The default strategy used by the gateway will not satisfy those needs, because the reply channel added to the header is anonymous and point-to-point. This means that no other subscriber can get a handle to it and even if it could, the channel has point-to-point behavior such that only one subscriber would get the Message. So by defining a default-reply-channel you can point to a channel of your choosing, which in this case would be a publish-subscribe-channel. The Gateway would create a bridge from it to the temporary, anonymous reply channel that is stored in the header.

Another case where you might want to provide a reply channel explicitly is for monitoring or auditing via an interceptor (e.g., wiretap). You need a named channel in order to configure a Channel Interceptor.

7.2.4 Gateway Configuration with Annotations and/or XML

The reason that the attributes on the 'gateway' element are named 'default-request-channel' and 'default-reply-channel' is that you may also provide per-method channel references by using the @Gateway annotation.

public interface Cafe {

    void placeOrder(Order order);


You may alternatively provide such content in method sub-elements if you prefer XML configuration (see the next paragraph).

It is also possible to pass values to be interpreted as Message headers on the Message that is created and sent to the request channel by using the @Header annotation:

public interface FileWriter {

    void write(byte[] content, @Header(FileHeaders.FILENAME) String filename);


If you prefer the XML approach of configuring Gateway methods, you can provide method sub-elements to the gateway configuration.

<int:gateway id="myGateway" service-interface="org.foo.bar.TestGateway"
  <int:default-header name="calledMethod" expression="#gatewayMethod.name"/>
  <int:method name="echo" request-channel="inputA" reply-timeout="2" request-timeout="200"/>
  <int:method name="echoUpperCase" request-channel="inputB"/>
  <int:method name="echoViaDefault"/>

You can also provide individual headers per method invocation via XML. This could be very useful if the headers you want to set are static in nature and you don't want to embed them in the gateway's method signature via @Header annotations. For example, in the Loan Broker example we want to influence how aggregation of the Loan quotes will be done based on what type of request was initiated (single quote or all quotes). Determining the type of the request by evaluating what gateway method was invoked, although possible, would violate the separation of concerns paradigm (the method is a java artifact),  but expressing your intention (meta information) via Message headers is natural in a Messaging architecture.

<int:gateway id="loanBrokerGateway"
  <int:method name="getLoanQuote" request-channel="loanBrokerPreProcessingChannel">
    <int:header name="RESPONSE_TYPE" value="BEST"/>
  <int:method name="getAllLoanQuotes" request-channel="loanBrokerPreProcessingChannel">
    <int:header name="RESPONSE_TYPE" value="ALL"/>

In the above case you can clearly see how a different value will be set for the 'RESPONSE_TYPE' header based on the gateway's method.

Expressions and "Global" Headers

The <header/> element supports expression as an alternative to value. The SpEL expression is evaluated to determine the value of the header. There is no #root object but the following variables are available:

  • #args - an Object[] containing the method arguments
  • #gatewayMethod - the java.reflect.Method object representing the method in the service-interface that was invoked. A header containing this variable can be used later in the flow, for example, for routing. For example, if you wish to route on the simple method name, you might add a header, with expression #gatewayMethod.name.
    The java.reflect.Method is not serializable; a header with expression #gatewayMethod will be lost if you later serialize the message. So, you may wish to use #gatewayMethod.name or #gatewayMethod.toString() in those cases; the toString() method provides a String representation of the method, including parameter and return types.
    Prior to 3.0, the #method variable was available, representing the method name only. This is still available, but deprecated; use #gatewayMethod.name instead.

Since 3.0, <default-header/>s can be defined to add headers to all messages produced by the gateway, regardless of the method invoked. Specific headers defined for a method take precedence over default headers. Specific headers defined for a method here will override any @Header annotations in the service interface. However, default headers will NOT override any @Header annotations in the service interface.

The gateway now also supports a default-payload-expression which will be applied for all methods (unless overridden).

7.2.5 Mapping Method Arguments to a Message

Using the configuration techniques in the previous section allows control of how method arguments are mapped to message elements (payload and header(s)). When no explicit configuration is used, certain conventions are used to perform the mapping. In some cases, these conventions cannot determine which argument is the payload and which should be mapped to headers.

public String send1(Object foo, Map bar);

public String send2(Map foo, Map bar);

In the first case, the convention will map the first argument to the payload (as long as it is not a Map) and the contents of the second become headers.

In the second case (or the first when the argument for parameter foo is a Map), the framework cannot determine which argument should be the payload; mapping will fail. This can generally be resolved using a payload-expression, a @Payload annotation and/or a @Headers annotation.

Alternatively, and whenever the conventions break down, you can take the entire responsibility for mapping the method calls to messages. To do this, implement an MethodArgsMessageMapper and provide it to the <gateway/> using the mapper attribute. The mapper maps a MethodArgsHolder, which is a simple class wrapping the java.reflect.Method instance and an Object[] containing the arguments. When providing a custom mapper, the default-payload-expression attribute and <default-header/> elements are not allowed on the gateway; similarly, the payload-expression attribute and <header/> elements are not allowed on any <method/> elements.

7.2.6 Invoking No-Argument Methods

When invoking methods on a Gateway interface that do not have any arguments, the default behavior is to receive a Message from a PollableChannel.

At times however, you may want to trigger no-argument methods so that you can in fact interact with other components downstream that do not require user-provided parameters, e.g. triggering no-argument SQL calls or Stored Procedures.

In order to achieve send-and-receive semantics, you must provide a payload. In order to generate a payload, method parameters on the interface are not necessary. You can either use the @Payload annotation or the payload-expression attribute in XML on the method sub-element. Below please find a few examples of what the payloads could be:

  • a literal string
  • #method (for the method name)
  • new java.util.Date()
  • @someBean.someMethod()'s return value

Here is an example using the @Payload annotation:

public interface Cafe {

    @Payload("new java.util.Date()")
    List<Order> retrieveOpenOrders();


If a method has no argument and no return value, but does contain a payload expression, it will be treated as a send-only operation.

7.2.7 Error Handling

Of course, the Gateway invocation might result in errors. By default any error that has occurred downstream will be re-thrown as a MessagingException (RuntimeException) upon the Gateway's method invocation. However there are times when you may want to simply log the error rather than propagating it, or you may want to treat an Exception as a valid reply, by mapping it to a Message that will conform to some "error message" contract that the caller understands. To accomplish this, our Gateway provides support for a Message Channel dedicated to the errors via the error-channel attribute. In the example below, you can see that a 'transformer' is used to create a reply Message from the Exception.

<int:gateway id="sampleGateway"

<int:transformer input-channel="exceptionTransformationChannel"
        ref="exceptionTransformer" method="createErrorResponse"/>

The exceptionTransformer could be a simple POJO that knows how to create the expected error response objects. That would then be the payload that is sent back to the caller. Obviously, you could do many more elaborate things in such an "error flow" if necessary. It might involve routers (including Spring Integration's ErrorMessageExceptionTypeRouter), filters, and so on. Most of the time, a simple 'transformer' should be sufficient, however.

Alternatively, you might want to only log the Exception (or send it somewhere asynchronously). If you provide a one-way flow, then nothing would be sent back to the caller. In the case that you want to completely suppress Exceptions, you can provide a reference to the global "nullChannel" (essentially a /dev/null approach). Finally, as mentioned above, if no "error-channel" is defined at all, then the Exceptions will propagate as usual.

Exposing the messaging system via simple POJI Gateways obviously provides benefits, but "hiding" the reality of the underlying messaging system does come at a price so there are certain things you should consider. We want our Java method to return as quickly as possible and not hang for an indefinite amount of time while the caller is waiting on it to return (void, return value, or a thrown Exception). When regular methods are used as a proxies in front of the Messaging system, we have to take into account the potentially asynchronous nature of the underlying messaging. This means that there might be a chance that a Message that was initiated by a Gateway could be dropped by a Filter, thus never reaching a component that is responsible for producing a reply. Some Service Activator method might result in an Exception, thus providing no reply (as we don't generate Null messages). So as you can see there are multiple scenarios where a reply message might not be coming. That is perfectly natural in messaging systems. However think about the implication on the gateway method. The Gateway's method input arguments  were incorporated into a Message and sent downstream. The reply Message would be converted to a return value of the Gateway's method. So you might want to ensure that for each Gateway call there will always be a reply Message. Otherwise, your Gateway method might never return and will hang indefinitely. One of the ways of handling this situation is via an Asynchronous Gateway (explained later in this section). Another way of handling it is to explicitly set the reply-timeout attribute. That way, the gateway will not hang any longer than the time specified by the reply-timeout and will return 'null' if that timeout does elapse. Finally, you might want to consider setting downstream flags such as 'requires-reply' on a service-activator or 'throw-exceptions-on-rejection' on a filter. These options will be discussed in more detail in the final section of this chapter.

7.2.8 Asynchronous Gateway

As a pattern the Messaging Gateway is a very nice way to hide messaging-specific code while still exposing the full capabilities of the messaging system. As you've seen, the GatewayProxyFactoryBean provides a convenient way to expose a Proxy over a service-interface thus giving you POJO-based access to a messaging system (based on objects in your own domain, or primitives/Strings, etc).  But when a gateway is exposed via simple POJO methods which return values it does imply that for each Request message (generated when the method is invoked) there must be a Reply message (generated when the method has returned). Since Messaging systems naturally are asynchronous you may not always be able to guarantee the contract where "for each request there will always be be a reply".  With Spring Integration 2.0 we are introducing support for an Asynchronous Gateway which is a convenient way to initiate flows where you may not know if a reply is expected or how long will it take for replies to arrive.

A natural way to handle these types of scenarios in Java would be relying upon java.util.concurrent.Future instances, and that is exactly what Spring Integration uses to support an Asynchronous Gateway.

From the XML configuration, there is nothing different and you still define Asynchronous Gateway the same way as a regular Gateway.

<int:gateway id="mathService" 

However the Gateway Interface (service-interface) is a bit different.

public interface MathServiceGateway {
  Future<Integer> multiplyByTwo(int i);

As you can see from the example above the return type for the gateway method is a Future. When GatewayProxyFactoryBean sees that the return type of the gateway method is a Future, it immediately switches to the async mode by utilizing an AsyncTaskExecutor. That is all. The call to such a method always returns immediately with a Future instance. Then, you can interact with the Future at your own pace to get the result, cancel, etc. And, as with any other use of Future instances, calling get() may reveal a timeout, an execution exception, and so on.

MathServiceGateway mathService = ac.getBean("mathService", MathServiceGateway.class);
Future<Integer> result = mathService.multiplyByTwo(number);
// do something else here since the reply might take a moment
int finalResult =  result.get(1000, TimeUnit.SECONDS);

For a more detailed example, please refer to the async-gateway sample distributed within the Spring Integration samples.

Asynchronous Gateway and AsyncTaskExecutor

By default GatewayProxyFactoryBean uses org.springframework.core.task.SimpleAsyncTaskExecutor when submitting internal AsyncInvocationTask instances for any gateway method whose return type is Future.class. However the async-executor attribute in the <gateway/> element's configuration allows you to provide a reference to any implementation of java.util.concurrent.Executor available within the Spring application context.

7.2.9 Gateway behavior when no response arrives

As it was explained earlier, the Gateway provides a convenient way of interacting with a Messaging system via POJO method invocations, but realizing that a typical method invocation, which is generally expected to always return (even with an Exception), might not always map one-to-one to message exchanges (e.g., a reply message might not arrive - which is equivalent to a method not returning). It is important to go over several scenarios especially in the Sync Gateway case and understand the default behavior of the Gateway and how to deal with these scenarios to make the Sync Gateway behavior more predictable regardless of the outcome of the message flow that was initialed from such Gateway.

There are certain attributes that could be configured to make Sync Gateway behavior more predictable, but some of them might not always work as you might have expected. One of them is reply-timeout. So, lets look at the reply-timeout attribute and see how it can/can't influence the behavior of the Sync Gateway in various scenarios. We will look at single-threaded scenario (all components downstream are connected via Direct Channel) and multi-threaded scenarios (e.g., somewhere downstream you may have Pollable or Executor Channel which breaks single-thread boundary)

Long running process downstream

Sync Gateway - single-threaded. If a component downstream is still running (e.g., infinite loop or a very slow service), then setting a reply-timeout has no effect and the Gateway method call will not return until such downstream service exits (via return or exception). Sync Gateway - multi-threaded. If a component downstream is still running (e.g., infinite loop or a very slow service), in a multi-threaded message flow setting the reply-timeout will have an effect by allowing gateway method invocation to return once the timeout has been reached, since the GatewayProxyFactoryBean  will simply poll on the reply channel waiting for a message until the timeout expires. However it could result in a 'null' return from the Gateway method if the timeout has been reached before the actual reply was produced. It is also important to understand that the reply message (if produced) will be sent to a reply channel after the Gateway method invocation might have returned, so you must be aware of that and design your flow with this in mind.

Downstream component returns 'null'

Sync Gateway - single-threaded. If a component downstream returns 'null' and no reply-timeout has been configured, the Gateway method call will hang indefinitely unless: a) a reply-timeout has been configured or b) the requires-reply attribute has been set on the downstream component (e.g., service-activator) that might return 'null'. In this case, an Exception would be thrown and propagated to the Gateway. Sync Gateway - multi-threaded. Behavior is the same as above.

Downstream component return signature is 'void' while Gateway method signature is non-void

Sync Gateway - single-threaded. If a component downstream returns 'void' and no reply-timeout has been configured, the Gateway method call will hang indefinitely unless a reply-timeout has been configured  Sync Gateway - multi-threaded Behavior is the same as above.

Downstream component results in Runtime Exception (regardless of the method signature)

Sync Gateway - single-threaded. If a component downstream throws a Runtime Exception, such exception will be propagated via an Error Message back to the gateway and re-thrown. Sync Gateway - multi-threaded Behavior is the same as above.

It is also important to understand that by default reply-timeout is unbounded* which means that if not explicitly set there are several scenarios (described above) where your Gateway method invocation might hang indefinitely. So, make sure you analyze your flow and if there is even a remote possibility of one of these scenarios to occur, set the reply-timeout attribute to a 'safe' value or, even better, set the requires-reply attribute of the downstream component to 'true' to ensure a timely response as produced by the throwing of an Exception as soon as that downstream component does return null internally. But also, realize that there are some scenarios (see the very first one) where reply-timeout will not help. That means it is also important to analyze your message flow and decide when to use a Sync Gateway vs an Async Gateway. As you've seen the latter case is simply a matter of defining Gateway methods that return Future instances. Then, you are guaranteed to receive that return value, and you will have more granular control over the results of the invocation.

Also, when dealing with a Router you should remember that setting the resolution-required attribute to 'true' will result in an Exception thrown by the router if it can not resolve a particular channel. Likewise, when dealing with a Filter, you can set the throw-exception-on-rejection attribute. In both of these cases, the resulting flow will behave like that containing a service-activator with the 'requires-reply' attribute. In other words, it will help to ensure a timely response from the Gateway method invocation.


* reply-timeout is unbounded for <gateway/> elements (created by the GatewayProxyFactoryBean). Inbound gateways for external integration (ws, http, etc.) share many characteristics and attributes with these gateways. However, for those inbound gateways, the default reply-timeout is 1000 milliseconds (1 second). If a downstream async handoff is made to another thread, you may need to increase this attribute to allow enough time for the flow to complete before the gateway times out.

7.3 Service Activator

7.3.1 Introduction

The Service Activator is the endpoint type for connecting any Spring-managed Object to an input channel so that it may play the role of a service. If the service produces output, it may also be connected to an output channel. Alternatively, an output producing service may be located at the end of a processing pipeline or message flow in which case, the inbound Message's "replyChannel" header can be used. This is the default behavior if no output channel is defined, and as with most of the configuration options you'll see here, the same behavior actually applies for most of the other components we have seen.

7.3.2 Configuring Service Activator

To create a Service Activator, use the 'service-activator' element with the 'input-channel' and 'ref' attributes:

<int:service-activator input-channel="exampleChannel" ref="exampleHandler"/>

The configuration above assumes that "exampleHandler" either contains a single method annotated with the @ServiceActivator annotation or that it contains only one public method at all. To delegate to an explicitly defined method of any object, simply add the "method" attribute.

<int:service-activator input-channel="exampleChannel" ref="somePojo" method="someMethod"/>

In either case, when the service method returns a non-null value, the endpoint will attempt to send the reply message to an appropriate reply channel. To determine the reply channel, it will first check if an "output-channel" was provided in the endpoint configuration:

<int:service-activator input-channel="exampleChannel" output-channel="replyChannel"
                       ref="somePojo" method="someMethod"/>

If no "output-channel" is available, it will then check the Message's replyChannel header value. If that value is available, it will then check its type. If it is a MessageChannel, the reply message will be sent to that channel. If it is a String, then the endpoint will attempt to resolve the channel name to a channel instance. If the channel cannot be resolved, then a ChannelResolutionException will be thrown. It it can be resolved, the Message will be sent there. This is the technique used for Request Reply messaging in Spring Integration, and it is also an example of the Return Address pattern.

The argument in the service method could be either a Message or an arbitrary type. If the latter, then it will be assumed that it is a Message payload, which will be extracted from the message and injected into such service method. This is generally the recommended approach as it follows and promotes a POJO model when working with Spring Integration. Arguments may also have @Header or @Headers annotations as described in Section F.5, “Annotation Support”

The service method is not required to have any arguments at all, which means you can implement event-style Service Activators, where all you care about is an invocation of the service method, not worrying about the contents of the message. Think of it as a NULL JMS message. An example use-case for such an implementation could be a simple counter/monitor of messages deposited on the input channel.

Using a "ref" attribute is generally recommended if the custom Service Activator handler implementation can be reused in other <service-activator> definitions. However if the custom Service Activator handler implementation is only used within a single definition of the <service-activator>, you can provide an inner bean definition:

<int:service-activator id="exampleServiceActivator" input-channel="inChannel"
            output-channel = "outChannel" method="foo">
    <beans:bean class="org.foo.ExampleServiceActivator"/>


Using both the "ref" attribute and an inner handler definition in the same <service-activator> configuration is not allowed, as it creates an ambiguous condition and will result in an Exception being thrown.

Service Activators and the Spring Expression Language (SpEL)

Since Spring Integration 2.0, Service Activators can also benefit from SpEL (http://static.springsource.org/spring/docs/3.0.x/spring-framework-reference/html/expressions.html).

For example, you may now invoke any bean method without pointing to the bean via a ref attribute or including it as an inner bean definition. For example:

<int:service-activator input-channel="in" output-channel="out"
	expression="@accountService.processAccount(payload, headers.accountId)"/>

	<bean id="accountService" class="foo.bar.Account"/>

In the above configuration instead of injecting 'accountService' using a ref or as an inner bean, we are simply using SpEL's @beanId notation and invoking a method which takes a type compatible with Message payload. We are also passing a header value. As you can see, any valid SpEL expression can be evaluated against any content in the Message. For simple scenarios your Service Activators do not even have to reference a bean if all logic can be encapsulated by such an expression.

<int:service-activator input-channel="in" output-channel="out" expression="payload * 2"/>

In the above configuration our service logic is to simply multiply the payload value by 2, and SpEL lets us handle it relatively easy.

7.4 Delayer

7.4.1 Introduction

A Delayer is a simple endpoint that allows a Message flow to be delayed by a certain interval. When a Message is delayed, the original sender will not block. Instead, the delayed Messages will be scheduled with an instance of org.springframework.scheduling.TaskScheduler to be sent to the output channel after the delay has passed. This approach is scalable even for rather long delays, since it does not result in a large number of blocked sender Threads. On the contrary, in the typical case a thread pool will be used for the actual execution of releasing the Messages. Below you will find several examples of configuring a Delayer.

7.4.2 Configuring Delayer

The <delayer> element is used to delay the Message flow between two Message Channels. As with the other endpoints, you can provide the 'input-channel' and 'output-channel' attributes, but the delayer also has 'default-delay' and 'expression' attributes (and 'expression' sub-element) that are used to determine the number of milliseconds that each Message should be delayed. The following delays all messages by 3 seconds:

<int:delayer id="delayer" input-channel="input"
             default-delay="3000" output-channel="output"/>

If you need per-Message determination of the delay, then you can also provide the SpEL expression using the 'expression' attribute:

<int:delayer id="delayer" input-channel="input" output-channel="output"
             default-delay="3000" expression="headers['delay']"/>

In the example above, the 3 second delay would only apply when the expression evaluates to null for a given inbound Message. If you only want to apply a delay to Messages that have a valid result of the expression evaluation, then you can use a 'default-delay' of 0 (the default). For any Message that has a delay of 0 (or less), the Message will be sent immediately, on the calling Thread.

The delay handler supports expression evaluation results that represent an interval in milliseconds (any Object whose toString() method produces a value that can be parsed into a Long) as well as java.util.Date instances representing an absolute time. In the first case, the milliseconds will be counted from the current time (e.g. a value of 5000 would delay the Message for at least 5 seconds from the time it is received by the Delayer). With a Date instance, the Message will not be released until the time represented by that Date object. In either case, a value that equates to a non-positive delay, or a Date in the past, will not result in any delay. Instead, it will be sent directly to the output channel on the original sender's Thread. If the expression evaluation result is not a Date, and can not be parsed as a Long, the default delay (if any) will be applied.

The expression evaluation may throw an evaluation Exception for various reasons, including an invalid expression, or other conditions. By default, such exceptions are ignored (logged at DEBUG level) and the delayer falls back to the default delay (if any). You can modify this behavior by setting the ignore-expression-failures attribute. By default this attribute is set to true and the Delayer behavior is as described above. However, if you wish to not ignore expression evaluation exceptions, and throw them to the delayer's caller, set the ignore-expression-failures attribute to false.

Notice in the example above that the delay expression is specified as headers['delay']. This is the SpEL Indexer syntax to access a Map element (MessageHeaders implements Map), it invokes: headers.get("delay"). For simple map element names (that do not contain '.') you can also use the SpEL dot accessor syntax, where the above header expression can be specified as headers.delay. But, different results are achieved if the header is missing. In the first case, the expression will evaluate to null; the second will result in something like:
 org.springframework.expression.spel.SpelEvaluationException: EL1008E:(pos 8):
		   Field or property 'delay' cannot be found on object of type 'org.springframework.integration.MessageHeaders'
So, if there is a possibility of the header being omitted, and you want to fall back to the default delay, it is generally more efficient (and recommended) to use the Indexer syntax instead of dot property accessor syntax, because detecting the null is faster than catching an exception.

The delayer delegates to an instance of Spring's TaskScheduler abstraction. The default scheduler used by the delayer is the ThreadPoolTaskScheduler instance provided by Spring Integration on startup: Section F.3, “Configuring the Task Scheduler”. If you want to delegate to a different scheduler, you can provide a reference through the delayer element's 'scheduler' attribute:

<int:delayer id="delayer" input-channel="input" output-channel="output"

<task:scheduler id="exampleTaskScheduler" pool-size="3"/>

If you configure an external ThreadPoolTaskScheduler you can set on this scheduler property waitForTasksToCompleteOnShutdown = true. It allows successful completion of 'delay' tasks, which already in the execution state (releasing the Message), when the application is shutdown. Before Spring Integration 2.2 this property was available on the <delayer> element, because DelayHandler could create its own scheduler on the background. Since 2.2 delayer requires an external scheduler instance and waitForTasksToCompleteOnShutdown was deleted; you should use the scheduler's own configuration.

Also keep in mind ThreadPoolTaskScheduler has a property errorHandler which can be injected with some implementation of org.springframework.util.ErrorHandler. This handler allows to process an Exception from the thread of the scheduled task sending the delayed message. By default it uses an org.springframework.scheduling.support.TaskUtils$LoggingErrorHandler and you will see a stack trace in the logs. You might want to consider using an org.springframework.integration.channel.MessagePublishingErrorHandler, which sends an ErrorMessage into an error-channel, either from the failed Message's header or into the default error-channel.

7.4.3 Delayer and Message Store

The DelayHandler persists delayed Messages into the Message Group in the provided MessageStore. (The 'groupId' is based on required 'id' attribute of <delayer> element.) A delayed message is removed from the MessageStore by the scheduled task just before the DelayHandler sends the Message to the output-channel. If the provided MessageStore is persistent (e.g. JdbcMessageStore) it provides the ability to not lose Messages on the application shutdown. After application startup, the DelayHandler reads Messages from its Message Group in the MessageStore and reschedules them with a delay based on the original arrival time of the Message (if the delay is numeric). For messages where the delay header was a Date, that is used when rescheduling. If a delayed Message remained in the MessageStore more than its 'delay', it will be sent immediately after startup.

The <delayer> can be enriched with mutually exclusive sub-elements <transactional> or <advice-chain>. The List of these AOP Advices is applied to the proxied internal DelayHandler.ReleaseMessageHandler, which has the responsibility to release the Message, after the delay, on a Thread of the scheduled task. It might be used, for example, when the downstream message flow throws an Exception and the ReleaseMessageHandler's transaction will be rolled back. In this case the delayed Message will remain in the persistent MessageStore. You can use any custom org.aopalliance.aop.Advice implementation within the <advice-chain>. A sample configuration of the <delayer> may look like this:

<int:delayer id="delayer" input-channel="input" output-channel="output"
        <beans:ref bean="customAdviceBean"/>
                <tx:method name="*" read-only="true"/>

The DelayHandler can be exported as a JMX MBean with managed operations getDelayedMessageCount and reschedulePersistedMessages, which allows the rescheduling of delayed persisted Messages at runtime, for example, if the TaskScheduler has previously been stopped. These operations can be invoked via a Control Bus command:

Message<String> delayerReschedulingMessage =

For more information regarding the Message Store, JMX and the Control Bus, please read Chapter 8, System Management.

7.5 Scripting support

With Spring Integration 2.1 we've added support for the JSR223 Scripting for Java specification, introduced in Java version 6. This allows you to use scripts written in any supported language including Ruby/JRuby, Javascript and Groovy to provide the logic for various integration components similar to the way the Spring Expression Language (SpEL) is used in Spring Integration. For more information about JSR223 please refer to the documentation

Note that this feature requires Java 6 or higher. Sun developed a JSR223 reference implementation which works with Java 5 but it is not officially supported and we have not tested it with Spring Integration.

In order to use a JVM scripting language, a JSR223 implementation for that language must be included in your class path. Java 6 natively supports Javascript. The Groovy and JRuby projects provide JSR233 support in their standard distribution. Other language implementations may be available or under development. Please refer to the appropriate project website for more information.

Various JSR223 language implementations have been developed by third parties. A particular implementation's compatibility with Spring Integration depends on how well it conforms to the specification and/or the implementer's interpretation of the specification.

If you plan to use Groovy as your scripting language, we recommended you use Section 7.6, “Groovy support” as it offers additional features specific to Groovy. However you will find this section relevant as well.

7.5.1 Script configuration

Depending on the complexity of your integration requirements scripts may be provided inline as CDATA in XML configuration or as a reference to a Spring resource containing the script. To enable scripting support Spring Integration defines a ScriptExecutingMessageProcessor which will bind the Message Payload to a variable named payload and the Message Headers to a headers variable, both accessible within the script execution context. All that is left for you to do is write a script that uses these variables. Below are a couple of sample configurations:


<int:filter input-channel="referencedScriptInput">
   <int-script:script lang="ruby" location="some/path/to/ruby/script/RubyFilterTests.rb"/>

<int:filter input-channel="inlineScriptInput">
     <int-script:script lang="groovy">
     return payload == 'good'

Here, you see that the script can be included inline or can reference a resource location via the location attribute. Additionally the lang attribute corresponds to the language name (or JSR223 alias)

Other Spring Integration endpoint elements which support scripting include router, service-activator, transformer, and splitter. The scripting configuration in each case would be identical to the above (besides the endpoint element).

Another useful feature of Scripting support is the ability to update (reload) scripts without having to restart the Application Context. To accomplish this, specify the refresh-check-delay attribute on the script element:

<int-script:script location="..." refresh-check-delay="5000"/>

In the above example, the script location will be checked for updates every 5 seconds. If the script is updated, any invocation that occurs later than 5 seconds since the update will result in execution of the new script.

<int-script:script location="..." refresh-check-delay="0"/>

In the above example the context will be updated with any script modifications as soon as such modification occurs, providing a simple mechanism for 'real-time' configuration. Any negative number value means the script will not be reloaded after initialization of the application context. This is the default behavior.

Inline scripts can not be reloaded.
<int-script:script location="..." refresh-check-delay="-1"/>

Script variable bindings

Variable bindings are required to enable the script to reference variables externally provided to the script's execution context. As we have seen, payload and headers are used as binding variables by default. You can bind additional variables to a script via <variable> sub-elements:

<script:script lang="js" location="foo/bar/MyScript.js">
	<script:variable name="foo" value="foo"/>
	<script:variable name="bar" value="bar"/>
	<script:variable name="date" ref="date"/>

As shown in the above example, you can bind a script variable either to a scalar value or a Spring bean reference. Note that payload and headers will still be included as binding variables.

With Spring Integration 3.0, in addition to the variable sub-element, the variables attribute has been introduced. This attribute and variable sub-elements aren't mutually exclusive and you can combine them within one script component. However variables must be unique, regardless of where they are defined. Also, since Spring Integration 3.0, variable bindings are allowed for inline scripts too:

<service-activator input-channel="input">
	<script:script lang="ruby" variables="foo=FOO, date-ref=dateBean">
		<script:variable name="bar" ref="barBean"/>
		<script:variable name="baz" value="bar"/>
   			payload.foo = foo
   			payload.date = date
   			payload.bar = bar
   			payload.baz = baz

The example above shows a combination of an inline script, a variable sub-element and a variables attribute. The variables attribute is a comma-separated value, where each segment contains an '=' separated pair of the variable and its value. The variable name can be suffixed with -ref, as in the date-ref variable above. That means that the binding variable will have the name date, but the value will be a reference to the dateBean bean from the application context. This may be useful when using Property Placeholder Configuration or command line arguments.

If you need more control over how variables are generated, you can implement your own Java class using the ScriptVariableGenerator strategy:

public interface ScriptVariableGenerator {

	Map<String, Object> generateScriptVariables(Message<?> message);


This interface requires you to implement the method generateScriptVariables(Message). The Message argument allows you to access any data available in the Message payload and headers and the return value is the Map of bound variables. This method will be called every time the script is executed for a Message. All you need to do is provide an implementation of ScriptVariableGenerator and reference it with the script-variable-generator attribute:

<int-script:script location="foo/bar/MyScript.groovy"

<bean id="variableGenerator" class="foo.bar.MyScriptVariableGenerator"/>

If a script-variable-generator is not provided, script components use org.springframework.integration.scripting.DefaultScriptVariableGenerator, which merges any provided <variable>s with payload and headers variables from the Message in its generateScriptVariables(Message) method.

You cannot provide both the script-variable-generator attribute and <variable> sub-element(s) as they are mutually exclusive.

7.6 Groovy support

In Spring Integration 2.0 we added Groovy support allowing you to use the Groovy scripting language to provide the logic for various integration components similar to the way the Spring Expression Language (SpEL) is supported for routing, transformation and other integration concerns. For more information about Groovy please refer to the Groovy documentation which you can find on the project website

7.6.1 Groovy configuration

With Spring Integration 2.1, Groovy Support's configuration namespace is an extension of Spring Integration's Scripting Support and shares the core configuration and behavior described in detail in the Section 7.5, “Scripting support” section. Even though Groovy scripts are well supported by generic Scripting Support, Groovy Support provides the Groovy configuration namespace which is backed by the Spring Framework's org.springframework.scripting.groovy.GroovyScriptFactory and related components, offering extended capabilities for using Groovy. Below are a couple of sample configurations:


<int:filter input-channel="referencedScriptInput">
   <int-groovy:script location="some/path/to/groovy/file/GroovyFilterTests.groovy"/>

<int:filter input-channel="inlineScriptInput">
     return payload == 'good'

As the above examples show, the configuration looks identical to the general Scripting Support configuration. The only difference is the use of the Groovy namespace as indicated in the examples by the int-groovy namespace prefix. Also note that the lang attribute on the <script> tag is not valid in this namespace.

Groovy object customization

If you need to customize the Groovy object itself, beyond setting variables, you can reference a bean that implements org.springframework.scripting.groovy.GroovyObjectCustomizer via the customizer attribute. For example, this might be useful if you want to implement a domain-specific language (DSL) by modifying the MetaClass and registering functions to be available within the script:

<int:service-activator input-channel="groovyChannel">
    <int-groovy:script location="foo/SomeScript.groovy" customizer="groovyCustomizer"/>

<beans:bean id="groovyCustomizer" class="org.foo.MyGroovyObjectCustomizer"/>

Setting a custom GroovyObjectCustomizer is not mutually exclusive with <variable> sub-elements or the script-variable-generator attribute. It can also be provided when defining an inline script.

With Spring Integration 3.0, in addition to the variable sub-element, the variables attribute has been introduced. Also, groovy scripts have the ability to resolve a variable to a bean in the BeanFactory, if a binding variable was not provided with the name:


where variable entityManager is an appropriate bean in the application context.

For more information regarding <variable>, variables, and script-variable-generator, see the paragraph 'Script variable bindings' of Section 7.5.1, “Script configuration”.

7.6.2 Control Bus

As described in (EIP), the idea behind the Control Bus is that the same messaging system can be used for monitoring and managing the components within the framework as is used for "application-level" messaging. In Spring Integration we build upon the adapters described above so that it's possible to send Messages as a means of invoking exposed operations. One option for those operations is Groovy scripts.

 <int-groovy:control-bus input-channel="operationChannel"/>

The Control Bus has an input channel that can be accessed for invoking operations on the beans in the application context.

The Groovy Control Bus executes messages on the input channel as Groovy scripts. It takes a message, compiles the body to a Script, customizes it with a GroovyObjectCustomizer, and then executes it. The Control Bus' MessageProcessor exposes all beans in the application context that are annotated with @ManagedResource, implement Spring's Lifecycle interface or extend Spring's CustomizableThreadCreator base class (e.g. several of the TaskExecutor and TaskScheduler implementations).

Be careful about using managed beans with custom scopes (e.g. 'request') in the Control Bus' command scripts, especially inside an async message flow. If The Control Bus' MessageProcessor can't expose a bean from the application context, you may end up with some BeansException during command script's executing. For example, if a custom scope's context is not established, the attempt to get a bean within that scope will trigger a BeanCreationException.

If you need to further customize the Groovy objects, you can also provide a reference to a bean that implements org.springframework.scripting.groovy.GroovyObjectCustomizer via the customizer attribute.

<int-groovy:control-bus input-channel="input"

<beans:bean id="groovyCustomizer" class="org.foo.MyGroovyObjectCustomizer"/>

7.7 Adding Behavior to Endpoints

Prior to Spring Integration 2.2, you could add behavior to an entire Integration flow by adding an AOP Advice to a poller's <advice-chain /> element. However, let's say you want to retry, say, just a ReST Web Service call, and not any downstream endpoints.

For example, consider the following flow:


If you configure some retry-logic into an advice chain on the poller, and, the call to http-gateway2 failed because of a network glitch, the retry would cause both http-gateway1 and http-gateway2 to be called a second time. Similarly, after a transient failure in the jdbc-outbound-adapter, both http-gateways would be called a second time before again calling the jdbc-outbound-adapter.

Spring Integration 2.2 adds the ability to add behavior to individual endpoints. This is achieved by the addition of the <request-handler-advice-chain /> element to many endpoints. For example:

<int-http:outbound-gateway id="withAdvice"
        <ref bean="myRetryAdvice" />

In this case, myRetryAdvice will only be applied locally to this gateway and will not apply to further actions taken downstream after the reply is sent to the nextChannel. The scope of the advice is limited to the endpoint itself.


At this time, you cannot advise an entire <chain/> of endpoints. The schema does not allow a <request-handler-advice-chain/> as a child element of the chain itself.

However, a <request-handler-advice-chain/> can be added to individual reply-producing endpoints within a <chain/> element. An exception is that, in a chain that produces no reply, because the last element in the chain is an outbound-channel-adapter, that last element cannot be advised. If you need to advise such an element, it must be moved outside of the chain (with the output-channel of the chain being the input-channel of the adapter. The adapter can then be advised as normal. For chains that produce a reply, every child element can be advised.

7.7.1 Provided Advice Classes

In addition to providing the general mechanism to apply AOP Advice classes in this way, three standard Advices are provided:

  • RequestHandlerRetryAdvice
  • RequestHandlerCircuitBreakerAdvice
  • ExpressionEvaluatingRequestHandlerAdvice

These are each described in detail in the following sections.

Retry Advice

The retry advice (o.s.i.handler.advice.RequestHandlerRetryAdvice) leverages the rich retry mechanisms provided by the Spring Retry project. The core component of spring-retry is the RetryTemplate, which allows configuration of sophisticated retry scenarios, including RetryPolicy and BackoffPolicy strategies, with a number of implementations, as well as a RecoveryCallback strategy to determine the action to take when retries are exhausted.

Stateless Retry

Stateless retry is the case where the retry activity is handled entirely within the advice, where the thread pauses (if so configured) and retries the action.

Stateful Retry

Stateful retry is the case where the retry state is managed within the advice, but where an exception is thrown and the caller resubmits the request. An example for stateful retry is when we want the message originator (e.g. JMS) to be responsible for resubmitting, rather than performing it on the current thread. Stateful retry needs some mechanism to detect a retried submission.

Further Information

For more information on spring-retry, refer to the project's javadocs, as well as the reference documentation for Spring Batch, where spring-retry originated.

The default back off behavior is no back off - retries are attempted immediately. Using a back off policy that causes threads to pause between attempts may cause performance issues, including excessive memory use and thread starvation. In high volume environments, back off policies should be used with caution.
Configuring the Retry Advice

The following examples use a simple <service-activator />> that always throws an exception:

public class FailingService {

    public void service(String message) {
        throw new RuntimeException("foo");

Simple Stateless Retry

This example uses the default RetryTemplate which has a SimpleRetryPolicy which tries 3 times. There is no BackoffPolicy so the 3 attempts are made back-to-back-to-back with no delay between attempts. There is no RecoveryCallback so, the result is to throw the exception to the caller after the final failed retry occurs. In a Spring Integration environment, this final exception might be handled using an error-channel on the inbound endpoint.

<int:service-activator input-channel="input" ref="failer" method="service">
        <bean class="o.s.i.handler.advice.RequestHandlerRetryAdvice"/>

DEBUG [task-scheduler-2]preSend on channel 'input', message: [Payload=...]
DEBUG [task-scheduler-2]Retry: count=0
DEBUG [task-scheduler-2]Checking for rethrow: count=1
DEBUG [task-scheduler-2]Retry: count=1
DEBUG [task-scheduler-2]Checking for rethrow: count=2
DEBUG [task-scheduler-2]Retry: count=2
DEBUG [task-scheduler-2]Checking for rethrow: count=3
DEBUG [task-scheduler-2]Retry failed last attempt: count=3

Simple Stateless Retry with Recovery

This example adds a RecoveryCallback to the above example; it uses a ErrorMessageSendingRecoverer to send an ErrorMessage to a channel.

<int:service-activator input-channel="input" ref="failer" method="service">
        <bean class="o.s.i.handler.advice.RequestHandlerRetryAdvice">
            <property name="recoveryCallback">
                <bean class="o.s.i.handler.advice.ErrorMessageSendingRecoverer">
                    <constructor-arg ref="myErrorChannel" />

DEBUG [task-scheduler-2]preSend on channel 'input', message: [Payload=...]
DEBUG [task-scheduler-2]Retry: count=0
DEBUG [task-scheduler-2]Checking for rethrow: count=1
DEBUG [task-scheduler-2]Retry: count=1
DEBUG [task-scheduler-2]Checking for rethrow: count=2
DEBUG [task-scheduler-2]Retry: count=2
DEBUG [task-scheduler-2]Checking for rethrow: count=3
DEBUG [task-scheduler-2]Retry failed last attempt: count=3
DEBUG [task-scheduler-2]Sending ErrorMessage :failedMessage:[Payload=...]

Stateless Retry with Customized Policies, and Recovery

For more sophistication, we can provide the advice with a customized RetryTemplate. This example continues to use the SimpleRetryPolicy but it increases the attempts to 4. It also adds an ExponentialBackoffPolicy where the first retry waits 1 second, the second waits 5 seconds and the third waits 25 (for 4 attempts in all).

<int:service-activator input-channel="input" ref="failer" method="service">
        <bean class="o.s.i.handler.advice.RequestHandlerRetryAdvice">
            <property name="recoveryCallback">
                <bean class="o.s.i.handler.advice.ErrorMessageSendingRecoverer">
                    <constructor-arg ref="myErrorChannel" />
            <property name="retryTemplate" ref="retryTemplate" />

<bean id="retryTemplate" class="org.springframework.retry.support.RetryTemplate">
	<property name="retryPolicy">
		<bean class="org.springframework.retry.policy.SimpleRetryPolicy">
			<property name="maxAttempts" value="4" />
	<property name="backOffPolicy">
		<bean class="org.springframework.retry.backoff.ExponentialBackOffPolicy">
			<property name="initialInterval" value="1000" />
			<property name="multiplier" value="5" />

27.058 DEBUG [task-scheduler-1]preSend on channel 'input', message: [Payload=...]
27.071 DEBUG [task-scheduler-1]Retry: count=0
27.080 DEBUG [task-scheduler-1]Sleeping for 1000
28.081 DEBUG [task-scheduler-1]Checking for rethrow: count=1
28.081 DEBUG [task-scheduler-1]Retry: count=1
28.081 DEBUG [task-scheduler-1]Sleeping for 5000
33.082 DEBUG [task-scheduler-1]Checking for rethrow: count=2
33.082 DEBUG [task-scheduler-1]Retry: count=2
33.083 DEBUG [task-scheduler-1]Sleeping for 25000
58.083 DEBUG [task-scheduler-1]Checking for rethrow: count=3
58.083 DEBUG [task-scheduler-1]Retry: count=3
58.084 DEBUG [task-scheduler-1]Checking for rethrow: count=4
58.084 DEBUG [task-scheduler-1]Retry failed last attempt: count=4
58.086 DEBUG [task-scheduler-1]Sending ErrorMessage :failedMessage:[Payload=...]

Simple Stateful Retry with Recovery

To make retry stateful, we need to provide the Advice with a RetryStateGenerator implementation. This class is used to identify a message as being a resubmission so that the RetryTemplate can determine the current state of retry for this message. The framework provides a SpelExpressionRetryStateGenerator which determines the message identifier using a SpEL expression. This is shown below; this example again uses the default policies (3 attempts with no back off); of course, as with stateless retry, these policies can be customized.

<int:service-activator input-channel="input" ref="failer" method="service">
        <bean class="o.s.i.handler.advice.RequestHandlerRetryAdvice">
            <property name="retryStateGenerator">
                <bean class="o.s.i.handler.advice.SpelExpressionRetryStateGenerator">
                    <constructor-arg value="headers['jms_messageId']" />
            <property name="recoveryCallback">
                <bean class="o.s.i.handler.advice.ErrorMessageSendingRecoverer">
                    <constructor-arg ref="myErrorChannel" />

24.351 DEBUG [Container#0-1]preSend on channel 'input', message: [Payload=...]
24.368 DEBUG [Container#0-1]Retry: count=0
24.387 DEBUG [Container#0-1]Checking for rethrow: count=1
24.387 DEBUG [Container#0-1]Rethrow in retry for policy: count=1
24.387 WARN  [Container#0-1]failure occurred in gateway sendAndReceive
org.springframework.integration.MessagingException: Failed to invoke handler
Caused by: java.lang.RuntimeException: foo
24.391 DEBUG [Container#0-1]Initiating transaction rollback on application exception
25.412 DEBUG [Container#0-1]preSend on channel 'input', message: [Payload=...]
25.412 DEBUG [Container#0-1]Retry: count=1
25.413 DEBUG [Container#0-1]Checking for rethrow: count=2
25.413 DEBUG [Container#0-1]Rethrow in retry for policy: count=2
25.413 WARN  [Container#0-1]failure occurred in gateway sendAndReceive
org.springframework.integration.MessagingException: Failed to invoke handler
Caused by: java.lang.RuntimeException: foo
25.414 DEBUG [Container#0-1]Initiating transaction rollback on application exception
26.418 DEBUG [Container#0-1]preSend on channel 'input', message: [Payload=...]
26.418 DEBUG [Container#0-1]Retry: count=2
26.419 DEBUG [Container#0-1]Checking for rethrow: count=3
26.419 DEBUG [Container#0-1]Rethrow in retry for policy: count=3
26.419 WARN  [Container#0-1]failure occurred in gateway sendAndReceive
org.springframework.integration.MessagingException: Failed to invoke handler
Caused by: java.lang.RuntimeException: foo
26.420 DEBUG [Container#0-1]Initiating transaction rollback on application exception
27.425 DEBUG [Container#0-1]preSend on channel 'input', message: [Payload=...]
27.426 DEBUG [Container#0-1]Retry failed last attempt: count=3
27.426 DEBUG [Container#0-1]Sending ErrorMessage :failedMessage:[Payload=...]

Comparing with the stateless examples, you can see that with stateful retry, the exception is thrown to the caller on each failure.

Exception Classification for Retry

Spring Retry has a great deal of flexibility for determining which exceptions can invoke retry. The default configuration will retry for all exceptions and the exception classifier just looks at the top level exception. If you configure it to, say, only retry on BarException and your application throws a FooException where the cause is a BarException, retry will not occur.

Since Spring Retry 1.0.3, the BinaryExceptionClassifier has a property traverseCauses (default false). When true it will traverse exception causes until it finds a match or there is no cause.

To use this classifier for retry, use a SimpleRetryPolicy created with the constructor that takes the max attempts, the Map of Exceptions and the boolean (traverseCauses), and inject this policy into the RetryTemplate.

Circuit Breaker Advice

The general idea of the Circuit Breaker Pattern is that, if a service is not currently available, then don't waste time (and resources) trying to use it. The o.s.i.handler.advice.RequestHandlerCircuitBreakerAdvice implements this pattern. When the circuit breaker is in the closed state, the endpoint will attempt to invoke the service. The circuit breaker goes to the open state if a certain number of consecutive attempts fail; when it is in the open state, new requests will "fail fast" and no attempt will be made to invoke the service until some time has expired.

When that time has expired, the circuit breaker is set to the half-open state. When in this state, if even a single attempt fails, the breaker will immediately go to the open state; if the attempt succeeds, the breaker will go to the closed state, in which case, it won't go to the open state again until the configured number of consecutive failures again occur. Any successful attempt resets the state to zero failures for the purpose of determining when the breaker might go to the open state again.

Typically, this Advice might be used for external services, where it might take some time to fail (such as a timeout attempting to make a network connection).

The RequestHandlerCircuitBreakerAdvice has two properties: threshold and halfOpenAfter. The threshold property represents the number of consecutive failures that need to occur before the breaker goes open. It defaults to 5. The halfOpenAfter property represents the time after the last failure that the breaker will wait before attempting another request. Default is 1000 milliseconds.


<int:service-activator input-channel="input" ref="failer" method="service">
        <bean class="o.s.i.handler.advice.RequestHandlerCircuitBreakerAdvice">
            <property name="threshold" value="2" />
            <property name="halfOpenAfter" value="12000" />

05.617 DEBUG [task-scheduler-1]preSend on channel 'input', message: [Payload=...]
05.638 ERROR [task-scheduler-1]org.springframework.integration.MessageHandlingException: java.lang.RuntimeException: foo
10.598 DEBUG [task-scheduler-2]preSend on channel 'input', message: [Payload=...]
10.600 ERROR [task-scheduler-2]org.springframework.integration.MessageHandlingException: java.lang.RuntimeException: foo
15.598 DEBUG [task-scheduler-3]preSend on channel 'input', message: [Payload=...]
15.599 ERROR [task-scheduler-3]org.springframework.integration.MessagingException: Circuit Breaker is Open for ServiceActivator
20.598 DEBUG [task-scheduler-2]preSend on channel 'input', message: [Payload=...]
20.598 ERROR [task-scheduler-2]org.springframework.integration.MessagingException: Circuit Breaker is Open for ServiceActivator
25.598 DEBUG [task-scheduler-5]preSend on channel 'input', message: [Payload=...]
25.601 ERROR [task-scheduler-5]org.springframework.integration.MessageHandlingException: java.lang.RuntimeException: foo
30.598 DEBUG [task-scheduler-1]preSend on channel 'input', message: [Payload=foo...]
30.599 ERROR [task-scheduler-1]org.springframework.integration.MessagingException: Circuit Breaker is Open for ServiceActivator

In the above example, the threshold is set to 2 and halfOpenAfter is set to 12 seconds; a new request arrives every 5 seconds. You can see that the first two attempts invoked the service; the third and fourth failed with an exception indicating the circuit breaker is open. The fifth request was attempted because the request was 15 seconds after the last failure; the sixth attempt fails immediately because the breaker immediately went to open.

Expression Evaluating Advice

The final supplied advice class is the o.s.i.handler.advice.ExpressionEvaluatingRequestHandlerAdvice. This advice is more general than the other two advices. It provides a mechanism to evaluate an expression on the original inbound message sent to the endpoint. Separate expressions are available to be evaluated, either after success, or failure. Optionally, a message containing the evaluation result, together with the input message, can be sent to a message channel.

A typical use case for this advice might be with an <ftp:outbound-channel-adapter />, perhaps to move the file to one directory if the transfer was successful, or to another directory if it fails:

The Advice has properties to set an expression when successful, an expression for failures, and corresponding channels for each. For the successful case, the message sent to the successChannel is an AdviceMessage, with the payload being the result of the expression evaluation, and an additional property inputMessage which contains the original message sent to the handler. A message sent to the failureChannel (when the handler throws an excecption) is an ErrorMessage with a payload of MessageHandlingExpressionEvaluatingAdviceException. Like all MessagingExceptions, this payload has failedMessage and cause properties, as well as an additional property evaluationResult, containing the result of the expression evaluation.

7.7.2 Custom Advice Classes

In addition to the provided Advice classes above, you can implement your own Advice classes. While you can provide any implementation of org.aopalliance.aop.Advice, it is generally recommended that you subclass o.s.i.handler.advice.AbstractRequestHandlerAdvice. This has the benefit of avoiding writing low-level Aspect Oriented Programming code as well as providing a starting point that is specifically tailored for use in this environment.

Subclasses need to implement the doInvoke() method:

 * Subclasses implement this method to apply behavior to the {@link MessageHandler} callback.execute()
 * invokes the handler method and returns its result, or null).
 * @param callback Subclasses invoke the execute() method on this interface to invoke the handler method.
 * @param target The target handler.
 * @param message The message that will be sent to the handler.
 * @return the result after invoking the {@link MessageHandler}.
 * @throws Exception
protected abstract Object doInvoke(ExecutionCallback callback, Object target, Message<?> message) throws Exception;

The callback parameter is simply a convenience to avoid subclasses dealing with AOP directly; invoking the callback.execute() method invokes the message handler.

The target parameter is provided for those subclasses that need to maintain state for a specific handler, perhaps by maintaining that state in a Map, keyed by the target. This allows the same advice to be applied to multiple handlers. The RequestHandlerCircuitBreakerAdvice uses this to keep circuit breaker state for each handler.

The message parameter is the message that will be sent to the handler. While the advice cannot modify the message before invoking the handler, it can modify the payload (if it has mutable properties). Typically, an advice would use the message for logging and/or to send a copy of the message somewhere before or after invoking the handler.

The return value would normally be the value returned by callback.execute(); but the advice does have the ability to modify the return value. Note that only AbstractReplyProducingMessageHandlers return a value.

public class MyAdvice extends AbstractRequestHandlerAdvice {

    protected Object doInvoke(ExecutionCallback callback, Object target, Message<?> message) throws Exception {
        // add code before the invocation
        Object result = callback.execute();
        // add code after the invocation
        return result;

In addition to the execute() method, the ExecutionCallback provides an additional method cloneAndExecute(). This method must be used in cases where the invocation might be called multiple times within a single execution of doInvoke(), such as in the RequestHandlerRetryAdvice. This is required because the Spring AOP org.springframework.aop.framework.ReflectiveMethodInvocation object maintains state of which advice in a chain was last invoked; this state must be reset for each call.

For more information, see the ReflectiveMethodInvocation JavaDocs.

7.7.3 Other Advice Chain Elements

While the abstract class mentioned above is provided as a convenience, you can add any Advice to the chain, including a transaction advice.

7.7.4 Advising Filters

There is an additional consideration when advising Filters. By default, any discard actions (when the filter returns false) are performed within the scope of the advice chain. This could include all the flow downstream of the discard channel. So, for example if an element downstream of the discard-channel throws an exception, and there is a retry advice, the process will be retried. This is also the case if throwExceptionOnRejection is set to true (the exception is thrown within the scope of the advice).

Setting discard-within-advice to "false" modifies this behavior and the discard (or exception) occurs after the advice chain is called.

7.7.5 Advising Endpoints Using Annotations

When configuring certain endpoints using annotations (@Filter, @ServiceActivator, @Splitter, and @Transformer), you can supply a bean name for the advice chain in the adviceChain attribute. In addition, the @Filter annotation also has the discardWithinAdvice attribute, which can be used to configure the discard behavior as discussed in Section 7.7.4, “Advising Filters”. An example with the discard being performed after the advice is shown below.

public class MyAdvisedFilter {

	@Filter(inputChannel="input", outputChannel="output",
			adviceChain="adviceChain", discardWithinAdvice="false")
	public boolean filter(String s) {
		return s.contains("good");

7.7.6 Ordering Advices within an Advice Chain

Advice classes are "around" advices and are applied in a nested fashion. The first advice is the outermost, the last advice the innermost (closest to the handler being advised). It is important to put the advice classes in the correct order to achieve the functionality you desire.

For example, let's say you want to add a retry advice and a transaction advice. You may want to place the retry advice advice first, followed by the transaction advice. Then, each retry will be performed in a new transaction. On the other hand, if you want all the attempts, and any recovery operations (in the retry RecoveryCallback), to be scoped within the transaction, you would put the transaction advice first.

7.8 Logging Channel Adapter

The <logging-channel-adapter/> is often used in conjunction with a Wire Tap, as discussed in the section called “Wire Tap”. However, it can also be used as the ultimate consumer of any flow. For example, consider a flow that ends with a <service-activator/> that returns a result, but you wish to discard that result. To do that, you could send the result to NullChannel. Alternatively, you can route it to an INFO level <logging-channel-adapter/>; that way, you can see the discarded message when logging at INFO level, but not see it when logging at, say, WARN level. With a NullChannel, you would only see the discarded message when logging at DEBUG level.



The channel connecting the logging adapter to an upstream component.


The logging level at which messages sent to this adapter will be logged. Default: INFO.


A SpEL expression representing exactly what part(s) of the message will be logged. Default: payload - just the payload will be logged. This attribute cannot be specified if log-full-message is specified.


When true, the entire message will be logged (including headers). Default: false - just the payload will be logged. This attribute cannot be specified if expression is specified.


Specifies the name of the logger (known as category in log4j) used for log messages created by this adapter. This enables setting the log name (in the logging subsystem) for individual adapters. By default, all adapters will log under the name org.springframework.integration.handler.LoggingHandler.

8. System Management

8.1 JMX Support

Spring Integration provides Channel Adapters for receiving and publishing JMX Notifications. There is also an Inbound Channel Adapter for polling JMX MBean attribute values, and an Outbound Channel Adapter for invoking JMX MBean operations.

8.1.1 Notification Listening Channel Adapter

The Notification-listening Channel Adapter requires a JMX ObjectName for the MBean that publishes notifications to which this listener should be registered. A very simple configuration might look like this:

<int-jmx:notification-listening-channel-adapter id="adapter"
The notification-listening-channel-adapter registers with an MBeanServer at startup, and the default bean name is mbeanServer which happens to be the same bean name generated when using Spring's <context:mbean-server/> element. If you need to use a different name, be sure to include the mbean-server attribute.

The adapter can also accept a reference to a NotificationFilter and a handback Object to provide some context that is passed back with each Notification. Both of those attributes are optional. Extending the above example to include those attributes as well as an explicit MBeanServer bean name would produce the following:

<int-jmx:notification-listening-channel-adapter id="adapter"

The Notification-listening Channel Adapter is event-driven and registered with the MBeanServer directly. It does not require any poller configuration.

For this component only, the object-name attribute can contain an ObjectName pattern (e.g. "org.foo:type=Bar,name=*") and the adapter will receive notifications from all MBeans with ObjectNames that match the pattern. In addition, the object-name attribute can contain a SpEL reference to a <util:list/> of ObjectName patterns:
<jmx:notification-listening-channel-adapter id="manyNotificationsAdapter"

<util:list id="patterns">
The names of the located MBean(s) will be logged when DEBUG level logging is enabled.

8.1.2 Notification Publishing Channel Adapter

The Notification-publishing Channel Adapter is relatively simple. It only requires a JMX ObjectName in its configuration as shown below.


<int-jmx:notification-publishing-channel-adapter id="adapter"

It does also require that an MBeanExporter be present in the context. That is why the <context:mbean-export/> element is shown above as well.

When Messages are sent to the channel for this adapter, the Notification is created from the Message content. If the payload is a String it will be passed as the message text for the Notification. Any other payload type will be passed as the userData of the Notification.

JMX Notifications also have a type, and it should be a dot-delimited String. There are two ways to provide the type. Precedence will always be given to a Message header value associated with the JmxHeaders.NOTIFICATION_TYPE key. On the other hand, you can rely on a fallback default-notification-type attribute provided in the configuration.


<int-jmx:notification-publishing-channel-adapter id="adapter"

8.1.3 Attribute Polling Channel Adapter

The Attribute Polling Channel Adapter is useful when you have a requirement, to periodically check on some value that is available through an MBean as a managed attribute. The poller can be configured in the same way as any other polling adapter in Spring Integration (or it's possible to rely on the default poller). The object-name and attribute-name are required. An MBeanServer reference is also required, but it will automatically check for a bean named mbeanServer by default, just like the Notification-listening Channel Adapter described above.

<int-jmx:attribute-polling-channel-adapter id="adapter"
        <int:poller max-messages-per-poll="1" fixed-rate="5000"/>

8.1.4 Tree Polling Channel Adapter

The Tree Polling Channel Adapter queries the JMX MBean tree and sends a message with a payload that is the graph of objects that matches the query. By default the MBeans are mapped to primitives and simple Objects like Map, List and arrays - permitting simple transformation, for example, to JSON. An MBeanServer reference is also required, but it will automatically check for a bean named mbeanServer by default, just like the Notification-listening Channel Adapter described above. A basic configuration would be:

<int-jmx:tree-polling-channel-adapter id="adapter"
        <int:poller max-messages-per-poll="1" fixed-rate="5000"/>

This will include all attributes on the MBeans selected. You can filter the attributes by providing an MBeanObjectConverter that has an appropriate filter configured. The converter can be provided as a reference to a bean definition using the converter attribute, or as an inner <bean/> definition. A DefaultMBeanObjectConverter is provided which can take a MBeanAttributeFilter in its constructor argument.

Two standard filters are provided; the NamedFieldsMBeanAttributeFilter allows you to specify a list of attributes to include and the NotNamedFieldsMBeanAttributeFilter allows you to specify a list of attributes to exclude. You can also implement your own filter

8.1.5 Operation Invoking Channel Adapter

The operation-invoking-channel-adapter enables Message-driven invocation of any managed operation exposed by an MBean. Each invocation requires the operation name to be invoked and the ObjectName of the target MBean. Both of these must be explicitly provided via adapter configuration:

<int-jmx:operation-invoking-channel-adapter id="adapter"

Then the adapter only needs to be able to discover the mbeanServer bean. If a different bean name is required, then provide the mbean-server attribute with a reference.

The payload of the Message will be mapped to the parameters of the operation, if any. A Map-typed payload with String keys is treated as name/value pairs, whereas a List or array would be passed as a simple argument list (with no explicit parameter names). If the operation requires a single parameter value, then the payload can represent that single value, and if the operation requires no parameters, then the payload would be ignored.

If you want to expose a channel for a single common operation to be invoked by Messages that need not contain headers, then that option works well.

8.1.6 Operation Invoking Outbound Gateway

Similar to the operation-invoking-channel-adapter Spring Integration also provides a operation-invoking-outbound-gateway, which could be used when dealing with non-void operations and a return value is required. Such return value will be sent as message payload to the reply-channel specified by this Gateway.

<int-jmx:operation-invoking-outbound-gateway request-channel="requestChannel"

If the reply-channel attribute is not provided, the reply message will be sent to the channel that is identified by the MessageHeaders.REPLY_CHANNEL header. That header is typically auto-created by the entry point into a message flow, such as any Gateway component. However, if the message flow was started by manually creating a Spring Integration Message and sending it directly to a Channel, then you must specify the message header explicitly or use the provided reply-channel attribute.

8.1.7 MBean Exporter

Spring Integration components themselves may be exposed as MBeans when the IntegrationMBeanExporter is configured. To create an instance of the IntegrationMBeanExporter, define a bean and provide a reference to an MBeanServer and a domain name (if desired). The domain can be left out, in which case the default domain is org.springframework.integration.

<int-jmx:mbean-export id="integrationMBeanExporter"
            default-domain="my.company.domain" server="mbeanServer"/>

<bean id="mbeanServer" class="org.springframework.jmx.support.MBeanServerFactoryBean">
    <property name="locateExistingServerIfPossible" value="true"/>

Once the exporter is defined, start up your application with:


Then start JConsole (free with the JDK), and connect to the local process on localhost:6969 to get a look at the management endpoints exposed. (The port and client are just examples to get you started quickly, there are other JMX clients available and some offer more sophisticated features than JConsole.)


The MBean exporter is orthogonal to the one provided in Spring core - it registers message channels and message handlers, but not itself. You can expose the exporter itself, and certain other components in Spring Integration, using the standard <context:mbean-export/> tag. The exporter has a some metrics attached to it, for instance a count of the number of active handlers and the number of queued messages.

It also has a useful operation, as discussed in the section called “Orderly Shutdown Managed Operation”.

MBean ObjectNames

All the MessageChannel, MessageHandler and MessageSource instances in the application are wrapped by the MBean exporter to provide management and monitoring features. The generated JMX object names for each component type are listed in the table below:

Table 8.1. 

Component TypeObjectName

The bean attribute in the object names for sources and handlers takes one of the values in the table below:

Table 8.2. 

Bean ValueDescription
endpointThe bean name of the enclosing endpoint (e.g. <service-activator>) if there is one
anonymousAn indication that the enclosing endpoint didn't have a user-specified bean name, so the JMX name is the input channel name
internalFor well-known Spring Integration default components
handlerNone of the above: fallback to the toString() of the object being monitored (handler or source)

Custom elements can be appended to the object name by providing a reference to a Properties object in the object-name-static-properties attribute.

Also, since Spring Integration 3.0, you can use a custom ObjectNamingStrategy using the object-naming-strategy attribute. This permits greater control over the naming of the MBeans. For example, to group all Integration MBeans under an 'Integration' type. A simple custom naming strategy implementation might be:

public class Namer implements ObjectNamingStrategy {

	private final ObjectNamingStrategy realNamer = new KeyNamingStrategy();
	public ObjectName getObjectName(Object managedBean, String beanKey) throws MalformedObjectNameException {
		String actualBeanKey = beanKey.replace("type=", "type=Integration,componentType=");
		return realNamer.getObjectName(managedBean, actualBeanKey);


The beanKey argument is a String containing the standard object name beginning with the default-domain and including any additional static properties. This example simply moves the standard type part to componentType and sets the type to 'Integration', enabling selection of all Integration MBeans in one query: "my.domain:type=Integration,*. This also groups the beans under one tree entry under the domain in tools like VisualVM.

The default naming strategy is a MetadataNamingStrategy. The exporter propagates the default-domain to that object to allow it to generate a fallback object name if parsing of the bean key fails. If your custom naming strategy is a MetadataNamingStrategy (or subclass), the exporter will not propagate the default-domain; you will need to configure it on your strategy bean.

MessageChannel MBean Features

Message channels report metrics according to their concrete type. If you are looking at a DirectChannel, you will see statistics for the send operation. If it is a QueueChannel, you will also see statistics for the receive operation, as well as the count of messages that are currently buffered by this QueueChannel. In both cases there are some metrics that are simple counters (message count and error count), and some that are estimates of averages of interesting quantities. The algorithms used to calculate these estimates are described briefly in the table below:

Table 8.3. 

Metric TypeExampleAlgorithm
CountSend CountSimple incrementer. Increase by one when an event occurs.
DurationSend Duration (method execution time in milliseconds) Exponential Moving Average with decay factor 10. Average of the method execution time over roughly the last 10 measurements.
RateSend Rate (number of operations per second)Inverse of Exponential Moving Average of the interval between events with decay in time (lapsing over 60 seconds) and per measurement (last 10 events).
RatioSend Error Ratio (ratio of errors to total sends)Estimate the success ratio as the Exponential Moving Average of the series composed of values 1 for success and 0 for failure (decaying as per the rate measurement over time and events). Error ratio is 1 - success ratio.

A feature of the time-based average estimates is that they decay with time if no new measurements arrive. To help interpret the behaviour over time, the time (in seconds) since the last measurement is also exposed as a metric.

There are two basic exponential models: decay per measurement (appropriate for duration and anything where the number of measurements is part of the metric), and decay per time unit (more suitable for rate measurements where the time in between measurements is part of the metric). Both models depend on the fact that

S(n) = sum(i=0,i=n) w(i) x(i)

has a special form when w(i) = r^i, with r=constant:

S(n) = x(n) + r S(n-1)

(so you only have to store S(n-1), not the whole series x(i), to generate a new metric estimate from the last measurement). The algorithms used in the duration metrics use r=exp(-1/M) with M=10. The net effect is that the estimate S(n) is more heavily weighted to recent measurements and is composed roughly of the last M measurements. So M is the "window" or lapse rate of the estimate In the case of the vanilla moving average, i is a counter over the number of measurements. In the case of the rate we interpret i as the elapsed time, or a combination of elapsed time and a counter (so the metric estimate contains contributions roughly from the last M measurements and the last T seconds).

Orderly Shutdown Managed Operation

The MBean exporter provides a JMX operation to shut down the application in an orderly manner, intended for use before terminating the JVM.

public void stopActiveComponents(boolean force, long howLong)

Its use and operation are described in Section 8.6, “Orderly Shutdown”.

8.2 Message History

The key benefit of a messaging architecture is loose coupling where participating components do not maintain any awareness about one another. This fact alone makes your application extremely flexible, allowing you to change components without affecting the rest of the flow, change messaging routes,   message consuming styles (polling vs event driven), and so on. However, this unassuming style of architecture could prove to be difficult when things go wrong. When debugging, you would probably like to get as much information about the message as you can (its origin, channels it has traversed, etc.)

Message History is one of those patterns that helps by giving you an option to maintain some level of awareness of a message path either for debugging purposes or to maintain an audit trail. Spring integration provides a simple way to configure your message flows to maintain the Message History by adding a header to the Message and updating that header every time a message passes through a tracked component.

8.2.1 Message History Configuration

To enable Message History all you need is to define the message-history element in your configuration.


Now every named component (component that has an 'id' defined) will be tracked. The framework will set the 'history' header in your Message. Its value is very simple - List<Properties>.

<int:gateway id="sampleGateway" 

<int:chain id="sampleChain" input-channel="chainChannel" output-channel="filterChannel">
    <int:header name="baz" value="baz"/>

The above configuration will produce a very simple Message History structure:

[{name=sampleGateway, type=gateway, timestamp=1283281668091},
 {name=sampleChain, type=chain, timestamp=1283281668094}]

To get access to Message History all you need is access the MessageHistory header. For example:

Iterator<Properties> historyIterator =
    message.getHeaders().get(MessageHistory.HEADER_NAME, MessageHistory.class).iterator();
Properties gatewayHistory = historyIterator.next();
assertEquals("sampleGateway", gatewayHistory.get("name"));
Properties chainHistory = historyIterator.next();
assertEquals("sampleChain", chainHistory.get("name"));

You might not want to track all of the components. To limit the history to certain components based on their names, all you need is provide the tracked-components attribute and specify a comma-delimited list of component names and/or patterns that match the components you want to track.

<int:message-history tracked-components="*Gateway, sample*, foo"/>

In the above example, Message History will only be maintained for all of the components that end with 'Gateway', start with 'sample', or match the name 'foo' exactly.

Remember that by definition the Message History header is immutable (you can't re-write history, although some try). Therefore, when writing Message History values, the components are either creating brand new Messages (when the component is an origin), or they are copying the history from a request Message, modifying it and setting the new list on a reply Message. In either case, the values can be appended even if the Message itself is crossing thread boundaries. That means that the history values can greatly simplify debugging in an asynchronous message flow.

8.3 Message Store

Enterprise Integration Patterns (EIP) identifies several patterns that have the capability to buffer messages. For example, an Aggregator buffers messages until they can be released and a QueueChannel buffers messages until consumers explicitly receive those messages from that channel. Because of the failures that can occur at any point within your message flow, EIP components that buffer messages also introduce a point where messages could be lost.

To mitigate the risk of losing Messages, EIP defines the Message Store pattern which allows EIP components to store Messages typically in some type of persistent store (e.g. RDBMS).

Spring Integration provides support for the Message Store pattern by a) defining a org.springframework.integration.store.MessageStore strategy interface, b) providing several implementations of this interface, and c) exposing a message-store attribute on all components that have the capability to buffer messages so that you can inject any instance that implements the MessageStore interface.

Details on how to configure a specific Message Store implementation and/or how to inject a MessageStore implementation into a specific buffering component are described throughout the manual (see the specific component, such as QueueChannel, Aggregator, Resequencer etc.), but here are a couple of samples to give you an idea:


<int:channel id="myQueueChannel">
    <int:queue message-store="refToMessageStore"/>


<int:aggregator  message-store="refToMessageStore"/>

By default Messages are stored in-memory using org.springframework.integration.store.SimpleMessageStore, an implementation of MessageStore. That might be fine for development or simple low-volume environments where the potential loss of non-persistent messages is not a concern. However, the typical production application will need a more robust option, not only to mitigate the risk of message loss but also to avoid potential out-of-memory errors. Therefore, we also provide MessageStore implementations for a variety of data-stores. Below is a complete list of supported implementations:


However be aware of some limitations while using persistent implementations of the MessageStore.

The Message data (payload and headers) is serialized and deserialized using different serialization strategies depending on the implementation of the MessageStore. For example, when using JdbcMessageStore, only Serializable data is persisted by default. In this case non-Serializable headers are removed before serialization occurs. Also be aware of the protocol specific headers that are injected by transport adapters (e.g., FTP, HTTP, JMS etc.). For example, <http:inbound-channel-adapter/> maps HTTP-headers into Message Headers and one of them is an ArrayList of non-Serializable org.springframework.http.MediaType instances. However you are able to inject your own implementation of the Serializer and/or Deserializer strategy interfaces into some MessageStore implementations (such as JdbcMessageStore) to change the behaviour of serialization and deserialization.

Special attention must be paid to the headers that represent certain types of data. For example, if one of the headers contains an instance of some Spring Bean, upon deserialization you may end up with a different instance of that bean, which directly affects some of the implicit headers created by the framework (e.g., REPLY_CHANNEL or ERROR_CHANNEL). Currently they are not serializable, but even if they were, the deserialized channel would not represent the expected instance.

Beginning with Spring Integration version 3.0, this issue can be resolved with a header enricher, configured to replace these headers with a name after registering the channel with the HeaderChannelRegistry.

Also when configuring a message-flow like this: gateway -> queue-channel (backed by a persistent Message Store) -> service-activator That gateway creates a Temporary Reply Channel, and it will be lost by the time the service-activator's poller reads from the queue. Again, you can use the header enricher to replace the headers with a String representation.

For more information, refer to the Section 6.2.2, “Header Enricher”.

8.4 Metadata Store

Many external systems, services or resources aren't transactional (Twitter, RSS, file system etc.) and there is no any ability to mark the data as read. Or there is just need to implement the Enterprise Integration Pattern Idempotent Receiver in some integration solutions. To achieve this goal and store some previous state of the Endpoint before the next interaction with external system, or deal with the next Message, Spring Integration provides the Metadata Store component being an implementation of the org.springframework.integration.metadata.MetadataStore interface with a general key-value contract.

The Metadata Store is designed to store various types of generic meta-data (e.g., published date of the last feed entry that has been processed) to help components such as the Feed adapter deal with duplicates. If a component is not directly provided with a reference to a MetadataStore, the algorithm for locating a metadata store is as follows: First, look for a bean with id metadataStore in the ApplicationContext. If one is found then it will be used, otherwise it will create a new instance of SimpleMetadataStore which is an in-memory implementation that will only persist metadata within the lifecycle of the currently running Application Context. This means that upon restart you may end up with duplicate entries.

If you need to persist metadata between Application Context restarts, two persistent MetadataStores are provided by the framework:

The PropertiesPersistingMetadataStore is backed by a properties file and a PropertiesPersister.

<bean id="metadataStore"

Alternatively, you can provide your own implementation of the MetadataStore interface (e.g. JdbcMetadataStore) and configure it as a bean in the Application Context.

8.4.1 Idempotent Receiver

The Metadata Store is useful for implementating the EIP Idempotent Receiver pattern, when there is need to filter an incoming Message if it has already been processed, and just discard it or perform some other logic on discarding. The following configuration is an example of how to do this:

<int:filter input-channel="serviceChannel"
			expression="@metadataStore.get(headers.businessKey) == null"/>

<int:publish-subscribe-channel id="idempotentServiceChannel"/>

<int:outbound-channel-adapter channel="idempotentServiceChannel"
                              expression="@metadataStore.put(headers.businessKey, '')"/>

<int:service-activator input-channel="idempotentServiceChannel" ref="service"/>

The value of the idempotent entry may be some expiration date, after which that entry should be removed from Metadata Store by some scheduled reaper.

8.5 Control Bus

As described in (EIP), the idea behind the Control Bus is that the same messaging system can be used for monitoring and managing the components within the framework as is used for "application-level" messaging. In Spring Integration we build upon the adapters described above so that it's possible to send Messages as a means of invoking exposed operations.

<int:control-bus input-channel="operationChannel"/>

The Control Bus has an input channel that can be accessed for invoking operations on the beans in the application context. It also has all the common properties of a service activating endpoint, e.g. you can specify an output channel if the result of the operation has a return value that you want to send on to a downstream channel.

The Control Bus executes messages on the input channel as Spring Expression Language expressions. It takes a message, compiles the body to an expression, adds some context, and then executes it. The default context supports any method that has been annotated with @ManagedAttribute or @ManagedOperation. It also supports the methods on Spring's Lifecycle interface, and it supports methods that are used to configure several of Spring's TaskExecutor and TaskScheduler implementations. The simplest way to ensure that your own methods are available to the Control Bus is to use the @ManagedAttribute and/or @ManagedOperation annotations. Since those are also used for exposing methods to a JMX MBean registry, it's a convenient by-product (often the same types of operations you want to expose to the Control Bus would be reasonable for exposing via JMS). Resolution of any particular instance within the application context is achieved in the typical SpEL syntax. Simply provide the bean name with the SpEL prefix for beans (@). For example, to execute a method on a Spring Bean a client could send a message to the operation channel as follows:

Message operation = MessageBuilder.withPayload("@myServiceBean.shutdown()").build();

The root of the context for the expression is the Message itself, so you also have access to the 'payload' and 'headers' as variables within your expression. This is consistent with all the other expression support in Spring Integration endpoints.

8.6 Orderly Shutdown

As described in Section 8.1.7, “MBean Exporter”, the MBean exporter provides a JMX operation stopActiveComponents, which is used to stop the application in an orderly manner. The operation has two parameters, a boolean and a long. The boolean indicates whether attempts will be made to stop (interrupt) active threads; in most cases this will be set to false for orderly shutdown. The long parameter indicates how long (in milliseconds) the operation will wait to allow in-flight messages to complete. The operation works as follows:

The first step calls beforeShutdown() on all beans that implement OrderlyShutdownCapable. This allows such components to prepare for shutdown. Examples of components that implement this interface, and what they do with this call include: JMS and AMQP message-driven adapters stop their listener containers; TCP server connection factories stop accepting new connections (while keeping existing connections open); TCP inbound endpoints drop (log) any new messages received; http inbound endpoints return 503 - Service Unavailable for any new requests.

The second step stops any active channels, such as JMS- or AMQP-backed channels.

The third step stops all TaskSchedulers, preventing any new scheduled operations (polling etc).

The fourth step stops all TaskExecutors, preventing any new tasks from running.

If the shutdown is running from a Spring-managed TaskExecutor, shutting down that executor would cause all the timeout time to be consumed by this step, because the thread won't terminate). For this reason, either use a dedicated executor (via the shutdownExecutor property on the MBean exporter), or do not use a Spring-managed executor to invoke this operation.

The fifth step stops all MessageSources.

The sixth step waits for any remaining time left, as defined by the value of the long parameter passed in to the operation. This is intended to allow any in-flight messages to complete their journeys. It is therefore important to select an appropriate timeout when invoking this operation.

The seventh step calls afterShutdown() on all OrderlyShutdownCapable components. This allows such components to perform final shutdown tasks (closing all open sockets, for example).

If no time is left when we get to step 6, it probably means some thread is hung; in which case, the operation attempts a forced shutdown on all schedulers and executors before exiting.

As discussed in the section called “Orderly Shutdown Managed Operation” this operation can be invoked using JMX. If you wish to programmatically invoke the method, you will need to inject, or otherwise get a reference to, the IntegrationMBeanExporter. If no id attribute is provided on the <int-jmx:mbean-export/> definition, the bean will have a generated name. This name contains a random component to avoid ObjectName collisions if multiple Spring Integration contexts exist in the same JVM (MBeanServer).

For this reason, if you wish to invoke the method programmatically, it is recommended that you provide the exporter with an id attribute so it can easily be accessed in the application context.

Finally, the operation can be invoked using the <control-bus>; see the monitoring Spring Integration sample application for details.

Part IV. Integration Endpoints

This section covers the various Channel Adapters and Messaging Gateways provided by Spring Integration to support Message-based communication with external systems.

9. Endpoint Quick Reference Table

As discussed in the sections above, Spring Integration provides a number of endpoints used to interface with external systems, file systems etc. The following is a summary of the various endpoints with quick links to the appropriate chapter.

To recap, Inbound Channel Adapters are used for one-way integration bringing data into the messagng application. Outbound Channel Adapters are used for one-way integration to send data out of the messaging application. Inbound Gateways are used for a bidirectional integration flow where some other system invokes the messaging application and receives a reply. Outbound Gateways are used for a bidirectional integration flow where the messaging application invokes some external service or entity, expecting a result.

Table 9.1. 

ModuleInbound AdapterOutbound AdapterInbound GatewayOutbound Gateway
AMQPSection 10.2, “Inbound Channel Adapter”Section 10.3, “Outbound Channel Adapter”Section 10.4, “Inbound Gateway”Section 10.5, “Outbound Gateway”
EventsSection 11.1, “Receiving Spring ApplicationEvents”Section 11.2, “Sending Spring ApplicationEvents”NN
FeedSection 12.2, “Feed Inbound Channel Adapter”NNN
FileSection 13.2, “Reading Files” and Section 13.2.1, “'Tail'ing Files”Section 13.3, “Writing files”NSection 13.3, “Writing files”
FTP(S)Section 14.3, “FTP Inbound Channel Adapter”Section 14.4, “FTP Outbound Channel Adapter”NSection 14.5, “FTP Outbound Gateway”
GemfireSection 15.2, “Inbound Channel Adapter” and Section 15.3, “Continuous Query Inbound Channel Adapter”Section 15.4, “Outbound Channel Adapter”NN
HTTPSection 16.4, “HTTP Namespace Support”Section 16.4, “HTTP Namespace Support”Section 16.2, “Http Inbound Gateway”Section 16.3, “Http Outbound Gateway”
JDBCSection 17.1, “Inbound Channel Adapter” and Section 17.5.6, “Stored Procedure Inbound Channel Adapter”Section 17.2, “Outbound Channel Adapter” and Section 17.5.7, “Stored Procedure Outbound Channel Adapter”NSection 17.3, “Outbound Gateway” and Section 17.5.8, “Stored Procedure Outbound Gateway”
JMSSection 19.1, “Inbound Channel Adapter” and Section 19.2, “Message-Driven Channel Adapter”Section 19.3, “Outbound Channel Adapter”Section 19.4, “Inbound Gateway”Section 19.5, “Outbound Gateway”
JMXSection 8.1.1, “Notification Listening Channel Adapter” and Section 8.1.3, “Attribute Polling Channel Adapter” and Section 8.1.4, “Tree Polling Channel Adapter”Section 8.1.2, “Notification Publishing Channel Adapter” and Section 8.1.5, “Operation Invoking Channel Adapter”NSection 8.1.6, “Operation Invoking Outbound Gateway”
JPASection 18.4, “Inbound Channel Adapter”Section 18.5, “Outbound Channel Adapter”NSection 18.6.2, “Updating Outbound Gateway” and Section 18.6.3, “Retrieving Outbound Gateway”
MailSection 20.2, “Mail-Receiving Channel Adapter”Section 20.1, “Mail-Sending Channel Adapter”NN
MongoDBSection 21.4, “MongoDB Inbound Channel Adapter”Section 21.5, “MongoDB Outbound Channel Adapter”NN
RedisSection 22.3.2, “Redis Inbound Channel Adapter” and Section 22.3.4, “Redis Queue Inbound Channel Adapter” and Section 22.6, “RedisStore Inbound Channel Adapter”Section 22.3.3, “Redis Outbound Channel Adapter” and Section 22.3.5, “Redis Queue Outbound Channel Adapter” and Section 22.7, “RedisStore Outbound Channel Adapter”NN
ResourceSection 23.2, “Resource Inbound Channel Adapter”NNN
RMINNSection 24.3, “Inbound RMI”Section 24.2, “Outbound RMI”
SFTPSection 25.5, “SFTP Inbound Channel Adapter”Section 25.6, “SFTP Outbound Channel Adapter”NSection 25.7, “SFTP Outbound Gateway”
StreamSection 26.2, “Reading from streams”Section 26.3, “Writing to streams”NN
SyslogSection 27.2, “Syslog <inbound-channel-adapter>”NNN
TCPSection 28.6, “TCP Adapters”Section 28.6, “TCP Adapters”Section 28.7, “TCP Gateways”Section 28.7, “TCP Gateways”
TwitterSection 29.4, “Twitter Inbound Adapters”Section 29.5, “Twitter Outbound Adapter”NN
UDPSection 28.2, “UDP Adapters”Section 28.2, “UDP Adapters”NN
Web ServicesNNSection 30.2, “Inbound Web Service Gateways”Section 30.1, “Outbound Web Service Gateways”
XMPPSection 32.3, “XMPP Messages” and Section 32.4, “XMPP Presence”Section 32.3, “XMPP Messages” and Section 32.4, “XMPP Presence”NN

In addition, as discussed in Part III, “Core Messaging”, endpoints are provided for interfacing with Plain Old Java Objects (POJOs). As discussed in Section 3.3, “Channel Adapter”, the <int:inbound-channel-adapter> allows polling a java method for data; the <int:outbound-channel-adapter> allows sending data to a void method, and as discussed in Section 7.2, “Messaging Gateways”, the <int:gateway> allows any Java program to invoke a messaging flow. Each of these without requiring any source level dependencies on Spring Integration. The equivalent of an outbound gateway in this context would be to use a Section 7.3, “Service Activator” to invoke a method that returns an Object of some kind.

10. AMQP Support

10.1 Introduction

Spring Integration provides Channel Adapters for receiving and sending messages using the Advanced Message Queuing Protocol (AMQP). The following adapters are available:

  • Inbound Channel Adapter
  • Outbound Channel Adapter
  • Inbound Gateway
  • Outbound Gateway

Spring Integration also provides a point-to-point Message Channel as well as a publish/subscribe Message Channel backed by AMQP Exchanges and Queues.

In order to provide AMQP support, Spring Integration relies on Spring AMQP (http://www.springsource.org/spring-amqp) which "applies core Spring concepts to the development of AMQP-based messaging solutions". Spring AMQP provides similar semantics as Spring JMS (http://static.springsource.org/spring/docs/current/spring-framework-reference/html/jms.html).

Whereas the provided AMQP Channel Adapters are intended for unidirectional Messaging (send or receive) only, Spring Integration also provides inbound and outbound AMQP Gateways for request/reply operations.


Please familiarize yourself with the reference documentation of the Spring AMQP project as well. It provides much more in-depth information regarding Spring's integration with AMQP in general and RabbitMQ in particular.

You can find the documentation at: http://static.springsource.org/spring-amqp/reference/html/

10.2 Inbound Channel Adapter

A configuration sample for an AMQP Inbound Channel Adapter is shown below.

<int-amqp:inbound-channel-adapter id="inboundAmqp"1


Unique ID for this adapter. Optional.


Message Channel to which converted Messages should be sent. Required.


Names of the AMQP Queues from which Messages should be consumed (comma-separated list). Required.


Acknowledge Mode for the MessageListenerContainer. Optional (Defaults to AUTO).


Extra AOP Advice(s) to handle cross cutting behavior associated with this Inbound Channel Adapter. Optional.


Flag to indicate that channels created by this component will be transactional. Ff true, tells the framework to use a transactional channel and to end all operations (send or receive) with a commit or rollback depending on the outcome, with an exception signalling a rollback. Optional (Defaults to false).


Specify the number of concurrent consumers to create. Default is 1. Raising the number of concurrent consumers is recommended in order to scale the consumption of messages coming in from a queue. However, note that any ordering guarantees are lost once multiple consumers are registered. In general, stick with 1 consumer for low-volume queues. Optional.


Bean reference to the RabbitMQ ConnectionFactory. Optional (Defaults to 'connectionFactory').


Message Channel to which error Messages should be sent. Optional.


Shall the listener channel (com.rabbitmq.client.Channel) be exposed to a registered ChannelAwareMessageListener. Optional (Defaults to true).


AmqpHeaderMapper to use when receiving AMQP Messages. Optional. By default only standard AMQP properties (e.g. contentType) will be copied to and from Spring Integration MessageHeaders. Any user-defined headers within the AMQP MessageProperties will NOT be copied to or from an AMQP Message unless explicitly identified via 'requestHeaderNames' and/or 'replyHeaderNames' properties of this DefaultAmqpHeaderMapper. If you need to copy all user-defined headers simply use wild-card character '*'.


Comma-separated list of names of AMQP Headers to be mapped from the AMQP request into the MessageHeaders. This can only be provided if the 'header-mapper' reference is not being set directly. The values in this list can also be simple patterns to be matched against the header names (e.g. "*" or "foo*, bar" or "*foo").


Comma-separated list of names of MessageHeaders to be mapped into the AMQP Message Properties of the AMQP reply message. All standard Headers (e.g., contentType) will be mapped to AMQP Message Properties while user-defined headers will be mapped to 'headers' property which itself is a Map. This can only be provided if the 'header-mapper' reference is not being set directly. The values in this list can also be simple patterns to be matched against the header names (e.g. "*" or "foo*, bar" or "*foo").


Reference to the SimpleMessageListenerContainer to use for receiving AMQP Messages. If this attribute is provided, then no other attribute related to the listener container configuration should be provided. In other words, by setting this reference, you must take full responsibility of the listener container configuration. The only exception is the MessageListener itself. Since that is actually the core responsibility of this Channel Adapter implementation, the referenced listener container must NOT already have its own MessageListener configured. Optional.

Note that when configuring an external container, you cannot use the Spring AMQP namespace to define the container. This is because the namespace requires at least one <listener/> element. In this environment, the listener is internal to the adapter. For this reason, you must define the container using a normal Spring <bean/> definition, such as:
<bean id="container"
	<property name="connectionFactory" ref="connectionFactory" />
	<property name="queueNames" value="foo.queue" />
	<property name="defaultRequeueRejected" value="false"/>


The MessageConverter to use when receiving AMQP Messages. Optional.


The MessagePropertiesConverter to use when receiving AMQP Messages. Optional.


Specify the phase in which the underlying SimpleMessageListenerContainer should be started and stopped. The startup order proceeds from lowest to highest, and the shutdown order is the reverse of that. By default this value is Integer.MAX_VALUE meaning that this container starts as late as possible and stops as soon as possible. Optional.


Tells the AMQP broker how many messages to send to each consumer in a single request. Often this can be set quite high to improve throughput. It should be greater than or equal to the transaction size (see attribute "tx-size"). Optional (Defaults to 1).


Receive timeout in milliseconds. Optional (Defaults to 1000).


Specifies the interval between recovery attempts of the underlying SimpleMessageListenerContainer (in milliseconds). Optional (Defaults to 5000).


The time to wait for workers in milliseconds after the underlying SimpleMessageListenerContainer is stopped, and before the AMQP connection is forced closed. If any workers are active when the shutdown signal comes they will be allowed to finish processing as long as they can finish within this timeout. Otherwise the connection is closed and messages remain unacked (if the channel is transactional). Defaults to 5000 milliseconds. Optional (Defaults to 5000).


By default, the underlying SimpleMessageListenerContainer uses a SimpleAsyncTaskExecutor implementation, that fires up a new Thread for each task, executing it asynchronously. By default, the number of concurrent threads is unlimited. NOTE: This implementation does not reuse threads. Consider a thread-pooling TaskExecutor implementation as an alternative. Optional (Defaults to SimpleAsyncTaskExecutor).


By default the underlying SimpleMessageListenerContainer creates a new instance of the DefaultTransactionAttribute (takes the EJB approach to rolling back on runtime, but not checked exceptions. Optional (Defaults to DefaultTransactionAttribute).


Sets a Bean reference to an external PlatformTransactionManager on the underlying SimpleMessageListenerContainer. The transaction manager works in conjunction with the "channel-transacted" attribute. If there is already a transaction in progress when the framework is sending or receiving a message, and the channelTransacted flag is true, then the commit or rollback of the messaging transaction will be deferred until the end of the current transaction. If the channelTransacted flag is false, then no transaction semantics apply to the messaging operation (it is auto-acked). For further information see chapter 1.9 of the Spring AMQP reference guide: http://static.springsource.org/spring-amqp/docs/1.0.x/reference/html/#d0e525 Optional.


Tells the SimpleMessageListenerContainer how many messages to process in a single transaction (if the channel is transactional). For best results it should be less than or equal to the set "prefetch-count". Optional (Defaults to 1).


Even though the Spring Integration JMS and AMQP support is very similar, important differences exist. The JMS Inbound Channel Adapter is using a JmsDestinationPollingSource under the covers and expects a configured Poller. The AMQP Inbound Channel Adapter on the other side uses a SimpleMessageListenerContainer and is message driven. In that regard it is more similar to the JMS Message Driven Channel Adapter.

10.3 Outbound Channel Adapter

A configuration sample for an AMQP Outbound Channel Adapter is shown below.

<int-amqp:outbound-channel-adapter id="outboundAmqp"1


Unique ID for this adapter. Optional.


Message Channel to which Messages should be sent in order to have them converted and published to an AMQP Exchange. Required.


Bean Reference to the configured AMQP Template Optional (Defaults to "amqpTemplate").


The name of the AMQP Exchange to which Messages should be sent. If not provided, Messages will be sent to the default, no-name Exchange. Optional.


The order for this consumer when multiple consumers are registered thereby enabling load- balancing and/or failover. Optional (Defaults to Ordered.LOWEST_PRECEDENCE [=Integer.MAX_VALUE]).


The fixed routing-key to use when sending Messages. By default, this will be an empty String. Optional.


The routing-key to use when sending Messages evaluated as an expression on the message (e.g. 'payload.key'). By default, this will be an empty String. Optional.


An expression defining correlation data. When provided, this configures the underlying amqp template to receive publisher confirms. Requires a dedicated RabbitTemplate and a CachingConnectionFactory with the publisherConfirms property set to true. When a publisher confirm is received, and correlation data is supplied, it is written to either the confirm-ack-channel, or the confirm-nack-channel, depending on the confirmation type. The payload of the confirm is the correlation data as defined by this expression and the message will have a header 'amqp_publishConfirm' set to true (ack) or false (nack). Examples: "headers['myCorrelationData']", "payload". Optional.


The channel to which positive (ack) publisher confirms are sent; payload is the correlation data defined by the confirm-correlation-expression. Optional, default=nullChannel.


The channel to which negative (nack) publisher confirms are sent; payload is the correlation data defined by the confirm-correlation-expression. Optional, default=nullChannel.


The channel to which returned messages are sent. When provided, the underlying amqp template is configured to return undeliverable messages to the adapter. The message will be constructed from the data received from amqp, with the following additional headers: amqp_returnReplyCode, amqp_returnReplyText, amqp_returnExchange, amqp_returnRoutingKey. Optional.

Using a return-channel requires a RabbitTemplate with the mandatory property set to true, and a CachingConnectionFactory with the publisherReturns property set to true. When using multiple outbound endpoints with returns, a separate RabbitTemplate is needed for each endpoint.

10.4 Inbound Gateway

A configuration sample for an AMQP Inbound Gateway is shown below.

<int-amqp:inbound-gateway id="inboundGateway"1


Unique ID for this adapter. Optional.


Message Channel to which converted Messages should be sent. Required.


Names of the AMQP Queues from which Messages should be consumed (comma-separated list). Required.


Extra AOP Advice(s) to handle cross cutting behavior associated with this Inbound Gateway. Optional.


Specify the number of concurrent consumers to create. Default is 1. Raising the number of concurrent consumers is recommended in order to scale the consumption of messages coming in from a queue. However, note that any ordering guarantees are lost once multiple consumers are registered. In general, stick with 1 consumer for low-volume queues. Optional (Defaults to 1).


Bean reference to the RabbitMQ ConnectionFactory. Optional (Defaults to 'connectionFactory').


Message Channel where reply Messages will be expected. Optional.

See the note in Section 10.2, “Inbound Channel Adapter” about configuring the listener-container attribute.

10.5 Outbound Gateway

A configuration sample for an AMQP Outbound Gateway is shown below.

<int-amqp:outbound-gateway id="inboundGateway"1


Unique ID for this adapter. Optional.


Message Channel to which Messages should be sent in order to have them converted and published to an AMQP Exchange. Required.


Bean Reference to the configured AMQP Template Optional (Defaults to "amqpTemplate").


The name of the AMQP Exchange to which Messages should be sent. If not provided, Messages will be sent to the default, no-name Exchange. Optional.


The order for this consumer when multiple consumers are registered thereby enabling load- balancing and/or failover. Optional (Defaults to Ordered.LOWEST_PRECEDENCE [=Integer.MAX_VALUE]).


Message Channel to which replies should be sent after being received from an AQMP Queue and converted. Optional.


The routing-key to use when sending Messages. By default, this will be an empty String. Optional.


The routing-key to use when sending Messages evealuated as an expression on the message (e.g. 'payload.key'). By default, this will be an empty String. Optional.


The channel to which returned messages are sent. When provided, the underlying amqp template is configured to return undeliverable messages to the gateway. The message will be constructed from the data received from amqp, with the following additional headers: amqp_returnReplyCode, amqp_returnReplyText, amqp_returnExchange, amqp_returnRoutingKey. Optional.

Using a return-channel requires a RabbitTemplate with the mandatory property set to true, and a CachingConnectionFactory with the publisherReturns property set to true. When using multiple outbound endpoints with returns, a separate RabbitTemplate is needed for each endpoint.


Prior to Spring Integration 2.2, and Spring AMQP 1.1, the outbound gateway used a new, temporary, reply queue for each request. This is still the default, but now the RabbitTemplate can be configured with a specific queue for replies; headers are added to the outbound message for request/reply correlation. It is important that the consuming application returns these headers unchanged. The headers are spring_reply_correlation and spring_reply_to. If the consuming application is a Spring Integration application, these headers will be managed automatically, including the case where that application might send a request/reply to a third application using an outbound gateway.

10.6 AMQP Backed Message Channels

There are two Message Channel implementations available. One is point-to-point, and the other is publish/subscribe. Both of these channels provide a wide range of configuration attributes for the underlying AmqpTemplate and SimpleMessageListenerContainer as you have seen on the Channel Adapters and Gateways. However, the examples we'll show here are going to have minimal configuration. Explore the XML schema to view the available attributes.

A point-to-point channel would look like this:

<int-amqp:channel id="p2pChannel"/>

Under the covers a Queue named "si.p2pChannel" would be declared, and this channel will send to that Queue (technically by sending to the no-name Direct Exchange with a routing key that matches this Queue's name). This channel will also register a consumer on that Queue. If for some reason, you want the Queue to be "pollable" instead of message-driven, then simply provide the "message-driven" flag with a value of false:

<int-amqp:channel id="p2pPollableChannel"  message-driven="false"/>

A publish/subscribe channel would look like this:

<int-amqp:publish-subscribe-channel id="pubSubChannel"/>

Under the covers a Fanout Exchange named "si.fanout.pubSubChannel" would be declared, and this channel will send to that Fanout Exchange. This channel will also declare a server-named exclusive, autodelete, non-durable Queue and bind that to the Fanout Exchange while registering a consumer on that Queue to receive Messages. There is no "pollable" option for a publish-subscribe-channel; it must be message-driven.

10.7 AMQP Message Headers

The Spring Integration AMPQ Adapters will map standard AMQP properties automatically. These properties will be copied by default to and from Spring Integration MessageHeaders using the DefaultAmqpHeaderMapper.

Of course, you can pass in your own implementation of AMQP specific header mappers, as the adapters have respective properties to support that.

Any user-defined headers within the AMQP MessageProperties will NOT be copied to or from an AMQP Message, unless explicitly specified by the requestHeaderNames and/or replyHeaderNames properties of the DefaultAmqpHeaderMapper.

When mapping user-defined headers, the values can also contain simple wildcard patterns (e.g. "foo*" or "*foo") to be matched. For example, if you need to copy all user-defined headers simply use the wild-card character '*'.

Class AmqpHeaders identifies the default headers that will be used by the DefaultAmqpHeaderMapper:

  • amqp_appId
  • amqp_clusterId
  • amqp_contentEncoding
  • amqp_contentLength
  • content-type
  • amqp_correlationId
  • amqp_deliveryMode
  • amqp_deliveryTag
  • amqp_expiration
  • amqp_messageCount
  • amqp_messageId
  • amqp_receivedExchange
  • amqp_receivedRoutingKey
  • amqp_redelivered
  • amqp_replyTo
  • amqp_timestamp
  • amqp_type
  • amqp_userId
  • amqp_springReplyCorrelation
  • amqp_springReplyToStack
  • amqp_publishConfirm
  • amqp_returnReplyCode
  • amqp_returnReplyText
  • amqp_returnExchange
  • amqp_returnRoutingKey

10.8 AMQP Samples

To experiment with the AMQP adapters, check out the samples available in the Spring Integration Samples Git repository at:

Currently there is one sample available that demonstrates the basic functionality of the Spring Integration AMQP Adapter using an Outbound Channel Adapter and an Inbound Channel Adapter. As AMQP Broker implementation the sample uses RabbitMQ (http://www.rabbitmq.com/).

In order to run the example you will need a running instance of RabbitMQ. A local installation with just the basic defaults will be sufficient. For detailed RabbitMQ installation procedures please visit: http://www.rabbitmq.com/install.html

Once the sample application is started, you enter some text on the command prompt and a message containing that entered text is dispatched to the AMQP queue. In return that message is retrieved via Spring Integration and then printed to the console.

The image belows illustrates the basic set of Spring Integration components used in this sample.

The Spring Integration graph of the AMQP sample

11. Spring ApplicationEvent Support

Spring Integration provides support for inbound and outbound ApplicationEvents as defined by the underlying Spring Framework. For more information about Spring's support for events and listeners, refer to the Spring Reference Manual.

11.1 Receiving Spring ApplicationEvents

To receive events and send them to a channel, simply define an instance of Spring Integration's ApplicationEventListeningMessageProducer. This class is an implementation of Spring's ApplicationListener interface. By default it will pass all received events as Spring Integration Messages. To limit based on the type of event, configure the list of event types that you want to receive with the 'eventTypes' property. If a received event has a Message instance as its 'source', then that will be passed as-is. Otherwise, if a SpEL-based "payloadExpression" has been provided, that will be evaluated against the ApplicationEvent instance. If the event's source is not a Message instance and no "payloadExpression" has been provided, then the ApplicationEvent itself will be passed as the payload.

For convenience namespace support is provided to configure an ApplicationEventListeningMessageProducer via the inbound-channel-adapter element.

<int-event:inbound-channel-adapter channel="eventChannel" 
                                   event-types="example.FooEvent, example.BarEvent"/>

<int:publish-subscribe-channel id="eventChannel"/>

In the above example, all Application Context events that match one of the types specified by the 'event-types' (optional) attribute will be delivered as Spring Integration Messages to the Message Channel named 'eventChannel'. If a downstream component throws an exception, a MessagingException containing the failed message and exception will be sent to the channel named 'eventErrorChannel'. If no "error-channel" is specified and the downstream channels are synchronous, the Exception will be propagated to the caller.

11.2 Sending Spring ApplicationEvents

To send Spring ApplicationEvents, create an instance of the ApplicationEventPublishingMessageHandler and register it within an endpoint. This implementation of the MessageHandler interface also implements Spring's ApplicationEventPublisherAware interface and thus acts as a bridge between Spring Integration Messages and ApplicationEvents.

For convenience namespace support is provided to configure an ApplicationEventPublishingMessageHandler via the outbound-channel-adapter element.

<int:channel id="eventChannel"/>

<int-event:outbound-channel-adapter channel="eventChannel"/>

If you are using a PollableChannel (e.g., Queue), you can also provide poller as a sub-element of the outbound-channel-adapter element. You can also optionally provide a task-executor reference for that poller. The following example demonstrates both.

<int:channel id="eventChannel">

<int-event:outbound-channel-adapter channel="eventChannel">
  <int:poller max-messages-per-poll="1" task-executor="executor" fixed-rate="100"/>

<task:executor id="executor" pool-size="5"/>

In the above example, all messages sent to the 'eventChannel' channel will be published as ApplicationEvents to any relevant ApplicationListener instances that are registered within the same Spring ApplicationContext. If the payload of the Message is an ApplicationEvent, it will be passed as-is. Otherwise the Message itself will be wrapped in a MessagingEvent instance.

12. Feed Adapter

Spring Integration provides support for Syndication via Feed Adapters

12.1 Introduction

Web syndication is a form of publishing material such as news stories, press releases, blog posts, and other items typically available on a website but also made available in a feed format such as RSS or ATOM.

Spring integration provides support for Web Syndication via its 'feed' adapter and provides convenient namespace-based configuration for it. To configure the 'feed' namespace, include the following elements within the headers of your XML configuration file:


12.2 Feed Inbound Channel Adapter

The only adapter that is really needed to provide support for retrieving feeds is an inbound channel adapter. This allows you to subscribe to a particular URL. Below is an example configuration:

<int-feed:inbound-channel-adapter id="feedAdapter"
	<int:poller fixed-rate="10000" max-messages-per-poll="100" />

In the above configuration, we are subscribing to a URL identified by the url attribute.

As news items are retrieved they will be converted to Messages and sent to a channel identified by the channel attribute. The payload of each message will be a com.sun.syndication.feed.synd.SyndEntry instance. That encapsulates various data about a news item (content, dates, authors, etc.).

You can also see that the Inbound Feed Channel Adapter is a Polling Consumer. That means you have to provide a poller configuration. However, one important thing you must understand with regard to Feeds is that its inner-workings are slightly different then most other poling consumers. When an Inbound Feed adapter is started, it does the first poll and receives a com.sun.syndication.feed.synd.SyndEntryFeed instance. That is an object that contains multiple SyndEntry objects. Each entry is stored in the local entry queue and is released based on the value in the max-messages-per-poll attribute such that each Message will contain a single entry. If during retrieval of the entries from the entry queue the queue had become empty, the adapter will attempt to update the Feed thereby populating the queue with more entries (SyndEntry instances) if available. Otherwise the next attempt to poll for a feed will be determined by the trigger of the poller (e.g., every 10 seconds in the above configuration).

Duplicate Entries

Polling for a Feed might result in entries that have already been processed ("I already read that news item, why are you showing it to me again?"). Spring Integration provides a convenient mechanism to eliminate the need to worry about duplicate entries. Each feed entry will have a published date field. Every time a new Message is generated and sent, Spring Integration will store the value of the latest published date in an instance of the MetadataStore strategy (Section 8.4, “Metadata Store”).

The key used to persist the latest published date is the value of the (required) id attribute of the Feed Inbound Channel Adapter component plus the feedUrl from the adapter's configuration.

13. File Support

13.1 Introduction

Spring Integration's File support extends the Spring Integration Core with a dedicated vocabulary to deal with reading, writing, and transforming files. It provides a namespace that enables elements defining Channel Adapters dedicated to files and support for Transformers that can read file contents into strings or byte arrays.

This section will explain the workings of FileReadingMessageSource and FileWritingMessageHandler and how to configure them as beans. Also the support for dealing with files through file specific implementations of Transformer will be discussed. Finally the file specific namespace will be explained.

13.2 Reading Files

A FileReadingMessageSource can be used to consume files from the filesystem. This is an implementation of MessageSource that creates messages from a file system directory.

<bean id="pollableFileSource"

To prevent creating messages for certain files, you may supply a FileListFilter. By default, an AcceptOnceFileListFilter is used. This filter ensures files are picked up only once from the directory.

The AcceptOnceFileListFilter stores its state in memory. If you wish the state to survive a system restart, consider using the FileSystemPersistentAcceptOnceFileListFilter instead. This filter stores the accepted file names in a MetadataStore strategy (Section 8.4, “Metadata Store”). This filter matches on the filename and modified time.

<bean id="pollableFileSource"

A common problem with reading files is that a file may be detected before it is ready. The default AcceptOnceFileListFilter does not prevent this. In most cases, this can be prevented if the file-writing process renames each file as soon as it is ready for reading. A filename-pattern or filename-regex filter that accepts only files that are ready (e.g. based on a known suffix), composed with the default AcceptOnceFileListFilter allows for this. The CompositeFileListFilter enables the composition.

<bean id="pollableFileSource"
<bean id="compositeFilter"
            <bean class="o.s.i.file.filters.AcceptOnceFileListFilter"/>
            <bean class="o.s.i.file.filters.RegexPatternFileListFilter">
                <constructor-arg value="^test.*$"/>

The configuration can be simplified using the file specific namespace. To do this use the following template.

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"

Within this namespace you can reduce the FileReadingMessageSource and wrap it in an inbound Channel Adapter like this:

<int-file:inbound-channel-adapter id="filesIn1"
    directory="file:${input.directory}" prevent-duplicates="true"/>

<int-file:inbound-channel-adapter id="filesIn2"
    filter="customFilterBean" />

<int-file:inbound-channel-adapter id="filesIn3"
    filename-pattern="test*" />

<int-file:inbound-channel-adapter id="filesIn4"
    filename-regex="test[0-9]+\.txt" />

The first channel adapter is relying on the default filter that just prevents duplication, the second is using a custom filter, the third is using the filename-pattern attribute to add an AntPathMatcher based filter, and the fourth is using the filename-regex attribute to add a regular expression Pattern based filter to the FileReadingMessageSource. The filename-pattern and filename-regex attributes are each mutually exclusive with the regular filter reference attribute. However, you can use the filter attribute to reference an instance of CompositeFileListFilter that combines any number of filters, including one or more pattern based filters to fit your particular needs.

When multiple processes are reading from the same directory it can be desirable to lock files to prevent them from being picked up concurrently. To do this you can use a FileLocker. There is a java.nio based implementation available out of the box, but it is also possible to implement your own locking scheme. The nio locker can be injected as follows

<int-file:inbound-channel-adapter id="filesIn"
    directory="file:${input.directory}" prevent-duplicates="true">

A custom locker you can configure like this:

<int-file:inbound-channel-adapter id="filesIn"
    directory="file:${input.directory}" prevent-duplicates="true">
    <int-file:locker ref="customLocker"/>

When a file inbound adapter is configured with a locker, it will take the responsibility to acquire a lock before the file is allowed to be received. It will not assume the responsibility to unlock the file. If you have processed the file and keeping the locks hanging around you have a memory leak. If this is a problem in your case you should call FileLocker.unlock(File file) yourself at the appropriate time.

When filtering and locking files is not enough it might be needed to control the way files are listed entirely. To implement this type of requirement you can use an implementation of DirectoryScanner. This scanner allows you to determine entirely what files are listed each poll. This is also the interface that Spring Integration uses internally to wire FileListFilters FileLocker to the FileReadingMessageSource. A custom DirectoryScanner can be injected into the <int-file:inbound-channel-adapter/> on the scanner attribute.

<int-file:inbound-channel-adapter id="filesIn" directory="file:${input.directory}"
    prevent-duplicates="true" scanner="customDirectoryScanner"/>

This gives you full freedom to choose the ordering, listing and locking strategies.

It is important to understand that filters (including patterns, regex, prevent-duplicates etc) and lockers, are actually used by the scanner. Any of these attributes set on the adapter are subsequently injected into the scanner. For this reason, if you need to provide a custom scanner and you have multiple file inbound adapters in the same application context, each adapter must be provided with its own instance of the scanner, either by declaring separate beans, or declaring scope="prototype" on the scanner bean so that the context will create a new instance for each use.

13.2.1 'Tail'ing Files

Another popular use case is to get 'lines' from the end (or tail) of a file, capturing new lines when they are added. Two implementations are provided; the first, OSDelegatingFileTailingMessageProducer, uses the native tail command (on operating systems that have one). This is likely the most efficient implementation on those platforms. For operating systems that do not have a tail command, the second implementation ApacheCommonsFileTailingMessageProducer which uses the Apache commons-io Tailer class.

In both cases, file system events, such as files being unavailable etc, are published as ApplicationEvents using the normal Spring event publishing mechanism. Examples of such events are:

[message=tail: cannot open `/tmp/foo' for reading: No such file or directory, file=/tmp/foo]

[message=tail: `/tmp/foo' has become accessible, file=/tmp/foo]

[message=tail: `/tmp/foo' has become inaccessible: No such file or directory, file=/tmp/foo]

[message=tail: `/tmp/foo' has appeared; following end of new file, file=/tmp/foo]

This sequence of events might occur, for example, when a file is rotated.

Not all platforms supporting a tail command provide these status messages.

Example configurations:

<int-file:tail-inbound-channel-adapter id="native"

This creates a native adapter with default '-F -n 0' options (follow the file name from the current end).

<int-file:tail-inbound-channel-adapter id="native"
	native-options="-F -n +0"

This creates a native adapter with '-F -n +0' options (follow the file name, emitting all existing lines). If the tail command fails (on some platforms, a missing file causes the tail to fail, even with -F specified), the command will be retried every 10 seconds.

<int-file:tail-inbound-channel-adapter id="apache"

This creates an Apache commons-io Tailer adapter that examines the file for new lines every 2 seconds, and checks for existence of a missing file every 10 seconds. The file will be tailed from the beginning (end="false") instead of the end (which is the default). The file will be reopened for each chunk (the default is to keep the file open).


Specifying the delay, end or reopen attributes, forces the use of the Apache commons-io adapter and the native-options attribute is not allowed.

13.3 Writing files

To write messages to the file system you can use a FileWritingMessageHandler. This class can deal with File, String, or byte array payloads.

You can configure the encoding and the charset that will be used in case of a String payload.

To make things easier, you can configure the FileWritingMessageHandler as part of an Outbound Channel Adapter or Outbound Gateway using the provided XML namespace support.

13.3.1 Generating Filenames

In its simplest form, the FileWritingMessageHandler only requires a destination directory for writing the files. The name of the file to be written is determined by the handler's FileNameGenerator. The default implementation looks for a Message header whose key matches the constant defined as FileHeaders.FILENAME.

Alternatively, you can specify an expression to be evaluated against the Message in order to generate a file name, e.g.: headers['myCustomHeader'] + '.foo'. The expression must evaluate to a String. For convenience, the DefaultFileNameGenerator also provides the setHeaderName method, allowing you to explicitly specify the Message header whose value shall be used as the filename.

Once setup, the DefaultFileNameGenerator will employ the following resolution steps to determine the filename for a given Message payload:

  1. Evaluate the expression against the Message and, if the result is a non-empty String, use it as the filename.
  2. Otherwise, if the payload is a java.io.File, use the file's filename.
  3. Otherwise, use the Message ID appended with .msg as the filename.

When using the XML namespace support, both, the File Oubound Channel Adapter and the File Outbound Gateway support the following two mutually exclusive configuration attributes:

  • filename-generator (a reference to a FileNameGenerator) implementation)
  • filename-generator-expression (an expression evaluating to a String)

While writing files, a temporary file suffix will be used (default: .writing). It is appended to the filename while the file is being written. To customize the suffix, you can set the temporary-file-suffix attribute on both, the File Oubound Channel Adapter and the File Outbound Gateway.

When using the APPEND file mode, the temporary-file-suffix attribute is ignored, since the data is appended to the file directly.

13.3.2 Specifying the Output Directory

Both, the File Oubound Channel Adapter and the File Outbound Gateway provide two configuration attributes for specifying the output directory:

  • directory

  • directory-expression

The directory-expression attribute is available since Spring Integration 2.2.

Using the directory attribute

When using the directory attribute, the output directory will be set to a fixed value, that is set at intialization time of the FileWritingMessageHandler. If you don't specify this attribute, then you must use the directory-expression attribute.

Using the directory-expression attribute

If you want to have full SpEL support you would choose the directory-expression attribute. This attribute accepts a SpEL expression that is evaluated for each message being processed. Thus, you have full access to a Message's payload and its headers to dynamically specify the output file directory.

The SpEL expression must resolve to either a String or to java.io.File. Furthermore the resulting String or File must point to a directory. If you don't specify the directory-expression attribute, then you must set the directory attribute.

Using the auto-create-directory attribute

If the destination directory does not exists, yet, by default the respective destination directory and any non-existing parent directories are being created automatically. You can set the auto-create-directory attribute to false in order to prevent that. This attribute applies to both, the directory and the directory-expression attribute.


When using the directory attribute and auto-create-directory is false, the following change was made starting with Spring Integration 2.2:

Instead of checking for the existence of the destination directory at initialization time of the adapter, this check is now performed for each message being processed.

Furthermore, if auto-create-directory is true and the directory was deleted between the processing of messages, the directory will be re-created for each message being processed.

13.3.3 Dealing with Existing Destination Files

When writing files and the destination file already exists, the default behavior is to overwrite that target file. This behavior, though, can be changed by setting the mode attribute on the respective File Outbound components. The following options exist:

  • REPLACE (Default)
  • FAIL
The mode attribute and the options APPEND, FAIL and IGNORE, are available since Spring Integration 2.2.


If the target file already exists, it will be overwritten. If the mode attribute is not specified, then this is the default behavior when writing files.


This mode allows you to append Message content to the existing file instead of creating a new file each time. Note that this attribute is mutually exclusive with temporary-file-suffix attribute since when appending content to the existing file, the adapter no longer uses a temporary file.


If the target file exists, a MessageHandlingException is thrown.


If the target file exists, the message payload is silently ignored.

When using a temporary file suffix (default: .writing), the IGNORE mode will apply if the final file name exists, or the temporary file name exists.

13.3.4 File Outbound Channel Adapter

<int-file:outbound-channel-adapter id="filesOut" directory="${input.directory.property}"/>

The namespace based configuration also supports a delete-source-files attribute. If set to true, it will trigger the deletion of the original source files after writing to a destination. The default value for that flag is false.

<int-file:outbound-channel-adapter id="filesOut"
The delete-source-files attribute will only have an effect if the inbound Message has a File payload or if the FileHeaders.ORIGINAL_FILE header value contains either the source File instance or a String representing the original file path.

13.3.5 Outbound Gateway

In cases where you want to continue processing messages based on the written file, you can use the outbound-gateway instead. It plays a very similar role as the outbound-channel-adapter. However, after writing the file, it will also send it to the reply channel as the payload of a Message.

<int-file:outbound-gateway id="mover" request-channel="moveInput"
    mode="REPLACE" delete-source-files="true"/>

As mentioned earlier, you can also specify the mode attribute, which defines the behavior of how to deal with situations where the destination file already exists. Please see Section 13.3.3, “Dealing with Existing Destination Files” for further details. Generally, when using the File Outbound Gateway, the result file is returned as the Message payload on the reply channel.

This also applies when specifying the IGNORE mode. In that case the pre-existing destination file is returned. If the payload of the request message was a file, you still have access to that original file through the Message Header FileHeaders.ORIGINAL_FILE.

The 'outbound-gateway' works well in cases where you want to first move a file and then send it through a processing pipeline. In such cases, you may connect the file namespace's 'inbound-channel-adapter' element to the 'outbound-gateway' and then connect that gateway's reply-channel to the beginning of the pipeline.

If you have more elaborate requirements or need to support additional payload types as input to be converted to file content you could extend the FileWritingMessageHandler, but a much better option is to rely on a Transformer.

13.4 File Transformers

To transform data read from the file system to objects and the other way around you need to do some work. Contrary to FileReadingMessageSource and to a lesser extent FileWritingMessageHandler, it is very likely that you will need your own mechanism to get the job done. For this you can implement the Transformer interface. Or extend the AbstractFilePayloadTransformer for inbound messages. Some obvious implementations have been provided.

FileToByteArrayTransformer transforms Files into byte[]s using Spring's FileCopyUtils. It is often better to use a sequence of transformers than to put all transformations in a single class. In that case the File to byte[] conversion might be a logical first step.

FileToStringTransformer will convert Files to Strings as the name suggests. If nothing else, this can be useful for debugging (consider using with a Wire Tap).

To configure File specific transformers you can use the appropriate elements from the file namespace.

<int-file:file-to-bytes-transformer  input-channel="input" output-channel="output"

<int-file:file-to-string-transformer input-channel="input" output-channel="output"
    delete-files="true" charset="UTF-8"/>

The delete-files option signals to the transformer that it should delete the inbound File after the transformation is complete. This is in no way a replacement for using the AcceptOnceFileListFilter when the FileReadingMessageSource is being used in a multi-threaded environment (e.g. Spring Integration in general).

14. FTP/FTPS Adapters

Spring Integration provides support for file transfer operations via FTP and FTPS.

14.1 Introduction

The File Transfer Protocol (FTP) is a simple network protocol which allows you to transfer files between two computers on the Internet.

There are two actors when it comes to FTP communication: client and server. To transfer files with FTP/FTPS, you use a client which initiates a connection to a remote computer that is running an FTP server. After the connection is established, the client can choose to send and/or receive copies of files.

Spring Integration supports sending and receiving files over FTP/FTPS by providing three client side endpoints: Inbound Channel Adapter, Outbound Channel Adapter, and Outbound Gateway. It also provides convenient namespace-based configuration options for defining these client components.

To use the FTP namespace, add the following to the header of your XML file:


14.2 FTP Session Factory

Starting with version 3.0, sessions are no longer cached by default. See Section 14.6, “FTP Session Caching”.

Before configuring FTP adapters you must configure an FTP Session Factory. You can configure the FTP Session Factory with a regular bean definition where the implementation class is org.springframework.integration.ftp.session.DefaultFtpSessionFactory: Below is a basic configuration:

<bean id="ftpClientFactory"
    <property name="host" value="localhost"/>
    <property name="port" value="22"/>
    <property name="username" value="kermit"/>
    <property name="password" value="frog"/>
    <property name="clientMode" value="0"/>
    <property name="fileType" value="2"/>
    <property name="bufferSize" value="100000"/>

For FTPS connections all you need to do is use org.springframework.integration.ftp.session.DefaultFtpsSessionFactory instead. Below is the complete configuration sample:

<bean id="ftpClientFactory"
    <property name="host" value="localhost"/>
    <property name="port" value="22"/>
    <property name="username" value="oleg"/>
    <property name="password" value="password"/>
    <property name="clientMode" value="1"/>
    <property name="fileType" value="2"/>
    <property name="useClientMode" value="true"/>
    <property name="cipherSuites" value="a,b.c"/>
    <property name="keyManager" ref="keyManager"/>
    <property name="protocol" value="SSL"/>
    <property name="trustManager" ref="trustManager"/>
    <property name="prot" value="P"/>
    <property name="needClientAuth" value="true"/>
    <property name="authValue" value="oleg"/>
    <property name="sessionCreation" value="true"/>
    <property name="protocols" value="SSL, TLS"/>
    <property name="implicit" value="true"/>

Every time an adapter requests a session object from its SessionFactory the session is returned from a session pool maintained by a caching wrapper around the factory. A Session in the session pool might go stale (if it has been disconnected by the server due to inactivity) so the SessionFactory will perform validation to make sure that it never returns a stale session to the adapter. If a stale session was encountered, it will be removed from the pool, and a new one will be created.

If you experience connectivity problems and would like to trace Session creation as well as see which Sessions are polled you may enable it by setting the logger to TRACE level (e.g., log4j.category.org.springframework.integration.file=TRACE)

Now all you need to do is inject these session factories into your adapters. Obviously the protocol (FTP or FTPS) that an adapter will use depends on the type of session factory that has been injected into the adapter.

A more practical way to provide values for FTP/FTPS Session Factories is by using Spring's property placeholder support (See: http://static.springsource.org/spring/docs/3.0.x/spring-framework-reference/html/beans.html#beans-factory-placeholderconfigurer).

Advanced Configuration

DefaultFtpSessionFactory provides an abstraction over the underlying client API which, since Spring Integration 2.0, is Apache Commons Net. This spares you from the low level configuration details of the org.apache.commons.net.ftp.FTPClient. However there are times when access to lower level FTPClient details is necessary to achieve more advanced configuration (e.g., setting data timeout, default timeout etc.). For that purpose, AbstractFtpSessionFactory (the base class for all FTP Session Factories) exposes hooks, in the form of the two post-processing methods below.

 * Will handle additional initialization after client.connect() method was invoked,
 * but before any action on the client has been taken
protected void postProcessClientAfterConnect(T t) throws IOException {
    // NOOP
 * Will handle additional initialization before client.connect() method was invoked.
protected void postProcessClientBeforeConnect(T client) throws IOException {
    // NOOP

As you can see, there is no default implementation for these two methods. However, by extending DefaultFtpSessionFactory you can override these methods to provide more advanced configuration of the FTPClient. For example:

public class AdvancedFtpSessionFactory extends DefaultFtpSessionFactory {

    protected void postProcessClientBeforeConnect(FTPClient ftpClient) throws IOException {

14.3 FTP Inbound Channel Adapter

The FTP Inbound Channel Adapter is a special listener that will connect to the FTP server and will listen for the remote directory events (e.g., new file created) at which point it will initiate a file transfer.

<int-ftp:inbound-channel-adapter id="ftpInbound"
    local-filename-generator-expression="#this.toUpperCase() + '.a'"
    <int:poller fixed-rate="1000"/>

As you can see from the configuration above you can configure an FTP Inbound Channel Adapter via the inbound-channel-adapter element while also providing values for various attributes such as local-directory, filename-pattern (which is based on simple pattern matching, not regular expressions), and of course the reference to a session-factory.

By default the transferred file will carry the same name as the original file. If you want to override this behavior you can set the local-filename-generator-expression attribute which allows you to provide a SpEL Expression to generate the name of the local file. Unlike outbound gateways and adapters where the root object of the SpEL Evaluation Context is a Message, this inbound adapter does not yet have the Message at the time of evaluation since that's what it ultimately generates with the transferred file as its payload. So, the root object of the SpEL Evaluation Context is the original name of the remote file (String).

Starting with Spring Integration 3.0, you can specify the preserve-timestamp attribute (default false); when true, the local file's modified timestamp will be set to the value retrieved from the server; otherwise it will be set to the current time.

Sometimes file filtering based on the simple pattern specified via filename-pattern attribute might not be sufficient. If this is the case, you can use the filename-regex attribute to specify a Regular Expression (e.g. filename-regex=".*\.test$"). And of course if you need complete control you can use filter attribute and provide a reference to any custom implementation of the org.springframework.integration.file.filters.FileListFilter, a strategy interface for filtering a list of files. This filter determines which remote files are retrieved. You can also combine a pattern based filter with other filters, such as an AcceptOnceFileListFilter to avoid synchronizing files that have previously been fetched, by using a CompositeFileListFilter.

The AcceptOnceFileListFilter stores its state in memory. If you wish the state to survive a system restart, consider using the FtpPersistentAcceptOnceFileListFilter instead. This filter stores the accepted file names in an instance of the MetadataStore strategy (Section 8.4, “Metadata Store”). This filter matches on the filename and the remote modified time.


Beginning with version 3.0, you can also specify a filter used to filter the files locally, once they have been retrieved. The default filter is an AcceptOnceFileListFilter which prevents processing files with the same name multiple times in the same JVM execution; this can now be overridden (for example with an AcceptAllFileListFilter), using the local-filter attribute. Previously, the default AcceptOnceFileListFilter could not be overridden.

The AcceptOnceFileListFilter stores its state in memory. If you wish the state to survive a system restart, consider using the FileSystemPersistentAcceptOnceFileListFilter as a local filter instead. This filter stores the accepted file names in an instance of the MetadataStore strategy (Section 8.4, “Metadata Store”).

This filter compares the filename and modified timestamp. If you wish to use this technique to avoid a re-synchronized file from being processed, you should use the preserve-timestamp attribute discussed above.

The 'remote-file-separator' attribute allows you to configure a file separator character to use if the default '/' is not applicable for your particular environment.

Please refer to the schema for more details on these attributes.

It is also important to understand that the FTP Inbound Channel Adapter is a Polling Consumer and therefore you must configure a poller (either via a global default or a local sub-element). Once a file has been transferred, a Message with a java.io.File as its payload will be generated and sent to the channel identified by the channel attribute.

More on File Filtering and Large Files

Sometimes the file that just appeared in the monitored (remote) directory is not complete. Typically such a file will be written with temporary extension (e.g., foo.txt.writing) and then renamed after the writing process finished. As a user in most cases you are only interested in files that are complete and would like to filter only files that are complete. To handle these scenarios you can use the filtering support provided by the filename-pattern, filename-regex and filter attributes. Here is an example that uses a custom Filter implementation.

	<int:poller fixed-rate="1000"/>

<bean id="customFilter" class="org.example.CustomFilter"/>

Poller configuration notes for the inbound FTP adapter

The job of the inbound FTP adapter consists of two tasks: 1) Communicate with a remote server in order to transfer files from a remote directory to a local directory. 2) For each transferred file, generate a Message with that file as a payload and send it to the channel identified by the 'channel' attribute. That is why they are called 'channel-adapters' rather than just 'adapters'. The main job of such an adapter is to generate a Message to be sent to a Message Channel. Essentially, the second task mentioned above takes precedence in such a way that *IF* your local directory already has one or more files it will first generate Messages from those, and *ONLY* when all local files have been processed, will it initiate the remote communication to retrieve more files.

Also, when configuring a trigger on the poller you should pay close attention to the max-messages-per-poll attribute. Its default value is 1 for all SourcePollingChannelAdapter instances (including FTP). This means that as soon as one file is processed, it will wait for the next execution time as determined by your trigger configuration. If you happened to have one or more files sitting in the local-directory, it would process those files before it would initiate communication with the remote FTP server. And, if the max-messages-per-poll were set to 1 (default), then it would be processing only one file at a time with intervals as defined by your trigger, essentially working as one-poll = one-file.

For typical file-transfer use cases, you most likely want the opposite behavior: to process all the files you can for each poll and only then wait for the next poll. If that is the case, set max-messages-per-poll to -1. Then, on each poll, the adapter will attempt to generate as many Messages as it possibly can. In other words, it will process everything in the local directory, and then it will connect to the remote directory to transfer everything that is available there to be processed locally. Only then is the poll operation considered complete, and the poller will wait for the next execution time.

You can alternatively set the 'max-messages-per-poll' value to a positive value indicating the upward limit of Messages to be created from files with each poll. For example, a value of 10 means that on each poll it will attempt to process no more than 10 files.

14.4 FTP Outbound Channel Adapter

The FTP Outbound Channel Adapter relies upon a MessageHandler implementation that will connect to the FTP server and initiate an FTP transfer for every file it receives in the payload of incoming Messages. It also supports several representations of the File so you are not limited only to java.io.File typed payloads. The FTP Outbound Channel Adapter supports the following payloads: 1) java.io.File - the actual file object; 2) byte[] - a byte array that represents the file contents; and 3) java.lang.String - text that represents the file contents.

<int-ftp:outbound-channel-adapter id="ftpOutbound"

As you can see from the configuration above you can configure an FTP Outbound Channel Adapter via the outbound-channel-adapter element while also providing values for various attributes such as filename-generator (an implementation of the org.springframework.integration.file.FileNameGenerator strategy interface), a reference to a session-factory, as well as other attributes. You can also see some examples of *expression attributes which allow you to use SpEL to configure things like remote-directory-expression, temporary-remote-directory-expression and remote-filename-generator-expression (a SpEL alternative to filename-generator shown above). As with any component that allows the usage of SpEL, access to Payload and Message Headers is available via 'payload' and 'headers' variables. Please refer to the schema for more details on the available attributes.

By default Spring Integration will use o.s.i.file.DefaultFileNameGenerator if none is specified. DefaultFileNameGenerator will determine the file name based on the value of the file_name header (if it exists) in the MessageHeaders, or if the payload of the Message is already a java.io.File, then it will use the original name of that file.

Defining certain values (e.g., remote-directory) might be platform/ftp server dependent. For example as it was reported on this forum http://forum.springsource.org/showthread.php?p=333478&posted=1#post333478 on some platforms you must add slash to the end of the directory definition (e.g., remote-directory="/foo/bar/" instead of remote-directory="/foo/bar")

Avoiding Partially Written Files

One of the common problems, when dealing with file transfers, is the possibility of processing a partial file - a file might appear in the file system before its transfer is actually complete.

To deal with this issue, Spring Integration FTP adapters use a very common algorithm where files are transferred under a temporary name and then renamed once they are fully transferred.

By default, every file that is in the process of being transferred will appear in the file system with an additional suffix which, by default, is .writing; this can be changed using the temporary-file-suffix attribute.

However, there may be situations where you don't want to use this technique (for example, if the server does not permit renaming files). For situations like this, you can disable this feature by setting use-temporary-file-name to false (default is true). When this attribute is false, the file is written with its final name and the consuming application will need some other mechanism to detect that the file is completely uploaded before accessing it.

14.5 FTP Outbound Gateway

The FTP Outbound Gateway provides a limited set of commands to interact with a remote FTP/FTPS server.

Commands supported are:

  • ls (list files)
  • get (retrieve file)
  • mget (retrieve file(s))
  • rm (remove file(s))
  • mv (move/rename file)
  • put (send file)
  • mput (send multiple files)


ls lists remote file(s) and supports the following options:

  • -1 - just retrieve a list of filenames, default is to retrieve a list of FileInfo objects.
  • -a - include all files (including those starting with '.')
  • -f - do not sort the list
  • -dirs - include directories (excluded by default)
  • -links - include symbolic links (excluded by default)
  • -R - list the remote directory recursively

In addition, filename filtering is provided, in the same manner as the inbound-channel-adapter.

The message payload resulting from an ls operation is a list of file names, or a list of FileInfo objects. These objects provide information such as modified time, permissions etc.

The remote directory that the ls command acted on is provided in the file_remoteDirectory header.

When using the recursive option (-R), the fileName includes any subdirectory elements, representing a relative path to the file (relative to the remote directory). If the -dirs option is included, each recursive directory is also returned as an element in the list. In this case, it is recommended that the -1 is not used because you would not be able to determine files Vs. directories, which is achievable using the FileInfo objects.


get retrieves a remote file and supports the following option:

  • -P - preserve the timestamp of the remote file

The message payload resulting from a get operation is a File object representing the retrieved file.

The remote directory is provided in the file_remoteDirectory header, and the filename is provided in the file_remoteFile header.


mget retrieves multiple remote files based on a pattern and supports the following option:

  • -P - preserve the timestamps of the remote files
  • -x - Throw an exception if no files match the pattern (otherwise an empty list is returned)

The message payload resulting from an mget operation is a List<File> object - a List of File objects, each representing a retrieved file.

The remote directory is provided in the file_remoteDirectory header, and the pattern for the filenames is provided in the file_remoteFile header.

[Note]Notes for when using recursion (-R)

The pattern is ignored, and * is assumed. By default, the entire remote tree is retrieved. However, files in the tree can be filtered, by providing a FileListFilter; directories in the tree can also be filtered this way. A FileListFilter can be provided by reference or by filename-pattern or filename-regex attributes. For example, filename-regex="(subDir|.*1.txt)" will retrieve all files ending with 1.txt in the remote directory and the subdirectory subDir. If a subdirectory is filtered, no additional traversal of that subdirectory is performed.

The -dirs option is not allowed (the recursive mget uses the recursive ls to obtain the directory tree and the directories themselves cannot be included in the list).

Typically, you would use the #remoteDirectory variable in the local-directory-expression so that the remote directory structure is retained locally.


put sends a file to the remote server; the payload of the message can be a java.io.File, a byte[] or a String. A remote-filename-generator (or expression) is used to name the remote file. Other available attributes include remote-directory, temporary-remote-directory (and their *-expression) equivalents, use-temporary-file-name, and auto-create-directory. Refer to the schema documentation for more information.

The message payload resulting from a put operation is a String representing the full path of the file on the server after transfer.


mput sends multiple files to the server and supports the following option:

  • -R - Recursive - send all files (possibly filtered) in the directory and subdirectories

The message payload must be a java.io.File representing a local directory.

The same attributes as the put command are supported. In addition, files in the local directory can be filtered with one of mput-pattern, mput-regex or mput-filter. The filter works with recursion, as long as the subdirectories themselves pass the filter. Subdirectories that do not pass the filter are not recursed.

The message payload resulting from an mget operation is a List<String> object - a List of remote file paths resulting from the transfer.


The rm command has no options.

The message payload resulting from an rm operation is Boolean.TRUE if the remove was successful, Boolean.FALSE otherwise. The remote directory is provided in the file_remoteDirectory header, and the filename is provided in the file_remoteFile header.


The mv command has no options.

The expression attribute defines the "from" path and the rename-expression attribute defines the "to" path. By default, the rename-expression is headers['file_renameTo']. This expression must not evaluate to null, or an empty String. If necessary, any remote directories needed will be created. The payload of the result message is Boolean.TRUE. The original remote directory is provided in the file_remoteDirectory header, and the filename is provided in the file_remoteFile header. The new path is in the file_renameTo header.

Additional Information

The get and mget commands support the local-filename-generator-expression attribute. It defines a SpEL expression to generate the name of local file(s) during the transfer. The root object of the evaluation context is the request Message but, in addition, the remoteFileName variable is also available, which is particularly useful for mget, for example: local-filename-generator-expression="#remoteFileName.toUpperCase() + headers.foo".

The get and mget commands support the local-directory-expression attribute. It defines a SpEL expression to generate the name of local directory(ies) during the transfer. The root object of the evaluation context is the request Message but, in addition, the remoteDirectory variable is also available, which is particularly useful for mget, for example: local-directory-expression="'/tmp/local/' + #remoteDirectory.toUpperCase() + headers.foo". This attribute is mutually exclusive with local-directory attribute.

For all commands, the PATH that the command acts on is provided by the 'expression' property of the gateway. For the mget command, the expression might evaluate to '*', meaning retrieve all files, or 'somedirectory/*' etc.

Here is an example of a gateway configured for an ls command...

<int-ftp:outbound-gateway id="gateway1"

The payload of the message sent to the toSplitter channel is a list of String objects containing the filename of each file. If the command-options was omitted, it would be a list of FileInfo objects. Options are provided space-delimited, e.g. command-options="-1 -dirs -links".

14.6 FTP Session Caching

Starting with Spring Integration version 3.0, sessions are no longer cached by default; the cache-sessions attribute is no longer supported on endpoints. You must use a CachingSessionFactory (see below) if you wish to cache sessions.

In versions prior to 3.0, the sessions were cached automatically by default. A cache-sessions attribute was available for disabling the auto caching, but that solution did not provide a way to configure other session caching attributes. For example, you could not limit on the number of sessions created. To support that requirement and other configuration options, a CachingSessionFactory was provided. It provides sessionCacheSize and sessionWaitTimeout properties. As its name suggests, the sessionCacheSize property controls how many active sessions the factory will maintain in its cache (the DEFAULT is unbounded). If the sessionCacheSize threshold has been reached, any attempt to acquire another session will block until either one of the cached sessions becomes available or until the wait time for a Session expires (the DEFAULT wait time is Integer.MAX_VALUE). The sessionWaitTimeout property enables configuration of that value.

If you want your Sessions to be cached, simply configure your default Session Factory as described above and then wrap it in an instance of CachingSessionFactory where you may provide those additional properties.

<bean id="ftpSessionFactory" class="o.s.i.ftp.session.DefaultFtpSessionFactory">
    <property name="host" value="localhost"/>

<bean id="cachingSessionFactory" class="o.s.i.file.remote.session.CachingSessionFactory">
    <constructor-arg ref="ftpSessionFactory"/>
    <constructor-arg value="10"/>
    <property name="sessionWaitTimeout" value="1000"/>

In the above example you see a CachingSessionFactory created with the sessionCacheSize set to 10 and the sessionWaitTimeout set to 1 second (its value is in millliseconds).

Starting with Spring Integration version 3.0, the CachingConnectionFactory provides a resetCache() method. When invoked, all idle sessions are immediately closed and in-use sessions are closed when they are returned to the cache. New requests for sessions will establish new sessions as necessary.

14.7 RemoteFileTemplate

Starting with Spring Integration version 3.0 a new abstraction is provided over the FtpSession object. The template provides methods to send, retrieve (as an InputStream), remove, and rename files. In addition an execute method is provided allowing the caller to execute multiple operations on the session. In all cases, the template takes care of reliably closing the session. For more information, refer to the javadocs for RemoteFileTemplate.

15. GemFire Support

Spring Integration provides support for VMWare vFabric GemFire

15.1 Introduction

VMWare vFabric GemFire (GemFire) is a distributed data management platform providing a key-value data grid along with advanced distributed system features such as event processing, continuous querying, and remote function execution. This guide assumes some familiarity with GemFire and its API.

Spring integration provides support for GemFire by providing inbound adapters for entry and continuous query events, an outbound adapter to write entries to the cache, and MessageStore and MessageGroupStore implementations. Spring integration leverages the Spring Gemfire project, providing a thin wrapper over its components.

To configure the 'int-gfe' namespace, include the following elements within the headers of your XML configuration file:


15.2 Inbound Channel Adapter

The inbound-channel-adapter produces messages on a channel triggered by a GemFire EntryEvent. GemFire generates events whenever an entry is CREATED, UPDATED, DESTROYED, or INVALIDATED in the associated region. The inbound channel adapter allows you to filter on a subset of these events. For example, you may want to only produce messages in response to an entry being CREATED. In addition, the inbound channel adapter can evaluate a SpEL expression if, for example, you want your message payload to contain an event property such as the new entry value.

<gfe:replicated-region id="region"/>
<int-gfe:inbound-channel-adapter id="inputChannel" region="region"
    cache-events="CREATED" expression="newValue"/>

In the above configuration, we are creating a GemFire Cache and Region using Spring GemFire's 'gfe' namespace. The inbound-channel-adapter requires a reference to the GemFire region for which the adapter will be listening for events. Optional attributes include cache-events which can contain a comma separated list of event types for which a message will be produced on the input channel. By default CREATED and UPDATED are enabled. Note that this adapter conforms to Spring integration conventions. If no channel attribute is provided, the channel will be created from the id attribute. This adapter also supports an error-channel. If expression is not provided the message payload will be a GemFire EntryEvent

15.3 Continuous Query Inbound Channel Adapter

The cq-inbound-channel-adapter produces messages a channel triggered by a GemFire continuous query or CqEvent event. Spring GemFire introduced continuous query support in release 1.1, including a ContinuousQueryListenerContainer which provides a nice abstraction over the GemFire native API. This adapter requires a reference to a ContinuousQueryListenerContainer, and creates a listener for a given query and executes the query. The continuous query acts as an event source that will fire whenever its result set changes state.

GemFire queries are written in OQL and are scoped to the entire cache (not just one region). Additionally, continuous queries require a remote (i.e., running in a separate process or remote host) cache server. Please consult the GemFire documentation for more information on implementing continuous queries.

<gfe:client-cache id="client-cache" pool-name="client-pool"/>

<gfe:pool id="client-pool" subscription-enabled="true" >
    <!--configure server or locator here required to address the cache server -->

<gfe:client-region id="test" cache-ref="client-cache" pool-name="client-pool"/>

<gfe:cq-listener-container id="queryListenerContainer" cache="client-cache"

<int-gfe:cq-inbound-channel-adapter id="inputChannel"
    query="select * from /test"/>

In the above configuration, we are creating a GemFire client cache (recall a remote cache server is required for this implementation and its address is configured as a sub-element of the pool), a client region and a ContinuousQueryListenerContainer using Spring GemFire. The continuous query inbound channel adapter requires a cq-listener-container attribute which contains a reference to the ContinuousQueryListenerContainer. Optionally, it accepts an expression attribute which uses SpEL to transform the CqEvent or extract an individual property as needed. The cq-inbound-channel-adapter provides a query-events attribute, containing a comma separated list of event types for which a message will be produced on the input channel. Available event types are CREATED, UPDATED, DESTROYED, REGION_DESTROYED, REGION_INVALIDATED. CREATED and UPDATED are enabled by default. Additional optional attributes include, query-name which provides an optional query name, and expression which works as described in the above section, and durable - a boolean value indicating if the query is durable (false by default). Note that this adapter conforms to Spring integration conventions. If no channel attribute is provided, the channel will be created from the id attribute. This adapter also supports an error-channel

15.4 Outbound Channel Adapter

The outbound-channel-adapter writes cache entries mapped from the message payload. In its simplest form, it expects a payload of type java.util.Map and puts the map entries into its configured region.

<int-gfe:outbound-channel-adapter id="cacheChannel" region="region"/>

Given the above configuration, an exception will be thrown if the payload is not a Map. Additionally, the outbound channel adapter can be configured to create a map of cache entries using SpEL of course.

<int-gfe:outbound-channel-adapter id="cacheChannel" region="region">
        <entry key="payload.toUpperCase()" value="payload.toLowerCase()"/>
        <entry key="'foo'" value="'bar'"/>

In the above configuration, the inner element cache-entries is semantically equivalent to Spring 'map' element. The adapter interprets the key and value attributes as SpEL expressions with the message as the evaluation context. Note that this contain arbitrary cache entries (not only those derived from the message) and that literal values must be enclosed in single quotes. In the above example, if the message sent to cacheChannel has a String payload with a value "Hello", two entries [HELLO:hello, foo:bar] will be written (created or updated) in the cache region. This adapter also supports the order attribute which may be useful if it is bound to a PublishSubscribeChannel.

15.5 Gemfire Message Store

As described in EIP, a Message Store allows you to persist Messages. This can be very useful when dealing with components that have a capability to buffer messages (QueueChannel, Aggregator, Resequencer, etc.) if reliability is a concern. In Spring Integration, the MessageStore strategy also provides the foundation for the ClaimCheck pattern, which is described in EIP as well.

Spring Integration's Gemfire module provides the GemfireMessageStore which is an implementation of both the the MessageStore strategy (mainly used by the QueueChannel and ClaimCheck patterns) and the MessageGroupStore strategy (mainly used by the Aggregator and Resequencer patterns).

<bean id="gemfireMessageStore" class="o.s.i.gemfire.store.GemfireMessageStore">
    <constructor-arg ref="myCache"/>

<bean id="myCache" class="org.springframework.data.gemfire.CacheFactoryBean"/>

<int:channel id="somePersistentQueueChannel">
    <int:queue message-store="gemfireMessageStore"/>

<int:aggregator input-channel="inputChannel" output-channel="outputChannel"

Above is a sample GemfireMessageStore configuration that shows its usage by a QueueChannel and an Aggregator. As you can see it is a normal Spring bean configuration. The simplest configuration requires a reference to a GemFireCache (created by CacheFactoryBean) as a constructor argument. If the cache is standalone, i.e., embedded in the same JVM, the MessageStore will create a message store region named "messageStoreRegion". If your application requires customization of the messageStore region, for example, multiple Gemfire message stores each with its own region, you can configure a region for each message store instance and use the Region as the constructor argument:

<bean id="gemfireMessageStore" class="o.s.i.gemfire.store.GemfireMessageStore">
    <constructor-arg ref="myRegion"/>


<gfe:replicated-region id="myRegion"/>

In the above examle, the cache and region are configured using the spring-gemfire namespace (not to be confused with the spring-integration-gemfire namespace). Often it is desirable for the message store to be maintained in one or more remote cache servers in a client-server configuration (See the GemFire product documentation for more details). In this case, you configure a client cache, client region, and client pool and inject the region into the MessageStore. Here is an example:

<bean id="gemfireMessageStore"
    <constructor-arg ref="myRegion"/>


<gfe:client-region id="myRegion" shortcut="PROXY" pool-name="messageStorePool"/>

<gfe:pool id="messageStorePool">
    <gfe:server host="localhost" port="40404" />

Note the pool element is configured with the address of a cache server (a locator may be substituted here). The region is configured as a 'PROXY' so that no data will be stored locally. The region's id corresponds to a region with the same name configured in the cache server.

16. HTTP Support

16.1 Introduction

The HTTP support allows for the execution of HTTP requests and the processing of inbound HTTP requests. Because interaction over HTTP is always synchronous, even if all that is returned is a 200 status code, the HTTP support consists of two gateway implementations: HttpInboundEndpoint and HttpRequestExecutingMessageHandler.

16.2 Http Inbound Gateway

To receive messages over HTTP, you need to use an HTTP Inbound Channel Adapter or Gateway. To support the HTTP Inbound Adapters, they need to be deployed within a servlet container such as Apache Tomcat or Jetty. The easiest way to do this is to use Spring's HttpRequestHandlerServlet, by providing the following servlet definition in the web.xml file:


Notice that the servlet name matches the bean name. For more information on using the HttpRequestHandlerServlet, see chapter "Remoting and web services using Spring", which is part of the Spring Framework Reference documentation.

If you are running within a Spring MVC application, then the aforementioned explicit servlet definition is not necessary. In that case, the bean name for your gateway can be matched against the URL path just like a Spring MVC Controller bean. For more information, please see the chapter "Web MVC framework", which is part of the Spring Framework Reference documentation.

For a sample application and the corresponding configuration, please see the Spring Integration Samples repository. It contains the Http Sample application demonstrating Spring Integration's HTTP support.

Below is an example bean definition for a simple HTTP inbound endpoint.

<bean id="httpInbound"
  <property name="requestChannel" ref="httpRequestChannel" />
  <property name="replyChannel" ref="httpReplyChannel" />

The HttpRequestHandlingMessagingGateway accepts a list of HttpMessageConverter instances or else relies on a default list. The converters allow customization of the mapping from HttpServletRequest to Message. The default converters encapsulate simple strategies, which for example will create a String message for a POST request where the content type starts with "text", see the Javadoc for full details. An additional flag (mergeWithDefaultConverters) can be set along with the list of custom HttpMessageConverter to add the default converters after the custom converters. By default this flag is set to false, meaning that the custom converters replace the default list.

Starting with Spring Integration 2.0, MultiPart File support is implemented. If the request has been wrapped as a MultipartHttpServletRequest, when using the default converters, that request will be converted to a Message payload that is a MultiValueMap containing values that may be byte arrays, Strings, or instances of Spring's MultipartFile depending on the content type of the individual parts.

The HTTP inbound Endpoint will locate a MultipartResolver in the context if one exists with the bean name "multipartResolver" (the same name expected by Spring's DispatcherServlet). If it does in fact locate that bean, then the support for MultipartFiles will be enabled on the inbound request mapper. Otherwise, it will fail when trying to map a multipart-file request to a Spring Integration Message. For more on Spring's support for MultipartResolvers, refer to the Spring Reference Manual.

In sending a response to the client there are a number of ways to customize the behavior of the gateway. By default the gateway will simply acknowledge that the request was received by sending a 200 status code back. It is possible to customize this response by providing a 'viewName' to be resolved by the Spring MVC ViewResolver. In the case that the gateway should expect a reply to the Message then setting the expectReply flag (constructor argument) will cause the gateway to wait for a reply Message before creating an HTTP response. Below is an example of a gateway configured to serve as a Spring MVC Controller with a view name. Because of the constructor arg value of TRUE, it wait for a reply. This also shows how to customize the HTTP methods accepted by the gateway, which are POST and GET by default.

<bean id="httpInbound"
  <constructor-arg value="true" /> <!-- indicates that a reply is expected -->
  <property name="requestChannel" ref="httpRequestChannel" />
  <property name="replyChannel" ref="httpReplyChannel" />
  <property name="viewName" value="jsonView" />
  <property name="supportedMethodNames" >

The reply message will be available in the Model map. The key that is used for that map entry by default is 'reply', but this can be overridden by setting the 'replyKey' property on the endpoint's configuration.

16.3 Http Outbound Gateway

To configure the HttpRequestExecutingMessageHandler write a bean definition like this:

<bean id="httpOutbound"
  <constructor-arg value="http://localhost:8080/example" />
  <property name="outputChannel" ref="responseChannel" />

This bean definition will execute HTTP requests by delegating to a RestTemplate. That template in turn delegates to a list of HttpMessageConverters to generate the HTTP request body from the Message payload. You can configure those converters as well as the ClientHttpRequestFactory instance to use:

<bean id="httpOutbound"
  <constructor-arg value="http://localhost:8080/example" />
  <property name="outputChannel" ref="responseChannel" />
  <property name="messageConverters" ref="messageConverterList" />
  <property name="requestFactory" ref="customRequestFactory" />

By default the HTTP request will be generated using an instance of SimpleClientHttpRequestFactory which uses the JDK HttpURLConnection. Use of the Apache Commons HTTP Client is also supported through the provided CommonsClientHttpRequestFactory which can be injected as shown above.

In the case of the Outbound Gateway, the reply message produced by the gateway will contain all Message Headers present in the request message.


Basic cookie support is provided by the transfer-cookies attribute on the outbound gateway. When set to true (default is false), a Set-Cookie header received from the server in a response will be converted to Cookie in the reply message. This header will then be used on subsequent sends. This enables simple stateful interactions, such as...


If transfer-cookies is false, any Set-Cookie header received will remain as Set-Cookie in the reply message, and will be dropped on subsequent sends.

[Note]Note: Empty Repsonse Bodies
HTTP is a request/response protocol. However the response may not have a body, just headers. In this case, the HttpRequestExecutingMessageHandler produces a reply Message with the payload being an org.springframework.http.HttpEntity, regardless of any provided expected-response-type. According to the HTTP RFC Status Code Definitions, there are many statuses which identify that a response MUST NOT contain a message-body (e.g. 204 No Content). There are also cases where calls to the same URL might, or might not, return a response body; for example, the first request to an HTTP resource returns content, but the second does not (e.g. 304 Not Modified). In all cases, however, the http_statusCode message header is populated. This can be used in some routing logic after the Http Outbound Gateway. You could also use a <payload-type-router/> to route messages with an HttpEntity to a different flow than that used for responses with a body.

16.4 HTTP Namespace Support

Spring Integration provides an http namespace and the corresponding schema definition. To include it in your configuration, simply provide the following namespace declaration in your application context configuration file:

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"


The XML Namespace provides two components for handling HTTP Inbound requests. In order to process requests without returning a dedicated response, use the inbound-channel-adapter:

<int-http:inbound-channel-adapter id="httpChannelAdapter" channel="requests"
    supported-methods="PUT, DELETE"/>

To process requests that do expect a response, use an inbound-gateway:

<int-http:inbound-gateway id="inboundGateway"

Request Mapping support

Spring Integration 3.0 is improving the REST support by introducing the IntegrationRequestMappingHandlerMapping. The implementation relies on the enhanced REST support provided by Spring Framework 3.1 or higher.

The parsing of the HTTP Inbound Gateway or the HTTP Inbound Channel Adapter registers an integrationRequestMappingHandlerMapping bean of type IntegrationRequestMappingHandlerMapping, in case there is none registered, yet. This particular implementation of the HandlerMapping delegates its logic to the RequestMappingInfoHandlerMapping. The implementation provides similar functionality as the one provided by the org.springframework.web.bind.annotation.RequestMapping annotation in Spring MVC.

For more information, please see Mapping Requests With @RequestMapping.

For this purpose, Spring Integration 3.0 introduces the <request-mapping> sub-element. This optional sub-element can be added to the <http:inbound-channel-adapter> and the <http:inbound-gateway>. It works in conjunction with the path and supported-methods attributes:

<inbound-gateway id="inboundController"
   <request-mapping headers="User-Agent"

Based on this configuration, the namespace parser creates an instance of the IntegrationRequestMappingHandlerMapping (if none exists, yet), a HttpRequestHandlingController bean and associated with it an instance of RequestMapping, which in turn, is converted to the Spring MVC RequestMappingInfo.

The <request-mapping> sub-element provides the following attributes:

  • headers
  • params
  • consumes
  • produces

With the path and supported-methods attributes of the <http:inbound-channel-adapter> or the <http:inbound-gateway>, <request-mapping> attributes translate directly into the respective options provided by the org.springframework.web.bind.annotation.RequestMapping annotation in Spring MVC.

The <request-mapping> sub-element allows you to configure several Spring Integration HTTP Inbound Endpoints to the same path (or even the same supported-methods) and to provide different downstream message flows based on incoming HTTP requests.

Alternatively, you can also declare just one HTTP Inbound Endpoint and apply routing and filtering logic within the Spring Integration flow to achieve the same result. This allows you to get the Message into the flow as early as possibly, e.g.:

<int-http:inbound-gateway request-channel="httpMethodRouter"

<int:router input-channel="httpMethodRouter" expression="headers.http_requestMethod">
    <int:mapping value="GET" channel="in1"/>
    <int:mapping value="DELETE" channel="in2"/>

<int:service-activator input-channel="in1" ref="service" method="getEntity"/>

<int:service-activator input-channel="in2" ref="service" method="delete"/>

For more information regarding Handler Mappings, please see:

URI Template Variables and Expressions

By Using the path attribute in conjunction with the payload-expression attribute as well as the header sub-element, you have a high degree of flexibility for mapping inbound request data.

In the following example configuration, an Inbound Channel Adapter is configured to accept requests using the following URI: /first-name/{firstName}/last-name/{lastName}

Using the payload-expression attribute, the URI template variable {firstName} is mapped to be the Message payload, while the {lastName} URI template variable will map to the lname Message header.

<int-http:inbound-channel-adapter id="inboundAdapterWithExpressions"
    <int-http:header name="lname" expression="#pathVariables.lastName"/>

For more information about URI template variables, please see the Spring Reference Manual:

Since Spring Integration 3.0, in addition to the existing #pathVariables and #requestParams variables being available in payload and header expressions, other useful variables have been added.

The entire list of available expression variables:

  • #requestParams - the MultiValueMap from the ServletRequest parameterMap.
  • #pathVariables - the Map from URI Template placeholders and their values;
  • #matrixVariables - the Map of MultiValueMap according to Spring MVC Specification. Note, #matrixVariables require Spring MVC 3.2 or higher;
  • #requestAttributes - the org.springframework.web.context.request.RequestAttributes associated with the current Request;
  • #requestHeaders - the org.springframework.http.HttpHeaders object from the current Request;
  • #cookies - the Map<String, Cookie> of javax.servlet.http.Cookies from the current Request.

Note, all these values (and others) can be accessed within expressions in the downstream message flow via the ThreadLocal org.springframework.web.context.request.RequestAttributes variable, if that message flow is single-threaded and lives within the request thread:



To configure the outbound gateway you can use the namespace support as well. The following code snippet shows the different configuration options for an outbound Http gateway. Most importantly, notice that the 'http-method' and 'expected-response-type' are provided. Those are two of the most commonly configured values. The default http-method is POST, and the default response type is null. With a null response type, the payload of the reply Message would contain the ResponseEntity as long as it's http status is a success (non-successful status codes will throw Exceptions). If you are expecting a different type, such as a String, then provide that fully-qualified class name as shown below. See also the note about empty response bodies in Section 16.3, “Http Outbound Gateway”.

Beginning with Spring Integration 2.1 the request-timeout attribute of the HTTP Outbound Gateway was renamed to reply-timeout to better reflect the intent.
<int-http:outbound-gateway id="example"

Since Spring Integration 2.2, Java serialization over HTTP is no longer enabled by default. Previously, when setting the expected-response-type attribute to a Serializable object, the Accept header was not properly set up. Since Spring Integration 2.2, the SerializingHttpMessageConverter has now been updated to set the Accept header to application/x-java-serialized-object.

However, because this could cause incompatibility with existing applications, it was decided to no longer automatically add this converter to the HTTP endpoints. If you wish to use Java serialization, you will need to add the SerializingHttpMessageConverter to the appropriate endpoints, using the message-converters attribute, when using XML configuration, or using the setMessageConverters() method. Alternatively, you may wish to consider using JSON instead which is enabled by simply having Jackson on the classpath.

Beginning with Spring Integration 2.2 you can also determine the HTTP Method dynamically using SpEL and the http-method-expression attribute. Note that this attribute is obviously murually exclusive with http-method You can also use expected-response-type-expression attribute instead of expected-response-type and provide any valid SpEL expression that determines the type of the response.

<int-http:outbound-gateway id="example"

If your outbound adapter is to be used in a unidirectional way, then you can use an outbound-channel-adapter instead. This means that a successful response will simply execute without sending any Messages to a reply channel. In the case of any non-successful response status code, it will throw an exception. The configuration looks very similar to the gateway:

<int-http:outbound-channel-adapter id="example"


To specify the URL; you can use either the 'url' attribute or the 'url-expression' attribute. The 'url' is a simple string (with placedholders for URI variables, as described below); the 'url-expression' is a SpEL expression, with the Message as the root object, enabling dynamic urls. The url resulting from the expression evaluation can still have placeholders for URI variables.

In previous releases, some users used the place holders to replace the entire URL with a URI variable. Changes in Spring 3.1 can cause some issues with escaped characters, such as '?'. For this reason, it is recommended that if you wish to generate the URL entirely at runtime, you use the 'url-expression' attribute.

Mapping URI Variables

If your URL contains URI variables, you can map them using the uri-variable sub-element. This sub-element is available for the Http Outbound Gateway and the Http Outbound Channel Adapter.

<int-http:outbound-gateway id="trafficGateway"
    <int-http:uri-variable name="zipCode" expression="payload.getZip()"/>

The uri-variable sub-element defines two attributes: name and expression. The name attribute identifies the name of the URI variable, while the expression attribute is used to set the actual value. Using the expression attribute, you can leverage the full power of the Spring Expression Language (SpEL) which gives you full dynamic access to the message payload and the message headers. For example, in the above configuration the getZip() method will be invoked on the payload object of the Message and the result of that method will be used as the value for the URI variable named 'zipCode'.

Since Spring Integration 3.0, HTTP Outbound Endpoints support the uri-variables-expression attribute to specify an Expression which should be evaluated, resulting in a Map for all URI variable placeholders within the URL template. It provides a mechanism whereby different variable expressions can be used, based on the outbound message. This attribute is mutually exclusive with the <uri-variable/> sub-element:


where uriVariablesBean might be:

public class UriVariablesBean {
	private static final ExpressionParser EXPRESSION_PARSER = new SpelExpressionParser();

	public Map<String, ?> populate(Object payload) {
		Map<String, Object> variables = new HashMap<String, Object>();
		if (payload instanceOf String.class)) {
			variables.put("foo", "foo"));
		else {
			variables.put("foo", EXPRESSION_PARSER.parseExpression("headers.bar"));
		return variables;


The uri-variables-expression must evaluate to a Map. The values of the Map must be instances of String or Expression. This Map is provided to an ExpressionEvalMap for further resolution of URI variable placeholders using those expressions in the context of the outbound Message.

Controlling URI Encoding

By default, the URL string is encoded (see UriComponentsBuilder) to the URI object before sending the request. In some scenarios with a non-standard URI (e.g. the RabbitMQ Rest API) it is undesirable to perform the encoding. The <http:outbound-gateway/> and <http:outbound-channel-adapter/> provide an encode-uri attribute. To disable encoding the URL, this attribute should be set to false (by default it is true). If you wish to partially encode some of the URL, this can be achieved using an expression within a <uri-variable/>:

<http:outbound-gateway url="http://somehost/%2f/fooApps?bar={param}" encode-uri="false">
          <http:uri-variable name="param"
                                             .encodeWithinQuery('Hellow World!')"/>

16.5 Timeout Handling

In the context of HTTP components, there are two timing areas that have to be considered.

  • Timeouts when interacting with Spring Integration Channels
  • Timeouts when interacting with a remote HTTP server

First, the components interact with Message Channels, for which timeouts can be specified. For example, an HTTP Inbound Gateway will forward messages received from connected HTTP Clients to a Message Channel (Request Timeout) and consequently the HTTP Inbound Gateway will receive a reply Message from the Reply Channel (Reply Timeout) that will be used to generate the HTTP Response. Please see the figure below for an illustration.

How timeout settings apply to an HTTP Inbound Gateway

For outbound endpoints, the second thing to consider is timing while interacting with the remote server.

How timeout settings apply to an HTTP Outbound Gateway

You may want to configure the HTTP related timeout behavior, when making active HTTP requests using the HTTP Oubound Gateway or the HTTP Outbound Channel Adapter. In those instances, these two components use Spring's RestTemplate support to execute HTTP requests.

In order to configure timeouts for the HTTP Oubound Gateway and the HTTP Outbound Channel Adapter, you can either reference a RestTemplate bean directly, using the rest-template attribute, or you can provide a reference to a ClientHttpRequestFactory bean using the request-factory attribute. Spring provides the following implementations of the ClientHttpRequestFactory interface:

SimpleClientHttpRequestFactory - Uses standard J2SE facilities for making HTTP Requests

HttpComponentsClientHttpRequestFactory - Uses Apache HttpComponents HttpClient (Since Spring 3.1)

ClientHttpRequestFactory - Uses Jakarta Commons HttpClient (Deprecated as of Spring 3.1)

If you don't explicitly configure the request-factory or rest-template attribute respectively, then a default RestTemplate which uses a SimpleClientHttpRequestFactory will be instantiated.


With some JVM implementations, the handling of timeouts using the URLConnection class may not be consistent.

E.g. from the Java™ Platform, Standard Edition 6 API Specification on setConnectTimeout: Some non-standard implmentation of this method may ignore the specified timeout. To see the connect timeout set, please call getConnectTimeout().

Please test your timeouts if you have specific needs. Consider using the HttpComponentsClientHttpRequestFactory which, in turn, uses Apache HttpComponents HttpClient instead.

When using the Apache HttpComponents HttpClient with a Pooling Connection Manager, be aware that, by default, the connection manager will create no more than 2 concurrent connections per given route and no more than 20 connections in total. For many real-world applications these limits may prove too constraining. Refer to the Apache documentation (link above) for information about configuring this important component.

Here is an example of how to configure an HTTP Outbound Gateway using a SimpleClientHttpRequestFactory, configured with connect and read timeouts of 5 seconds respectively:

<int-http:outbound-gateway url="http://www.google.com/ig/api?weather={city}"
    <int-http:uri-variable name="city" expression="payload"/>

<bean id="requestFactory"
    <property name="connectTimeout" value="5000"/>
    <property name="readTimeout"    value="5000"/>

HTTP Outbound Gateway

For the HTTP Outbound Gateway, the XML Schema defines only the reply-timeout. The reply-timeout maps to the sendTimeout property of the org.springframework.integration.http.outbound.HttpRequestExecutingMessageHandler class. More precisely, the property is set on the extended AbstractReplyProducingMessageHandler class, which ultimatelly sets the property on the MessagingTemplate.

The value of the sendTimeout property defaults to "-1" and will be applied to the connected MessageChannel. This means, that depending on the implementation, the Message Channel's send method may block indefinitely. Furthermore, the sendTimeout property is only used, when the actual MessageChannel implementation has a blocking send (such as 'full' bounded QueueChannel).

HTTP Inbound Gateway

For the HTTP Inbound Gateway, the XML Schema defines the request-timeout attribute, which will be used to set the requestTimeout property on the HttpRequestHandlingMessagingGateway class (on the extended MessagingGatewaySupport class). Secondly, the reply-timeout attribute exists and it maps to the replyTimeout property on the same class.

The default for both timeout properties is "1000ms". Ultimately, the request-timeout property will be used to set the sendTimeout on the used MessagingTemplate instance. The replyTimeout property on the other hand, will be used to set the receiveTimeout property on the used MessagingTemplate instance.

In order to simulate connection timeouts, connect to a non-routable IP address, for example

16.6 HTTP Proxy configuration

If you are behind a proxy and need to configure proxy settings for HTTP outbound adapters and/or gateways, you can apply one of two approaches. In most cases, you can rely on the standard Java System Properties that control the proxy settings. Otherwise, you can explicitly configure a Spring bean for the HTTP client request factory instance.

Standard Java Proxy configuration

There are 3 System Properties you can set to configure the proxy settings that will be used by the HTTP protocol handler:

  • http.proxyHost - the host name of the proxy server.

  • http.proxyPort - the port number, the default value being 80.

  • http.nonProxyHosts - a list of hosts that should be reached directly, bypassing the proxy. This is a list of patterns separated by '|'. The patterns may start or end with a '*' for wildcards. Any host matching one of these patterns will be reached through a direct connection instead of through a proxy.

And for HTTPS:

  • https.proxyHost - the host name of the proxy server.

  • https.proxyPort - the port number, the default value being 80.

For more information please refer to this document: http://download.oracle.com/javase/6/docs/technotes/guides/net/proxies.html

Spring's SimpleClientHttpRequestFactory

If for any reason, you need more explicit control over the proxy configuration, you can use Spring's SimpleClientHttpRequestFactory and configure its 'proxy' property as such:

<bean id="requestFactory"
    <property name="proxy">
        <bean id="proxy" class="java.net.Proxy">
                <util:constant static-field="java.net.Proxy.Type.HTTP"/>
                <bean class="java.net.InetSocketAddress">
                    <constructor-arg value=""/>
                    <constructor-arg value="8080"/>

16.7  HTTP Header Mappings

Spring Integration provides support for Http Header mapping for both HTTP Request and HTTP Responses.

By default all standard Http Headers as defined here http://en.wikipedia.org/wiki/List_of_HTTP_header_fields will be mapped from the message to HTTP request/response headers without further configuration. However if you do need further customization you may provide additional configuration via convenient namespace support. You can provide a comma-separated list of header names, and you can also include simple patterns with the '*' character acting as a wildcard. If you do provide such values, it will override the default behavior. Basically, it assumes you are in complete control at that point. However, if you do want to include all of the standard HTTP headers, you can use the shortcut patterns: HTTP_REQUEST_HEADERS and HTTP_RESPONSE_HEADERS. Here are some examples:

<int-http:outbound-gateway id="httpGateway"
    mapped-request-headers="foo, bar"
    mapped-response-headers="X-*, HTTP_RESPONSE_HEADERS"

<int-http:outbound-channel-adapter id="httpAdapter"
    mapped-request-headers="foo, bar, HTTP_REQUEST_HEADERS"

The adapters and gateways will use the DefaultHttpHeaderMapper which now provides two static factory methods for "inbound" and "outbound" adapters so that the proper direction can be applied (mapping HTTP requests/responses IN/OUT as appropriate).

If further customization is required you can also configure a DefaultHttpHeaderMapper independently and inject it into the adapter via the header-mapper attribute.

<int-http:outbound-gateway id="httpGateway"

<bean id="headerMapper" class="o.s.i.http.support.DefaultHttpHeaderMapper">
    <property name="inboundHeaderNames" value="foo*, *bar, baz"/>
    <property name="outboundHeaderNames" value="a*b, d"/>

Of course, you can even implement the HeaderMapper strategy interface directly and provide a reference to that if you need to do something other than what the DefaultHttpHeaderMapper supports.

16.8 HTTP Samples

16.8.1 Multipart HTTP request - RestTemplate (client) and Http Inbound Gateway (server)

This example demonstrates how simple it is to send a Multipart HTTP request via Spring's RestTemplate and receive it with a Spring Integration HTTP Inbound Adapter. All we are doing is creating a MultiValueMap and populating it with multi-part data. The RestTemplate will take care of the rest (no pun intended) by converting it to a MultipartHttpServletRequest . This particular client will send a multipart HTTP Request which contains the name of the company as well as an image file with the company logo.

RestTemplate template = new RestTemplate();
String uri = "http://localhost:8080/multipart-http/inboundAdapter.htm";
Resource s2logo = 
   new ClassPathResource("org/springframework/samples/multipart/spring09_logo.png");
MultiValueMap map = new LinkedMultiValueMap();
map.add("company-logo", s2logo);
HttpHeaders headers = new HttpHeaders();
headers.setContentType(new MediaType("multipart""form-data"));
HttpEntity request = new HttpEntity(map, headers);
ResponseEntity<?> httpResponse = template.exchange(uri, HttpMethod.POST, request, null);

That is all for the client.

On the server side we have the following configuration:

<int-http:inbound-channel-adapter id="httpInboundAdapter"
    supported-methods="GET, POST"/>

<int:channel id="receiveChannel"/>

<int:service-activator input-channel="receiveChannel">
    <bean class="org.springframework.integration.samples.multipart.MultipartReceiver"/>

<bean id="multipartResolver"

The 'httpInboundAdapter' will receive the request, convert it to a Message with a payload that is a LinkedMultiValueMap. We then are parsing that in the 'multipartReceiver' service-activator;

public void receive(LinkedMultiValueMap<String, Object> multipartRequest){
    System.out.println("### Successfully received multipart request ###");
    for (String elementName : multipartRequest.keySet()) {
        if (elementName.equals("company")){
            System.out.println("\t" + elementName + " - " +
                ((String[]) multipartRequest.getFirst("company"))[0]);
        else if (elementName.equals("company-logo")){
            System.out.println("\t" + elementName + " - as UploadedMultipartFile: " +
                ((UploadedMultipartFile) multipartRequest

You should see the following output:

### Successfully received multipart request ###
   company - SpringSource
   company-logo - as UploadedMultipartFile: spring09_logo.png

17. JDBC Support

Spring Integration provides Channel Adapters for receiving and sending messages via database queries. Through those adapters Spring Integration supports not only plain JDBC SQL Queries, but also Stored Procedure and Stored Function calls.

The following JDBC components are available by default:

Furthermore, the Spring Integration JDBC Module also provides a JDBC Message Store

17.1 Inbound Channel Adapter

The main function of an inbound Channel Adapter is to execute a SQL SELECT query and turn the result set as a message. The message payload is the whole result set, expressed as a List, and the types of the items in the list depend on the row-mapping strategy that is used. The default strategy is a generic mapper that just returns a Map for each row in the query result. Optionally, this can be changed by adding a reference to a RowMapper instance (see the Spring JDBC documentation for more detailed information about row mapping).

If you want to convert rows in the SELECT query result to individual messages you can use a downstream splitter.

The inbound adapter also requires a reference to either a JdbcTemplate instance or a DataSource.

As well as the SELECT statement to generate the messages, the adapter above also has an UPDATE statement that is being used to mark the records as processed so that they don't show up in the next poll. The update can be parameterized by the list of ids from the original select. This is done through a naming convention by default (a column in the input result set called "id" is translated into a list in the parameter map for the update called "id"). The following example defines an inbound Ch