This section describes how to capture metrics for Spring Integration. In recent versions, we have relied more on Micrometer (see https://micrometer.io), and we plan to use Micrometer even more in future releases.

The key benefit of a messaging architecture is loose coupling such that participating components do not maintain any awareness about one another. This fact alone makes an application extremely flexible, letting you change components without affecting the rest of the flow, change messaging routes, change message consuming styles (polling versus event driven), and so on. However, this unassuming style of architecture could prove to be difficult when things go wrong. When debugging, you probably want as much information (its origin, the channels it has traversed, and other details) about the message as you can get.

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 for maintaining 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.

The Enterprise Integration Patterns (EIP) book identifies several patterns that have the ability 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 lets EIP components store messages, typically in some type of persistent store (such as an RDBMS).

Spring Integration provides support for the message store pattern by:

Details on how to configure a specific message store implementation and how to inject a MessageStore implementation into a specific buffering component are described throughout the manual (see the specific component, such as QueueChannel, Aggregator, Delayer, and others). The following pair of examples show how to add a reference to a message store for a QueueChannel and for an aggregator:

By default, messages are stored in-memory by using o.s.i.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 needs 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. The following is a complete list of supported implementations:

Spring Integration 4.0 introduced two new interfaces:

The real behavior depends on the implementation. The framework provides the following implementations, which can be used as a persistent MessageStore for QueueChannel and PriorityChannel:

Many external systems, services, or resources are not transactional (Twitter, RSS, file systems, and so on), and there is not any ability to mark the data as read. Also, sometimes, you may 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 to deal with the next message, Spring Integration provides the metadata store component as an 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 metadata (for example, the 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 a metadataStore ID in the application context. If one is found, use it. Otherwise, create a new instance of SimpleMetadataStore, which is an in-memory implementation that persists only 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, the framework provides the following persistent MetadataStores:

The PropertiesPersistingMetadataStore is backed by a properties file and a PropertiesPersister.

By default, it persists only the state when the application context is closed normally. It implements Flushable so that you can persist the state at will, by invoking flush(). The following example shows how to configure a 'PropertiesPersistingMetadataStore' with XML:

Alternatively, you can provide your own implementation of the MetadataStore interface (for example, JdbcMetadataStore) and configure it as a bean in the application context.

Starting with version 4.0, SimpleMetadataStore, PropertiesPersistingMetadataStore, and RedisMetadataStore implement ConcurrentMetadataStore. These provide for atomic updates and can be used across multiple component or application instances.

As described in the Enterprise Integration Patterns (EIP) book, 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 you can send messages as a means of invoking exposed operations.

The following example shows how to configure a control bus with XML:

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. For example, 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 runs messages on the input channel as Spring Expression Language (SpEL) expressions. It takes a message, compiles the body to an expression, adds some context, and then runs 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 its Pausable extension since version 5.2), 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 or @ManagedOperation annotations. Since those annotations are also used for exposing methods to a JMX MBean registry, they offer a convenient by-product: Often, the same types of operations you want to expose to the control bus are reasonable for exposing through JMX). Resolution of any particular instance within the application context is achieved in the typical SpEL syntax. To do so, 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:

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.

With Java annotations, you can configured the control bus as follows:

Similarly, you can configure Java DSL flow definitions as follows:

If you prefer to use lambdas with automatic DirectChannel creation, you can create a control bus as follows:

In this case, the channel is named controlBus.input.

As described in "MBean Exporter", the MBean exporter provides a JMX operation called stopActiveComponents, which is used to stop the application in an orderly manner. The operation has a single Long parameter. The parameter indicates how long (in milliseconds) the operation waits to allow in-flight messages to complete. The operation works as follows:

As discussed in Orderly Shutdown Managed Operation, this operation can be invoked by using JMX. If you wish to programmatically invoke the method, you 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 has 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, we recommend that you provide the exporter with an id attribute so that you can easily access it in the application context.

Finally, the operation can be invoked by using the <control-bus> element. See the monitoring Spring Integration sample application for details.

Starting with version 4.3, Spring Integration provides access to an application’s runtime object model, which can, optionally, include component metrics. It is exposed as a graph, which may be used to visualize the current state of the integration application. The o.s.i.support.management.graph package contains all the required classes to collect, build, and render the runtime state of Spring Integration components as a single tree-like Graph object. The IntegrationGraphServer should be declared as a bean to build, retrieve, and refresh the Graph object. The resulting Graph object can be serialized to any format, although JSON is flexible and convenient to parse and represent on the client side. A Spring Integration application with only the default components would expose a graph as follows:

In the preceding example, the graph consists of three top-level elements.

The contentDescriptor graph element contains general information about the application providing the data. The name can be customized on the IntegrationGraphServer bean or in the spring.application.name application context environment property. Other properties are provided by the framework and let you distinguish a similar model from other sources.

The links graph element represents connections between nodes from the nodes graph element and, therefore, between integration components in the source Spring Integration application. For example, from a MessageChannel to an EventDrivenConsumer with some MessageHandler or from an AbstractReplyProducingMessageHandler to a MessageChannel. For convenience and to let you determine a link’s purpose, the model includes the type attribute. The possible types are:

The information from this element can be used by a visualization tool to render connections between nodes from the nodes graph element, where the from and to numbers represent the value from the nodeId property of the linked nodes. For example, the link element can be used to determine the proper port on the target node.

The following “text image” shows the relationships between the types:

The nodes graph element is perhaps the most interesting, because its elements contain not only the runtime components with their componentType instances and name values but can also optionally contain metrics exposed by the component. Node elements contain various properties that are generally self-explanatory. For example, expression-based components include the expression property that contains the primary expression string for the component. To enable the metrics, add an @EnableIntegrationManagement to a @Configuration class or add an <int:management/> element to your XML configuration. See Metrics and Management for complete information.

The nodeId represents a unique incremental identifier to let you distinguish one component from another. It is also used in the links element to represent a relationship (connection) of this component to others, if any. The input and output attributes are for the inputChannel and outputChannel properties of the AbstractEndpoint, MessageHandler, SourcePollingChannelAdapter, or MessageProducerSupport. See the next section for more information.

Starting with version 5.1, the IntegrationGraphServer accepts a Function<NamedComponent, Map<String, Object>> additionalPropertiesCallback for population of additional properties on the IntegrationNode for a particular NamedComponent. For example, you can expose the SmartLifecycle autoStartup and running properties into the target graph:

If your application is web-based (or built on top of Spring Boot with an embedded web container) and the Spring Integration HTTP or WebFlux module (see HTTP Support and WebFlux Support, respectively) is present on the classpath, you can use a IntegrationGraphController to expose the IntegrationGraphServer functionality as a REST service. For this purpose, the @EnableIntegrationGraphController and @Configuration class annotations and the <int-http:graph-controller/> XML element are available in the HTTP module. Together with the @EnableWebMvc annotation (or <mvc:annotation-driven/> for XML definitions), this configuration registers an IntegrationGraphController @RestController where its @RequestMapping.path can be configured on the @EnableIntegrationGraphController annotation or <int-http:graph-controller/> element. The default path is /integration.

The IntegrationGraphController @RestController provides the following services:

You can set security and cross-origin restrictions for the IntegrationGraphController with the standard configuration options and components provided by the Spring Security and Spring MVC projects. The following example achieves those goals:

The following example shows how to do the same thing with Java configuration:

Note that, for convenience, the @EnableIntegrationGraphController annotation provides an allowedOrigins attribute. This provides GET access to the path. For more sophistication, you can configure the CORS mappings by using standard Spring MVC mechanisms.