Spring Boot Reference Guide

Authors

Phillip Webb, Dave Syer, Josh Long, Stéphane Nicoll, Rob Winch, Andy Wilkinson, Marcel Overdijk, Christian Dupuis, Sébastien Deleuze, Michael Simons, Vedran Pavić, Jay Bryant, Madhura Bhave

2.0.3.RELEASE

Copies of this document may be made for your own use and for distribution to others, provided that you do not charge any fee for such copies and further provided that each copy contains this Copyright Notice, whether distributed in print or electronically.


Table of Contents

I. Spring Boot Documentation
1. About the Documentation
2. Getting Help
3. First Steps
4. Working with Spring Boot
5. Learning about Spring Boot Features
6. Moving to Production
7. Advanced Topics
II. Getting Started
8. Introducing Spring Boot
9. System Requirements
9.1. Servlet Containers
10. Installing Spring Boot
10.1. Installation Instructions for the Java Developer
10.1.1. Maven Installation
10.1.2. Gradle Installation
10.2. Installing the Spring Boot CLI
10.2.1. Manual Installation
10.2.2. Installation with SDKMAN!
10.2.3. OSX Homebrew Installation
10.2.4. MacPorts Installation
10.2.5. Command-line Completion
10.2.6. Windows Scoop Installation
10.2.7. Quick-start Spring CLI Example
10.3. Upgrading from an Earlier Version of Spring Boot
11. Developing Your First Spring Boot Application
11.1. Creating the POM
11.2. Adding Classpath Dependencies
11.3. Writing the Code
11.3.1. The @RestController and @RequestMapping Annotations
11.3.2. The @EnableAutoConfiguration Annotation
11.3.3. The “main” Method
11.4. Running the Example
11.5. Creating an Executable Jar
12. What to Read Next
III. Using Spring Boot
13. Build Systems
13.1. Dependency Management
13.2. Maven
13.2.1. Inheriting the Starter Parent
13.2.2. Using Spring Boot without the Parent POM
13.2.3. Using the Spring Boot Maven Plugin
13.3. Gradle
13.4. Ant
13.5. Starters
14. Structuring Your Code
14.1. Using the “default” Package
14.2. Locating the Main Application Class
15. Configuration Classes
15.1. Importing Additional Configuration Classes
15.2. Importing XML Configuration
16. Auto-configuration
16.1. Gradually Replacing Auto-configuration
16.2. Disabling Specific Auto-configuration Classes
17. Spring Beans and Dependency Injection
18. Using the @SpringBootApplication Annotation
19. Running Your Application
19.1. Running from an IDE
19.2. Running as a Packaged Application
19.3. Using the Maven Plugin
19.4. Using the Gradle Plugin
19.5. Hot Swapping
20. Developer Tools
20.1. Property Defaults
20.2. Automatic Restart
20.2.1. Logging changes in condition evaluation
20.2.2. Excluding Resources
20.2.3. Watching Additional Paths
20.2.4. Disabling Restart
20.2.5. Using a Trigger File
20.2.6. Customizing the Restart Classloader
20.2.7. Known Limitations
20.3. LiveReload
20.4. Global Settings
20.5. Remote Applications
20.5.1. Running the Remote Client Application
20.5.2. Remote Update
21. Packaging Your Application for Production
22. What to Read Next
IV. Spring Boot features
23. SpringApplication
23.1. Startup Failure
23.2. Customizing the Banner
23.3. Customizing SpringApplication
23.4. Fluent Builder API
23.5. Application Events and Listeners
23.6. Web Environment
23.7. Accessing Application Arguments
23.8. Using the ApplicationRunner or CommandLineRunner
23.9. Application Exit
23.10. Admin Features
24. Externalized Configuration
24.1. Configuring Random Values
24.2. Accessing Command Line Properties
24.3. Application Property Files
24.4. Profile-specific Properties
24.5. Placeholders in Properties
24.6. Using YAML Instead of Properties
24.6.1. Loading YAML
24.6.2. Exposing YAML as Properties in the Spring Environment
24.6.3. Multi-profile YAML Documents
24.6.4. YAML Shortcomings
24.7. Type-safe Configuration Properties
24.7.1. Third-party Configuration
24.7.2. Relaxed Binding
24.7.3. Merging Complex Types
24.7.4. Properties Conversion
Converting durations
24.7.5. @ConfigurationProperties Validation
24.7.6. @ConfigurationProperties vs. @Value
25. Profiles
25.1. Adding Active Profiles
25.2. Programmatically Setting Profiles
25.3. Profile-specific Configuration Files
26. Logging
26.1. Log Format
26.2. Console Output
26.2.1. Color-coded Output
26.3. File Output
26.4. Log Levels
26.5. Custom Log Configuration
26.6. Logback Extensions
26.6.1. Profile-specific Configuration
26.6.2. Environment Properties
27. Developing Web Applications
27.1. The “Spring Web MVC Framework”
27.1.1. Spring MVC Auto-configuration
27.1.2. HttpMessageConverters
27.1.3. Custom JSON Serializers and Deserializers
27.1.4. MessageCodesResolver
27.1.5. Static Content
27.1.6. Welcome Page
27.1.7. Custom Favicon
27.1.8. Path Matching and Content Negotiation
27.1.9. ConfigurableWebBindingInitializer
27.1.10. Template Engines
27.1.11. Error Handling
Custom Error Pages
Mapping Error Pages outside of Spring MVC
27.1.12. Spring HATEOAS
27.1.13. CORS Support
27.2. The “Spring WebFlux Framework”
27.2.1. Spring WebFlux Auto-configuration
27.2.2. HTTP Codecs with HttpMessageReaders and HttpMessageWriters
27.2.3. Static Content
27.2.4. Template Engines
27.2.5. Error Handling
Custom Error Pages
27.2.6. Web Filters
27.3. JAX-RS and Jersey
27.4. Embedded Servlet Container Support
27.4.1. Servlets, Filters, and listeners
Registering Servlets, Filters, and Listeners as Spring Beans
27.4.2. Servlet Context Initialization
Scanning for Servlets, Filters, and listeners
27.4.3. The ServletWebServerApplicationContext
27.4.4. Customizing Embedded Servlet Containers
Programmatic Customization
Customizing ConfigurableServletWebServerFactory Directly
27.4.5. JSP Limitations
28. Security
28.1. MVC Security
28.2. WebFlux Security
28.3. OAuth2
28.3.1. Client
28.3.2. Server
28.4. Actuator Security
28.4.1. Cross Site Request Forgery Protection
29. Working with SQL Databases
29.1. Configure a DataSource
29.1.1. Embedded Database Support
29.1.2. Connection to a Production Database
29.1.3. Connection to a JNDI DataSource
29.2. Using JdbcTemplate
29.3. JPA and “Spring Data”
29.3.1. Entity Classes
29.3.2. Spring Data JPA Repositories
29.3.3. Creating and Dropping JPA Databases
29.3.4. Open EntityManager in View
29.4. Using H2’s Web Console
29.4.1. Changing the H2 Console’s Path
29.5. Using jOOQ
29.5.1. Code Generation
29.5.2. Using DSLContext
29.5.3. jOOQ SQL Dialect
29.5.4. Customizing jOOQ
30. Working with NoSQL Technologies
30.1. Redis
30.1.1. Connecting to Redis
30.2. MongoDB
30.2.1. Connecting to a MongoDB Database
30.2.2. MongoTemplate
30.2.3. Spring Data MongoDB Repositories
30.2.4. Embedded Mongo
30.3. Neo4j
30.3.1. Connecting to a Neo4j Database
30.3.2. Using the Embedded Mode
30.3.3. Neo4jSession
30.3.4. Spring Data Neo4j Repositories
30.3.5. Repository Example
30.4. Gemfire
30.5. Solr
30.5.1. Connecting to Solr
30.5.2. Spring Data Solr Repositories
30.6. Elasticsearch
30.6.1. Connecting to Elasticsearch by Using Jest
30.6.2. Connecting to Elasticsearch by Using Spring Data
30.6.3. Spring Data Elasticsearch Repositories
30.7. Cassandra
30.7.1. Connecting to Cassandra
30.7.2. Spring Data Cassandra Repositories
30.8. Couchbase
30.8.1. Connecting to Couchbase
30.8.2. Spring Data Couchbase Repositories
30.9. LDAP
30.9.1. Connecting to an LDAP Server
30.9.2. Spring Data LDAP Repositories
30.9.3. Embedded In-memory LDAP Server
30.10. InfluxDB
30.10.1. Connecting to InfluxDB
31. Caching
31.1. Supported Cache Providers
31.1.1. Generic
31.1.2. JCache (JSR-107)
31.1.3. EhCache 2.x
31.1.4. Hazelcast
31.1.5. Infinispan
31.1.6. Couchbase
31.1.7. Redis
31.1.8. Caffeine
31.1.9. Simple
31.1.10. None
32. Messaging
32.1. JMS
32.1.1. ActiveMQ Support
32.1.2. Artemis Support
32.1.3. Using a JNDI ConnectionFactory
32.1.4. Sending a Message
32.1.5. Receiving a Message
32.2. AMQP
32.2.1. RabbitMQ support
32.2.2. Sending a Message
32.2.3. Receiving a Message
32.3. Apache Kafka Support
32.3.1. Sending a Message
32.3.2. Receiving a Message
32.3.3. Additional Kafka Properties
33. Calling REST Services with RestTemplate
33.1. RestTemplate Customization
34. Calling REST Services with WebClient
34.1. WebClient Customization
35. Validation
36. Sending Email
37. Distributed Transactions with JTA
37.1. Using an Atomikos Transaction Manager
37.2. Using a Bitronix Transaction Manager
37.3. Using a Narayana Transaction Manager
37.4. Using a Java EE Managed Transaction Manager
37.5. Mixing XA and Non-XA JMS Connections
37.6. Supporting an Alternative Embedded Transaction Manager
38. Hazelcast
39. Quartz Scheduler
40. Spring Integration
41. Spring Session
42. Monitoring and Management over JMX
43. Testing
43.1. Test Scope Dependencies
43.2. Testing Spring Applications
43.3. Testing Spring Boot Applications
43.3.1. Detecting Web Application Type
43.3.2. Detecting Test Configuration
43.3.3. Excluding Test Configuration
43.3.4. Testing with a running server
43.3.5. Using JMX
43.3.6. Mocking and Spying Beans
43.3.7. Auto-configured Tests
43.3.8. Auto-configured JSON Tests
43.3.9. Auto-configured Spring MVC Tests
43.3.10. Auto-configured Spring WebFlux Tests
43.3.11. Auto-configured Data JPA Tests
43.3.12. Auto-configured JDBC Tests
43.3.13. Auto-configured jOOQ Tests
43.3.14. Auto-configured Data MongoDB Tests
43.3.15. Auto-configured Data Neo4j Tests
43.3.16. Auto-configured Data Redis Tests
43.3.17. Auto-configured Data LDAP Tests
43.3.18. Auto-configured REST Clients
43.3.19. Auto-configured Spring REST Docs Tests
Auto-configured Spring REST Docs Tests with Mock MVC
Auto-configured Spring REST Docs Tests with REST Assured
43.3.20. User Configuration and Slicing
43.3.21. Using Spock to Test Spring Boot Applications
43.4. Test Utilities
43.4.1. ConfigFileApplicationContextInitializer
43.4.2. TestPropertyValues
43.4.3. OutputCapture
43.4.4. TestRestTemplate
44. WebSockets
45. Web Services
46. Creating Your Own Auto-configuration
46.1. Understanding Auto-configured Beans
46.2. Locating Auto-configuration Candidates
46.3. Condition Annotations
46.3.1. Class Conditions
46.3.2. Bean Conditions
46.3.3. Property Conditions
46.3.4. Resource Conditions
46.3.5. Web Application Conditions
46.3.6. SpEL Expression Conditions
46.4. Testing your Auto-configuration
46.4.1. Simulating a Web Context
46.4.2. Overriding the Classpath
46.5. Creating Your Own Starter
46.5.1. Naming
46.5.2. autoconfigure Module
46.5.3. Starter Module
47. Kotlin support
47.1. Requirements
47.2. Null-safety
47.3. Kotlin API
47.3.1. runApplication
47.3.2. Extensions
47.4. Dependency management
47.5. @ConfigurationProperties
47.6. Testing
47.7. Resources
47.7.1. Further reading
47.7.2. Examples
48. What to Read Next
V. Spring Boot Actuator: Production-ready features
49. Enabling Production-ready Features
50. Endpoints
50.1. Enabling Endpoints
50.2. Exposing Endpoints
50.3. Securing HTTP Endpoints
50.4. Configuring Endpoints
50.5. Hypermedia for Actuator Web Endpoints
50.6. Actuator Web Endpoint Paths
50.7. CORS Support
50.8. Implementing Custom Endpoints
50.8.1. Receiving Input
Input type conversion
50.8.2. Custom Web Endpoints
Web Endpoint Request Predicates
Path
HTTP method
Consumes
Produces
Web Endpoint Response Status
Web Endpoint Range Requests
Web Endpoint Security
50.8.3. Servlet endpoints
50.8.4. Controller endpoints
50.9. Health Information
50.9.1. Auto-configured HealthIndicators
50.9.2. Writing Custom HealthIndicators
50.9.3. Reactive Health Indicators
50.9.4. Auto-configured ReactiveHealthIndicators
50.10. Application Information
50.10.1. Auto-configured InfoContributors
50.10.2. Custom Application Information
50.10.3. Git Commit Information
50.10.4. Build Information
50.10.5. Writing Custom InfoContributors
51. Monitoring and Management over HTTP
51.1. Customizing the Management Endpoint Paths
51.2. Customizing the Management Server Port
51.3. Configuring Management-specific SSL
51.4. Customizing the Management Server Address
51.5. Disabling HTTP Endpoints
52. Monitoring and Management over JMX
52.1. Customizing MBean Names
52.2. Disabling JMX Endpoints
52.3. Using Jolokia for JMX over HTTP
52.3.1. Customizing Jolokia
52.3.2. Disabling Jolokia
53. Loggers
53.1. Configure a Logger
54. Metrics
54.1. Getting started
54.2. Supported monitoring systems
54.2.1. Atlas
54.2.2. Datadog
54.2.3. Ganglia
54.2.4. Graphite
54.2.5. Influx
54.2.6. JMX
54.2.7. New Relic
54.2.8. Prometheus
54.2.9. SignalFx
54.2.10. Simple
54.2.11. StatsD
54.2.12. Wavefront
54.3. Supported Metrics
54.3.1. Spring MVC Metrics
54.3.2. Spring WebFlux Metrics
54.3.3. RestTemplate Metrics
54.3.4. Cache Metrics
54.3.5. DataSource Metrics
54.3.6. RabbitMQ Metrics
54.4. Registering custom metrics
54.5. Customizing individual metrics
54.5.1. Per-meter properties
54.6. Metrics endpoint
55. Auditing
56. HTTP Tracing
56.1. Custom HTTP tracing
57. Process Monitoring
57.1. Extending Configuration
57.2. Programmatically
58. Cloud Foundry Support
58.1. Disabling Extended Cloud Foundry Actuator Support
58.2. Cloud Foundry Self-signed Certificates
58.3. Custom context path
59. What to Read Next
VI. Deploying Spring Boot Applications
60. Deploying to the Cloud
60.1. Cloud Foundry
60.1.1. Binding to Services
60.2. Heroku
60.3. OpenShift
60.4. Amazon Web Services (AWS)
60.4.1. AWS Elastic Beanstalk
Using the Tomcat Platform
Using the Java SE Platform
60.4.2. Summary
60.5. Boxfuse and Amazon Web Services
60.6. Google Cloud
61. Installing Spring Boot Applications
61.1. Supported Operating Systems
61.2. Unix/Linux Services
61.2.1. Installation as an init.d Service (System V)
Securing an init.d Service
61.2.2. Installation as a systemd Service
61.2.3. Customizing the Startup Script
Customizing the Start Script when It Is Written
Customizing a Script When It Runs
61.3. Microsoft Windows Services
62. What to Read Next
VII. Spring Boot CLI
63. Installing the CLI
64. Using the CLI
64.1. Running Applications with the CLI
64.1.1. Deduced “grab” Dependencies
64.1.2. Deduced “grab” Coordinates
64.1.3. Default Import Statements
64.1.4. Automatic Main Method
64.1.5. Custom Dependency Management
64.2. Applications with Multiple Source Files
64.3. Packaging Your Application
64.4. Initialize a New Project
64.5. Using the Embedded Shell
64.6. Adding Extensions to the CLI
65. Developing Applications with the Groovy Beans DSL
66. Configuring the CLI with settings.xml
67. What to Read Next
VIII. Build tool plugins
68. Spring Boot Maven Plugin
68.1. Including the Plugin
68.2. Packaging Executable Jar and War Files
69. Spring Boot Gradle Plugin
70. Spring Boot AntLib Module
70.1. Spring Boot Ant Tasks
70.1.1. spring-boot:exejar
70.1.2. Examples
70.2. spring-boot:findmainclass
70.2.1. Examples
71. Supporting Other Build Systems
71.1. Repackaging Archives
71.2. Nested Libraries
71.3. Finding a Main Class
71.4. Example Repackage Implementation
72. What to Read Next
IX. ‘How-to’ guides
73. Spring Boot Application
73.1. Create Your Own FailureAnalyzer
73.2. Troubleshoot Auto-configuration
73.3. Customize the Environment or ApplicationContext Before It Starts
73.4. Build an ApplicationContext Hierarchy (Adding a Parent or Root Context)
73.5. Create a Non-web Application
74. Properties and Configuration
74.1. Automatically Expand Properties at Build Time
74.1.1. Automatic Property Expansion Using Maven
74.1.2. Automatic Property Expansion Using Gradle
74.2. Externalize the Configuration of SpringApplication
74.3. Change the Location of External Properties of an Application
74.4. Use ‘Short’ Command Line Arguments
74.5. Use YAML for External Properties
74.6. Set the Active Spring Profiles
74.7. Change Configuration Depending on the Environment
74.8. Discover Built-in Options for External Properties
75. Embedded Web Servers
75.1. Use Another Web Server
75.2. Disabling the Web Server
75.3. Change the HTTP Port
75.4. Use a Random Unassigned HTTP Port
75.5. Discover the HTTP Port at Runtime
75.6. Enable HTTP Response Compression
75.7. Configure SSL
75.8. Configure HTTP/2
75.8.1. HTTP/2 with Undertow
75.8.2. HTTP/2 with Jetty
75.8.3. HTTP/2 with Tomcat
75.9. Configure the Web Server
75.10. Add a Servlet, Filter, or Listener to a Application
75.10.1. Add a Servlet, Filter, or Listener by Using a Spring Bean
Disable Registration of a Servlet or Filter
75.10.2. Add Servlets, Filters, and Listeners by Using Classpath Scanning
75.11. Configure Access Logging
75.12. Running Behind a Front-end Proxy Server
75.12.1. Customize Tomcat’s Proxy Configuration
75.13. Enable Multiple Connectors with Tomcat
75.14. Use Tomcat’s LegacyCookieProcessor
75.15. Enable Multiple Listeners with Undertow
75.16. Create WebSocket Endpoints Using @ServerEndpoint
76. Spring MVC
76.1. Write a JSON REST Service
76.2. Write an XML REST Service
76.3. Customize the Jackson ObjectMapper
76.4. Customize the @ResponseBody Rendering
76.5. Handling Multipart File Uploads
76.6. Switch Off the Spring MVC DispatcherServlet
76.7. Switch off the Default MVC Configuration
76.8. Customize ViewResolvers
77. Jersey
77.1. Secure Jersey endpoints with Spring Security
78. HTTP Clients
78.1. Configure RestTemplate to Use a Proxy
79. Logging
79.1. Configure Logback for Logging
79.1.1. Configure Logback for File-only Output
79.2. Configure Log4j for Logging
79.2.1. Use YAML or JSON to Configure Log4j 2
80. Data Access
80.1. Configure a Custom DataSource
80.2. Configure Two DataSources
80.3. Use Spring Data Repositories
80.4. Separate @Entity Definitions from Spring Configuration
80.5. Configure JPA Properties
80.6. Configure Hibernate Naming Strategy
80.7. Use a Custom EntityManagerFactory
80.8. Use Two EntityManagers
80.9. Use a Traditional persistence.xml File
80.10. Use Spring Data JPA and Mongo Repositories
80.11. Expose Spring Data Repositories as REST Endpoint
80.12. Configure a Component that is Used by JPA
80.13. Configure jOOQ with Two DataSources
81. Database Initialization
81.1. Initialize a Database Using JPA
81.2. Initialize a Database Using Hibernate
81.3. Initialize a Database
81.4. Initialize a Spring Batch Database
81.5. Use a Higher-level Database Migration Tool
81.5.1. Execute Flyway Database Migrations on Startup
81.5.2. Execute Liquibase Database Migrations on Startup
82. Messaging
82.1. Disable Transacted JMS Session
83. Batch Applications
83.1. Execute Spring Batch Jobs on Startup
84. Actuator
84.1. Change the HTTP Port or Address of the Actuator Endpoints
84.2. Customize the ‘whitelabel’ Error Page
84.3. Sanitize sensible values
85. Security
85.1. Switch off the Spring Boot Security Configuration
85.2. Change the UserDetailsService and Add User Accounts
85.3. Enable HTTPS When Running behind a Proxy Server
86. Hot Swapping
86.1. Reload Static Content
86.2. Reload Templates without Restarting the Container
86.2.1. Thymeleaf Templates
86.2.2. FreeMarker Templates
86.2.3. Groovy Templates
86.3. Fast Application Restarts
86.4. Reload Java Classes without Restarting the Container
87. Build
87.1. Generate Build Information
87.2. Generate Git Information
87.3. Customize Dependency Versions
87.4. Create an Executable JAR with Maven
87.5. Use a Spring Boot Application as a Dependency
87.6. Extract Specific Libraries When an Executable Jar Runs
87.7. Create a Non-executable JAR with Exclusions
87.8. Remote Debug a Spring Boot Application Started with Maven
87.9. Build an Executable Archive from Ant without Using spring-boot-antlib
88. Traditional Deployment
88.1. Create a Deployable War File
88.2. Convert an Existing Application to Spring Boot
88.3. Deploying a WAR to WebLogic
88.4. Use Jedis Instead of Lettuce
X. Appendices
A. Common application properties
B. Configuration Metadata
B.1. Metadata Format
B.1.1. Group Attributes
B.1.2. Property Attributes
B.1.3. Hint Attributes
B.1.4. Repeated Metadata Items
B.2. Providing Manual Hints
B.2.1. Value Hint
B.2.2. Value Providers
Any
Class Reference
Handle As
Logger Name
Spring Bean Reference
Spring Profile Name
B.3. Generating Your Own Metadata by Using the Annotation Processor
B.3.1. Nested Properties
B.3.2. Adding Additional Metadata
C. Auto-configuration classes
C.1. From the “spring-boot-autoconfigure” module
C.2. From the “spring-boot-actuator-autoconfigure” module
D. Test auto-configuration annotations
E. The Executable Jar Format
E.1. Nested JARs
E.1.1. The Executable Jar File Structure
E.1.2. The Executable War File Structure
E.2. Spring Boot’s “JarFile” Class
E.2.1. Compatibility with the Standard Java “JarFile”
E.3. Launching Executable Jars
E.3.1. Launcher Manifest
E.3.2. Exploded Archives
E.4. PropertiesLauncher Features
E.5. Executable Jar Restrictions
E.6. Alternative Single Jar Solutions
F. Dependency versions

Part I. Spring Boot Documentation

This section provides a brief overview of Spring Boot reference documentation. It serves as a map for the rest of the document.

1. About the Documentation

The Spring Boot reference guide is available as

The latest copy is available at docs.spring.io/spring-boot/docs/current/reference.

Copies of this document may be made for your own use and for distribution to others, provided that you do not charge any fee for such copies and further provided that each copy contains this Copyright Notice, whether distributed in print or electronically.

2. Getting Help

If you have trouble with Spring Boot, we would like to help.

[Note]Note

All of Spring Boot is open source, including the documentation. If you find problems with the docs or if you want to improve them, please get involved.

3. First Steps

If you are getting started with Spring Boot or 'Spring' in general, start with the following topics:

4. Working with Spring Boot

Ready to actually start using Spring Boot? We have you covered:

5. Learning about Spring Boot Features

Need more details about Spring Boot’s core features? The following content is for you:

6. Moving to Production

When you are ready to push your Spring Boot application to production, we have some tricks that you might like:

7. Advanced Topics

Finally, we have a few topics for more advanced users:

Part II. Getting Started

If you are getting started with Spring Boot, or “Spring” in general, start by reading this section. It answers the basic “what?”, “how?” and “why?” questions. It includes an introduction to Spring Boot, along with installation instructions. We then walk you through building your first Spring Boot application, discussing some core principles as we go.

8. Introducing Spring Boot

Spring Boot makes it easy to create stand-alone, production-grade Spring-based Applications that you can run. We take an opinionated view of the Spring platform and third-party libraries, so that you can get started with minimum fuss. Most Spring Boot applications need very little Spring configuration.

You can use Spring Boot to create Java applications that can be started by using java -jar or more traditional war deployments. We also provide a command line tool that runs “spring scripts”.

Our primary goals are:

  • Provide a radically faster and widely accessible getting-started experience for all Spring development.
  • Be opinionated out of the box but get out of the way quickly as requirements start to diverge from the defaults.
  • Provide a range of non-functional features that are common to large classes of projects (such as embedded servers, security, metrics, health checks, and externalized configuration).
  • Absolutely no code generation and no requirement for XML configuration.

9. System Requirements

Spring Boot 2.0.3.RELEASE requires Java 8 or 9 and Spring Framework 5.0.7.RELEASE or above. Explicit build support is provided for Maven 3.2+ and Gradle 4.

9.1 Servlet Containers

Spring Boot supports the following embedded servlet containers:

NameServlet Version

Tomcat 8.5

3.1

Jetty 9.4

3.1

Undertow 1.4

3.1

You can also deploy Spring Boot applications to any Servlet 3.1+ compatible container.

10. Installing Spring Boot

Spring Boot can be used with “classic” Java development tools or installed as a command line tool. Either way, you need Java SDK v1.8 or higher. Before you begin, you should check your current Java installation by using the following command:

$ java -version

If you are new to Java development or if you want to experiment with Spring Boot, you might want to try the Spring Boot CLI (Command Line Interface) first. Otherwise, read on for “classic” installation instructions.

10.1 Installation Instructions for the Java Developer

You can use Spring Boot in the same way as any standard Java library. To do so, include the appropriate spring-boot-*.jar files on your classpath. Spring Boot does not require any special tools integration, so you can use any IDE or text editor. Also, there is nothing special about a Spring Boot application, so you can run and debug a Spring Boot application as you would any other Java program.

Although you could copy Spring Boot jars, we generally recommend that you use a build tool that supports dependency management (such as Maven or Gradle).

10.1.1 Maven Installation

Spring Boot is compatible with Apache Maven 3.2 or above. If you do not already have Maven installed, you can follow the instructions at maven.apache.org.

[Tip]Tip

On many operating systems, Maven can be installed with a package manager. If you use OSX Homebrew, try brew install maven. Ubuntu users can run sudo apt-get install maven. Windows users with Chocolatey can run choco install maven from an elevated (administrator) prompt.

Spring Boot dependencies use the org.springframework.boot groupId. Typically, your Maven POM file inherits from the spring-boot-starter-parent project and declares dependencies to one or more “Starters”. Spring Boot also provides an optional Maven plugin to create executable jars.

The following listing shows a typical pom.xml file:

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion>

	<groupId>com.example</groupId>
	<artifactId>myproject</artifactId>
	<version>0.0.1-SNAPSHOT</version>

	<!-- Inherit defaults from Spring Boot -->
	<parent>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-parent</artifactId>
		<version>2.0.3.RELEASE</version>
	</parent>

	<!-- Add typical dependencies for a web application -->
	<dependencies>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-web</artifactId>
		</dependency>
	</dependencies>

	<!-- Package as an executable jar -->
	<build>
		<plugins>
			<plugin>
				<groupId>org.springframework.boot</groupId>
				<artifactId>spring-boot-maven-plugin</artifactId>
			</plugin>
		</plugins>
	</build>

</project>
[Tip]Tip

The spring-boot-starter-parent is a great way to use Spring Boot, but it might not be suitable all of the time. Sometimes you may need to inherit from a different parent POM, or you might not like our default settings. In those cases, see Section 13.2.2, “Using Spring Boot without the Parent POM” for an alternative solution that uses an import scope.

10.1.2 Gradle Installation

Spring Boot is compatible with Gradle 4. If you do not already have Gradle installed, you can follow the instructions at gradle.org.

Spring Boot dependencies can be declared by using the org.springframework.boot group. Typically, your project declares dependencies to one or more “Starters”. Spring Boot provides a useful Gradle plugin that can be used to simplify dependency declarations and to create executable jars.

The following example shows a typical build.gradle file:

plugins {
	id 'org.springframework.boot' version '2.0.3.RELEASE'
	id 'java'
}


jar {
	baseName = 'myproject'
	version =  '0.0.1-SNAPSHOT'
}

repositories {
	jcenter()
}

dependencies {
	compile("org.springframework.boot:spring-boot-starter-web")
	testCompile("org.springframework.boot:spring-boot-starter-test")
}

10.2 Installing the Spring Boot CLI

The Spring Boot CLI (Command Line Interface) is a command line tool that you can use to quickly prototype with Spring. It lets you run Groovy scripts, which means that you have a familiar Java-like syntax without so much boilerplate code.

You do not need to use the CLI to work with Spring Boot, but it is definitely the quickest way to get a Spring application off the ground.

10.2.1 Manual Installation

You can download the Spring CLI distribution from the Spring software repository:

Cutting edge snapshot distributions are also available.

Once downloaded, follow the INSTALL.txt instructions from the unpacked archive. In summary, there is a spring script (spring.bat for Windows) in a bin/ directory in the .zip file. Alternatively, you can use java -jar with the .jar file (the script helps you to be sure that the classpath is set correctly).

10.2.2 Installation with SDKMAN!

SDKMAN! (The Software Development Kit Manager) can be used for managing multiple versions of various binary SDKs, including Groovy and the Spring Boot CLI. Get SDKMAN! from sdkman.io and install Spring Boot by using the following commands:

$ sdk install springboot
$ spring --version
Spring Boot v2.0.3.RELEASE

If you develop features for the CLI and want easy access to the version you built, use the following commands:

$ sdk install springboot dev /path/to/spring-boot/spring-boot-cli/target/spring-boot-cli-2.0.3.RELEASE-bin/spring-2.0.3.RELEASE/
$ sdk default springboot dev
$ spring --version
Spring CLI v2.0.3.RELEASE

The preceding instructions install a local instance of spring called the dev instance. It points at your target build location, so every time you rebuild Spring Boot, spring is up-to-date.

You can see it by running the following command:

$ sdk ls springboot

================================================================================
Available Springboot Versions
================================================================================
> + dev
* 2.0.3.RELEASE

================================================================================
+ - local version
* - installed
> - currently in use
================================================================================

10.2.3 OSX Homebrew Installation

If you are on a Mac and use Homebrew, you can install the Spring Boot CLI by using the following commands:

$ brew tap pivotal/tap
$ brew install springboot

Homebrew installs spring to /usr/local/bin.

[Note]Note

If you do not see the formula, your installation of brew might be out-of-date. In that case, run brew update and try again.

10.2.4 MacPorts Installation

If you are on a Mac and use MacPorts, you can install the Spring Boot CLI by using the following command:

$ sudo port install spring-boot-cli

10.2.5 Command-line Completion

The Spring Boot CLI includes scripts that provide command completion for the BASH and zsh shells. You can source the script (also named spring) in any shell or put it in your personal or system-wide bash completion initialization. On a Debian system, the system-wide scripts are in /shell-completion/bash and all scripts in that directory are executed when a new shell starts. For example, to run the script manually if you have installed by using SDKMAN!, use the following commands:

$ . ~/.sdkman/candidates/springboot/current/shell-completion/bash/spring
$ spring <HIT TAB HERE>
  grab  help  jar  run  test  version
[Note]Note

If you install the Spring Boot CLI by using Homebrew or MacPorts, the command-line completion scripts are automatically registered with your shell.

10.2.6 Windows Scoop Installation

If you are on a Windows and use Scoop, you can install the Spring Boot CLI by using the following commands:

> scoop bucket add extras
> scoop install springboot

Scoop installs spring to ~/scoop/apps/springboot/current/bin.

[Note]Note

If you do not see the app manifest, your installation of scoop might be out-of-date. In that case, run scoop update and try again.

10.2.7 Quick-start Spring CLI Example

You can use the following web application to test your installation. To start, create a file called app.groovy, as follows:

@RestController
class ThisWillActuallyRun {

	@RequestMapping("/")
	String home() {
		"Hello World!"
	}

}

Then run it from a shell, as follows:

$ spring run app.groovy
[Note]Note

The first run of your application is slow, as dependencies are downloaded. Subsequent runs are much quicker.

Open localhost:8080 in your favorite web browser. You should see the following output:

Hello World!

10.3 Upgrading from an Earlier Version of Spring Boot

If you are upgrading from an earlier release of Spring Boot, check the “migration guide” on the project wiki that provides detailed upgrade instructions. Check also the “release notes” for a list of “new and noteworthy” features for each release.

To upgrade an existing CLI installation, use the appropriate package manager command (for example, brew upgrade) or, if you manually installed the CLI, follow the standard instructions, remembering to update your PATH environment variable to remove any older references.

11. Developing Your First Spring Boot Application

This section describes how to develop a simple “Hello World!” web application that highlights some of Spring Boot’s key features. We use Maven to build this project, since most IDEs support it.

[Tip]Tip

The spring.io web site contains many “Getting Started” guides that use Spring Boot. If you need to solve a specific problem, check there first.

You can shortcut the steps below by going to start.spring.io and choosing the "Web" starter from the dependencies searcher. Doing so generates a new project structure so that you can start coding right away. Check the Spring Initializr documentation for more details.

Before we begin, open a terminal and run the following commands to ensure that you have valid versions of Java and Maven installed:

$ java -version
java version "1.8.0_102"
Java(TM) SE Runtime Environment (build 1.8.0_102-b14)
Java HotSpot(TM) 64-Bit Server VM (build 25.102-b14, mixed mode)
$ mvn -v
Apache Maven 3.3.9 (bb52d8502b132ec0a5a3f4c09453c07478323dc5; 2015-11-10T16:41:47+00:00)
Maven home: /usr/local/Cellar/maven/3.3.9/libexec
Java version: 1.8.0_102, vendor: Oracle Corporation
[Note]Note

This sample needs to be created in its own folder. Subsequent instructions assume that you have created a suitable folder and that it is your current directory.

11.1 Creating the POM

We need to start by creating a Maven pom.xml file. The pom.xml is the recipe that is used to build your project. Open your favorite text editor and add the following:

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion>

	<groupId>com.example</groupId>
	<artifactId>myproject</artifactId>
	<version>0.0.1-SNAPSHOT</version>

	<parent>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-parent</artifactId>
		<version>2.0.3.RELEASE</version>
	</parent>

	<!-- Additional lines to be added here... -->

</project>

The preceding listing should give you a working build. You can test it by running mvn package (for now, you can ignore the “jar will be empty - no content was marked for inclusion!” warning).

[Note]Note

At this point, you could import the project into an IDE (most modern Java IDEs include built-in support for Maven). For simplicity, we continue to use a plain text editor for this example.

11.2 Adding Classpath Dependencies

Spring Boot provides a number of “Starters” that let you add jars to your classpath. Our sample application has already used spring-boot-starter-parent in the parent section of the POM. The spring-boot-starter-parent is a special starter that provides useful Maven defaults. It also provides a dependency-management section so that you can omit version tags for “blessed” dependencies.

Other “Starters” provide dependencies that you are likely to need when developing a specific type of application. Since we are developing a web application, we add a spring-boot-starter-web dependency. Before that, we can look at what we currently have by running the following command:

$ mvn dependency:tree

[INFO] com.example:myproject:jar:0.0.1-SNAPSHOT

The mvn dependency:tree command prints a tree representation of your project dependencies. You can see that spring-boot-starter-parent provides no dependencies by itself. To add the necessary dependencies, edit your pom.xml and add the spring-boot-starter-web dependency immediately below the parent section:

<dependencies>
	<dependency>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-web</artifactId>
	</dependency>
</dependencies>

If you run mvn dependency:tree again, you see that there are now a number of additional dependencies, including the Tomcat web server and Spring Boot itself.

11.3 Writing the Code

To finish our application, we need to create a single Java file. By default, Maven compiles sources from src/main/java, so you need to create that folder structure and then add a file named src/main/java/Example.java to contain the following code:

import org.springframework.boot.*;
import org.springframework.boot.autoconfigure.*;
import org.springframework.web.bind.annotation.*;

@RestController
@EnableAutoConfiguration
public class Example {

	@RequestMapping("/")
	String home() {
		return "Hello World!";
	}

	public static void main(String[] args) throws Exception {
		SpringApplication.run(Example.class, args);
	}

}

Although there is not much code here, quite a lot is going on. We step through the important parts in the next few sections.

11.3.1 The @RestController and @RequestMapping Annotations

The first annotation on our Example class is @RestController. This is known as a stereotype annotation. It provides hints for people reading the code and for Spring that the class plays a specific role. In this case, our class is a web @Controller, so Spring considers it when handling incoming web requests.

The @RequestMapping annotation provides “routing” information. It tells Spring that any HTTP request with the / path should be mapped to the home method. The @RestController annotation tells Spring to render the resulting string directly back to the caller.

[Tip]Tip

The @RestController and @RequestMapping annotations are Spring MVC annotations. (They are not specific to Spring Boot.) See the MVC section in the Spring Reference Documentation for more details.

11.3.2 The @EnableAutoConfiguration Annotation

The second class-level annotation is @EnableAutoConfiguration. This annotation tells Spring Boot to “guess” how you want to configure Spring, based on the jar dependencies that you have added. Since spring-boot-starter-web added Tomcat and Spring MVC, the auto-configuration assumes that you are developing a web application and sets up Spring accordingly.

11.3.3 The “main” Method

The final part of our application is the main method. This is just a standard method that follows the Java convention for an application entry point. Our main method delegates to Spring Boot’s SpringApplication class by calling run. SpringApplication bootstraps our application, starting Spring, which, in turn, starts the auto-configured Tomcat web server. We need to pass Example.class as an argument to the run method to tell SpringApplication which is the primary Spring component. The args array is also passed through to expose any command-line arguments.

11.4 Running the Example

At this point, your application should work. Since you used the spring-boot-starter-parent POM, you have a useful run goal that you can use to start the application. Type mvn spring-boot:run from the root project directory to start the application. You should see output similar to the following:

$ mvn spring-boot:run

  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::  (v2.0.3.RELEASE)
....... . . .
....... . . . (log output here)
....... . . .
........ Started Example in 2.222 seconds (JVM running for 6.514)

If you open a web browser to localhost:8080, you should see the following output:

Hello World!

To gracefully exit the application, press ctrl-c.

11.5 Creating an Executable Jar

We finish our example by creating a completely self-contained executable jar file that we could run in production. Executable jars (sometimes called “fat jars”) are archives containing your compiled classes along with all of the jar dependencies that your code needs to run.

To create an executable jar, we need to add the spring-boot-maven-plugin to our pom.xml. To do so, insert the following lines just below the dependencies section:

<build>
	<plugins>
		<plugin>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-maven-plugin</artifactId>
		</plugin>
	</plugins>
</build>
[Note]Note

The spring-boot-starter-parent POM includes <executions> configuration to bind the repackage goal. If you do not use the parent POM, you need to declare this configuration yourself. See the plugin documentation for details.

Save your pom.xml and run mvn package from the command line, as follows:

$ mvn package

[INFO] Scanning for projects...
[INFO]
[INFO] ------------------------------------------------------------------------
[INFO] Building myproject 0.0.1-SNAPSHOT
[INFO] ------------------------------------------------------------------------
[INFO] .... ..
[INFO] --- maven-jar-plugin:2.4:jar (default-jar) @ myproject ---
[INFO] Building jar: /Users/developer/example/spring-boot-example/target/myproject-0.0.1-SNAPSHOT.jar
[INFO]
[INFO] --- spring-boot-maven-plugin:2.0.3.RELEASE:repackage (default) @ myproject ---
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------

If you look in the target directory, you should see myproject-0.0.1-SNAPSHOT.jar. The file should be around 10 MB in size. If you want to peek inside, you can use jar tvf, as follows:

$ jar tvf target/myproject-0.0.1-SNAPSHOT.jar

You should also see a much smaller file named myproject-0.0.1-SNAPSHOT.jar.original in the target directory. This is the original jar file that Maven created before it was repackaged by Spring Boot.

To run that application, use the java -jar command, as follows:

$ java -jar target/myproject-0.0.1-SNAPSHOT.jar

  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::  (v2.0.3.RELEASE)
....... . . .
....... . . . (log output here)
....... . . .
........ Started Example in 2.536 seconds (JVM running for 2.864)

As before, to exit the application, press ctrl-c.

12. What to Read Next

Hopefully, this section provided some of the Spring Boot basics and got you on your way to writing your own applications. If you are a task-oriented type of developer, you might want to jump over to spring.io and check out some of the getting started guides that solve specific “How do I do that with Spring?” problems. We also have Spring Boot-specific “How-to” reference documentation.

The Spring Boot repository also has a bunch of samples you can run. The samples are independent of the rest of the code (that is, you do not need to build the rest to run or use the samples).

Otherwise, the next logical step is to read Part III, “Using Spring Boot”. If you are really impatient, you could also jump ahead and read about Spring Boot features.

Part III. Using Spring Boot

This section goes into more detail about how you should use Spring Boot. It covers topics such as build systems, auto-configuration, and how to run your applications. We also cover some Spring Boot best practices. Although there is nothing particularly special about Spring Boot (it is just another library that you can consume), there are a few recommendations that, when followed, make your development process a little easier.

If you are starting out with Spring Boot, you should probably read the Getting Started guide before diving into this section.

13. Build Systems

It is strongly recommended that you choose a build system that supports dependency management and that can consume artifacts published to the “Maven Central” repository. We would recommend that you choose Maven or Gradle. It is possible to get Spring Boot to work with other build systems (Ant, for example), but they are not particularly well supported.

13.1 Dependency Management

Each release of Spring Boot provides a curated list of dependencies that it supports. In practice, you do not need to provide a version for any of these dependencies in your build configuration, as Spring Boot manages that for you. When you upgrade Spring Boot itself, these dependencies are upgraded as well in a consistent way.

[Note]Note

You can still specify a version and override Spring Boot’s recommendations if you need to do so.

The curated list contains all the spring modules that you can use with Spring Boot as well as a refined list of third party libraries. The list is available as a standard Bills of Materials (spring-boot-dependencies) that can be used with both Maven and Gradle.

[Warning]Warning

Each release of Spring Boot is associated with a base version of the Spring Framework. We highly recommend that you not specify its version.

13.2 Maven

Maven users can inherit from the spring-boot-starter-parent project to obtain sensible defaults. The parent project provides the following features:

  • Java 1.8 as the default compiler level.
  • UTF-8 source encoding.
  • A Dependency Management section, inherited from the spring-boot-dependencies pom, that manages the versions of common dependencies. This dependency management lets you omit <version> tags for those dependencies when used in your own pom.
  • Sensible resource filtering.
  • Sensible plugin configuration (exec plugin, Git commit ID, and shade).
  • Sensible resource filtering for application.properties and application.yml including profile-specific files (for example, application-dev.properties and application-dev.yml)

Note that, since the application.properties and application.yml files accept Spring style placeholders (${…​}), the Maven filtering is changed to use @[email protected] placeholders. (You can override that by setting a Maven property called resource.delimiter.)

13.2.1 Inheriting the Starter Parent

To configure your project to inherit from the spring-boot-starter-parent, set the parent as follows:

<!-- Inherit defaults from Spring Boot -->
<parent>
	<groupId>org.springframework.boot</groupId>
	<artifactId>spring-boot-starter-parent</artifactId>
	<version>2.0.3.RELEASE</version>
</parent>
[Note]Note

You should need to specify only the Spring Boot version number on this dependency. If you import additional starters, you can safely omit the version number.

With that setup, you can also override individual dependencies by overriding a property in your own project. For instance, to upgrade to another Spring Data release train, you would add the following to your pom.xml:

<properties>
	<spring-data-releasetrain.version>Fowler-SR2</spring-data-releasetrain.version>
</properties>
[Tip]Tip

Check the spring-boot-dependencies pom for a list of supported properties.

13.2.2 Using Spring Boot without the Parent POM

Not everyone likes inheriting from the spring-boot-starter-parent POM. You may have your own corporate standard parent that you need to use or you may prefer to explicitly declare all your Maven configuration.

If you do not want to use the spring-boot-starter-parent, you can still keep the benefit of the dependency management (but not the plugin management) by using a scope=import dependency, as follows:

<dependencyManagement>
		<dependencies>
		<dependency>
			<!-- Import dependency management from Spring Boot -->
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-dependencies</artifactId>
			<version>2.0.3.RELEASE</version>
			<type>pom</type>
			<scope>import</scope>
		</dependency>
	</dependencies>
</dependencyManagement>

The preceding sample setup does not let you override individual dependencies by using a property, as explained above. To achieve the same result, you need to add an entry in the dependencyManagement of your project before the spring-boot-dependencies entry. For instance, to upgrade to another Spring Data release train, you could add the following element to your pom.xml:

<dependencyManagement>
	<dependencies>
		<!-- Override Spring Data release train provided by Spring Boot -->
		<dependency>
			<groupId>org.springframework.data</groupId>
			<artifactId>spring-data-releasetrain</artifactId>
			<version>Fowler-SR2</version>
			<type>pom</type>
			<scope>import</scope>
		</dependency>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-dependencies</artifactId>
			<version>2.0.3.RELEASE</version>
			<type>pom</type>
			<scope>import</scope>
		</dependency>
	</dependencies>
</dependencyManagement>
[Note]Note

In the preceding example, we specify a BOM, but any dependency type can be overridden in the same way.

13.2.3 Using the Spring Boot Maven Plugin

Spring Boot includes a Maven plugin that can package the project as an executable jar. Add the plugin to your <plugins> section if you want to use it, as shown in the following example:

<build>
	<plugins>
		<plugin>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-maven-plugin</artifactId>
		</plugin>
	</plugins>
</build>
[Note]Note

If you use the Spring Boot starter parent pom, you need to add only the plugin. There is no need to configure it unless you want to change the settings defined in the parent.

13.3 Gradle

To learn about using Spring Boot with Gradle, please refer to the documentation for Spring Boot’s Gradle plugin:

13.4 Ant

It is possible to build a Spring Boot project using Apache Ant+Ivy. The spring-boot-antlib “AntLib” module is also available to help Ant create executable jars.

To declare dependencies, a typical ivy.xml file looks something like the following example:

<ivy-module version="2.0">
	<info organisation="org.springframework.boot" module="spring-boot-sample-ant" />
	<configurations>
		<conf name="compile" description="everything needed to compile this module" />
		<conf name="runtime" extends="compile" description="everything needed to run this module" />
	</configurations>
	<dependencies>
		<dependency org="org.springframework.boot" name="spring-boot-starter"
			rev="${spring-boot.version}" conf="compile" />
	</dependencies>
</ivy-module>

A typical build.xml looks like the following example:

<project
	xmlns:ivy="antlib:org.apache.ivy.ant"
	xmlns:spring-boot="antlib:org.springframework.boot.ant"
	name="myapp" default="build">

	<property name="spring-boot.version" value="2.0.3.RELEASE" />

	<target name="resolve" description="--> retrieve dependencies with ivy">
		<ivy:retrieve pattern="lib/[conf]/[artifact]-[type]-[revision].[ext]" />
	</target>

	<target name="classpaths" depends="resolve">
		<path id="compile.classpath">
			<fileset dir="lib/compile" includes="*.jar" />
		</path>
	</target>

	<target name="init" depends="classpaths">
		<mkdir dir="build/classes" />
	</target>

	<target name="compile" depends="init" description="compile">
		<javac srcdir="src/main/java" destdir="build/classes" classpathref="compile.classpath" />
	</target>

	<target name="build" depends="compile">
		<spring-boot:exejar destfile="build/myapp.jar" classes="build/classes">
			<spring-boot:lib>
				<fileset dir="lib/runtime" />
			</spring-boot:lib>
		</spring-boot:exejar>
	</target>
</project>
[Tip]Tip

If you do not want to use the spring-boot-antlib module, see the Section 87.9, “Build an Executable Archive from Ant without Using spring-boot-antlib “How-to” .

13.5 Starters

Starters are a set of convenient dependency descriptors that you can include in your application. You get a one-stop shop for all the Spring and related technologies that you need without having to hunt through sample code and copy-paste loads of dependency descriptors. For example, if you want to get started using Spring and JPA for database access, include the spring-boot-starter-data-jpa dependency in your project.

The starters contain a lot of the dependencies that you need to get a project up and running quickly and with a consistent, supported set of managed transitive dependencies.

The following application starters are provided by Spring Boot under the org.springframework.boot group:

Table 13.1. Spring Boot application starters

NameDescriptionPom

spring-boot-starter

Core starter, including auto-configuration support, logging and YAML

Pom

spring-boot-starter-activemq

Starter for JMS messaging using Apache ActiveMQ

Pom

spring-boot-starter-amqp

Starter for using Spring AMQP and Rabbit MQ

Pom

spring-boot-starter-aop

Starter for aspect-oriented programming with Spring AOP and AspectJ

Pom

spring-boot-starter-artemis

Starter for JMS messaging using Apache Artemis

Pom

spring-boot-starter-batch

Starter for using Spring Batch

Pom

spring-boot-starter-cache

Starter for using Spring Framework’s caching support

Pom

spring-boot-starter-cloud-connectors

Starter for using Spring Cloud Connectors which simplifies connecting to services in cloud platforms like Cloud Foundry and Heroku

Pom

spring-boot-starter-data-cassandra

Starter for using Cassandra distributed database and Spring Data Cassandra

Pom

spring-boot-starter-data-cassandra-reactive

Starter for using Cassandra distributed database and Spring Data Cassandra Reactive

Pom

spring-boot-starter-data-couchbase

Starter for using Couchbase document-oriented database and Spring Data Couchbase

Pom

spring-boot-starter-data-couchbase-reactive

Starter for using Couchbase document-oriented database and Spring Data Couchbase Reactive

Pom

spring-boot-starter-data-elasticsearch

Starter for using Elasticsearch search and analytics engine and Spring Data Elasticsearch

Pom

spring-boot-starter-data-jpa

Starter for using Spring Data JPA with Hibernate

Pom

spring-boot-starter-data-ldap

Starter for using Spring Data LDAP

Pom

spring-boot-starter-data-mongodb

Starter for using MongoDB document-oriented database and Spring Data MongoDB

Pom

spring-boot-starter-data-mongodb-reactive

Starter for using MongoDB document-oriented database and Spring Data MongoDB Reactive

Pom

spring-boot-starter-data-neo4j

Starter for using Neo4j graph database and Spring Data Neo4j

Pom

spring-boot-starter-data-redis

Starter for using Redis key-value data store with Spring Data Redis and the Lettuce client

Pom

spring-boot-starter-data-redis-reactive

Starter for using Redis key-value data store with Spring Data Redis reactive and the Lettuce client

Pom

spring-boot-starter-data-rest

Starter for exposing Spring Data repositories over REST using Spring Data REST

Pom

spring-boot-starter-data-solr

Starter for using the Apache Solr search platform with Spring Data Solr

Pom

spring-boot-starter-freemarker

Starter for building MVC web applications using FreeMarker views

Pom

spring-boot-starter-groovy-templates

Starter for building MVC web applications using Groovy Templates views

Pom

spring-boot-starter-hateoas

Starter for building hypermedia-based RESTful web application with Spring MVC and Spring HATEOAS

Pom

spring-boot-starter-integration

Starter for using Spring Integration

Pom

spring-boot-starter-jdbc

Starter for using JDBC with the HikariCP connection pool

Pom

spring-boot-starter-jersey

Starter for building RESTful web applications using JAX-RS and Jersey. An alternative to spring-boot-starter-web

Pom

spring-boot-starter-jooq

Starter for using jOOQ to access SQL databases. An alternative to spring-boot-starter-data-jpa or spring-boot-starter-jdbc

Pom

spring-boot-starter-json

Starter for reading and writing json

Pom

spring-boot-starter-jta-atomikos

Starter for JTA transactions using Atomikos

Pom

spring-boot-starter-jta-bitronix

Starter for JTA transactions using Bitronix

Pom

spring-boot-starter-jta-narayana

Starter for JTA transactions using Narayana

Pom

spring-boot-starter-mail

Starter for using Java Mail and Spring Framework’s email sending support

Pom

spring-boot-starter-mustache

Starter for building web applications using Mustache views

Pom

spring-boot-starter-quartz

Starter for using the Quartz scheduler

Pom

spring-boot-starter-security

Starter for using Spring Security

Pom

spring-boot-starter-test

Starter for testing Spring Boot applications with libraries including JUnit, Hamcrest and Mockito

Pom

spring-boot-starter-thymeleaf

Starter for building MVC web applications using Thymeleaf views

Pom

spring-boot-starter-validation

Starter for using Java Bean Validation with Hibernate Validator

Pom

spring-boot-starter-web

Starter for building web, including RESTful, applications using Spring MVC. Uses Tomcat as the default embedded container

Pom

spring-boot-starter-web-services

Starter for using Spring Web Services

Pom

spring-boot-starter-webflux

Starter for building WebFlux applications using Spring Framework’s Reactive Web support

Pom

spring-boot-starter-websocket

Starter for building WebSocket applications using Spring Framework’s WebSocket support

Pom


In addition to the application starters, the following starters can be used to add production ready features:

Table 13.2. Spring Boot production starters

NameDescriptionPom

spring-boot-starter-actuator

Starter for using Spring Boot’s Actuator which provides production ready features to help you monitor and manage your application

Pom


Finally, Spring Boot also includes the following starters that can be used if you want to exclude or swap specific technical facets:

Table 13.3. Spring Boot technical starters

NameDescriptionPom

spring-boot-starter-jetty

Starter for using Jetty as the embedded servlet container. An alternative to spring-boot-starter-tomcat

Pom

spring-boot-starter-log4j2

Starter for using Log4j2 for logging. An alternative to spring-boot-starter-logging

Pom

spring-boot-starter-logging

Starter for logging using Logback. Default logging starter

Pom

spring-boot-starter-reactor-netty

Starter for using Reactor Netty as the embedded reactive HTTP server.

Pom

spring-boot-starter-tomcat

Starter for using Tomcat as the embedded servlet container. Default servlet container starter used by spring-boot-starter-web

Pom

spring-boot-starter-undertow

Starter for using Undertow as the embedded servlet container. An alternative to spring-boot-starter-tomcat

Pom


[Tip]Tip

For a list of additional community contributed starters, see the README file in the spring-boot-starters module on GitHub.

14. Structuring Your Code

Spring Boot does not require any specific code layout to work. However, there are some best practices that help.

14.1 Using the “default” Package

When a class does not include a package declaration, it is considered to be in the “default package”. The use of the “default package” is generally discouraged and should be avoided. It can cause particular problems for Spring Boot applications that use the @ComponentScan, @EntityScan, or @SpringBootApplication annotations, since every class from every jar is read.

[Tip]Tip

We recommend that you follow Java’s recommended package naming conventions and use a reversed domain name (for example, com.example.project).

14.2 Locating the Main Application Class

We generally recommend that you locate your main application class in a root package above other classes. The @SpringBootApplication annotation is often placed on your main class, and it implicitly defines a base “search package” for certain items. For example, if you are writing a JPA application, the package of the @SpringBootApplication annotated class is used to search for @Entity items. Using a root package also allows component scan to apply only on your project.

[Tip]Tip

If you don’t want to use @SpringBootApplication, the @EnableAutoConfiguration and @ComponentScan annotations that it imports defines that behaviour so you can also use that instead.

The following listing shows a typical layout:

com
 +- example
     +- myapplication
         +- Application.java
         |
         +- customer
         |   +- Customer.java
         |   +- CustomerController.java
         |   +- CustomerService.java
         |   +- CustomerRepository.java
         |
         +- order
             +- Order.java
             +- OrderController.java
             +- OrderService.java
             +- OrderRepository.java

The Application.java file would declare the main method, along with the basic @SpringBootApplication, as follows:

package com.example.myapplication;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class Application {

	public static void main(String[] args) {
		SpringApplication.run(Application.class, args);
	}

}

15. Configuration Classes

Spring Boot favors Java-based configuration. Although it is possible to use SpringApplication with XML sources, we generally recommend that your primary source be a single @Configuration class. Usually the class that defines the main method is a good candidate as the primary @Configuration.

[Tip]Tip

Many Spring configuration examples have been published on the Internet that use XML configuration. If possible, always try to use the equivalent Java-based configuration. Searching for Enable* annotations can be a good starting point.

15.1 Importing Additional Configuration Classes

You need not put all your @Configuration into a single class. The @Import annotation can be used to import additional configuration classes. Alternatively, you can use @ComponentScan to automatically pick up all Spring components, including @Configuration classes.

15.2 Importing XML Configuration

If you absolutely must use XML based configuration, we recommend that you still start with a @Configuration class. You can then use an @ImportResource annotation to load XML configuration files.

16. Auto-configuration

Spring Boot auto-configuration attempts to automatically configure your Spring application based on the jar dependencies that you have added. For example, if HSQLDB is on your classpath, and you have not manually configured any database connection beans, then Spring Boot auto-configures an in-memory database.

You need to opt-in to auto-configuration by adding the @EnableAutoConfiguration or @SpringBootApplication annotations to one of your @Configuration classes.

[Tip]Tip

You should only ever add one @SpringBootApplication or @EnableAutoConfiguration annotation. We generally recommend that you add one or the other to your primary @Configuration class only.

16.1 Gradually Replacing Auto-configuration

Auto-configuration is non-invasive. At any point, you can start to define your own configuration to replace specific parts of the auto-configuration. For example, if you add your own DataSource bean, the default embedded database support backs away.

If you need to find out what auto-configuration is currently being applied, and why, start your application with the --debug switch. Doing so enables debug logs for a selection of core loggers and logs a conditions report to the console.

16.2 Disabling Specific Auto-configuration Classes

If you find that specific auto-configuration classes that you do not want are being applied, you can use the exclude attribute of @EnableAutoConfiguration to disable them, as shown in the following example:

import org.springframework.boot.autoconfigure.*;
import org.springframework.boot.autoconfigure.jdbc.*;
import org.springframework.context.annotation.*;

@Configuration
@EnableAutoConfiguration(exclude={DataSourceAutoConfiguration.class})
public class MyConfiguration {
}

If the class is not on the classpath, you can use the excludeName attribute of the annotation and specify the fully qualified name instead. Finally, you can also control the list of auto-configuration classes to exclude by using the spring.autoconfigure.exclude property.

[Tip]Tip

You can define exclusions both at the annotation level and by using the property.

17. Spring Beans and Dependency Injection

You are free to use any of the standard Spring Framework techniques to define your beans and their injected dependencies. For simplicity, we often find that using @ComponentScan (to find your beans) and using @Autowired (to do constructor injection) works well.

If you structure your code as suggested above (locating your application class in a root package), you can add @ComponentScan without any arguments. All of your application components (@Component, @Service, @Repository, @Controller etc.) are automatically registered as Spring Beans.

The following example shows a @Service Bean that uses constructor injection to obtain a required RiskAssessor bean:

package com.example.service;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

@Service
public class DatabaseAccountService implements AccountService {

	private final RiskAssessor riskAssessor;

	@Autowired
	public DatabaseAccountService(RiskAssessor riskAssessor) {
		this.riskAssessor = riskAssessor;
	}

	// ...

}

If a bean has one constructor, you can omit the @Autowired, as shown in the following example:

@Service
public class DatabaseAccountService implements AccountService {

	private final RiskAssessor riskAssessor;

	public DatabaseAccountService(RiskAssessor riskAssessor) {
		this.riskAssessor = riskAssessor;
	}

	// ...

}
[Tip]Tip

Notice how using constructor injection lets the riskAssessor field be marked as final, indicating that it cannot be subsequently changed.

18. Using the @SpringBootApplication Annotation

Many Spring Boot developers like their apps to use auto-configuration, component scan and be able to define extra configuration on their "application class". A single @SpringBootApplication annotation can be used to enable those three features, that is:

The @SpringBootApplication annotation is equivalent to using @Configuration, @EnableAutoConfiguration, and @ComponentScan with their default attributes, as shown in the following example:

package com.example.myapplication;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication // same as @Configuration @EnableAutoConfiguration @ComponentScan
public class Application {

	public static void main(String[] args) {
		SpringApplication.run(Application.class, args);
	}

}
[Note]Note

@SpringBootApplication also provides aliases to customize the attributes of @EnableAutoConfiguration and @ComponentScan.

[Note]Note

None of these features are mandatory and you may chose to replace this single annotation by any of the features that it enables. For instance, you may not want to use component scan in your application:

package com.example.myapplication;

import org.springframework.boot.SpringApplication;
import org.springframework.context.annotation.ComponentScan
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Import;

@Configuration
@EnableAutoConfiguration
@Import({ MyConfig.class, MyAnotherConfig.class })
public class Application {

	public static void main(String[] args) {
			SpringApplication.run(Application.class, args);
	}

}

In this example, Application is just like any other Spring Boot application except that @Component-annotated classes are not detected automatically and the user-defined beans are imported explicitly (see @Import).

19. Running Your Application

One of the biggest advantages of packaging your application as a jar and using an embedded HTTP server is that you can run your application as you would any other. Debugging Spring Boot applications is also easy. You do not need any special IDE plugins or extensions.

[Note]Note

This section only covers jar based packaging. If you choose to package your application as a war file, you should refer to your server and IDE documentation.

19.1 Running from an IDE

You can run a Spring Boot application from your IDE as a simple Java application. However, you first need to import your project. Import steps vary depending on your IDE and build system. Most IDEs can import Maven projects directly. For example, Eclipse users can select Import…​Existing Maven Projects from the File menu.

If you cannot directly import your project into your IDE, you may be able to generate IDE metadata by using a build plugin. Maven includes plugins for Eclipse and IDEA. Gradle offers plugins for various IDEs.

[Tip]Tip

If you accidentally run a web application twice, you see a “Port already in use” error. STS users can use the Relaunch button rather than the Run button to ensure that any existing instance is closed.

19.2 Running as a Packaged Application

If you use the Spring Boot Maven or Gradle plugins to create an executable jar, you can run your application using java -jar, as shown in the following example:

$ java -jar target/myapplication-0.0.1-SNAPSHOT.jar

It is also possible to run a packaged application with remote debugging support enabled. Doing so lets you attach a debugger to your packaged application, as shown in the following example:

$ java -Xdebug -Xrunjdwp:server=y,transport=dt_socket,address=8000,suspend=n \
       -jar target/myapplication-0.0.1-SNAPSHOT.jar

19.3 Using the Maven Plugin

The Spring Boot Maven plugin includes a run goal that can be used to quickly compile and run your application. Applications run in an exploded form, as they do in your IDE. The following example shows a typical Maven command to run a Spring Boot application:

$ mvn spring-boot:run

You might also want to use the MAVEN_OPTS operating system environment variable, as shown in the following example:

$ export MAVEN_OPTS=-Xmx1024m

19.4 Using the Gradle Plugin

The Spring Boot Gradle plugin also includes a bootRun task that can be used to run your application in an exploded form. The bootRun task is added whenever you apply the org.springframework.boot and java plugins and is shown in the following example:

$ gradle bootRun

You might also want to use the JAVA_OPTS operating system environment variable, as shown in the following example:

$ export JAVA_OPTS=-Xmx1024m

19.5 Hot Swapping

Since Spring Boot applications are just plain Java applications, JVM hot-swapping should work out of the box. JVM hot swapping is somewhat limited with the bytecode that it can replace. For a more complete solution, JRebel can be used.

The spring-boot-devtools module also includes support for quick application restarts. See the Chapter 20, Developer Tools section later in this chapter and the Hot swapping “How-to” for details.

20. Developer Tools

Spring Boot includes an additional set of tools that can make the application development experience a little more pleasant. The spring-boot-devtools module can be included in any project to provide additional development-time features. To include devtools support, add the module dependency to your build, as shown in the following listings for Maven and Gradle:

Maven. 

<dependencies>
	<dependency>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-devtools</artifactId>
		<optional>true</optional>
	</dependency>
</dependencies>

Gradle. 

dependencies {
	compile("org.springframework.boot:spring-boot-devtools")
}

[Note]Note

Developer tools are automatically disabled when running a fully packaged application. If your application is launched from java -jar or if it is started from a special classloader, then it is considered a “production application”. Flagging the dependency as optional in Maven or using compileOnly in Gradle is a best practice that prevents devtools from being transitively applied to other modules that use your project.

[Tip]Tip

Repackaged archives do not contain devtools by default. If you want to use a certain remote devtools feature, you need to disable the excludeDevtools build property to include it. The property is supported with both the Maven and Gradle plugins.

20.1 Property Defaults

Several of the libraries supported by Spring Boot use caches to improve performance. For example, template engines cache compiled templates to avoid repeatedly parsing template files. Also, Spring MVC can add HTTP caching headers to responses when serving static resources.

While caching is very beneficial in production, it can be counter-productive during development, preventing you from seeing the changes you just made in your application. For this reason, spring-boot-devtools disables the caching options by default.

Cache options are usually configured by settings in your application.properties file. For example, Thymeleaf offers the spring.thymeleaf.cache property. Rather than needing to set these properties manually, the spring-boot-devtools module automatically applies sensible development-time configuration.

[Tip]Tip

For a complete list of the properties that are applied by the devtools, see DevToolsPropertyDefaultsPostProcessor.

20.2 Automatic Restart

Applications that use spring-boot-devtools automatically restart whenever files on the classpath change. This can be a useful feature when working in an IDE, as it gives a very fast feedback loop for code changes. By default, any entry on the classpath that points to a folder is monitored for changes. Note that certain resources, such as static assets and view templates, do not need to restart the application.

[Note]Note

As long as forking is enabled, you can also start your application by using the supported build plugins (Maven and Gradle), since DevTools needs an isolated application classloader to operate properly. By default, Gradle and Maven do that when they detect DevTools on the classpath.

[Tip]Tip

Automatic restart works very well when used with LiveReload. See the LiveReload section for details. If you use JRebel, automatic restarts are disabled in favor of dynamic class reloading. Other devtools features (such as LiveReload and property overrides) can still be used.

[Note]Note

DevTools relies on the application context’s shutdown hook to close it during a restart. It does not work correctly if you have disabled the shutdown hook (SpringApplication.setRegisterShutdownHook(false)).

[Note]Note

When deciding if an entry on the classpath should trigger a restart when it changes, DevTools automatically ignores projects named spring-boot, spring-boot-devtools, spring-boot-autoconfigure, spring-boot-actuator, and spring-boot-starter.

[Note]Note

DevTools needs to customize the ResourceLoader used by the ApplicationContext. If your application provides one already, it is going to be wrapped. Direct override of the getResource method on the ApplicationContext is not supported.

20.2.1 Logging changes in condition evaluation

By default, each time your application restarts, a report showing the condition evaluation delta is logged. The report shows the changes to your application’s auto-configuration as you make changes such as adding or removing beans and setting configuration properties.

To disable the logging of the report, set the following property:

spring.devtools.restart.log-condition-evaluation-delta=false

20.2.2 Excluding Resources

Certain resources do not necessarily need to trigger a restart when they are changed. For example, Thymeleaf templates can be edited in-place. By default, changing resources in /META-INF/maven, /META-INF/resources, /resources, /static, /public, or /templates does not trigger a restart but does trigger a live reload. If you want to customize these exclusions, you can use the spring.devtools.restart.exclude property. For example, to exclude only /static and /public you would set the following property:

spring.devtools.restart.exclude=static/**,public/**
[Tip]Tip

If you want to keep those defaults and add additional exclusions, use the spring.devtools.restart.additional-exclude property instead.

20.2.3 Watching Additional Paths

You may want your application to be restarted or reloaded when you make changes to files that are not on the classpath. To do so, use the spring.devtools.restart.additional-paths property to configure additional paths to watch for changes. You can use the spring.devtools.restart.exclude property described earlier to control whether changes beneath the additional paths trigger a full restart or a live reload.

20.2.4 Disabling Restart

If you do not want to use the restart feature, you can disable it by using the spring.devtools.restart.enabled property. In most cases, you can set this property in your application.properties (doing so still initializes the restart classloader, but it does not watch for file changes).

If you need to completely disable restart support (for example, because it does not work with a specific library), you need to set the spring.devtools.restart.enabled System property to false before calling SpringApplication.run(…​), as shown in the following example:

public static void main(String[] args) {
	System.setProperty("spring.devtools.restart.enabled", "false");
	SpringApplication.run(MyApp.class, args);
}

20.2.5 Using a Trigger File

If you work with an IDE that continuously compiles changed files, you might prefer to trigger restarts only at specific times. To do so, you can use a “trigger file”, which is a special file that must be modified when you want to actually trigger a restart check. Changing the file only triggers the check and the restart only occurs if Devtools has detected it has to do something. The trigger file can be updated manually or with an IDE plugin.

To use a trigger file, set the spring.devtools.restart.trigger-file property to the path of your trigger file.

[Tip]Tip

You might want to set spring.devtools.restart.trigger-file as a global setting, so that all your projects behave in the same way.

20.2.6 Customizing the Restart Classloader

As described earlier in the Restart vs Reload section, restart functionality is implemented by using two classloaders. For most applications, this approach works well. However, it can sometimes cause classloading issues.

By default, any open project in your IDE is loaded with the “restart” classloader, and any regular .jar file is loaded with the “base” classloader. If you work on a multi-module project, and not every module is imported into your IDE, you may need to customize things. To do so, you can create a META-INF/spring-devtools.properties file.

The spring-devtools.properties file can contain properties prefixed with restart.exclude and restart.include. The include elements are items that should be pulled up into the “restart” classloader, and the exclude elements are items that should be pushed down into the “base” classloader. The value of the property is a regex pattern that is applied to the classpath, as shown in the following example:

restart.exclude.companycommonlibs=/mycorp-common-[\\w-]+\.jar
restart.include.projectcommon=/mycorp-myproj-[\\w-]+\.jar
[Note]Note

All property keys must be unique. As long as a property starts with restart.include. or restart.exclude. it is considered.

[Tip]Tip

All META-INF/spring-devtools.properties from the classpath are loaded. You can package files inside your project, or in the libraries that the project consumes.

20.2.7 Known Limitations

Restart functionality does not work well with objects that are deserialized by using a standard ObjectInputStream. If you need to deserialize data, you may need to use Spring’s ConfigurableObjectInputStream in combination with Thread.currentThread().getContextClassLoader().

Unfortunately, several third-party libraries deserialize without considering the context classloader. If you find such a problem, you need to request a fix with the original authors.

20.3 LiveReload

The spring-boot-devtools module includes an embedded LiveReload server that can be used to trigger a browser refresh when a resource is changed. LiveReload browser extensions are freely available for Chrome, Firefox and Safari from livereload.com.

If you do not want to start the LiveReload server when your application runs, you can set the spring.devtools.livereload.enabled property to false.

[Note]Note

You can only run one LiveReload server at a time. Before starting your application, ensure that no other LiveReload servers are running. If you start multiple applications from your IDE, only the first has LiveReload support.

20.4 Global Settings

You can configure global devtools settings by adding a file named .spring-boot-devtools.properties to your $HOME folder (note that the filename starts with “.”). Any properties added to this file apply to all Spring Boot applications on your machine that use devtools. For example, to configure restart to always use a trigger file, you would add the following property:

~/.spring-boot-devtools.properties. 

spring.devtools.reload.trigger-file=.reloadtrigger

20.5 Remote Applications

The Spring Boot developer tools are not limited to local development. You can also use several features when running applications remotely. Remote support is opt-in. To enable it, you need to make sure that devtools is included in the repackaged archive, as shown in the following listing:

<build>
	<plugins>
		<plugin>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-maven-plugin</artifactId>
			<configuration>
				<excludeDevtools>false</excludeDevtools>
			</configuration>
		</plugin>
	</plugins>
</build>

Then you need to set a spring.devtools.remote.secret property, as shown in the following example:

spring.devtools.remote.secret=mysecret
[Warning]Warning

Enabling spring-boot-devtools on a remote application is a security risk. You should never enable support on a production deployment.

Remote devtools support is provided in two parts: a server-side endpoint that accepts connections and a client application that you run in your IDE. The server component is automatically enabled when the spring.devtools.remote.secret property is set. The client component must be launched manually.

20.5.1 Running the Remote Client Application

The remote client application is designed to be run from within your IDE. You need to run org.springframework.boot.devtools.RemoteSpringApplication with the same classpath as the remote project that you connect to. The application’s single required argument is the remote URL to which it connects.

For example, if you are using Eclipse or STS and you have a project named my-app that you have deployed to Cloud Foundry, you would do the following:

  • Select Run Configurations…​ from the Run menu.
  • Create a new Java Application “launch configuration”.
  • Browse for the my-app project.
  • Use org.springframework.boot.devtools.RemoteSpringApplication as the main class.
  • Add https://myapp.cfapps.io to the Program arguments (or whatever your remote URL is).

A running remote client might resemble the following listing:

  .   ____          _                                              __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _          ___               _      \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` |        | _ \___ _ __  ___| |_ ___ \ \ \ \
 \\/  ___)| |_)| | | | | || (_| []::::::[]   / -_) '  \/ _ \  _/ -_) ) ) ) )
  '  |____| .__|_| |_|_| |_\__, |        |_|_\___|_|_|_\___/\__\___|/ / / /
 =========|_|==============|___/===================================/_/_/_/
 :: Spring Boot Remote :: 2.0.3.RELEASE

2015-06-10 18:25:06.632  INFO 14938 --- [           main] o.s.b.devtools.RemoteSpringApplication   : Starting RemoteSpringApplication on pwmbp with PID 14938 (/Users/pwebb/projects/spring-boot/code/spring-boot-devtools/target/classes started by pwebb in /Users/pwebb/projects/spring-boot/code/spring-boot-samples/spring-boot-sample-devtools)
2015-06-10 18:25:06.671  INFO 14938 --- [           main] s.c.a.AnnotationConfigApplicationContext : Refreshing org.spring[email protected]2a17b7b6: startup date [Wed Jun 10 18:25:06 PDT 2015]; root of context hierarchy
2015-06-10 18:25:07.043  WARN 14938 --- [           main] o.s.b.d.r.c.RemoteClientConfiguration    : The connection to http://localhost:8080 is insecure. You should use a URL starting with 'https://'.
2015-06-10 18:25:07.074  INFO 14938 --- [           main] o.s.b.d.a.OptionalLiveReloadServer       : LiveReload server is running on port 35729
2015-06-10 18:25:07.130  INFO 14938 --- [           main] o.s.b.devtools.RemoteSpringApplication   : Started RemoteSpringApplication in 0.74 seconds (JVM running for 1.105)
[Note]Note

Because the remote client is using the same classpath as the real application it can directly read application properties. This is how the spring.devtools.remote.secret property is read and passed to the server for authentication.

[Tip]Tip

It is always advisable to use https:// as the connection protocol, so that traffic is encrypted and passwords cannot be intercepted.

[Tip]Tip

If you need to use a proxy to access the remote application, configure the spring.devtools.remote.proxy.host and spring.devtools.remote.proxy.port properties.

20.5.2 Remote Update

The remote client monitors your application classpath for changes in the same way as the local restart. Any updated resource is pushed to the remote application and (if required) triggers a restart. This can be helpful if you iterate on a feature that uses a cloud service that you do not have locally. Generally, remote updates and restarts are much quicker than a full rebuild and deploy cycle.

[Note]Note

Files are only monitored when the remote client is running. If you change a file before starting the remote client, it is not pushed to the remote server.

21. Packaging Your Application for Production

Executable jars can be used for production deployment. As they are self-contained, they are also ideally suited for cloud-based deployment.

For additional “production ready” features, such as health, auditing, and metric REST or JMX end-points, consider adding spring-boot-actuator. See Part V, “Spring Boot Actuator: Production-ready features” for details.

22. What to Read Next

You should now understand how you can use Spring Boot and some best practices that you should follow. You can now go on to learn about specific Spring Boot features in depth, or you could skip ahead and read about the “production ready” aspects of Spring Boot.

Part IV. Spring Boot features

This section dives into the details of Spring Boot. Here you can learn about the key features that you may want to use and customize. If you have not already done so, you might want to read the "Part II, “Getting Started”" and "Part III, “Using Spring Boot”" sections, so that you have a good grounding of the basics.

23. SpringApplication

The SpringApplication class provides a convenient way to bootstrap a Spring application that is started from a main() method. In many situations, you can delegate to the static SpringApplication.run method, as shown in the following example:

public static void main(String[] args) {
	SpringApplication.run(MySpringConfiguration.class, args);
}

When your application starts, you should see something similar to the following output:

  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::   v2.0.3.RELEASE

2013-07-31 00:08:16.117  INFO 56603 --- [           main] o.s.b.s.app.SampleApplication            : Starting SampleApplication v0.1.0 on mycomputer with PID 56603 (/apps/myapp.jar started by pwebb)
2013-07-31 00:08:16.166  INFO 56603 --- [           main] ationConfigServletWebServerApplicationContext : Refreshing org.springframework.boot.web.ser[email protected]6e5a8246: startup date [Wed Jul 31 00:08:16 PDT 2013]; root of context hierarchy
2014-03-04 13:09:54.912  INFO 41370 --- [           main] .t.TomcatServletWebServerFactory : Server initialized with port: 8080
2014-03-04 13:09:56.501  INFO 41370 --- [           main] o.s.b.s.app.SampleApplication            : Started SampleApplication in 2.992 seconds (JVM running for 3.658)

By default, INFO logging messages are shown, including some relevant startup details, such as the user that launched the application. If you need a log level other than INFO, you can set it, as described in Section 26.4, “Log Levels”,

23.1 Startup Failure

If your application fails to start, registered FailureAnalyzers get a chance to provide a dedicated error message and a concrete action to fix the problem. For instance, if you start a web application on port 8080 and that port is already in use, you should see something similar to the following message:

***************************
APPLICATION FAILED TO START
***************************

Description:

Embedded servlet container failed to start. Port 8080 was already in use.

Action:

Identify and stop the process that's listening on port 8080 or configure this application to listen on another port.
[Note]Note

Spring Boot provides numerous FailureAnalyzer implementations, and you can add your own.

If no failure analyzers are able to handle the exception, you can still display the full conditions report to better understand what went wrong. To do so, you need to enable the debug property or enable DEBUG logging for org.springframework.boot.autoconfigure.logging.ConditionEvaluationReportLoggingListener.

For instance, if you are running your application by using java -jar, you can enable the debug property as follows:

$ java -jar myproject-0.0.1-SNAPSHOT.jar --debug

23.2 Customizing the Banner

The banner that is printed on start up can be changed by adding a banner.txt file to your classpath or by setting the spring.banner.location property to the location of such a file. If the file has an encoding other than UTF-8, you can set spring.banner.charset. In addition to a text file, you can also add a banner.gif, banner.jpg, or banner.png image file to your classpath or set the spring.banner.image.location property. Images are converted into an ASCII art representation and printed above any text banner.

Inside your banner.txt file, you can use any of the following placeholders:

Table 23.1. Banner variables

VariableDescription

${application.version}

The version number of your application, as declared in MANIFEST.MF. For example, Implementation-Version: 1.0 is printed as 1.0.

${application.formatted-version}

The version number of your application, as declared in MANIFEST.MF and formatted for display (surrounded with brackets and prefixed with v). For example (v1.0).

${spring-boot.version}

The Spring Boot version that you are using. For example 2.0.3.RELEASE.

${spring-boot.formatted-version}

The Spring Boot version that you are using, formatted for display (surrounded with brackets and prefixed with v). For example (v2.0.3.RELEASE).

${Ansi.NAME} (or ${AnsiColor.NAME}, ${AnsiBackground.NAME}, ${AnsiStyle.NAME})

Where NAME is the name of an ANSI escape code. See AnsiPropertySource for details.

${application.title}

The title of your application, as declared in MANIFEST.MF. For example Implementation-Title: MyApp is printed as MyApp.


[Tip]Tip

The SpringApplication.setBanner(…​) method can be used if you want to generate a banner programmatically. Use the org.springframework.boot.Banner interface and implement your own printBanner() method.

You can also use the spring.main.banner-mode property to determine if the banner has to be printed on System.out (console), sent to the configured logger (log), or not produced at all (off).

The printed banner is registered as a singleton bean under the following name: springBootBanner.

[Note]Note

YAML maps off to false, so be sure to add quotes if you want to disable the banner in your application, as shown in the following example:

spring:
	main:
		banner-mode: "off"

23.3 Customizing SpringApplication

If the SpringApplication defaults are not to your taste, you can instead create a local instance and customize it. For example, to turn off the banner, you could write:

public static void main(String[] args) {
	SpringApplication app = new SpringApplication(MySpringConfiguration.class);
	app.setBannerMode(Banner.Mode.OFF);
	app.run(args);
}
[Note]Note

The constructor arguments passed to SpringApplication are configuration sources for Spring beans. In most cases, these are references to @Configuration classes, but they could also be references to XML configuration or to packages that should be scanned.

It is also possible to configure the SpringApplication by using an application.properties file. See Chapter 24, Externalized Configuration for details.

For a complete list of the configuration options, see the SpringApplication Javadoc.

23.4 Fluent Builder API

If you need to build an ApplicationContext hierarchy (multiple contexts with a parent/child relationship) or if you prefer using a “fluent” builder API, you can use the SpringApplicationBuilder.

The SpringApplicationBuilder lets you chain together multiple method calls and includes parent and child methods that let you create a hierarchy, as shown in the following example:

new SpringApplicationBuilder()
		.sources(Parent.class)
		.child(Application.class)
		.bannerMode(Banner.Mode.OFF)
		.run(args);
[Note]Note

There are some restrictions when creating an ApplicationContext hierarchy. For example, Web components must be contained within the child context, and the same Environment is used for both parent and child contexts. See the SpringApplicationBuilder Javadoc for full details.

23.5 Application Events and Listeners

In addition to the usual Spring Framework events, such as ContextRefreshedEvent, a SpringApplication sends some additional application events.

[Note]Note

Some events are actually triggered before the ApplicationContext is created, so you cannot register a listener on those as a @Bean. You can register them with the SpringApplication.addListeners(…​) method or the SpringApplicationBuilder.listeners(…​) method.

If you want those listeners to be registered automatically, regardless of the way the application is created, you can add a META-INF/spring.factories file to your project and reference your listener(s) by using the org.springframework.context.ApplicationListener key, as shown in the following example:

org.springframework.context.ApplicationListener=com.example.project.MyListener

Application events are sent in the following order, as your application runs:

  1. An ApplicationStartingEvent is sent at the start of a run but before any processing, except for the registration of listeners and initializers.
  2. An ApplicationEnvironmentPreparedEvent is sent when the Environment to be used in the context is known but before the context is created.
  3. An ApplicationPreparedEvent is sent just before the refresh is started but after bean definitions have been loaded.
  4. An ApplicationStartedEvent is sent after the context has been refreshed but before any application and command-line runners have been called.
  5. An ApplicationReadyEvent is sent after any application and command-line runners have been called. It indicates that the application is ready to service requests.
  6. An ApplicationFailedEvent is sent if there is an exception on startup.
[Tip]Tip

You often need not use application events, but it can be handy to know that they exist. Internally, Spring Boot uses events to handle a variety of tasks.

Application events are sent by using Spring Framework’s event publishing mechanism. Part of this mechanism ensures that an event published to the listeners in a child context is also published to the listeners in any ancestor contexts. As a result of this, if your application uses a hierarchy of SpringApplication instances, a listener may receive multiple instances of the same type of application event.

To allow your listener to distinguish between an event for its context and an event for a descendant context, it should request that its application context is injected and then compare the injected context with the context of the event. The context can be injected by implementing ApplicationContextAware or, if the listener is a bean, by using @Autowired.

23.6 Web Environment

A SpringApplication attempts to create the right type of ApplicationContext on your behalf. The algorithm used to determine a WebApplicationType is fairly simple:

  • If Spring MVC is present, an AnnotationConfigServletWebServerApplicationContext is used
  • If Spring MVC is not present and Spring WebFlux is present, an AnnotationConfigReactiveWebServerApplicationContext is used
  • Otherwise, AnnotationConfigApplicationContext is used

This means that if you are using Spring MVC and the new WebClient from Spring WebFlux in the same application, Spring MVC will be used by default. You can override that easily by calling setWebApplicationType(WebApplicationType).

It is also possible to take complete control of the ApplicationContext type that is used by calling setApplicationContextClass(…​).

[Tip]Tip

It is often desirable to call setWebApplicationType(WebApplicationType.NONE) when using SpringApplication within a JUnit test.

23.7 Accessing Application Arguments

If you need to access the application arguments that were passed to SpringApplication.run(…​), you can inject a org.springframework.boot.ApplicationArguments bean. The ApplicationArguments interface provides access to both the raw String[] arguments as well as parsed option and non-option arguments, as shown in the following example:

import org.springframework.boot.*;
import org.springframework.beans.factory.annotation.*;
import org.springframework.stereotype.*;

@Component
public class MyBean {

	@Autowired
	public MyBean(ApplicationArguments args) {
		boolean debug = args.containsOption("debug");
		List<String> files = args.getNonOptionArgs();
		// if run with "--debug logfile.txt" debug=true, files=["logfile.txt"]
	}

}
[Tip]Tip

Spring Boot also registers a CommandLinePropertySource with the Spring Environment. This lets you also inject single application arguments by using the @Value annotation.

23.8 Using the ApplicationRunner or CommandLineRunner

If you need to run some specific code once the SpringApplication has started, you can implement the ApplicationRunner or CommandLineRunner interfaces. Both interfaces work in the same way and offer a single run method, which is called just before SpringApplication.run(…​) completes.

The CommandLineRunner interfaces provides access to application arguments as a simple string array, whereas the ApplicationRunner uses the ApplicationArguments interface discussed earlier. The following example shows a CommandLineRunner with a run method:

import org.springframework.boot.*;
import org.springframework.stereotype.*;

@Component
public class MyBean implements CommandLineRunner {

	public void run(String... args) {
		// Do something...
	}

}

If several CommandLineRunner or ApplicationRunner beans are defined that must be called in a specific order, you can additionally implement the org.springframework.core.Ordered interface or use the org.springframework.core.annotation.Order annotation.

23.9 Application Exit

Each SpringApplication registers a shutdown hook with the JVM to ensure that the ApplicationContext closes gracefully on exit. All the standard Spring lifecycle callbacks (such as the DisposableBean interface or the @PreDestroy annotation) can be used.

In addition, beans may implement the org.springframework.boot.ExitCodeGenerator interface if they wish to return a specific exit code when SpringApplication.exit() is called. This exit code can then be passed to System.exit() to return it as a status code, as shown in the following example:

@SpringBootApplication
public class ExitCodeApplication {

	@Bean
	public ExitCodeGenerator exitCodeGenerator() {
		return () -> 42;
	}

	public static void main(String[] args) {
		System.exit(SpringApplication
				.exit(SpringApplication.run(ExitCodeApplication.class, args)));
	}

}

Also, the ExitCodeGenerator interface may be implemented by exceptions. When such an exception is encountered, Spring Boot returns the exit code provided by the implemented getExitCode() method.

23.10 Admin Features

It is possible to enable admin-related features for the application by specifying the spring.application.admin.enabled property. This exposes the SpringApplicationAdminMXBean on the platform MBeanServer. You could use this feature to administer your Spring Boot application remotely. This feature could also be useful for any service wrapper implementation.

[Tip]Tip

If you want to know on which HTTP port the application is running, get the property with a key of local.server.port.

[Caution]Caution

Take care when enabling this feature, as the MBean exposes a method to shutdown the application.

24. Externalized Configuration

Spring Boot lets you externalize your configuration so that you can work with the same application code in different environments. You can use properties files, YAML files, environment variables, and command-line arguments to externalize configuration. Property values can be injected directly into your beans by using the @Value annotation, accessed through Spring’s Environment abstraction, or be bound to structured objects through @ConfigurationProperties.

Spring Boot uses a very particular PropertySource order that is designed to allow sensible overriding of values. Properties are considered in the following order:

  1. Devtools global settings properties on your home directory (~/.spring-boot-devtools.properties when devtools is active).
  2. @TestPropertySource annotations on your tests.
  3. @SpringBootTest#properties annotation attribute on your tests.
  4. Command line arguments.
  5. Properties from SPRING_APPLICATION_JSON (inline JSON embedded in an environment variable or system property).
  6. ServletConfig init parameters.
  7. ServletContext init parameters.
  8. JNDI attributes from java:comp/env.
  9. Java System properties (System.getProperties()).
  10. OS environment variables.
  11. A RandomValuePropertySource that has properties only in random.*.
  12. Profile-specific application properties outside of your packaged jar (application-{profile}.properties and YAML variants).
  13. Profile-specific application properties packaged inside your jar (application-{profile}.properties and YAML variants).
  14. Application properties outside of your packaged jar (application.properties and YAML variants).
  15. Application properties packaged inside your jar (application.properties and YAML variants).
  16. @PropertySource annotations on your @Configuration classes.
  17. Default properties (specified by setting SpringApplication.setDefaultProperties).

To provide a concrete example, suppose you develop a @Component that uses a name property, as shown in the following example:

import org.springframework.stereotype.*;
import org.springframework.beans.factory.annotation.*;

@Component
public class MyBean {

    @Value("${name}")
    private String name;

    // ...

}

On your application classpath (for example, inside your jar) you can have an application.properties file that provides a sensible default property value for name. When running in a new environment, an application.properties file can be provided outside of your jar that overrides the name. For one-off testing, you can launch with a specific command line switch (for example, java -jar app.jar --name="Spring").

[Tip]Tip

The SPRING_APPLICATION_JSON properties can be supplied on the command line with an environment variable. For example, you could use the following line in a UN*X shell:

$ SPRING_APPLICATION_JSON='{"acme":{"name":"test"}}' java -jar myapp.jar

In the preceding example, you end up with acme.name=test in the Spring Environment. You can also supply the JSON as spring.application.json in a System property, as shown in the following example:

$ java -Dspring.application.json='{"name":"test"}' -jar myapp.jar

You can also supply the JSON by using a command line argument, as shown in the following example:

$ java -jar myapp.jar --spring.application.json='{"name":"test"}'

You can also supply the JSON as a JNDI variable, as follows: java:comp/env/spring.application.json.

24.1 Configuring Random Values

The RandomValuePropertySource is useful for injecting random values (for example, into secrets or test cases). It can produce integers, longs, uuids, or strings, as shown in the following example:

my.secret=${random.value}
my.number=${random.int}
my.bignumber=${random.long}
my.uuid=${random.uuid}
my.number.less.than.ten=${random.int(10)}
my.number.in.range=${random.int[1024,65536]}

The random.int* syntax is OPEN value (,max) CLOSE where the OPEN,CLOSE are any character and value,max are integers. If max is provided, then value is the minimum value and max is the maximum value (exclusive).

24.2 Accessing Command Line Properties

By default, SpringApplication converts any command line option arguments (that is, arguments starting with --, such as --server.port=9000) to a property and adds them to the Spring Environment. As mentioned previously, command line properties always take precedence over other property sources.

If you do not want command line properties to be added to the Environment, you can disable them by using SpringApplication.setAddCommandLineProperties(false).

24.3 Application Property Files

SpringApplication loads properties from application.properties files in the following locations and adds them to the Spring Environment:

  1. A /config subdirectory of the current directory
  2. The current directory
  3. A classpath /config package
  4. The classpath root

The list is ordered by precedence (properties defined in locations higher in the list override those defined in lower locations).

[Note]Note

You can also use YAML ('.yml') files as an alternative to '.properties'.

If you do not like application.properties as the configuration file name, you can switch to another file name by specifying a spring.config.name environment property. You can also refer to an explicit location by using the spring.config.location environment property (which is a comma-separated list of directory locations or file paths). The following example shows how to specify a different file name:

$ java -jar myproject.jar --spring.config.name=myproject

The following example shows how to specify two locations:

$ java -jar myproject.jar --spring.config.location=classpath:/default.properties,classpath:/override.properties
[Warning]Warning

spring.config.name and spring.config.location are used very early to determine which files have to be loaded, so they must be defined as an environment property (typically an OS environment variable, a system property, or a command-line argument).

If spring.config.location contains directories (as opposed to files), they should end in / (and, at runtime, be appended with the names generated from spring.config.name before being loaded, including profile-specific file names). Files specified in spring.config.location are used as-is, with no support for profile-specific variants, and are overridden by any profile-specific properties.

Config locations are searched in reverse order. By default, the configured locations are classpath:/,classpath:/config/,file:./,file:./config/. The resulting search order is the following:

  1. file:./config/
  2. file:./
  3. classpath:/config/
  4. classpath:/

When custom config locations are configured by using spring.config.location, they replace the default locations. For example, if spring.config.location is configured with the value classpath:/custom-config/,file:./custom-config/, the search order becomes the following:

  1. file:./custom-config/
  2. classpath:custom-config/

Alternatively, when custom config locations are configured by using spring.config.additional-location, they are used in addition to the default locations. Additional locations are searched before the default locations. For example, if additional locations of classpath:/custom-config/,file:./custom-config/ are configured, the search order becomes the following:

  1. file:./custom-config/
  2. classpath:custom-config/
  3. file:./config/
  4. file:./
  5. classpath:/config/
  6. classpath:/

This search ordering lets you specify default values in one configuration file and then selectively override those values in another. You can provide default values for your application in application.properties (or whatever other basename you choose with spring.config.name) in one of the default locations. These default values can then be overridden at runtime with a different file located in one of the custom locations.

[Note]Note

If you use environment variables rather than system properties, most operating systems disallow period-separated key names, but you can use underscores instead (for example, SPRING_CONFIG_NAME instead of spring.config.name).

[Note]Note

If your application runs in a container, then JNDI properties (in java:comp/env) or servlet context initialization parameters can be used instead of, or as well as, environment variables or system properties.

24.4 Profile-specific Properties

In addition to application.properties files, profile-specific properties can also be defined by using the following naming convention: application-{profile}.properties. The Environment has a set of default profiles (by default, [default]) that are used if no active profiles are set. In other words, if no profiles are explicitly activated, then properties from application-default.properties are loaded.

Profile-specific properties are loaded from the same locations as standard application.properties, with profile-specific files always overriding the non-specific ones, whether or not the profile-specific files are inside or outside your packaged jar.

If several profiles are specified, a last-wins strategy applies. For example, profiles specified by the spring.profiles.active property are added after those configured through the SpringApplication API and therefore take precedence.

[Note]Note

If you have specified any files in spring.config.location, profile-specific variants of those files are not considered. Use directories in spring.config.location if you want to also use profile-specific properties.

24.5 Placeholders in Properties

The values in application.properties are filtered through the existing Environment when they are used, so you can refer back to previously defined values (for example, from System properties).

app.name=MyApp
app.description=${app.name} is a Spring Boot application
[Tip]Tip

You can also use this technique to create “short” variants of existing Spring Boot properties. See the Section 74.4, “Use ‘Short’ Command Line Arguments” how-to for details.

24.6 Using YAML Instead of Properties

YAML is a superset of JSON and, as such, is a convenient format for specifying hierarchical configuration data. The SpringApplication class automatically supports YAML as an alternative to properties whenever you have the SnakeYAML library on your classpath.

[Note]Note

If you use “Starters”, SnakeYAML is automatically provided by spring-boot-starter.

24.6.1 Loading YAML

Spring Framework provides two convenient classes that can be used to load YAML documents. The YamlPropertiesFactoryBean loads YAML as Properties and the YamlMapFactoryBean loads YAML as a Map.

For example, consider the following YAML document:

environments:
	dev:
		url: http://dev.example.com
		name: Developer Setup
	prod:
		url: http://another.example.com
		name: My Cool App

The preceding example would be transformed into the following properties:

environments.dev.url=http://dev.example.com
environments.dev.name=Developer Setup
environments.prod.url=http://another.example.com
environments.prod.name=My Cool App

YAML lists are represented as property keys with [index] dereferencers. For example, consider the following YAML:

my:
servers:
	- dev.example.com
	- another.example.com

The preceding example would be transformed into these properties:

my.servers[0]=dev.example.com
my.servers[1]=another.example.com

To bind to properties like that by using Spring Boot’s Binder utilities (which is what @ConfigurationProperties does), you need to have a property in the target bean of type java.util.List (or Set) and you either need to provide a setter or initialize it with a mutable value. For example, the following example binds to the properties shown previously:

@ConfigurationProperties(prefix="my")
public class Config {

	private List<String> servers = new ArrayList<String>();

	public List<String> getServers() {
		return this.servers;
	}
}

24.6.2 Exposing YAML as Properties in the Spring Environment

The YamlPropertySourceLoader class can be used to expose YAML as a PropertySource in the Spring Environment. Doing so lets you use the @Value annotation with placeholders syntax to access YAML properties.

24.6.3 Multi-profile YAML Documents

You can specify multiple profile-specific YAML documents in a single file by using a spring.profiles key to indicate when the document applies, as shown in the following example:

server:
	address: 192.168.1.100
---
spring:
	profiles: development
server:
	address: 127.0.0.1
---
spring:
	profiles: production
server:
	address: 192.168.1.120

In the preceding example, if the development profile is active, the server.address property is 127.0.0.1. Similarly, if the production profile is active, the server.address property is 192.168.1.120. If the development and production profiles are not enabled, then the value for the property is 192.168.1.100.

If none are explicitly active when the application context starts, the default profiles are activated. So, in the following YAML, we set a value for spring.security.user.password that is available only in the "default" profile:

server:
  port: 8000
---
spring:
  profiles: default
  security:
    user:
      password: weak

Whereas, in the following example, the password is always set because it is not attached to any profile, and it would have to be explicitly reset in all other profiles as necessary:

server:
  port: 8000
spring:
  security:
    user:
      password: weak

Spring profiles designated by using the spring.profiles element may optionally be negated by using the ! character. If both negated and non-negated profiles are specified for a single document, at least one non-negated profile must match, and no negated profiles may match.

24.6.4 YAML Shortcomings

YAML files cannot be loaded by using the @PropertySource annotation. So, in the case that you need to load values that way, you need to use a properties file.

24.7 Type-safe Configuration Properties

Using the @Value("${property}") annotation to inject configuration properties can sometimes be cumbersome, especially if you are working with multiple properties or your data is hierarchical in nature. Spring Boot provides an alternative method of working with properties that lets strongly typed beans govern and validate the configuration of your application, as shown in the following example:

package com.example;

import java.net.InetAddress;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

import org.springframework.boot.context.properties.ConfigurationProperties;

@ConfigurationProperties("acme")
public class AcmeProperties {

	private boolean enabled;

	private InetAddress remoteAddress;

	private final Security security = new Security();

	public boolean isEnabled() { ... }

	public void setEnabled(boolean enabled) { ... }

	public InetAddress getRemoteAddress() { ... }

	public void setRemoteAddress(InetAddress remoteAddress) { ... }

	public Security getSecurity() { ... }

	public static class Security {

		private String username;

		private String password;

		private List<String> roles = new ArrayList<>(Collections.singleton("USER"));

		public String getUsername() { ... }

		public void setUsername(String username) { ... }

		public String getPassword() { ... }

		public void setPassword(String password) { ... }

		public List<String> getRoles() { ... }

		public void setRoles(List<String> roles) { ... }

	}
}

The preceding POJO defines the following properties:

  • acme.enabled, with a value of false by default.
  • acme.remote-address, with a type that can be coerced from String.
  • acme.security.username, with a nested "security" object whose name is determined by the name of the property. In particular, the return type is not used at all there and could have been SecurityProperties.
  • acme.security.password.
  • acme.security.roles, with a collection of String.
[Note]Note

Getters and setters are usually mandatory, since binding is through standard Java Beans property descriptors, just like in Spring MVC. A setter may be omitted in the following cases:

  • Maps, as long as they are initialized, need a getter but not necessarily a setter, since they can be mutated by the binder.
  • Collections and arrays can be accessed either through an index (typically with YAML) or by using a single comma-separated value (properties). In the latter case, a setter is mandatory. We recommend to always add a setter for such types. If you initialize a collection, make sure it is not immutable (as in the preceding example).
  • If nested POJO properties are initialized (like the Security field in the preceding example), a setter is not required. If you want the binder to create the instance on the fly by using its default constructor, you need a setter.

Some people use Project Lombok to add getters and setters automatically. Make sure that Lombok does not generate any particular constructor for such a type, as it is used automatically by the container to instantiate the object.

Finally, only standard Java Bean properties are considered and binding on static properties are not supported.

You also need to list the properties classes to register in the @EnableConfigurationProperties annotation, as shown in the following example:

@Configuration
@EnableConfigurationProperties(AcmeProperties.class)
public class MyConfiguration {
}
[Note]Note

When the @ConfigurationProperties bean is registered that way, the bean has a conventional name: <prefix>-<fqn>, where <prefix> is the environment key prefix specified in the @ConfigurationProperties annotation and <fqn> is the fully qualified name of the bean. If the annotation does not provide any prefix, only the fully qualified name of the bean is used.

The bean name in the example above is acme-com.example.AcmeProperties.

Even if the preceding configuration creates a regular bean for AcmeProperties, we recommend that @ConfigurationProperties only deal with the environment and, in particular, does not inject other beans from the context. Having said that, the @EnableConfigurationProperties annotation is also automatically applied to your project so that any existing bean annotated with @ConfigurationProperties is configured from the Environment. You could shortcut MyConfiguration by making sure AcmeProperties is already a bean, as shown in the following example:

@Component
@ConfigurationProperties(prefix="acme")
public class AcmeProperties {

	// ... see the preceding example

}

This style of configuration works particularly well with the SpringApplication external YAML configuration, as shown in the following example:

# application.yml

acme:
	remote-address: 192.168.1.1
	security:
		username: admin
		roles:
		  - USER
		  - ADMIN

# additional configuration as required

To work with @ConfigurationProperties beans, you can inject them in the same way as any other bean, as shown in the following example:

@Service
public class MyService {

	private final AcmeProperties properties;

	@Autowired
	public MyService(AcmeProperties properties) {
	    this.properties = properties;
	}

 	//...

	@PostConstruct
	public void openConnection() {
		Server server = new Server(this.properties.getRemoteAddress());
		// ...
	}

}
[Tip]Tip

Using @ConfigurationProperties also lets you generate metadata files that can be used by IDEs to offer auto-completion for your own keys. See the Appendix B, Configuration Metadata appendix for details.

24.7.1 Third-party Configuration

As well as using @ConfigurationProperties to annotate a class, you can also use it on public @Bean methods. Doing so can be particularly useful when you want to bind properties to third-party components that are outside of your control.

To configure a bean from the Environment properties, add @ConfigurationProperties to its bean registration, as shown in the following example:

@ConfigurationProperties(prefix = "another")
@Bean
public AnotherComponent anotherComponent() {
	...
}

Any property defined with the another prefix is mapped onto that AnotherComponent bean in manner similar to the preceding AcmeProperties example.

24.7.2 Relaxed Binding

Spring Boot uses some relaxed rules for binding Environment properties to @ConfigurationProperties beans, so there does not need to be an exact match between the Environment property name and the bean property name. Common examples where this is useful include dash-separated environment properties (for example, context-path binds to contextPath), and capitalized environment properties (for example, PORT binds to port).

For example, consider the following @ConfigurationProperties class:

@ConfigurationProperties(prefix="acme.my-project.person")
public class OwnerProperties {

	private String firstName;

	public String getFirstName() {
		return this.firstName;
	}

	public void setFirstName(String firstName) {
		this.firstName = firstName;
	}

}

In the preceding example, the following properties names can all be used:

Table 24.1. relaxed binding

PropertyNote

acme.my-project.person.first-name

Kebab case, which is recommended for use in .properties and .yml files.

acme.myProject.person.firstName

Standard camel case syntax.

acme.my_project.person.first_name

Underscore notation, which is an alternative format for use in .properties and .yml files.

ACME_MYPROJECT_PERSON_FIRSTNAME

Upper case format, which is recommended when using system environment variables.


[Note]Note

The prefix value for the annotation must be in kebab case (lowercase and separated by -, such as acme.my-project.person).

Table 24.2. relaxed binding rules per property source

Property SourceSimpleList

Properties Files

Camel case, kebab case, or underscore notation

Standard list syntax using [ ] or comma-separated values

YAML Files

Camel case, kebab case, or underscore notation

Standard YAML list syntax or comma-separated values

Environment Variables

Upper case format with underscore as the delimiter. _ should not be used within a property name

Numeric values surrounded by underscores, such as MY_ACME_1_OTHER = my.acme[1].other

System properties

Camel case, kebab case, or underscore notation

Standard list syntax using [ ] or comma-separated values


[Tip]Tip

We recommend that, when possible, properties are stored in lower-case kebab format, such as my.property-name=acme.

24.7.3 Merging Complex Types

When lists are configured in more than one place, overriding works by replacing the entire list.

For example, assume a MyPojo object with name and description attributes that are null by default. The following example exposes a list of MyPojo objects from AcmeProperties:

@ConfigurationProperties("acme")
public class AcmeProperties {

	private final List<MyPojo> list = new ArrayList<>();

	public List<MyPojo> getList() {
		return this.list;
	}

}

Consider the following configuration:

acme:
  list:
    - name: my name
      description: my description
---
spring:
  profiles: dev
acme:
  list:
    - name: my another name

If the dev profile is not active, AcmeProperties.list contains one MyPojo entry, as previously defined. If the dev profile is enabled, however, the list still contains only one entry (with a name of my another name and a description of null). This configuration does not add a second MyPojo instance to the list, and it does not merge the items.

When a List is specified in multiple profiles, the one with the highest priority (and only that one) is used. Consider the following example:

acme:
  list:
    - name: my name
      description: my description
    - name: another name
      description: another description
---
spring:
  profiles: dev
acme:
  list:
    - name: my another name

In the preceding example, if the dev profile is active, AcmeProperties.list contains one MyPojo entry (with a name of my another name and a description of null). For YAML, both comma-separated lists and YAML lists can be used for completely overriding the contents of the list.

For Map properties, you can bind with property values drawn from multiple sources. However, for the same property in multiple sources, the one with the highest priority is used. The following example exposes a Map<String, MyPojo> from AcmeProperties:

@ConfigurationProperties("acme")
public class AcmeProperties {

	private final Map<String, MyPojo> map = new HashMap<>();

	public Map<String, MyPojo> getMap() {
		return this.map;
	}

}

Consider the following configuration:

acme:
  map:
    key1:
      name: my name 1
      description: my description 1
---
spring:
  profiles: dev
acme:
  map:
    key1:
      name: dev name 1
    key2:
      name: dev name 2
      description: dev description 2

If the dev profile is not active, AcmeProperties.map contains one entry with key key1 (with a name of my name 1 and a description of my description 1). If the dev profile is enabled, however, map contains two entries with keys key1 (with a name of dev name 1 and a description of my description 1) and key2 (with a name of dev name 2 and a description of dev description 2).

[Note]Note

The preceding merging rules apply to properties from all property sources and not just YAML files.

24.7.4 Properties Conversion

Spring Boot attempts to coerce the external application properties to the right type when it binds to the @ConfigurationProperties beans. If you need custom type conversion, you can provide a ConversionService bean (with a bean named conversionService) or custom property editors (through a CustomEditorConfigurer bean) or custom Converters (with bean definitions annotated as @ConfigurationPropertiesBinding).

[Note]Note

As this bean is requested very early during the application lifecycle, make sure to limit the dependencies that your ConversionService is using. Typically, any dependency that you require may not be fully initialized at creation time. You may want to rename your custom ConversionService if it is not required for configuration keys coercion and only rely on custom converters qualified with @ConfigurationPropertiesBinding.

Converting durations

Spring Boot has dedicated support for expressing durations. If you expose a java.time.Duration property, the following formats in application properties are available:

  • A regular long representation (using milliseconds as the default unit unless a @DurationUnit has been specified)
  • The standard ISO-8601 format used by java.util.Duration
  • A more readable format where the value and the unit are coupled (e.g. 10s means 10 seconds)

Consider the following example:

@ConfigurationProperties("app.system")
public class AppSystemProperties {

	@DurationUnit(ChronoUnit.SECONDS)
	private Duration sessionTimeout = Duration.ofSeconds(30);

	private Duration readTimeout = Duration.ofMillis(1000);

	public Duration getSessionTimeout() {
		return this.sessionTimeout;
	}

	public void setSessionTimeout(Duration sessionTimeout) {
		this.sessionTimeout = sessionTimeout;
	}

	public Duration getReadTimeout() {
		return this.readTimeout;
	}

	public void setReadTimeout(Duration readTimeout) {
		this.readTimeout = readTimeout;
	}

}

To specify a session timeout of 30 seconds, 30, PT30S and 30s are all equivalent. A read timeout of 500ms can be specified in any of the following form: 500, PT0.5S and 500ms.

You can also use any of the supported unit. These are:

  • ns for nanoseconds
  • ms for milliseconds
  • s for seconds
  • m for minutes
  • h for hours
  • d for days

The default unit is milliseconds and can be overridden using @DurationUnit as illustrated in the sample above.

[Tip]Tip

If you are upgrading from a previous version that is simply using Long to express the duration, make sure to define the unit (using @DurationUnit) if it isn’t milliseconds alongside the switch to Duration. Doing so gives a transparent upgrade path while supporting a much richer format.

24.7.5 @ConfigurationProperties Validation

Spring Boot attempts to validate @ConfigurationProperties classes whenever they are annotated with Spring’s @Validated annotation. You can use JSR-303 javax.validation constraint annotations directly on your configuration class. To do so, ensure that a compliant JSR-303 implementation is on your classpath and then add constraint annotations to your fields, as shown in the following example:

@ConfigurationProperties(prefix="acme")
@Validated
public class AcmeProperties {

	@NotNull
	private InetAddress remoteAddress;

	// ... getters and setters

}
[Tip]Tip

You can also trigger validation by annotating the @Bean method that creates the configuration properties with @Validated.

Although nested properties will also be validated when bound, it’s good practice to also annotate the associated field as @Valid. This ensure that validation is triggered even if no nested properties are found. The following example builds on the preceding AcmeProperties example:

@ConfigurationProperties(prefix="acme")
@Validated
public class AcmeProperties {

	@NotNull
	private InetAddress remoteAddress;

	@Valid
	private final Security security = new Security();

	// ... getters and setters

	public static class Security {

		@NotEmpty
		public String username;

		// ... getters and setters

	}

}

You can also add a custom Spring Validator by creating a bean definition called configurationPropertiesValidator. The @Bean method should be declared static. The configuration properties validator is created very early in the application’s lifecycle, and declaring the @Bean method as static lets the bean be created without having to instantiate the @Configuration class. Doing so avoids any problems that may be caused by early instantiation. There is a property validation sample that shows how to set things up.

[Tip]Tip

The spring-boot-actuator module includes an endpoint that exposes all @ConfigurationProperties beans. Point your web browser to /actuator/configprops or use the equivalent JMX endpoint. See the "Production ready features" section for details.

24.7.6 @ConfigurationProperties vs. @Value

The @Value annotation is a core container feature, and it does not provide the same features as type-safe configuration properties. The following table summarizes the features that are supported by @ConfigurationProperties and @Value:

Feature@ConfigurationProperties@Value

Relaxed binding

Yes

No

Meta-data support

Yes

No

SpEL evaluation

No

Yes

If you define a set of configuration keys for your own components, we recommend you group them in a POJO annotated with @ConfigurationProperties. You should also be aware that, since @Value does not support relaxed binding, it is not a good candidate if you need to provide the value by using environment variables.

Finally, while you can write a SpEL expression in @Value, such expressions are not processed from application property files.

25. Profiles

Spring Profiles provide a way to segregate parts of your application configuration and make it be available only in certain environments. Any @Component or @Configuration can be marked with @Profile to limit when it is loaded, as shown in the following example:

@Configuration
@Profile("production")
public class ProductionConfiguration {

	// ...

}

You can use a spring.profiles.active Environment property to specify which profiles are active. You can specify the property in any of the ways described earlier in this chapter. For example, you could include it in your application.properties, as shown in the following example:

spring.profiles.active=dev,hsqldb

You could also specify it on the command line by using the following switch: --spring.profiles.active=dev,hsqldb.

25.1 Adding Active Profiles

The spring.profiles.active property follows the same ordering rules as other properties: The highest PropertySource wins. This means that you can specify active profiles in application.properties and then replace them by using the command line switch.

Sometimes, it is useful to have profile-specific properties that add to the active profiles rather than replace them. The spring.profiles.include property can be used to unconditionally add active profiles. The SpringApplication entry point also has a Java API for setting additional profiles (that is, on top of those activated by the spring.profiles.active property). See the setAdditionalProfiles() method in SpringApplication.

For example, when an application with the following properties is run by using the switch, --spring.profiles.active=prod, the proddb and prodmq profiles are also activated:

---
my.property: fromyamlfile
---
spring.profiles: prod
spring.profiles.include:
  - proddb
  - prodmq
[Note]Note

Remember that the spring.profiles property can be defined in a YAML document to determine when this particular document is included in the configuration. See Section 74.7, “Change Configuration Depending on the Environment” for more details.

25.2 Programmatically Setting Profiles

You can programmatically set active profiles by calling SpringApplication.setAdditionalProfiles(…​) before your application runs. It is also possible to activate profiles by using Spring’s ConfigurableEnvironment interface.

25.3 Profile-specific Configuration Files

Profile-specific variants of both application.properties (or application.yml) and files referenced through @ConfigurationProperties are considered as files and loaded. See "Section 24.4, “Profile-specific Properties”" for details.

26. Logging

Spring Boot uses Commons Logging for all internal logging but leaves the underlying log implementation open. Default configurations are provided for Java Util Logging, Log4J2, and Logback. In each case, loggers are pre-configured to use console output with optional file output also available.

By default, if you use the “Starters”, Logback is used for logging. Appropriate Logback routing is also included to ensure that dependent libraries that use Java Util Logging, Commons Logging, Log4J, or SLF4J all work correctly.

[Tip]Tip

There are a lot of logging frameworks available for Java. Do not worry if the above list seems confusing. Generally, you do not need to change your logging dependencies and the Spring Boot defaults work just fine.

26.1 Log Format

The default log output from Spring Boot resembles the following example:

2014-03-05 10:57:51.112  INFO 45469 --- [           main] org.apache.catalina.core.StandardEngine  : Starting Servlet Engine: Apache Tomcat/7.0.52
2014-03-05 10:57:51.253  INFO 45469 --- [ost-startStop-1] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring embedded WebApplicationContext
2014-03-05 10:57:51.253  INFO 45469 --- [ost-startStop-1] o.s.web.context.ContextLoader            : Root WebApplicationContext: initialization completed in 1358 ms
2014-03-05 10:57:51.698  INFO 45469 --- [ost-startStop-1] o.s.b.c.e.ServletRegistrationBean        : Mapping servlet: 'dispatcherServlet' to [/]
2014-03-05 10:57:51.702  INFO 45469 --- [ost-startStop-1] o.s.b.c.embedded.FilterRegistrationBean  : Mapping filter: 'hiddenHttpMethodFilter' to: [/*]

The following items are output:

  • Date and Time: Millisecond precision and easily sortable.
  • Log Level: ERROR, WARN, INFO, DEBUG, or TRACE.
  • Process ID.
  • A --- separator to distinguish the start of actual log messages.
  • Thread name: Enclosed in square brackets (may be truncated for console output).
  • Logger name: This is usually the source class name (often abbreviated).
  • The log message.
[Note]Note

Logback does not have a FATAL level. It is mapped to ERROR.

26.2 Console Output

The default log configuration echoes messages to the console as they are written. By default, ERROR-level, WARN-level, and INFO-level messages are logged. You can also enable a “debug” mode by starting your application with a --debug flag.

$ java -jar myapp.jar --debug
[Note]Note

You can also specify debug=true in your application.properties.

When the debug mode is enabled, a selection of core loggers (embedded container, Hibernate, and Spring Boot) are configured to output more information. Enabling the debug mode does not configure your application to log all messages with DEBUG level.

Alternatively, you can enable a “trace” mode by starting your application with a --trace flag (or trace=true in your application.properties). Doing so enables trace logging for a selection of core loggers (embedded container, Hibernate schema generation, and the whole Spring portfolio).

26.2.1 Color-coded Output

If your terminal supports ANSI, color output is used to aid readability. You can set spring.output.ansi.enabled to a supported value to override the auto detection.

Color coding is configured by using the %clr conversion word. In its simplest form, the converter colors the output according to the log level, as shown in the following example:

%clr(%5p)

The following table describes the mapping of log levels to colors:

LevelColor

FATAL

Red

ERROR

Red

WARN

Yellow

INFO

Green

DEBUG

Green

TRACE

Green

Alternatively, you can specify the color or style that should be used by providing it as an option to the conversion. For example, to make the text yellow, use the following setting:

%clr(%d{yyyy-MM-dd HH:mm:ss.SSS}){yellow}

The following colors and styles are supported:

  • blue
  • cyan
  • faint
  • green
  • magenta
  • red
  • yellow

26.3 File Output

By default, Spring Boot logs only to the console and does not write log files. If you want to write log files in addition to the console output, you need to set a logging.file or logging.path property (for example, in your application.properties).

The following table shows how the logging.* properties can be used together:

Table 26.1. Logging properties

logging.filelogging.pathExampleDescription

(none)

(none)

 

Console only logging.

Specific file

(none)

my.log

Writes to the specified log file. Names can be an exact location or relative to the current directory.

(none)

Specific directory

/var/log

Writes spring.log to the specified directory. Names can be an exact location or relative to the current directory.


Log files rotate when they reach 10 MB and, as with console output, ERROR-level, WARN-level, and INFO-level messages are logged by default. Size limits can be changed using the logging.file.max-size property. Previously rotated files are archived indefinitely unless the logging.file.max-history property has been set.

[Note]Note

The logging system is initialized early in the application lifecycle. Consequently, logging properties are not found in property files loaded through @PropertySource annotations.

[Tip]Tip

Logging properties are independent of the actual logging infrastructure. As a result, specific configuration keys (such as logback.configurationFile for Logback) are not managed by spring Boot.

26.4 Log Levels

All the supported logging systems can have the logger levels set in the Spring Environment (for example, in application.properties) by using logging.level.<logger-name>=<level> where level is one of TRACE, DEBUG, INFO, WARN, ERROR, FATAL, or OFF. The root logger can be configured by using logging.level.root.

The following example shows potential logging settings in application.properties:

logging.level.root=WARN
logging.level.org.springframework.web=DEBUG
logging.level.org.hibernate=ERROR

26.5 Custom Log Configuration

The various logging systems can be activated by including the appropriate libraries on the classpath and can be further customized by providing a suitable configuration file in the root of the classpath or in a location specified by the following Spring Environment property: logging.config.

You can force Spring Boot to use a particular logging system by using the org.springframework.boot.logging.LoggingSystem system property. The value should be the fully qualified class name of a LoggingSystem implementation. You can also disable Spring Boot’s logging configuration entirely by using a value of none.

[Note]Note

Since logging is initialized before the ApplicationContext is created, it is not possible to control logging from @PropertySources in Spring @Configuration files. The only way to change the logging system or disable it entirely is via System properties.

Depending on your logging system, the following files are loaded:

Logging SystemCustomization

Logback

logback-spring.xml, logback-spring.groovy, logback.xml, or logback.groovy

Log4j2

log4j2-spring.xml or log4j2.xml

JDK (Java Util Logging)

logging.properties

[Note]Note

When possible, we recommend that you use the -spring variants for your logging configuration (for example, logback-spring.xml rather than logback.xml). If you use standard configuration locations, Spring cannot completely control log initialization.

[Warning]Warning

There are known classloading issues with Java Util Logging that cause problems when running from an 'executable jar'. We recommend that you avoid it when running from an 'executable jar' if at all possible.

To help with the customization, some other properties are transferred from the Spring Environment to System properties, as described in the following table:

Spring EnvironmentSystem PropertyComments

logging.exception-conversion-word

LOG_EXCEPTION_CONVERSION_WORD

The conversion word used when logging exceptions.

logging.file

LOG_FILE

If defined, it is used in the default log configuration.

logging.file.max-size

LOG_FILE_MAX_SIZE

Maximum log file size (if LOG_FILE enabled). (Only supported with the default Logback setup.)

logging.file.max-history

LOG_FILE_MAX_HISTORY

Maximum number of archive log files to keep (if LOG_FILE enabled). (Only supported with the default Logback setup.)

logging.path

LOG_PATH

If defined, it is used in the default log configuration.

logging.pattern.console

CONSOLE_LOG_PATTERN

The log pattern to use on the console (stdout). (Only supported with the default Logback setup.)

logging.pattern.dateformat

LOG_DATEFORMAT_PATTERN

Appender pattern for log date format. (Only supported with the default Logback setup.)

logging.pattern.file

FILE_LOG_PATTERN

The log pattern to use in a file (if LOG_FILE is enabled). (Only supported with the default Logback setup.)

logging.pattern.level

LOG_LEVEL_PATTERN

The format to use when rendering the log level (default %5p). (Only supported with the default Logback setup.)

PID

PID

The current process ID (discovered if possible and when not already defined as an OS environment variable).

All the supported logging systems can consult System properties when parsing their configuration files. See the default configurations in spring-boot.jar for examples:

[Tip]Tip

If you want to use a placeholder in a logging property, you should use Spring Boot’s syntax and not the syntax of the underlying framework. Notably, if you use Logback, you should use : as the delimiter between a property name and its default value and not use :-.

[Tip]Tip

You can add MDC and other ad-hoc content to log lines by overriding only the LOG_LEVEL_PATTERN (or logging.pattern.level with Logback). For example, if you use logging.pattern.level=user:%X{user} %5p, then the default log format contains an MDC entry for "user", if it exists, as shown in the following example.

2015-09-30 12:30:04.031 user:someone INFO 22174 --- [  nio-8080-exec-0] demo.Controller
Handling authenticated request

26.6 Logback Extensions

Spring Boot includes a number of extensions to Logback that can help with advanced configuration. You can use these extensions in your logback-spring.xml configuration file.

[Note]Note

Because the standard logback.xml configuration file is loaded too early, you cannot use extensions in it. You need to either use logback-spring.xml or define a logging.config property.

[Warning]Warning

The extensions cannot be used with Logback’s configuration scanning. If you attempt to do so, making changes to the configuration file results in an error similar to one of the following being logged:

ERROR in [email protected]:71 - no applicable action for [springProperty], current ElementPath is [[configuration][springProperty]]
ERROR in [email protected]:71 - no applicable action for [springProfile], current ElementPath is [[configuration][springProfile]]

26.6.1 Profile-specific Configuration

The <springProfile> tag lets you optionally include or exclude sections of configuration based on the active Spring profiles. Profile sections are supported anywhere within the <configuration> element. Use the name attribute to specify which profile accepts the configuration. Multiple profiles can be specified with a comma-separated list. The following listing shows three sample profiles:

<springProfile name="staging">
	<!-- configuration to be enabled when the "staging" profile is active -->
</springProfile>

<springProfile name="dev, staging">
	<!-- configuration to be enabled when the "dev" or "staging" profiles are active -->
</springProfile>

<springProfile name="!production">
	<!-- configuration to be enabled when the "production" profile is not active -->
</springProfile>

26.6.2 Environment Properties

The <springProperty> tag lets you expose properties from the Spring Environment for use within Logback. Doing so can be useful if you want to access values from your application.properties file in your Logback configuration. The tag works in a similar way to Logback’s standard <property> tag. However, rather than specifying a direct value, you specify the source of the property (from the Environment). If you need to store the property somewhere other than in local scope, you can use the scope attribute. If you need a fallback value (in case the property is not set in the Environment), you can use the defaultValue attribute. The following example shows how to expose properties for use within Logback:

<springProperty scope="context" name="fluentHost" source="myapp.fluentd.host"
		defaultValue="localhost"/>
<appender name="FLUENT" class="ch.qos.logback.more.appenders.DataFluentAppender">
	<remoteHost>${fluentHost}</remoteHost>
	...
</appender>
[Note]Note

The source must be specified in kebab case (such as my.property-name). However, properties can be added to the Environment by using the relaxed rules.

27. Developing Web Applications

Spring Boot is well suited for web application development. You can create a self-contained HTTP server by using embedded Tomcat, Jetty, Undertow, or Netty. Most web applications use the spring-boot-starter-web module to get up and running quickly. You can also choose to build reactive web applications by using the spring-boot-starter-webflux module.

If you have not yet developed a Spring Boot web application, you can follow the "Hello World!" example in the Getting started section.

27.1 The “Spring Web MVC Framework”

The Spring Web MVC framework (often referred to as simply “Spring MVC”) is a rich “model view controller” web framework. Spring MVC lets you create special @Controller or @RestController beans to handle incoming HTTP requests. Methods in your controller are mapped to HTTP by using @RequestMapping annotations.

The following code shows a typical @RestController that serves JSON data:

@RestController
@RequestMapping(value="/users")
public class MyRestController {

	@RequestMapping(value="/{user}", method=RequestMethod.GET)
	public User getUser(@PathVariable Long user) {
		// ...
	}

	@RequestMapping(value="/{user}/customers", method=RequestMethod.GET)
	List<Customer> getUserCustomers(@PathVariable Long user) {
		// ...
	}

	@RequestMapping(value="/{user}", method=RequestMethod.DELETE)
	public User deleteUser(@PathVariable Long user) {
		// ...
	}

}

Spring MVC is part of the core Spring Framework, and detailed information is available in the reference documentation. There are also several guides that cover Spring MVC available at spring.io/guides.

27.1.1 Spring MVC Auto-configuration

Spring Boot provides auto-configuration for Spring MVC that works well with most applications.

The auto-configuration adds the following features on top of Spring’s defaults:

  • Inclusion of ContentNegotiatingViewResolver and BeanNameViewResolver beans.
  • Support for serving static resources, including support for WebJars (covered later in this document)).
  • Automatic registration of Converter, GenericConverter, and Formatter beans.
  • Support for HttpMessageConverters (covered later in this document).
  • Automatic registration of MessageCodesResolver (covered later in this document).
  • Static index.html support.
  • Custom Favicon support (covered later in this document).
  • Automatic use of a ConfigurableWebBindingInitializer bean (covered later in this document).

If you want to keep Spring Boot MVC features and you want to add additional MVC configuration (interceptors, formatters, view controllers, and other features), you can add your own @Configuration class of type WebMvcConfigurer but without @EnableWebMvc. If you wish to provide custom instances of RequestMappingHandlerMapping, RequestMappingHandlerAdapter, or ExceptionHandlerExceptionResolver, you can declare a WebMvcRegistrationsAdapter instance to provide such components.

If you want to take complete control of Spring MVC, you can add your own @Configuration annotated with @EnableWebMvc.

27.1.2 HttpMessageConverters

Spring MVC uses the HttpMessageConverter interface to convert HTTP requests and responses. Sensible defaults are included out of the box. For example, objects can be automatically converted to JSON (by using the Jackson library) or XML (by using the Jackson XML extension, if available, or by using JAXB if the Jackson XML extension is not available). By default, strings are encoded in UTF-8.

If you need to add or customize converters, you can use Spring Boot’s HttpMessageConverters class, as shown in the following listing:

import org.springframework.boot.autoconfigure.web.HttpMessageConverters;
import org.springframework.context.annotation.*;
import org.springframework.http.converter.*;

@Configuration
public class MyConfiguration {

	@Bean
	public HttpMessageConverters customConverters() {
		HttpMessageConverter<?> additional = ...
		HttpMessageConverter<?> another = ...
		return new HttpMessageConverters(additional, another);
	}

}

Any HttpMessageConverter bean that is present in the context is added to the list of converters. You can also override default converters in the same way.

27.1.3 Custom JSON Serializers and Deserializers

If you use Jackson to serialize and deserialize JSON data, you might want to write your own JsonSerializer and JsonDeserializer classes. Custom serializers are usually registered with Jackson through a module, but Spring Boot provides an alternative @JsonComponent annotation that makes it easier to directly register Spring Beans.

You can use the @JsonComponent annotation directly on JsonSerializer or JsonDeserializer implementations. You can also use it on classes that contain serializers/deserializers as inner classes, as shown in the following example:

import java.io.*;
import com.fasterxml.jackson.core.*;
import com.fasterxml.jackson.databind.*;
import org.springframework.boot.jackson.*;

@JsonComponent
public class Example {

	public static class Serializer extends JsonSerializer<SomeObject> {
		// ...
	}

	public static class Deserializer extends JsonDeserializer<SomeObject> {
		// ...
	}

}

All @JsonComponent beans in the ApplicationContext are automatically registered with Jackson. Because @JsonComponent is meta-annotated with @Component, the usual component-scanning rules apply.

Spring Boot also provides JsonObjectSerializer and JsonObjectDeserializer base classes that provide useful alternatives to the standard Jackson versions when serializing objects. See JsonObjectSerializer and JsonObjectDeserializer in the Javadoc for details.

27.1.4 MessageCodesResolver

Spring MVC has a strategy for generating error codes for rendering error messages from binding errors: MessageCodesResolver. If you set the spring.mvc.message-codes-resolver.format property PREFIX_ERROR_CODE or POSTFIX_ERROR_CODE, Spring Boot creates one for you (see the enumeration in DefaultMessageCodesResolver.Format).

27.1.5 Static Content

By default, Spring Boot serves static content from a directory called /static (or /public or /resources or /META-INF/resources) in the classpath or from the root of the ServletContext. It uses the ResourceHttpRequestHandler from Spring MVC so that you can modify that behavior by adding your own WebMvcConfigurer and overriding the addResourceHandlers method.

In a stand-alone web application, the default servlet from the container is also enabled and acts as a fallback, serving content from the root of the ServletContext if Spring decides not to handle it. Most of the time, this does not happen (unless you modify the default MVC configuration), because Spring can always handle requests through the DispatcherServlet.

By default, resources are mapped on /**, but you can tune that with the spring.mvc.static-path-pattern property. For instance, relocating all resources to /resources/** can be achieved as follows:

spring.mvc.static-path-pattern=/resources/**

You can also customize the static resource locations by using the spring.resources.static-locations property (replacing the default values with a list of directory locations). The root Servlet context path, "/", is automatically added as a location as well.

In addition to the “standard” static resource locations mentioned earlier, a special case is made for Webjars content. Any resources with a path in /webjars/** are served from jar files if they are packaged in the Webjars format.

[Tip]Tip

Do not use the src/main/webapp directory if your application is packaged as a jar. Although this directory is a common standard, it works only with war packaging, and it is silently ignored by most build tools if you generate a jar.

Spring Boot also supports the advanced resource handling features provided by Spring MVC, allowing use cases such as cache-busting static resources or using version agnostic URLs for Webjars.

To use version agnostic URLs for Webjars, add the webjars-locator-core dependency. Then declare your Webjar. Using jQuery as an example, adding "/webjars/jquery/jquery.min.js" results in "/webjars/jquery/x.y.z/jquery.min.js". where x.y.z is the Webjar version.

[Note]Note

If you use JBoss, you need to declare the webjars-locator-jboss-vfs dependency instead of the webjars-locator-core. Otherwise, all Webjars resolve as a 404.

To use cache busting, the following configuration configures a cache busting solution for all static resources, effectively adding a content hash, such as <link href="/css/spring-2a2d595e6ed9a0b24f027f2b63b134d6.css"/>, in URLs:

spring.resources.chain.strategy.content.enabled=true
spring.resources.chain.strategy.content.paths=/**
[Note]Note

Links to resources are rewritten in templates at runtime, thanks to a ResourceUrlEncodingFilter that is auto-configured for Thymeleaf and FreeMarker. You should manually declare this filter when using JSPs. Other template engines are currently not automatically supported but can be with custom template macros/helpers and the use of the ResourceUrlProvider.

When loading resources dynamically with, for example, a JavaScript module loader, renaming files is not an option. That is why other strategies are also supported and can be combined. A "fixed" strategy adds a static version string in the URL without changing the file name, as shown in the following example:

spring.resources.chain.strategy.content.enabled=true
spring.resources.chain.strategy.content.paths=/**
spring.resources.chain.strategy.fixed.enabled=true
spring.resources.chain.strategy.fixed.paths=/js/lib/
spring.resources.chain.strategy.fixed.version=v12

With this configuration, JavaScript modules located under "/js/lib/" use a fixed versioning strategy ("/v12/js/lib/mymodule.js"), while other resources still use the content one (<link href="/css/spring-2a2d595e6ed9a0b24f027f2b63b134d6.css"/>).

See ResourceProperties for more supported options.

[Tip]Tip

This feature has been thoroughly described in a dedicated blog post and in Spring Framework’s reference documentation.

27.1.6 Welcome Page

Spring Boot supports both static and templated welcome pages. It first looks for an index.html file in the configured static content locations. If one is not found, it then looks for an index template. If either is found, it is automatically used as the welcome page of the application.

27.1.7 Custom Favicon

Spring Boot looks for a favicon.ico in the configured static content locations and the root of the classpath (in that order). If such a file is present, it is automatically used as the favicon of the application.

27.1.8 Path Matching and Content Negotiation

Spring MVC can map incoming HTTP requests to handlers by looking at the request path and matching it to the mappings defined in your application (for example, @GetMapping annotations on Controller methods).

Spring Boot chooses to disable suffix pattern matching by default, which means that requests like "GET /projects/spring-boot.json" won’t be matched to @GetMapping("/projects/spring-boot") mappings. This is considered as a best practice for Spring MVC applications. This feature was mainly useful in the past for HTTP clients which did not send proper "Accept" request headers; we needed to make sure to send the correct Content Type to the client. Nowadays, Content Negotiation is much more reliable.

There are other ways to deal with HTTP clients that don’t consistently send proper "Accept" request headers. Instead of using suffix matching, we can use a query parameter to ensure that requests like "GET /projects/spring-boot?format=json" will be mapped to @GetMapping("/projects/spring-boot"):

spring.mvc.contentnegotiation.favor-parameter=true

# We can change the parameter name, which is "format" by default:
# spring.mvc.contentnegotiation.parameter-name=myparam

# We can also register additional file extensions/media types with:
spring.mvc.contentnegotiation.media-types.markdown=text/markdown

If you understand the caveats and would still like your application to use suffix pattern matching, the following configuration is required:

spring.mvc.contentnegotiation.favor-path-extension=true

# You can also restrict that feature to known extensions only
# spring.mvc.pathmatch.use-registered-suffix-pattern=true

# We can also register additional file extensions/media types with:
# spring.mvc.contentnegotiation.media-types.adoc=text/asciidoc

27.1.9 ConfigurableWebBindingInitializer

Spring MVC uses a WebBindingInitializer to initialize a WebDataBinder for a particular request. If you create your own ConfigurableWebBindingInitializer @Bean, Spring Boot automatically configures Spring MVC to use it.

27.1.10 Template Engines

As well as REST web services, you can also use Spring MVC to serve dynamic HTML content. Spring MVC supports a variety of templating technologies, including Thymeleaf, FreeMarker, and JSPs. Also, many other templating engines include their own Spring MVC integrations.

Spring Boot includes auto-configuration support for the following templating engines:

[Tip]Tip

If possible, JSPs should be avoided. There are several known limitations when using them with embedded servlet containers.

When you use one of these templating engines with the default configuration, your templates are picked up automatically from src/main/resources/templates.

[Tip]Tip

Depending on how you run your application, IntelliJ IDEA orders the classpath differently. Running your application in the IDE from its main method results in a different ordering than when you run your application by using Maven or Gradle or from its packaged jar. This can cause Spring Boot to fail to find the templates on the classpath. If you have this problem, you can reorder the classpath in the IDE to place the module’s classes and resources first. Alternatively, you can configure the template prefix to search every templates directory on the classpath, as follows: classpath*:/templates/.

27.1.11 Error Handling

By default, Spring Boot provides an /error mapping that handles all errors in a sensible way, and it is registered as a “global” error page in the servlet container. For machine clients, it produces a JSON response with details of the error, the HTTP status, and the exception message. For browser clients, there is a “whitelabel” error view that renders the same data in HTML format (to customize it, add a View that resolves to error). To replace the default behavior completely, you can implement ErrorController and register a bean definition of that type or add a bean of type ErrorAttributes to use the existing mechanism but replace the contents.

[Tip]Tip

The BasicErrorController can be used as a base class for a custom ErrorController. This is particularly useful if you want to add a handler for a new content type (the default is to handle text/html specifically and provide a fallback for everything else). To do so, extend BasicErrorController, add a public method with a @RequestMapping that has a produces attribute, and create a bean of your new type.

You can also define a class annotated with @ControllerAdvice to customize the JSON document to return for a particular controller and/or exception type, as shown in the following example:

@ControllerAdvice(basePackageClasses = AcmeController.class)
public class AcmeControllerAdvice extends ResponseEntityExceptionHandler {

	@ExceptionHandler(YourException.class)
	@ResponseBody
	ResponseEntity<?> handleControllerException(HttpServletRequest request, Throwable ex) {
		HttpStatus status = getStatus(request);
		return new ResponseEntity<>(new CustomErrorType(status.value(), ex.getMessage()), status);
	}

	private HttpStatus getStatus(HttpServletRequest request) {
		Integer statusCode = (Integer) request.getAttribute("javax.servlet.error.status_code");
		if (statusCode == null) {
			return HttpStatus.INTERNAL_SERVER_ERROR;
		}
		return HttpStatus.valueOf(statusCode);
	}

}

In the preceding example, if YourException is thrown by a controller defined in the same package as AcmeController, a JSON representation of the CustomErrorType POJO is used instead of the ErrorAttributes representation.

Custom Error Pages

If you want to display a custom HTML error page for a given status code, you can add a file to an /error folder. Error pages can either be static HTML (that is, added under any of the static resource folders) or be built by using templates. The name of the file should be the exact status code or a series mask.

For example, to map 404 to a static HTML file, your folder structure would be as follows:

src/
 +- main/
     +- java/
     |   + <source code>
     +- resources/
         +- public/
             +- error/
             |   +- 404.html
             +- <other public assets>

To map all 5xx errors by using a FreeMarker template, your folder structure would be as follows:

src/
 +- main/
     +- java/
     |   + <source code>
     +- resources/
         +- templates/
             +- error/
             |   +- 5xx.ftl
             +- <other templates>

For more complex mappings, you can also add beans that implement the ErrorViewResolver interface, as shown in the following example:

public class MyErrorViewResolver implements ErrorViewResolver {

	@Override
	public ModelAndView resolveErrorView(HttpServletRequest request,
			HttpStatus status, Map<String, Object> model) {
		// Use the request or status to optionally return a ModelAndView
		return ...
	}

}

You can also use regular Spring MVC features such as @ExceptionHandler methods and @ControllerAdvice. The ErrorController then picks up any unhandled exceptions.

Mapping Error Pages outside of Spring MVC

For applications that do not use Spring MVC, you can use the ErrorPageRegistrar interface to directly register ErrorPages. This abstraction works directly with the underlying embedded servlet container and works even if you do not have a Spring MVC DispatcherServlet.

@Bean
public ErrorPageRegistrar errorPageRegistrar(){
	return new MyErrorPageRegistrar();
}

// ...

private static class MyErrorPageRegistrar implements ErrorPageRegistrar {

	@Override
	public void registerErrorPages(ErrorPageRegistry registry) {
		registry.addErrorPages(new ErrorPage(HttpStatus.BAD_REQUEST, "/400"));
	}

}
[Note]Note

If you register an ErrorPage with a path that ends up being handled by a Filter (as is common with some non-Spring web frameworks, like Jersey and Wicket), then the Filter has to be explicitly registered as an ERROR dispatcher, as shown in the following example:

@Bean
public FilterRegistrationBean myFilter() {
	FilterRegistrationBean registration = new FilterRegistrationBean();
	registration.setFilter(new MyFilter());
	...
	registration.setDispatcherTypes(EnumSet.allOf(DispatcherType.class));
	return registration;
}

Note that the default FilterRegistrationBean does not include the ERROR dispatcher type.

CAUTION:When deployed to a servlet container, Spring Boot uses its error page filter to forward a request with an error status to the appropriate error page. The request can only be forwarded to the correct error page if the response has not already been committed. By default, WebSphere Application Server 8.0 and later commits the response upon successful completion of a servlet’s service method. You should disable this behavior by setting com.ibm.ws.webcontainer.invokeFlushAfterService to false.

27.1.12 Spring HATEOAS

If you develop a RESTful API that makes use of hypermedia, Spring Boot provides auto-configuration for Spring HATEOAS that works well with most applications. The auto-configuration replaces the need to use @EnableHypermediaSupport and registers a number of beans to ease building hypermedia-based applications, including a LinkDiscoverers (for client side support) and an ObjectMapper configured to correctly marshal responses into the desired representation. The ObjectMapper is customized by setting the various spring.jackson.* properties or, if one exists, by a Jackson2ObjectMapperBuilder bean.

You can take control of Spring HATEOAS’s configuration by using @EnableHypermediaSupport. Note that doing so disables the ObjectMapper customization described earlier.

27.1.13 CORS Support

Cross-origin resource sharing (CORS) is a W3C specification implemented by most browsers that lets you specify in a flexible way what kind of cross-domain requests are authorized, instead of using some less secure and less powerful approaches such as IFRAME or JSONP.

As of version 4.2, Spring MVC supports CORS. Using controller method CORS configuration with @CrossOrigin annotations in your Spring Boot application does not require any specific configuration. Global CORS configuration can be defined by registering a WebMvcConfigurer bean with a customized addCorsMappings(CorsRegistry) method, as shown in the following example:

@Configuration
public class MyConfiguration {

	@Bean
	public WebMvcConfigurer corsConfigurer() {
		return new WebMvcConfigurer() {
			@Override
			public void addCorsMappings(CorsRegistry registry) {
				registry.addMapping("/api/**");
			}
		};
	}
}

27.2 The “Spring WebFlux Framework”

Spring WebFlux is the new reactive web framework introduced in Spring Framework 5.0. Unlike Spring MVC, it does not require the Servlet API, is fully asynchronous and non-blocking, and implements the Reactive Streams specification through the Reactor project.

Spring WebFlux comes in two flavors: functional and annotation-based. The annotation-based one is quite close to the Spring MVC model, as shown in the following example:

@RestController
@RequestMapping("/users")
public class MyRestController {

	@GetMapping("/{user}")
	public Mono<User> getUser(@PathVariable Long user) {
		// ...
	}

	@GetMapping("/{user}/customers")
	public Flux<Customer> getUserCustomers(@PathVariable Long user) {
		// ...
	}

	@DeleteMapping("/{user}")
	public Mono<User> deleteUser(@PathVariable Long user) {
		// ...
	}

}

“WebFlux.fn”, the functional variant, separates the routing configuration from the actual handling of the requests, as shown in the following example:

@Configuration
public class RoutingConfiguration {

	@Bean
	public RouterFunction<ServerResponse> monoRouterFunction(UserHandler userHandler) {
		return route(GET("/{user}").and(accept(APPLICATION_JSON)), userHandler::getUser)
				.andRoute(GET("/{user}/customers").and(accept(APPLICATION_JSON)), userHandler::getUserCustomers)
				.andRoute(DELETE("/{user}").and(accept(APPLICATION_JSON)), userHandler::deleteUser);
	}

}

@Component
public class UserHandler {

	public Mono<ServerResponse> getUser(ServerRequest request) {
		// ...
	}

	public Mono<ServerResponse> getUserCustomers(ServerRequest request) {
		// ...
	}

	public Mono<ServerResponse> deleteUser(ServerRequest request) {
		// ...
	}
}

WebFlux is part of the Spring Framework and detailed information is available in its reference documentation.

[Tip]Tip

You can define as many RouterFunction beans as you like to modularize the definition of the router. Beans can be ordered if you need to apply a precedence.

To get started, add the spring-boot-starter-webflux module to your application.

[Note]Note

Adding both spring-boot-starter-web and spring-boot-starter-webflux modules in your application results in Spring Boot auto-configuring Spring MVC, not WebFlux. This behavior has been chosen because many Spring developers add spring-boot-starter-webflux to their Spring MVC application to use the reactive WebClient. You can still enforce your choice by setting the chosen application type to SpringApplication.setWebApplicationType(WebApplicationType.REACTIVE).

27.2.1 Spring WebFlux Auto-configuration

Spring Boot provides auto-configuration for Spring WebFlux that works well with most applications.

The auto-configuration adds the following features on top of Spring’s defaults:

If you want to keep Spring Boot WebFlux features and you want to add additional WebFlux configuration, you can add your own @Configuration class of type WebFluxConfigurer but without @EnableWebFlux.

If you want to take complete control of Spring WebFlux, you can add your own @Configuration annotated with @EnableWebFlux.

27.2.2 HTTP Codecs with HttpMessageReaders and HttpMessageWriters

Spring WebFlux uses the HttpMessageReader and HttpMessageWriter interfaces to convert HTTP requests and responses. They are configured with CodecConfigurer to have sensible defaults by looking at the libraries available in your classpath.

Spring Boot applies further customization by using CodecCustomizer instances. For example, spring.jackson.* configuration keys are applied to the Jackson codec.

If you need to add or customize codecs, you can create a custom CodecCustomizer component, as shown in the following example:

import org.springframework.boot.web.codec.CodecCustomizer;

@Configuration
public class MyConfiguration {

	@Bean
	public CodecCustomizer myCodecCustomizer() {
		return codecConfigurer -> {
			// ...
		}
	}

}

You can also leverage Boot’s custom JSON serializers and deserializers.

27.2.3 Static Content

By default, Spring Boot serves static content from a directory called /static (or /public or /resources or /META-INF/resources) in the classpath. It uses the ResourceWebHandler from Spring WebFlux so that you can modify that behavior by adding your own WebFluxConfigurer and overriding the addResourceHandlers method.

By default, resources are mapped on /**, but you can tune that by setting the spring.webflux.static-path-pattern property. For instance, relocating all resources to /resources/** can be achieved as follows:

spring.webflux.static-path-pattern=/resources/**

You can also customize the static resource locations by using spring.resources.static-locations. Doing so replaces the default values with a list of directory locations. If you do so, the default welcome page detection switches to your custom locations. So, if there is an index.html in any of your locations on startup, it is the home page of the application.

In addition to the “standard” static resource locations listed earlier, a special case is made for Webjars content. Any resources with a path in /webjars/** are served from jar files if they are packaged in the Webjars format.

[Tip]Tip

Spring WebFlux applications do not strictly depend on the Servlet API, so they cannot be deployed as war files and do not use the src/main/webapp directory.

27.2.4 Template Engines

As well as REST web services, you can also use Spring WebFlux to serve dynamic HTML content. Spring WebFlux supports a variety of templating technologies, including Thymeleaf, FreeMarker, and Mustache.

Spring Boot includes auto-configuration support for the following templating engines:

When you use one of these templating engines with the default configuration, your templates are picked up automatically from src/main/resources/templates.

27.2.5 Error Handling

Spring Boot provides a WebExceptionHandler that handles all errors in a sensible way. Its position in the processing order is immediately before the handlers provided by WebFlux, which are considered last. For machine clients, it produces a JSON response with details of the error, the HTTP status, and the exception message. For browser clients, there is a “whitelabel” error handler that renders the same data in HTML format. You can also provide your own HTML templates to display errors (see the next section).

The first step to customizing this feature often involves using the existing mechanism but replacing or augmenting the error contents. For that, you can add a bean of type ErrorAttributes.

To change the error handling behavior, you can implement ErrorWebExceptionHandler and register a bean definition of that type. Because a WebExceptionHandler is quite low-level, Spring Boot also provides a convenient AbstractErrorWebExceptionHandler to let you handle errors in a WebFlux functional way, as shown in the following example:

public class CustomErrorWebExceptionHandler extends AbstractErrorWebExceptionHandler {

	// Define constructor here

	@Override
	protected RouterFunction<ServerResponse> getRoutingFunction(ErrorAttributes errorAttributes) {

		return RouterFunctions
				.route(aPredicate, aHandler)
				.andRoute(anotherPredicate, anotherHandler);
	}

}

For a more complete picture, you can also subclass DefaultErrorWebExceptionHandler directly and override specific methods.

Custom Error Pages

If you want to display a custom HTML error page for a given status code, you can add a file to an /error folder. Error pages can either be static HTML (that is, added under any of the static resource folders) or built with templates. The name of the file should be the exact status code or a series mask.

For example, to map 404 to a static HTML file, your folder structure would be as follows:

src/
 +- main/
     +- java/
     |   + <source code>
     +- resources/
         +- public/
             +- error/
             |   +- 404.html
             +- <other public assets>

To map all 5xx errors by using a Mustache template, your folder structure would be as follows:

src/
 +- main/
     +- java/
     |   + <source code>
     +- resources/
         +- templates/
             +- error/
             |   +- 5xx.mustache
             +- <other templates>

27.2.6 Web Filters

Spring WebFlux provides a WebFilter interface that can be implemented to filter HTTP request-response exchanges. WebFilter beans found in the application context will be automatically used to filter each exchange.

Where the order of the filters is important they can implement Ordered or be annotated with @Order. Spring Boot auto-configuration may configure web filters for you. When it does so, the orders shown in the following table will be used:

Web FilterOrder

MetricsWebFilter

Ordered.HIGHEST_PRECEDENCE + 1

WebFilterChainProxy (Spring Security)

-100

HttpTraceWebFilter

Ordered.LOWEST_PRECEDENCE - 10

27.3 JAX-RS and Jersey

If you prefer the JAX-RS programming model for REST endpoints, you can use one of the available implementations instead of Spring MVC. Jersey 1.x and Apache CXF work quite well out of the box if you register their Servlet or Filter as a @Bean in your application context. Jersey 2.x has some native Spring support, so we also provide auto-configuration support for it in Spring Boot, together with a starter.

To get started with Jersey 2.x, include the spring-boot-starter-jersey as a dependency and then you need one @Bean of type ResourceConfig in which you register all the endpoints, as shown in the following example:

@Component
public class JerseyConfig extends ResourceConfig {

	public JerseyConfig() {
		register(Endpoint.class);
	}

}
[Warning]Warning

Jersey’s support for scanning executable archives is rather limited. For example, it cannot scan for endpoints in a package found in WEB-INF/classes when running an executable war file. To avoid this limitation, the packages method should not be used, and endpoints should be registered individually by using the register method, as shown in the preceding example.

For more advanced customizations, you can also register an arbitrary number of beans that implement ResourceConfigCustomizer.

All the registered endpoints should be @Components with HTTP resource annotations (@GET and others), as shown in the following example:

@Component
@Path("/hello")
public class Endpoint {

	@GET
	public String message() {
		return "Hello";
	}

}

Since the Endpoint is a Spring @Component, its lifecycle is managed by Spring and you can use the @Autowired annotation to inject dependencies and use the @Value annotation to inject external configuration. By default, the Jersey servlet is registered and mapped to /*. You can change the mapping by adding @ApplicationPath to your ResourceConfig.

By default, Jersey is set up as a Servlet in a @Bean of type ServletRegistrationBean named jerseyServletRegistration. By default, the servlet is initialized lazily, but you can customize that behavior by setting spring.jersey.servlet.load-on-startup. You can disable or override that bean by creating one of your own with the same name. You can also use a filter instead of a servlet by setting spring.jersey.type=filter (in which case, the @Bean to replace or override is jerseyFilterRegistration). The filter has an @Order, which you can set with spring.jersey.filter.order. Both the servlet and the filter registrations can be given init parameters by using spring.jersey.init.* to specify a map of properties.

There is a Jersey sample so that you can see how to set things up. There is also a Jersey 1.x sample. Note that, in the Jersey 1.x sample, the spring-boot maven plugin has been configured to unpack some Jersey jars so that they can be scanned by the JAX-RS implementation (because the sample asks for them to be scanned in its Filter registration). If any of your JAX-RS resources are packaged as nested jars, you may need to do the same.

27.4 Embedded Servlet Container Support

Spring Boot includes support for embedded Tomcat, Jetty, and Undertow servers. Most developers use the appropriate “Starter” to obtain a fully configured instance. By default, the embedded server listens for HTTP requests on port 8080.

[Warning]Warning

If you choose to use Tomcat on CentOS, be aware that, by default, a temporary directory is used to store compiled JSPs, file uploads, and so on. This directory may be deleted by tmpwatch while your application is running, leading to failures. To avoid this behavior, you may want to customize your tmpwatch configuration such that tomcat.* directories are not deleted or configure server.tomcat.basedir such that embedded Tomcat uses a different location.

27.4.1 Servlets, Filters, and listeners

When using an embedded servlet container, you can register servlets, filters, and all the listeners (such as HttpSessionListener) from the Servlet spec, either by using Spring beans or by scanning for Servlet components.

Registering Servlets, Filters, and Listeners as Spring Beans

Any Servlet, Filter, or servlet *Listener instance that is a Spring bean is registered with the embedded container. This can be particularly convenient if you want to refer to a value from your application.properties during configuration.

By default, if the context contains only a single Servlet, it is mapped to /. In the case of multiple servlet beans, the bean name is used as a path prefix. Filters map to /*.

If convention-based mapping is not flexible enough, you can use the ServletRegistrationBean, FilterRegistrationBean, and ServletListenerRegistrationBean classes for complete control.

Spring Boot ships with many auto-configurations that may define Filter beans. Here are a few examples of Filters and their respective order (lower order value means higher precedence):

Servlet FilterOrder

OrderedCharacterEncodingFilter

Ordered.HIGHEST_PRECEDENCE

WebMvcMetricsFilter

Ordered.HIGHEST_PRECEDENCE + 1

ErrorPageFilter

Ordered.HIGHEST_PRECEDENCE + 1

HttpTraceFilter

Ordered.LOWEST_PRECEDENCE - 10

It is usually safe to leave Filter beans unordered.

If a specific order is required, you should avoid configuring a Filter that reads the request body at Ordered.HIGHEST_PRECEDENCE, since it might go against the character encoding configuration of your application. If a Servlet filter wraps the request, it should be configured with an order that is less than or equal to FilterRegistrationBean.REQUEST_WRAPPER_FILTER_MAX_ORDER.

27.4.2 Servlet Context Initialization

Embedded servlet containers do not directly execute the Servlet 3.0+ javax.servlet.ServletContainerInitializer interface or Spring’s org.springframework.web.WebApplicationInitializer interface. This is an intentional design decision intended to reduce the risk that third party libraries designed to run inside a war may break Spring Boot applications.

If you need to perform servlet context initialization in a Spring Boot application, you should register a bean that implements the org.springframework.boot.web.servlet.ServletContextInitializer interface. The single onStartup method provides access to the ServletContext and, if necessary, can easily be used as an adapter to an existing WebApplicationInitializer.

Scanning for Servlets, Filters, and listeners

When using an embedded container, automatic registration of classes annotated with @WebServlet, @WebFilter, and @WebListener can be enabled by using @ServletComponentScan.

[Tip]Tip

@ServletComponentScan has no effect in a standalone container, where the container’s built-in discovery mechanisms are used instead.

27.4.3 The ServletWebServerApplicationContext

Under the hood, Spring Boot uses a different type of ApplicationContext for embedded servlet container support. The ServletWebServerApplicationContext is a special type of WebApplicationContext that bootstraps itself by searching for a single ServletWebServerFactory bean. Usually a TomcatServletWebServerFactory, JettyServletWebServerFactory, or UndertowServletWebServerFactory has been auto-configured.

[Note]Note

You usually do not need to be aware of these implementation classes. Most applications are auto-configured, and the appropriate ApplicationContext and ServletWebServerFactory are created on your behalf.

27.4.4 Customizing Embedded Servlet Containers

Common servlet container settings can be configured by using Spring Environment properties. Usually, you would define the properties in your application.properties file.

Common server settings include:

  • Network settings: Listen port for incoming HTTP requests (server.port), interface address to bind to server.address, and so on.
  • Session settings: Whether the session is persistent (server.servlet.session.persistence), session timeout (server.servlet.session.timeout), location of session data (server.servlet.session.store-dir), and session-cookie configuration (server.servlet.session.cookie.*).
  • Error management: Location of the error page (server.error.path) and so on.
  • SSL
  • HTTP compression

Spring Boot tries as much as possible to expose common settings, but this is not always possible. For those cases, dedicated namespaces offer server-specific customizations (see server.tomcat and server.undertow). For instance, access logs can be configured with specific features of the embedded servlet container.

[Tip]Tip

See the ServerProperties class for a complete list.

Programmatic Customization

If you need to programmatically configure your embedded servlet container, you can register a Spring bean that implements the WebServerFactoryCustomizer interface. WebServerFactoryCustomizer provides access to the ConfigurableServletWebServerFactory, which includes numerous customization setter methods. The following example shows programmatically setting the port:

import org.springframework.boot.web.server.WebServerFactoryCustomizer;
import org.springframework.boot.web.servlet.server.ConfigurableServletWebServerFactory;
import org.springframework.stereotype.Component;

@Component
public class CustomizationBean implements WebServerFactoryCustomizer<ConfigurableServletWebServerFactory> {

	@Override
	public void customize(ConfigurableServletWebServerFactory server) {
		server.setPort(9000);
	}

}
[Note]Note

TomcatServletWebServerFactory, JettyServletWebServerFactory and UndertowServletWebServerFactory are dedicated variants of ConfigurableServletWebServerFactory that have additional customization setter methods for Tomcat, Jetty and Undertow respectively.

Customizing ConfigurableServletWebServerFactory Directly

If the preceding customization techniques are too limited, you can register the TomcatServletWebServerFactory, JettyServletWebServerFactory, or UndertowServletWebServerFactory bean yourself.

@Bean
public ConfigurableServletWebServerFactory webServerFactory() {
	TomcatServletWebServerFactory factory = new TomcatServletWebServerFactory();
	factory.setPort(9000);
	factory.setSessionTimeout(10, TimeUnit.MINUTES);
	factory.addErrorPages(new ErrorPage(HttpStatus.NOT_FOUND, "/notfound.html"));
	return factory;
}

Setters are provided for many configuration options. Several protected method “hooks” are also provided should you need to do something more exotic. See the source code documentation for details.

27.4.5 JSP Limitations

When running a Spring Boot application that uses an embedded servlet container (and is packaged as an executable archive), there are some limitations in the JSP support.

  • With Jetty and Tomcat, it should work if you use war packaging. An executable war will work when launched with java -jar, and will also be deployable to any standard container. JSPs are not supported when using an executable jar.
  • Undertow does not support JSPs.
  • Creating a custom error.jsp page does not override the default view for error handling. Custom error pages should be used instead.

There is a JSP sample so that you can see how to set things up.

28. Security

If Spring Security is on the classpath, then web applications are secured by default. Spring Boot relies on Spring Security’s content-negotiation strategy to determine whether to use httpBasic or formLogin. To add method-level security to a web application, you can also add @EnableGlobalMethodSecurity with your desired settings. Additional information can be found in the Spring Security Reference Guide.

The default UserDetailsService has a single user. The user name is user, and the password is random and is printed at INFO level when the application starts, as shown in the following example:

Using generated security password: 78fa095d-3f4c-48b1-ad50-e24c31d5cf35
[Note]Note

If you fine-tune your logging configuration, ensure that the org.springframework.boot.autoconfigure.security category is set to log INFO-level messages. Otherwise, the default password is not printed.

You can change the username and password by providing a spring.security.user.name and spring.security.user.password.

The basic features you get by default in a web application are:

  • A UserDetailsService (or ReactiveUserDetailsService in case of a WebFlux application) bean with in-memory store and a single user with a generated password (see SecurityProperties.User for the properties of the user).
  • Form-based login or HTTP Basic security (depending on Content-Type) for the entire application (including actuator endpoints if actuator is on the classpath).
  • A DefaultAuthenticationEventPublisher for publishing authentication events.

You can provide a different AuthenticationEventPublisher by adding a bean for it.

28.1 MVC Security

The default security configuration is implemented in SecurityAutoConfiguration and UserDetailsServiceAutoConfiguration. SecurityAutoConfiguration imports SpringBootWebSecurityConfiguration for web security and UserDetailsServiceAutoConfiguration configures authentication, which is also relevant in non-web applications. To switch off the default web application security configuration completely, you can add a bean of type WebSecurityConfigurerAdapter (doing so does not disable the UserDetailsService configuration or Actuator’s security).

To also switch off the UserDetailsService configuration, you can add a bean of type UserDetailsService, AuthenticationProvider, or AuthenticationManager. There are several secure applications in the Spring Boot samples to get you started with common use cases.

Access rules can be overridden by adding a custom WebSecurityConfigurerAdapter. Spring Boot provides convenience methods that can be used to override access rules for actuator endpoints and static resources. EndpointRequest can be used to create a RequestMatcher that is based on the management.endpoints.web.base-path property. PathRequest can be used to create a RequestMatcher for resources in commonly used locations.

28.2 WebFlux Security

Similar to Spring MVC applications, you can secure your WebFlux applications by adding the spring-boot-starter-security dependency. The default security configuration is implemented in ReactiveSecurityAutoConfiguration and UserDetailsServiceAutoConfiguration. ReactiveSecurityAutoConfiguration imports WebFluxSecurityConfiguration for web security and UserDetailsServiceAutoConfiguration configures authentication, which is also relevant in non-web applications. To switch off the default web application security configuration completely, you can add a bean of type WebFilterChainProxy (doing so does not disable the UserDetailsService configuration or Actuator’s security).

To also switch off the UserDetailsService configuration, you can add a bean of type ReactiveUserDetailsService or ReactiveAuthenticationManager.

Access rules can be configured by adding a custom SecurityWebFilterChain. Spring Boot provides convenience methods that can be used to override access rules for actuator endpoints and static resources. EndpointRequest can be used to create a ServerWebExchangeMatcher that is based on the management.endpoints.web.base-path property.

PathRequest can be used to create a ServerWebExchangeMatcher for resources in commonly used locations.

For example, you can customize your security configuration by adding something like:

@Bean
public SecurityWebFilterChain springSecurityFilterChain(ServerHttpSecurity http) {
	return http
		.authorizeExchange()
			.matchers(PathRequest.toStaticResources().atCommonLocations()).permitAll()
			.pathMatchers("/foo", "/bar")
				.authenticated().and()
			.formLogin().and()
		.build();
}

28.3 OAuth2

OAuth2 is a widely used authorization framework that is supported by Spring.

28.3.1 Client

If you have spring-security-oauth2-client on your classpath, you can take advantage of some auto-configuration to make it easy to set up an OAuth2 Client. This configuration makes use of the properties under OAuth2ClientProperties.

You can register multiple OAuth2 clients and providers under the spring.security.oauth2.client prefix, as shown in the following example:

spring.security.oauth2.client.registration.my-client-1.client-id=abcd
spring.security.oauth2.client.registration.my-client-1.client-secret=password
spring.security.oauth2.client.registration.my-client-1.client-name=Client for user scope
spring.security.oauth2.client.registration.my-client-1.provider=my-oauth-provider
spring.security.oauth2.client.registration.my-client-1.scope=user
spring.security.oauth2.client.registration.my-client-1.redirect-uri-template=http://my-redirect-uri.com
spring.security.oauth2.client.registration.my-client-1.client-authentication-method=basic
spring.security.oauth2.client.registration.my-client-1.authorization-grant-type=authorization_code

spring.security.oauth2.client.registration.my-client-2.client-id=abcd
spring.security.oauth2.client.registration.my-client-2.client-secret=password
spring.security.oauth2.client.registration.my-client-2.client-name=Client for email scope
spring.security.oauth2.client.registration.my-client-2.provider=my-oauth-provider
spring.security.oauth2.client.registration.my-client-2.scope=email
spring.security.oauth2.client.registration.my-client-2.redirect-uri-template=http://my-redirect-uri.com
spring.security.oauth2.client.registration.my-client-2.client-authentication-method=basic
spring.security.oauth2.client.registration.my-client-2.authorization-grant-type=authorization_code

spring.security.oauth2.client.provider.my-oauth-provider.authorization-uri=http://my-auth-server/oauth/authorize
spring.security.oauth2.client.provider.my-oauth-provider.token-uri=http://my-auth-server/oauth/token
spring.security.oauth2.client.provider.my-oauth-provider.user-info-uri=http://my-auth-server/userinfo
spring.security.oauth2.client.provider.my-oauth-provider.jwk-set-uri=http://my-auth-server/token_keys
spring.security.oauth2.client.provider.my-oauth-provider.user-name-attribute=name

By default, Spring Security’s OAuth2LoginAuthenticationFilter only processes URLs matching /login/oauth2/code/*. If you want to customize the redirect-uri-template to use a different pattern, you need to provide configuration to process that custom pattern. For example, you can add your own WebSecurityConfigurerAdapter that resembles the following:

public class OAuth2LoginSecurityConfig extends WebSecurityConfigurerAdapter {

	@Override
	protected void configure(HttpSecurity http) throws Exception {
		http
			.authorizeRequests()
				.anyRequest().authenticated()
				.and()
			.oauth2Login()
				.redirectionEndpoint()
					.baseUri("/custom-callback");
	}
}

For common OAuth2 and OpenID providers, including Google, Github, Facebook, and Okta, we provide a set of provider defaults (google, github, facebook, and okta, respectively).

If you do not need to customize these providers, you can set the provider attribute to the one for which you need to infer defaults. Also, if the ID of your client matches the default supported provider, Spring Boot infers that as well.

In other words, the two configurations in the following example use the Google provider:

spring.security.oauth2.client.registration.my-client.client-id=abcd
spring.security.oauth2.client.registration.my-client.client-secret=password
spring.security.oauth2.client.registration.my-client.provider=google

spring.security.oauth2.client.registration.google.client-id=abcd
spring.security.oauth2.client.registration.google.client-secret=password

28.3.2 Server

Currently, Spring Security does not provide support for implementing an OAuth 2.0 Authorization Server or Resource Server. However, this functionality is available from the Spring Security OAuth project, which will eventually be superseded by Spring Security completely. Until then, you can use the spring-security-oauth2-autoconfigure module to easily set up an OAuth 2.0 server; see its documentation for instructions.

28.4 Actuator Security

For security purposes, all actuators other than /health and /info are disabled by default. The management.endpoints.web.exposure.include property can be used to enable the actuators.

If Spring Security is on the classpath and no other WebSecurityConfigurerAdapter is present, the actuators are secured by Spring Boot auto-config. If you define a custom WebSecurityConfigurerAdapter, Spring Boot auto-config will back off and you will be in full control of actuator access rules.

[Note]Note

Before setting the management.endpoints.web.exposure.include, ensure that the exposed actuators do not contain sensitive information and/or are secured by placing them behind a firewall or by something like Spring Security.

28.4.1 Cross Site Request Forgery Protection

Since Spring Boot relies on Spring Security’s defaults, CSRF protection is turned on by default. This means that the actuator endpoints that require a POST (shutdown and loggers endpoints), PUT or DELETE will get a 403 forbidden error when the default security configuration is in use.

[Note]Note

We recommend disabling CSRF protection completely only if you are creating a service that is used by non-browser clients.

Additional information about CSRF protection can be found in the Spring Security Reference Guide.

29. Working with SQL Databases

The Spring Framework provides extensive support for working with SQL databases, from direct JDBC access using JdbcTemplate to complete “object relational mapping” technologies such as Hibernate. Spring Data provides an additional level of functionality: creating Repository implementations directly from interfaces and using conventions to generate queries from your method names.

29.1 Configure a DataSource

Java’s javax.sql.DataSource interface provides a standard method of working with database connections. Traditionally, a 'DataSource' uses a URL along with some credentials to establish a database connection.

[Tip]Tip

See the “How-to” section for more advanced examples, typically to take full control over the configuration of the DataSource.

29.1.1 Embedded Database Support

It is often convenient to develop applications by using an in-memory embedded database. Obviously, in-memory databases do not provide persistent storage. You need to populate your database when your application starts and be prepared to throw away data when your application ends.

[Tip]Tip

The “How-to” section includes a section on how to initialize a database.

Spring Boot can auto-configure embedded H2, HSQL, and Derby databases. You need not provide any connection URLs. You need only include a build dependency to the embedded database that you want to use.

[Note]Note

If you are using this feature in your tests, you may notice that the same database is reused by your whole test suite regardless of the number of application contexts that you use. If you want to make sure that each context has a separate embedded database, you should set spring.datasource.generate-unique-name to true.

For example, the typical POM dependencies would be as follows:

<dependency>
	<groupId>org.springframework.boot</groupId>
	<artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>
<dependency>
	<groupId>org.hsqldb</groupId>
	<artifactId>hsqldb</artifactId>
	<scope>runtime</scope>
</dependency>
[Note]Note

You need a dependency on spring-jdbc for an embedded database to be auto-configured. In this example, it is pulled in transitively through spring-boot-starter-data-jpa.

[Tip]Tip

If, for whatever reason, you do configure the connection URL for an embedded database, take care to ensure that the database’s automatic shutdown is disabled. If you use H2, you should use DB_CLOSE_ON_EXIT=FALSE to do so. If you use HSQLDB, you should ensure that shutdown=true is not used. Disabling the database’s automatic shutdown lets Spring Boot control when the database is closed, thereby ensuring that it happens once access to the database is no longer needed.

29.1.2 Connection to a Production Database

Production database connections can also be auto-configured by using a pooling DataSource. Spring Boot uses the following algorithm for choosing a specific implementation:

  1. We prefer HikariCP for its performance and concurrency. If HikariCP is available, we always choose it.
  2. Otherwise, if the Tomcat pooling DataSource is available, we use it.
  3. If neither HikariCP nor the Tomcat pooling datasource are available and if Commons DBCP2 is available, we use it.

If you use the spring-boot-starter-jdbc or spring-boot-starter-data-jpa “starters”, you automatically get a dependency to HikariCP.

[Note]Note

You can bypass that algorithm completely and specify the connection pool to use by setting the spring.datasource.type property. This is especially important if you run your application in a Tomcat container, as tomcat-jdbc is provided by default.

[Tip]Tip

Additional connection pools can always be configured manually. If you define your own DataSource bean, auto-configuration does not occur.

DataSource configuration is controlled by external configuration properties in spring.datasource.*. For example, you might declare the following section in application.properties:

spring.datasource.url=jdbc:mysql://localhost/test
spring.datasource.username=dbuser
spring.datasource.password=dbpass
spring.datasource.driver-class-name=com.mysql.jdbc.Driver
[Note]Note

You should at least specify the URL by setting the spring.datasource.url property. Otherwise, Spring Boot tries to auto-configure an embedded database.

[Tip]Tip

You often do not need to specify the driver-class-name, since Spring Boot can deduce it for most databases from the url.

[Note]Note

For a pooling DataSource to be created, we need to be able to verify that a valid Driver class is available, so we check for that before doing anything. In other words, if you set spring.datasource.driver-class-name=com.mysql.jdbc.Driver, then that class has to be loadable.

See DataSourceProperties for more of the supported options. These are the standard options that work regardless of the actual implementation. It is also possible to fine-tune implementation-specific settings by using their respective prefix (spring.datasource.hikari.*, spring.datasource.tomcat.*, and spring.datasource.dbcp2.*). Refer to the documentation of the connection pool implementation you are using for more details.

For instance, if you use the Tomcat connection pool, you could customize many additional settings, as shown in the following example:

# Number of ms to wait before throwing an exception if no connection is available.
spring.datasource.tomcat.max-wait=10000

# Maximum number of active connections that can be allocated from this pool at the same time.
spring.datasource.tomcat.max-active=50

# Validate the connection before borrowing it from the pool.
spring.datasource.tomcat.test-on-borrow=true

29.1.3 Connection to a JNDI DataSource

If you deploy your Spring Boot application to an Application Server, you might want to configure and manage your DataSource by using your Application Server’s built-in features and access it by using JNDI.

The spring.datasource.jndi-name property can be used as an alternative to the spring.datasource.url, spring.datasource.username, and spring.datasource.password properties to access the DataSource from a specific JNDI location. For example, the following section in application.properties shows how you can access a JBoss AS defined DataSource:

spring.datasource.jndi-name=java:jboss/datasources/customers

29.2 Using JdbcTemplate

Spring’s JdbcTemplate and NamedParameterJdbcTemplate classes are auto-configured, and you can @Autowire them directly into your own beans, as shown in the following example:

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.jdbc.core.JdbcTemplate;
import org.springframework.stereotype.Component;

@Component
public class MyBean {

	private final JdbcTemplate jdbcTemplate;

	@Autowired
	public MyBean(JdbcTemplate jdbcTemplate) {
		this.jdbcTemplate = jdbcTemplate;
	}

	// ...

}

You can customize some properties of the template by using the spring.jdbc.template.* properties, as shown in the following example:

spring.jdbc.template.max-rows=500
[Note]Note

The NamedParameterJdbcTemplate reuses the same JdbcTemplate instance behind the scenes. If more than one JdbcTemplate is defined and no primary candidate exists, the NamedParameterJdbcTemplate is not auto-configured.

29.3 JPA and “Spring Data”

The Java Persistence API is a standard technology that lets you “map” objects to relational databases. The spring-boot-starter-data-jpa POM provides a quick way to get started. It provides the following key dependencies:

  • Hibernate: One of the most popular JPA implementations.
  • Spring Data JPA: Makes it easy to implement JPA-based repositories.
  • Spring ORMs: Core ORM support from the Spring Framework.
[Tip]Tip

We do not go into too many details of JPA or Spring Data here. You can follow the “Accessing Data with JPA” guide from spring.io and read the Spring Data JPA and Hibernate reference documentation.

29.3.1 Entity Classes

Traditionally, JPA “Entity” classes are specified in a persistence.xml file. With Spring Boot, this file is not necessary and “Entity Scanning” is used instead. By default, all packages below your main configuration class (the one annotated with @EnableAutoConfiguration or @SpringBootApplication) are searched.

Any classes annotated with @Entity, @Embeddable, or @MappedSuperclass are considered. A typical entity class resembles the following example:

package com.example.myapp.domain;

import java.io.Serializable;
import javax.persistence.*;

@Entity
public class City implements Serializable {

	@Id
	@GeneratedValue
	private Long id;

	@Column(nullable = false)
	private String name;

	@Column(nullable = false)
	private String state;

	// ... additional members, often include @OneToMany mappings

	protected City() {
		// no-args constructor required by JPA spec
		// this one is protected since it shouldn't be used directly
	}

	public City(String name, String state) {
		this.name = name;
		this.country = country;
	}

	public String getName() {
		return this.name;
	}

	public String getState() {
		return this.state;
	}

	// ... etc

}
[Tip]Tip

You can customize entity scanning locations by using the @EntityScan annotation. See the “Section 80.4, “Separate @Entity Definitions from Spring Configuration”” how-to.

29.3.2 Spring Data JPA Repositories

Spring Data JPA repositories are interfaces that you can define to access data. JPA queries are created automatically from your method names. For example, a CityRepository interface might declare a findAllByState(String state) method to find all the cities in a given state.

For more complex queries, you can annotate your method with Spring Data’s Query annotation.

Spring Data repositories usually extend from the Repository or CrudRepository interfaces. If you use auto-configuration, repositories are searched from the package containing your main configuration class (the one annotated with @EnableAutoConfiguration or @SpringBootApplication) down.

The following example shows a typical Spring Data repository interface definition:

package com.example.myapp.domain;

import org.springframework.data.domain.*;
import org.springframework.data.repository.*;

public interface CityRepository extends Repository<City, Long> {

	Page<City> findAll(Pageable pageable);

	City findByNameAndCountryAllIgnoringCase(String name, String country);

}
[Tip]Tip

We have barely scratched the surface of Spring Data JPA. For complete details, see the Spring Data JPA reference documentation.

29.3.3 Creating and Dropping JPA Databases

By default, JPA databases are automatically created only if you use an embedded database (H2, HSQL, or Derby). You can explicitly configure JPA settings by using spring.jpa.* properties. For example, to create and drop tables you can add the following line to your application.properties:

spring.jpa.hibernate.ddl-auto=create-drop
[Note]Note

Hibernate’s own internal property name for this (if you happen to remember it better) is hibernate.hbm2ddl.auto. You can set it, along with other Hibernate native properties, by using spring.jpa.properties.* (the prefix is stripped before adding them to the entity manager). The following line shows an example of setting JPA properties for Hibernate:

spring.jpa.properties.hibernate.globally_quoted_identifiers=true

The line in the preceding example passes a value of true for the hibernate.globally_quoted_identifiers property to the Hibernate entity manager.

By default, the DDL execution (or validation) is deferred until the ApplicationContext has started. There is also a spring.jpa.generate-ddl flag, but it is not used if Hibernate auto-configuration is active, because the ddl-auto settings are more fine-grained.

29.3.4 Open EntityManager in View

If you are running a web application, Spring Boot by default registers OpenEntityManagerInViewInterceptor to apply the “Open EntityManager in View” pattern, to allow for lazy loading in web views. If you do not want this behavior, you should set spring.jpa.open-in-view to false in your application.properties.

29.4 Using H2’s Web Console

The H2 database provides a browser-based console that Spring Boot can auto-configure for you. The console is auto-configured when the following conditions are met:

[Tip]Tip

If you are not using Spring Boot’s developer tools but would still like to make use of H2’s console, you can configure the spring.h2.console.enabled property with a value of true.

[Note]Note

The H2 console is only intended for use during development, so you should take care to ensure that spring.h2.console.enabled is not set to true in production.

29.4.1 Changing the H2 Console’s Path

By default, the console is available at /h2-console. You can customize the console’s path by using the spring.h2.console.path property.

29.5 Using jOOQ

Java Object Oriented Querying (jOOQ) is a popular product from Data Geekery which generates Java code from your database and lets you build type-safe SQL queries through its fluent API. Both the commercial and open source editions can be used with Spring Boot.

29.5.1 Code Generation

In order to use jOOQ type-safe queries, you need to generate Java classes from your database schema. You can follow the instructions in the jOOQ user manual. If you use the jooq-codegen-maven plugin and you also use the spring-boot-starter-parent “parent POM”, you can safely omit the plugin’s <version> tag. You can also use Spring Boot-defined version variables (such as h2.version) to declare the plugin’s database dependency. The following listing shows an example:

<plugin>
	<groupId>org.jooq</groupId>
	<artifactId>jooq-codegen-maven</artifactId>
	<executions>
		...
	</executions>
	<dependencies>
		<dependency>
			<groupId>com.h2database</groupId>
			<artifactId>h2</artifactId>
			<version>${h2.version}</version>
		</dependency>
	</dependencies>
	<configuration>
		<jdbc>
			<driver>org.h2.Driver</driver>
			<url>jdbc:h2:~/yourdatabase</url>
		</jdbc>
		<generator>
			...
		</generator>
	</configuration>
</plugin>

29.5.2 Using DSLContext

The fluent API offered by jOOQ is initiated through the org.jooq.DSLContext interface. Spring Boot auto-configures a DSLContext as a Spring Bean and connects it to your application DataSource. To use the DSLContext, you can @Autowire it, as shown in the following example:

@Component
public class JooqExample implements CommandLineRunner {

	private final DSLContext create;

	@Autowired
	public JooqExample(DSLContext dslContext) {
		this.create = dslContext;
	}

}
[Tip]Tip

The jOOQ manual tends to use a variable named create to hold the DSLContext.

You can then use the DSLContext to construct your queries, as shown in the following example:

public List<GregorianCalendar> authorsBornAfter1980() {
	return this.create.selectFrom(AUTHOR)
		.where(AUTHOR.DATE_OF_BIRTH.greaterThan(new GregorianCalendar(1980, 0, 1)))
		.fetch(AUTHOR.DATE_OF_BIRTH);
}

29.5.3 jOOQ SQL Dialect

Unless the spring.jooq.sql-dialect property has been configured, Spring Boot determines the SQL dialect to use for your datasource. If Spring Boot could not detect the dialect, it uses DEFAULT.

[Note]Note

Spring Boot can only auto-configure dialects supported by the open source version of jOOQ.

29.5.4 Customizing jOOQ

More advanced customizations can be achieved by defining your own @Bean definitions, which is used when the jOOQ Configuration is created. You can define beans for the following jOOQ Types:

  • ConnectionProvider
  • TransactionProvider
  • RecordMapperProvider
  • RecordUnmapperProvider
  • RecordListenerProvider
  • ExecuteListenerProvider
  • VisitListenerProvider
  • TransactionListenerProvider

You can also create your own org.jooq.Configuration @Bean if you want to take complete control of the jOOQ configuration.

30. Working with NoSQL Technologies

Spring Data provides additional projects that help you access a variety of NoSQL technologies, including: MongoDB, Neo4J, Elasticsearch, Solr, Redis, Gemfire, Cassandra, Couchbase and LDAP. Spring Boot provides auto-configuration for Redis, MongoDB, Neo4j, Elasticsearch, Solr Cassandra, Couchbase, and LDAP. You can make use of the other projects, but you must configure them yourself. Refer to the appropriate reference documentation at projects.spring.io/spring-data.

30.1 Redis

Redis is a cache, message broker, and richly-featured key-value store. Spring Boot offers basic auto-configuration for the Lettuce and Jedis client libraries and the abstractions on top of them provided by Spring Data Redis.

There is a spring-boot-starter-data-redis “Starter” for collecting the dependencies in a convenient way. By default, it uses Lettuce. That starter handles both traditional and reactive applications.

[Tip]Tip

we also provide a spring-boot-starter-data-redis-reactive “Starter” for consistency with the other stores with reactive support.

30.1.1 Connecting to Redis

You can inject an auto-configured RedisConnectionFactory, StringRedisTemplate, or vanilla RedisTemplate instance as you would any other Spring Bean. By default, the instance tries to connect to a Redis server at localhost:6379. The following listing shows an example of such a bean:

@Component
public class MyBean {

	private StringRedisTemplate template;

	@Autowired
	public MyBean(StringRedisTemplate template) {
		this.template = template;
	}

	// ...

}
[Tip]Tip

You can also register an arbitrary number of beans that implement LettuceClientConfigurationBuilderCustomizer for more advanced customizations. If you use Jedis, JedisClientConfigurationBuilderCustomizer is also available.

If you add your own @Bean of any of the auto-configured types, it replaces the default (except in the case of RedisTemplate, when the exclusion is based on the bean name, redisTemplate, not its type). By default, if commons-pool2 is on the classpath, you get a pooled connection factory.

30.2 MongoDB

MongoDB is an open-source NoSQL document database that uses a JSON-like schema instead of traditional table-based relational data. Spring Boot offers several conveniences for working with MongoDB, including the spring-boot-starter-data-mongodb and spring-boot-starter-data-mongodb-reactive “Starters”.

30.2.1 Connecting to a MongoDB Database

To access Mongo databases, you can inject an auto-configured org.springframework.data.mongodb.MongoDbFactory. By default, the instance tries to connect to a MongoDB server at mongodb://localhost/test The following example shows how to connect to a MongoDB database:

import org.springframework.data.mongodb.MongoDbFactory;
import com.mongodb.DB;

@Component
public class MyBean {

	private final MongoDbFactory mongo;

	@Autowired
	public MyBean(MongoDbFactory mongo) {
		this.mongo = mongo;
	}

	// ...

	public void example() {
		DB db = mongo.getDb();
		// ...
	}

}

You can set the spring.data.mongodb.uri property to change the URL and configure additional settings such as the replica set, as shown in the following example:

spring.data.mongodb.uri=mongodb://user:[email protected]:12345,mongo2.example.com:23456/test

Alternatively, as long as you use Mongo 2.x, you can specify a host/port. For example, you might declare the following settings in your application.properties:

spring.data.mongodb.host=mongoserver
spring.data.mongodb.port=27017
[Note]Note

If you use the Mongo 3.0 Java driver, spring.data.mongodb.host and spring.data.mongodb.port are not supported. In such cases, spring.data.mongodb.uri should be used to provide all of the configuration.

[Tip]Tip

If spring.data.mongodb.port is not specified, the default of 27017 is used. You could delete this line from the example shown earlier.

[Tip]Tip

If you do not use Spring Data Mongo, you can inject com.mongodb.MongoClient beans instead of using MongoDbFactory. If you want to take complete control of establishing the MongoDB connection, you can also declare your own MongoDbFactory or MongoClient bean.

[Note]Note

If you are using the reactive driver, Netty is required for SSL. The auto-configuration configures this factory automatically if Netty is available and the factory to use hasn’t been customized already.

30.2.2 MongoTemplate

Spring Data MongoDB provides a MongoTemplate class that is very similar in its design to Spring’s JdbcTemplate. As with JdbcTemplate, Spring Boot auto-configures a bean for you to inject the template, as follows:

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.data.mongodb.core.MongoTemplate;
import org.springframework.stereotype.Component;

@Component
public class MyBean {

	private final MongoTemplate mongoTemplate;

	@Autowired
	public MyBean(MongoTemplate mongoTemplate) {
		this.mongoTemplate = mongoTemplate;
	}

	// ...

}

See the MongoOperations Javadoc for complete details.

30.2.3 Spring Data MongoDB Repositories

Spring Data includes repository support for MongoDB. As with the JPA repositories discussed earlier, the basic principle is that queries are constructed automatically, based on method names.

In fact, both Spring Data JPA and Spring Data MongoDB share the same common infrastructure. You could take the JPA example from earlier and, assuming that City is now a Mongo data class rather than a JPA @Entity, it works in the same way, as shown in the following example:

package com.example.myapp.domain;

import org.springframework.data.domain.*;
import org.springframework.data.repository.*;

public interface CityRepository extends Repository<City, Long> {

	Page<City> findAll(Pageable pageable);

	City findByNameAndCountryAllIgnoringCase(String name, String country);

}
[Tip]Tip

You can customize document scanning locations by using the @EntityScan annotation.

[Tip]Tip

For complete details of Spring Data MongoDB, including its rich object mapping technologies, refer to its reference documentation.

30.2.4 Embedded Mongo

Spring Boot offers auto-configuration for Embedded Mongo. To use it in your Spring Boot application, add a dependency on de.flapdoodle.embed:de.flapdoodle.embed.mongo.

The port that Mongo listens on can be configured by setting the spring.data.mongodb.port property. To use a randomly allocated free port, use a value of 0. The MongoClient created by MongoAutoConfiguration is automatically configured to use the randomly allocated port.

[Note]Note

If you do not configure a custom port, the embedded support uses a random port (rather than 27017) by default.

If you have SLF4J on the classpath, the output produced by Mongo is automatically routed to a logger named org.springframework.boot.autoconfigure.mongo.embedded.EmbeddedMongo.

You can declare your own IMongodConfig and IRuntimeConfig beans to take control of the Mongo instance’s configuration and logging routing.

30.3 Neo4j

Neo4j is an open-source NoSQL graph database that uses a rich data model of nodes related by first class relationships, which is better suited for connected big data than traditional rdbms approaches. Spring Boot offers several conveniences for working with Neo4j, including the spring-boot-starter-data-neo4j “Starter”.

30.3.1 Connecting to a Neo4j Database

You can inject an auto-configured Neo4jSession, Session, or Neo4jOperations instance as you would any other Spring Bean. By default, the instance tries to connect to a Neo4j server at localhost:7474. The following example shows how to inject a Neo4j bean:

@Component
public class MyBean {

	private final Neo4jTemplate neo4jTemplate;

	@Autowired
	public MyBean(Neo4jTemplate neo4jTemplate) {
		this.neo4jTemplate = neo4jTemplate;
	}

	// ...

}

You can take full control of the configuration by adding a org.neo4j.ogm.config.Configuration @Bean of your own. Also, adding a @Bean of type Neo4jOperations disables the auto-configuration.

You can configure the user and credentials to use by setting the spring.data.neo4j.* properties, as shown in the following example:

spring.data.neo4j.uri=http://my-server:7474
spring.data.neo4j.username=neo4j
spring.data.neo4j.password=secret

30.3.2 Using the Embedded Mode

If you add org.neo4j:neo4j-ogm-embedded-driver to the dependencies of your application, Spring Boot automatically configures an in-process embedded instance of Neo4j that does not persist any data when your application shuts down. You can explicitly disable that mode by setting spring.data.neo4j.embedded.enabled=false. You can also enable persistence for the embedded mode by providing a path to a database file, as shown in the following example:

	spring.data.neo4j.uri=file://var/tmp/graph.db
[Note]Note

The Neo4j OGM embedded driver does not provide the Neo4j kernel. Users are expected to provide this dependency manually. See the documentation for more details.

30.3.3 Neo4jSession

By default, if you are running a web application, the session is bound to the thread for the entire processing of the request (that is, it uses the "Open Session in View" pattern). If you do not want this behavior, add the following line to your application.properties file:

spring.data.neo4j.open-in-view=false

30.3.4 Spring Data Neo4j Repositories

Spring Data includes repository support for Neo4j.

In fact, both Spring Data JPA and Spring Data Neo4j share the same common infrastructure. You could take the JPA example from earlier and, assuming that City is now a Neo4j OGM @NodeEntity rather than a JPA @Entity, it works in the same way.

[Tip]Tip

You can customize entity scanning locations by using the @EntityScan annotation.

To enable repository support (and optionally support for @Transactional), add the following two annotations to your Spring configuration:

@EnableNeo4jRepositories(basePackages = "com.example.myapp.repository")
@EnableTransactionManagement

30.3.5 Repository Example

The following example shows an interface definition for a Neo4j repository:

package com.example.myapp.domain;

import org.springframework.data.domain.*;
import org.springframework.data.repository.*;

public interface CityRepository extends GraphRepository<City> {

	Page<City> findAll(Pageable pageable);

	City findByNameAndCountry(String name, String country);

}
[Tip]Tip

For complete details of Spring Data Neo4j, including its rich object mapping technologies, refer to the reference documentation.

30.4 Gemfire

Spring Data Gemfire provides convenient Spring-friendly tools for accessing the Pivotal Gemfire data management platform. There is a spring-boot-starter-data-gemfire “Starter” for collecting the dependencies in a convenient way. There is currently no auto-configuration support for Gemfire, but you can enable Spring Data Repositories with a single annotation: @EnableGemfireRepositories.

30.5 Solr

Apache Solr is a search engine. Spring Boot offers basic auto-configuration for the Solr 5 client library and the abstractions on top of it provided by Spring Data Solr. There is a spring-boot-starter-data-solr “Starter” for collecting the dependencies in a convenient way.

30.5.1 Connecting to Solr

You can inject an auto-configured SolrClient instance as you would any other Spring bean. By default, the instance tries to connect to a server at localhost:8983/solr. The following example shows how to inject a Solr bean:

@Component
public class MyBean {

	private SolrClient solr;

	@Autowired
	public MyBean(SolrClient solr) {
		this.solr = solr;
	}

	// ...

}

If you add your own @Bean of type SolrClient, it replaces the default.

30.5.2 Spring Data Solr Repositories

Spring Data includes repository support for Apache Solr. As with the JPA repositories discussed earlier, the basic principle is that queries are automatically constructed for \ you based on method names.

In fact, both Spring Data JPA and Spring Data Solr share the same common infrastructure. You could take the JPA example from earlier and, assuming that City is now a @SolrDocument class rather than a JPA @Entity, it works in the same way.

[Tip]Tip

For complete details of Spring Data Solr, refer to the reference documentation.

30.6 Elasticsearch

Elasticsearch is an open source, distributed, real-time search and analytics engine. Spring Boot offers basic auto-configuration for Elasticsearch and the abstractions on top of it provided by Spring Data Elasticsearch. There is a spring-boot-starter-data-elasticsearch “Starter” for collecting the dependencies in a convenient way. Spring Boot also supports Jest.

30.6.1 Connecting to Elasticsearch by Using Jest

If you have Jest on the classpath, you can inject an auto-configured JestClient that by default targets localhost:9200. You can further tune how the client is configured, as shown in the following example:

spring.elasticsearch.jest.uris=http://search.example.com:9200
spring.elasticsearch.jest.read-timeout=10000
spring.elasticsearch.jest.username=user
spring.elasticsearch.jest.password=secret

You can also register an arbitrary number of beans that implement HttpClientConfigBuilderCustomizer for more advanced customizations. The following example tunes additional HTTP settings:

static class HttpSettingsCustomizer implements HttpClientConfigBuilderCustomizer {

	@Override
	public void customize(HttpClientConfig.Builder builder) {
		builder.maxTotalConnection(100).defaultMaxTotalConnectionPerRoute(5);
	}

}

To take full control over the registration, define a JestClient bean.

30.6.2 Connecting to Elasticsearch by Using Spring Data

To connect to Elasticsearch, you must provide the address of one or more cluster nodes. The address can be specified by setting the spring.data.elasticsearch.cluster-nodes property to a comma-separated host:port list. With this configuration in place, an ElasticsearchTemplate or TransportClient can be injected like any other Spring bean, as shown in the following example:

spring.data.elasticsearch.cluster-nodes=localhost:9300
@Component
public class MyBean {

	private final ElasticsearchTemplate template;

	public MyBean(ElasticsearchTemplate template) {
		this.template = template;
	}

	// ...

}

If you add your own ElasticsearchTemplate or TransportClient @Bean, it replaces the default.

30.6.3 Spring Data Elasticsearch Repositories

Spring Data includes repository support for Elasticsearch. As with the JPA repositories discussed earlier, the basic principle is that queries are constructed for you automatically based on method names.

In fact, both Spring Data JPA and Spring Data Elasticsearch share the same common infrastructure. You could take the JPA example from earlier and, assuming that City is now an Elasticsearch @Document class rather than a JPA @Entity, it works in the same way.

[Tip]Tip

For complete details of Spring Data Elasticsearch, refer to the reference documentation.

30.7 Cassandra

Cassandra is an open source, distributed database management system designed to handle large amounts of data across many commodity servers. Spring Boot offers auto-configuration for Cassandra and the abstractions on top of it provided by Spring Data Cassandra. There is a spring-boot-starter-data-cassandra “Starter” for collecting the dependencies in a convenient way.

30.7.1 Connecting to Cassandra

You can inject an auto-configured CassandraTemplate or a Cassandra Session instance as you would with any other Spring Bean. The spring.data.cassandra.* properties can be used to customize the connection. Generally, you provide keyspace-name and contact-points properties, as shown in the following example:

spring.data.cassandra.keyspace-name=mykeyspace
spring.data.cassandra.contact-points=cassandrahost1,cassandrahost2

The following code listing shows how to inject a Cassandra bean:

@Component
public class MyBean {

	private CassandraTemplate template;

	@Autowired
	public MyBean(CassandraTemplate template) {
		this.template = template;
	}

	// ...

}

If you add your own @Bean of type CassandraTemplate, it replaces the default.

30.7.2 Spring Data Cassandra Repositories

Spring Data includes basic repository support for Cassandra. Currently, this is more limited than the JPA repositories discussed earlier and needs to annotate finder methods with @Query.

[Tip]Tip

For complete details of Spring Data Cassandra, refer to the reference documentation.

30.8 Couchbase

Couchbase is an open-source, distributed, multi-model NoSQL document-oriented database that is optimized for interactive applications. Spring Boot offers auto-configuration for Couchbase and the abstractions on top of it provided by Spring Data Couchbase. There are spring-boot-starter-data-couchbase and spring-boot-starter-data-couchbase-reactive “Starters” for collecting the dependencies in a convenient way.

30.8.1 Connecting to Couchbase

You can get a Bucket and Cluster by adding the Couchbase SDK and some configuration. The spring.couchbase.* properties can be used to customize the connection. Generally, you provide the bootstrap hosts, bucket name, and password, as shown in the following example:

spring.couchbase.bootstrap-hosts=my-host-1,192.168.1.123
spring.couchbase.bucket.name=my-bucket
spring.couchbase.bucket.password=secret
[Tip]Tip

You need to provide at least the bootstrap host(s), in which case the bucket name is default and the password is an empty String. Alternatively, you can define your own org.springframework.data.couchbase.config.CouchbaseConfigurer @Bean to take control over the whole configuration.

It is also possible to customize some of the CouchbaseEnvironment settings. For instance, the following configuration changes the timeout to use to open a new Bucket and enables SSL support:

spring.couchbase.env.timeouts.connect=3000
spring.couchbase.env.ssl.key-store=/location/of/keystore.jks
spring.couchbase.env.ssl.key-store-password=secret

Check the spring.couchbase.env.* properties for more details.

30.8.2 Spring Data Couchbase Repositories

Spring Data includes repository support for Couchbase. For complete details of Spring Data Couchbase, refer to the reference documentation.

You can inject an auto-configured CouchbaseTemplate instance as you would with any other Spring Bean, provided a default CouchbaseConfigurer is available (which happens when you enable Couchbase support, as explained earlier).

The following examples shows how to inject a Couchbase bean:

@Component
public class MyBean {

	private final CouchbaseTemplate template;

	@Autowired
	public MyBean(CouchbaseTemplate template) {
		this.template = template;
	}

	// ...

}

There are a few beans that you can define in your own configuration to override those provided by the auto-configuration:

  • A CouchbaseTemplate @Bean with a name of couchbaseTemplate.
  • An IndexManager @Bean with a name of couchbaseIndexManager.
  • A CustomConversions @Bean with a name of couchbaseCustomConversions.

To avoid hard-coding those names in your own config, you can reuse BeanNames provided by Spring Data Couchbase. For instance, you can customize the converters to use, as follows:

@Configuration
public class SomeConfiguration {

	@Bean(BeanNames.COUCHBASE_CUSTOM_CONVERSIONS)
	public CustomConversions myCustomConversions() {
		return new CustomConversions(...);
	}

	// ...

}
[Tip]Tip

If you want to fully bypass the auto-configuration for Spring Data Couchbase, provide your own implementation of org.springframework.data.couchbase.config.AbstractCouchbaseDataConfiguration.

30.9 LDAP

LDAP (Lightweight Directory Access Protocol) is an open, vendor-neutral, industry standard application protocol for accessing and maintaining distributed directory information services over an IP network. Spring Boot offers auto-configuration for any compliant LDAP server as well as support for the embedded in-memory LDAP server from UnboundID.

LDAP abstractions are provided by Spring Data LDAP. There is a spring-boot-starter-data-ldap “Starter” for collecting the dependencies in a convenient way.

30.9.1 Connecting to an LDAP Server

To connect to an LDAP server, make sure you declare a dependency on the spring-boot-starter-data-ldap “Starter” or spring-ldap-core and then declare the URLs of your server in your application.properties, as shown in the following example:

spring.ldap.urls=ldap://myserver:1235
spring.ldap.username=admin
spring.ldap.password=secret

If you need to customize connection settings, you can use the spring.ldap.base and spring.ldap.base-environment properties.

30.9.2 Spring Data LDAP Repositories

Spring Data includes repository support for LDAP. For complete details of Spring Data LDAP, refer to the reference documentation.

You can also inject an auto-configured LdapTemplate instance as you would with any other Spring Bean, as shown in the following example:

@Component
public class MyBean {

	private final LdapTemplate template;

	@Autowired
	public MyBean(LdapTemplate template) {
		this.template = template;
	}

	// ...

}

30.9.3 Embedded In-memory LDAP Server

For testing purposes, Spring Boot supports auto-configuration of an in-memory LDAP server from UnboundID. To configure the server, add a dependency to com.unboundid:unboundid-ldapsdk and declare a base-dn property, as follows:

spring.ldap.embedded.base-dn=dc=spring,dc=io
[Note]Note

It is possible to define multiple base-dn values, however, since distinguished names usually contain commas, they must be defined using the correct notation.

In yaml files, you can use the yaml list notation:

spring.ldap.embedded.base-dn:
  - dc=spring,dc=io
  - dc=pivotal,dc=io

In properties files, you must include the index as part of the property name:

spring.ldap.embedded.base-dn[0]=dc=spring,dc=io
spring.ldap.embedded.base-dn[1]=dc=pivotal,dc=io

By default, the server starts on a random port and triggers the regular LDAP support. There is no need to specify a spring.ldap.urls property.

If there is a schema.ldif file on your classpath, it is used to initialize the server. If you want to load the initialization script from a different resource, you can also use the spring.ldap.embedded.ldif property.

By default, a standard schema is used to validate LDIF files. You can turn off validation altogether by setting the spring.ldap.embedded.validation.enabled property. If you have custom attributes, you can use spring.ldap.embedded.validation.schema to define your custom attribute types or object classes.

30.10 InfluxDB

InfluxDB is an open-source time series database optimized for fast, high-availability storage and retrieval of time series data in fields such as operations monitoring, application metrics, Internet-of-Things sensor data, and real-time analytics.

30.10.1 Connecting to InfluxDB

Spring Boot auto-configures an InfluxDB instance, provided the influxdb-java client is on the classpath and the URL of the database is set, as shown in the following example:

spring.influx.url=http://172.0.0.1:8086

If the connection to InfluxDB requires a user and password, you can set the spring.influx.user and spring.influx.password properties accordingly.

InfluxDB relies on OkHttp. If you need to tune the http client InfluxDB uses behind the scenes, you can register an OkHttpClient.Builder bean.

31. Caching

The Spring Framework provides support for transparently adding caching to an application. At its core, the abstraction applies caching to methods, thus reducing the number of executions based on the information available in the cache. The caching logic is applied transparently, without any interference to the invoker. Spring Boot auto-configures the cache infrastructure as long as caching support is enabled via the @EnableCaching annotation.

[Note]Note

Check the relevant section of the Spring Framework reference for more details.

In a nutshell, adding caching to an operation of your service is as easy as adding the relevant annotation to its method, as shown in the following example:

   import org.springframework.cache.annotation.Cacheable;
import org.springframework.stereotype.Component;

@Component
public class MathService {

	@Cacheable("piDecimals")
	public int computePiDecimal(int i) {
		// ...
	}

}

This example demonstrates the use of caching on a potentially costly operation. Before invoking computePiDecimal, the abstraction looks for an entry in the piDecimals cache that matches the i argument. If an entry is found, the content in the cache is immediately returned to the caller, and the method is not invoked. Otherwise, the method is invoked, and the cache is updated before returning the value.

[Caution]Caution

You can also use the standard JSR-107 (JCache) annotations (such as @CacheResult) transparently. However, we strongly advise you to not mix and match the Spring Cache and JCache annotations.

If you do not add any specific cache library, Spring Boot auto-configures a simple provider that uses concurrent maps in memory. When a cache is required (such as piDecimals in the preceding example), this provider creates it for you. The simple provider is not really recommended for production usage, but it is great for getting started and making sure that you understand the features. When you have made up your mind about the cache provider to use, please make sure to read its documentation to figure out how to configure the caches that your application uses. Nearly all providers require you to explicitly configure every cache that you use in the application. Some offer a way to customize the default caches defined by the spring.cache.cache-names property.

[Tip]Tip

It is also possible to transparently update or evict data from the cache.

31.1 Supported Cache Providers

The cache abstraction does not provide an actual store and relies on abstraction materialized by the org.springframework.cache.Cache and org.springframework.cache.CacheManager interfaces.

If you have not defined a bean of type CacheManager or a CacheResolver named cacheResolver (see CachingConfigurer), Spring Boot tries to detect the following providers (in the indicated order):

[Tip]Tip

It is also possible to force a particular cache provider by setting the spring.cache.type property. Use this property if you need to disable caching altogether in certain environment (such as tests).

[Tip]Tip

Use the spring-boot-starter-cache “Starter” to quickly add basic caching dependencies. The starter brings in spring-context-support. If you add dependencies manually, you must include spring-context-support in order to use the JCache, EhCache 2.x, or Guava support.

If the CacheManager is auto-configured by Spring Boot, you can further tune its configuration before it is fully initialized by exposing a bean that implements the CacheManagerCustomizer interface. The following example sets a flag to say that null values should be passed down to the underlying map:

@Bean
public CacheManagerCustomizer<ConcurrentMapCacheManager> cacheManagerCustomizer() {
	return new CacheManagerCustomizer<ConcurrentMapCacheManager>() {
		@Override
		public void customize(ConcurrentMapCacheManager cacheManager) {
			cacheManager.setAllowNullValues(false);
		}
	};
}
[Note]Note

In the preceding example, an auto-configured ConcurrentMapCacheManager is expected. If that is not the case (either you provided your own config or a different cache provider was auto-configured), the customizer is not invoked at all. You can have as many customizers as you want, and you can also order them by using @Order or Ordered.

31.1.1 Generic

Generic caching is used if the context defines at least one org.springframework.cache.Cache bean. A CacheManager wrapping all beans of that type is created.

31.1.2 JCache (JSR-107)

JCache is bootstrapped through the presence of a javax.cache.spi.CachingProvider on the classpath (that is, a JSR-107 compliant caching library exists on the classpath), and the JCacheCacheManager is provided by the spring-boot-starter-cache “Starter”. Various compliant libraries are available, and Spring Boot provides dependency management for Ehcache 3, Hazelcast, and Infinispan. Any other compliant library can be added as well.

It might happen that more than one provider is present, in which case the provider must be explicitly specified. Even if the JSR-107 standard does not enforce a standardized way to define the location of the configuration file, Spring Boot does its best to accommodate setting a cache with implementation details, as shown in the following example:

   # Only necessary if more than one provider is present
spring.cache.jcache.provider=com.acme.MyCachingProvider
spring.cache.jcache.config=classpath:acme.xml
[Note]Note

When a cache library offers both a native implementation and JSR-107 support, Spring Boot prefers the JSR-107 support, so that the same features are available if you switch to a different JSR-107 implementation.

[Tip]Tip

Spring Boot has general support for Hazelcast. If a single HazelcastInstance is available, it is automatically reused for the CacheManager as well, unless the spring.cache.jcache.config property is specified.

There are two ways to customize the underlying javax.cache.cacheManager:

  • Caches can be created on startup by setting the spring.cache.cache-names property. If a custom javax.cache.configuration.Configuration bean is defined, it is used to customize them.
  • org.springframework.boot.autoconfigure.cache.JCacheManagerCustomizer beans are invoked with the reference of the CacheManager for full customization.
[Tip]Tip

If a standard javax.cache.CacheManager bean is defined, it is wrapped automatically in an org.springframework.cache.CacheManager implementation that the abstraction expects. No further customization is applied to it.

31.1.3 EhCache 2.x

EhCache 2.x is used if a file named ehcache.xml can be found at the root of the classpath. If EhCache 2.x is found, the EhCacheCacheManager provided by the spring-boot-starter-cache “Starter” is used to bootstrap the cache manager. An alternate configuration file can be provided as well, as shown in the following example:

spring.cache.ehcache.config=classpath:config/another-config.xml

31.1.4 Hazelcast

Spring Boot has general support for Hazelcast. If a HazelcastInstance has been auto-configured, it is automatically wrapped in a CacheManager.

31.1.5 Infinispan

Infinispan has no default configuration file location, so it must be specified explicitly. Otherwise, the default bootstrap is used.

spring.cache.infinispan.config=infinispan.xml

Caches can be created on startup by setting the spring.cache.cache-names property. If a custom ConfigurationBuilder bean is defined, it is used to customize the caches.

[Note]Note

The support of Infinispan in Spring Boot is restricted to the embedded mode and is quite basic. If you want more options, you should use the official Infinispan Spring Boot starter instead. See Infinispan’s documentation for more details.

31.1.6 Couchbase

If the Couchbase Java client and the couchbase-spring-cache implementation are available and Couchbase is configured, a CouchbaseCacheManager is auto-configured. It is also possible to create additional caches on startup by setting the spring.cache.cache-names property. These caches operate on the Bucket that was auto-configured. You can also create additional caches on another Bucket by using the customizer. Assume you need two caches (cache1 and cache2) on the "main" Bucket and one (cache3) cache with a custom time to live of 2 seconds on the “another” Bucket. You can create the first two caches through configuration, as follows:

spring.cache.cache-names=cache1,cache2

Then you can define a @Configuration class to configure the extra Bucket and the cache3 cache, as follows:

@Configuration
public class CouchbaseCacheConfiguration {

	private final Cluster cluster;

	public CouchbaseCacheConfiguration(Cluster cluster) {
		this.cluster = cluster;
	}

	@Bean
	public Bucket anotherBucket() {
		return this.cluster.openBucket("another", "secret");
	}

	@Bean
	public CacheManagerCustomizer<CouchbaseCacheManager> cacheManagerCustomizer() {
		return c -> {
			c.prepareCache("cache3", CacheBuilder.newInstance(anotherBucket())
					.withExpiration(2));
		};
	}

}

This sample configuration reuses the Cluster that was created through auto-configuration.

31.1.7 Redis

If Redis is available and configured, a RedisCacheManager is auto-configured. It is possible to create additional caches on startup by setting the spring.cache.cache-names property and cache defaults can be configured by using spring.cache.redis.* properties. For instance, the following configuration creates cache1 and cache2 caches with a time to live of 10 minutes:

spring.cache.cache-names=cache1,cache2
spring.cache.redis.time-to-live=600000
[Note]Note

By default, a key prefix is added so that, if two separate caches use the same key, Redis does not have overlapping keys and cannot return invalid values. We strongly recommend keeping this setting enabled if you create your own RedisCacheManager.

[Tip]Tip

You can take full control of the configuration by adding a RedisCacheConfiguration @Bean of your own. This can be useful if you’re looking for customizing the serialization strategy.

31.1.8 Caffeine

Caffeine is a Java 8 rewrite of Guava’s cache that supersedes support for Guava. If Caffeine is present, a CaffeineCacheManager (provided by the spring-boot-starter-cache “Starter”) is auto-configured. Caches can be created on startup by setting the spring.cache.cache-names property and can be customized by one of the following (in the indicated order):

  1. A cache spec defined by spring.cache.caffeine.spec
  2. A com.github.benmanes.caffeine.cache.CaffeineSpec bean is defined
  3. A com.github.benmanes.caffeine.cache.Caffeine bean is defined

For instance, the following configuration creates cache1 and cache2 caches with a maximum size of 500 and a time to live of 10 minutes

spring.cache.cache-names=cache1,cache2
spring.cache.caffeine.spec=maximumSize=500,expireAfterAccess=600s

If a com.github.benmanes.caffeine.cache.CacheLoader bean is defined, it is automatically associated to the CaffeineCacheManager. Since the CacheLoader is going to be associated with all caches managed by the cache manager, it must be defined as CacheLoader<Object, Object>. The auto-configuration ignores any other generic type.

31.1.9 Simple

If none of the other providers can be found, a simple implementation using a ConcurrentHashMap as the cache store is configured. This is the default if no caching library is present in your application. By default, caches are created as needed, but you can restrict the list of available caches by setting the cache-names property. For instance, if you want only cache1 and cache2 caches, set the cache-names property as follows:

spring.cache.cache-names=cache1,cache2

If you do so and your application uses a cache not listed, then it fails at runtime when the cache is needed, but not on startup. This is similar to the way the "real" cache providers behave if you use an undeclared cache.

31.1.10 None

When @EnableCaching is present in your configuration, a suitable cache configuration is expected as well. If you need to disable caching altogether in certain environments, force the cache type to none to use a no-op implementation, as shown in the following example:

spring.cache.type=none

32. Messaging

The Spring Framework provides extensive support for integrating with messaging systems, from simplified use of the JMS API using JmsTemplate to a complete infrastructure to receive messages asynchronously. Spring AMQP provides a similar feature set for the Advanced Message Queuing Protocol. Spring Boot also provides auto-configuration options for RabbitTemplate and RabbitMQ. Spring WebSocket natively includes support for STOMP messaging, and Spring Boot has support for that through starters and a small amount of auto-configuration. Spring Boot also has support for Apache Kafka.

32.1 JMS

The javax.jms.ConnectionFactory interface provides a standard method of creating a javax.jms.Connection for interacting with a JMS broker. Although Spring needs a ConnectionFactory to work with JMS, you generally need not use it directly yourself and can instead rely on higher level messaging abstractions. (See the relevant section of the Spring Framework reference documentation for details.) Spring Boot also auto-configures the necessary infrastructure to send and receive messages.

32.1.1 ActiveMQ Support

When ActiveMQ is available on the classpath, Spring Boot can also configure a ConnectionFactory. If the broker is present, an embedded broker is automatically started and configured (provided no broker URL is specified through configuration).

[Note]Note

If you use spring-boot-starter-activemq, the necessary dependencies to connect or embed an ActiveMQ instance are provided, as is the Spring infrastructure to integrate with JMS.

ActiveMQ configuration is controlled by external configuration properties in spring.activemq.*. For example, you might declare the following section in application.properties:

spring.activemq.broker-url=tcp://192.168.1.210:9876
spring.activemq.user=admin
spring.activemq.password=secret

You can also pool JMS resources by adding a dependency to org.apache.activemq:activemq-pool and configuring the PooledConnectionFactory accordingly, as shown in the following example:

spring.activemq.pool.enabled=true
spring.activemq.pool.max-connections=50
[Tip]Tip

See ActiveMQProperties for more of the supported options. You can also register an arbitrary number of beans that implement ActiveMQConnectionFactoryCustomizer for more advanced customizations.

By default, ActiveMQ creates a destination if it does not yet exist so that destinations are resolved against their provided names.

32.1.2 Artemis Support

Spring Boot can auto-configure a ConnectionFactory when it detects that Artemis is available on the classpath. If the broker is present, an embedded broker is automatically started and configured (unless the mode property has been explicitly set). The supported modes are embedded (to make explicit that an embedded broker is required and that an error should occur if the broker is not available on the classpath) and native (to connect to a broker using the netty transport protocol). When the latter is configured, Spring Boot configures a ConnectionFactory that connects to a broker running on the local machine with the default settings.

[Note]Note

If you use spring-boot-starter-artemis, the necessary dependencies to connect to an existing Artemis instance are provided, as well as the Spring infrastructure to integrate with JMS. Adding org.apache.activemq:artemis-jms-server to your application lets you use embedded mode.

Artemis configuration is controlled by external configuration properties in spring.artemis.*. For example, you might declare the following section in application.properties:

spring.artemis.mode=native
spring.artemis.host=192.168.1.210
spring.artemis.port=9876
spring.artemis.user=admin
spring.artemis.password=secret

When embedding the broker, you can choose if you want to enable persistence and list the destinations that should be made available. These can be specified as a comma-separated list to create them with the default options, or you can define bean(s) of type org.apache.activemq.artemis.jms.server.config.JMSQueueConfiguration or org.apache.activemq.artemis.jms.server.config.TopicConfiguration, for advanced queue and topic configurations, respectively.

See ArtemisProperties for more supported options.

No JNDI lookup is involved, and destinations are resolved against their names, using either the name attribute in the Artemis configuration or the names provided through configuration.

32.1.3 Using a JNDI ConnectionFactory

If you are running your application in an application server, Spring Boot tries to locate a JMS ConnectionFactory by using JNDI. By default, the java:/JmsXA and java:/XAConnectionFactory location are checked. You can use the spring.jms.jndi-name property if you need to specify an alternative location, as shown in the following example:

spring.jms.jndi-name=java:/MyConnectionFactory

32.1.4 Sending a Message

Spring’s JmsTemplate is auto-configured, and you can autowire it directly into your own beans, as shown in the following example:

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.jms.core.JmsTemplate;
import org.springframework.stereotype.Component;

@Component
public class MyBean {

	private final JmsTemplate jmsTemplate;

	@Autowired
	public MyBean(JmsTemplate jmsTemplate) {
		this.jmsTemplate = jmsTemplate;
	}

	// ...

}
[Note]Note

JmsMessagingTemplate can be injected in a similar manner. If a DestinationResolver or a MessageConverter bean is defined, it is associated automatically to the auto-configured JmsTemplate.

32.1.5 Receiving a Message

When the JMS infrastructure is present, any bean can be annotated with @JmsListener to create a listener endpoint. If no JmsListenerContainerFactory has been defined, a default one is configured automatically. If a DestinationResolver or a MessageConverter beans is defined, it is associated automatically to the default factory.

By default, the default factory is transactional. If you run in an infrastructure where a JtaTransactionManager is present, it is associated to the listener container by default. If not, the sessionTransacted flag is enabled. In that latter scenario, you can associate your local data store transaction to the processing of an incoming message by adding @Transactional on your listener method (or a delegate thereof). This ensures that the incoming message is acknowledged, once the local transaction has completed. This also includes sending response messages that have been performed on the same JMS session.

The following component creates a listener endpoint on the someQueue destination:

@Component
public class MyBean {

	@JmsListener(destination = "someQueue")
	public void processMessage(String content) {
		// ...
	}

}
[Tip]Tip

See the Javadoc of @EnableJms for more details.

If you need to create more JmsListenerContainerFactory instances or if you want to override the default, Spring Boot provides a DefaultJmsListenerContainerFactoryConfigurer that you can use to initialize a DefaultJmsListenerContainerFactory with the same settings as the one that is auto-configured.

For instance, the following example exposes another factory that uses a specific MessageConverter:

@Configuration
static class JmsConfiguration {

	@Bean
	public DefaultJmsListenerContainerFactory myFactory(
			DefaultJmsListenerContainerFactoryConfigurer configurer) {
		DefaultJmsListenerContainerFactory factory =
				new DefaultJmsListenerContainerFactory();
		configurer.configure(factory, connectionFactory());
		factory.setMessageConverter(myMessageConverter());
		return factory;
	}

}

Then you can use the factory in any @JmsListener-annotated method as follows:

@Component
public class MyBean {

	@JmsListener(destination = "someQueue", containerFactory="myFactory")
	public void processMessage(String content) {
		// ...
	}

}

32.2 AMQP

The Advanced Message Queuing Protocol (AMQP) is a platform-neutral, wire-level protocol for message-oriented middleware. The Spring AMQP project applies core Spring concepts to the development of AMQP-based messaging solutions. Spring Boot offers several conveniences for working with AMQP through RabbitMQ, including the spring-boot-starter-amqp “Starter”.

32.2.1 RabbitMQ support

RabbitMQ is a lightweight, reliable, scalable, and portable message broker based on the AMQP protocol. Spring uses RabbitMQ to communicate through the AMQP protocol.

RabbitMQ configuration is controlled by external configuration properties in spring.rabbitmq.*. For example, you might declare the following section in application.properties:

spring.rabbitmq.host=localhost
spring.rabbitmq.port=5672
spring.rabbitmq.username=admin
spring.rabbitmq.password=secret

If a ConnectionNameStrategy bean exists in the context, it will be automatically used to name connections created by the auto-configured ConnectionFactory. See RabbitProperties for more of the supported options.

32.2.2 Sending a Message

Spring’s AmqpTemplate and AmqpAdmin are auto-configured, and you can autowire them directly into your own beans, as shown in the following example:

import org.springframework.amqp.core.AmqpAdmin;
import org.springframework.amqp.core.AmqpTemplate;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;

@Component
public class MyBean {

	private final AmqpAdmin amqpAdmin;
	private final AmqpTemplate amqpTemplate;

	@Autowired
	public MyBean(AmqpAdmin amqpAdmin, AmqpTemplate amqpTemplate) {
		this.amqpAdmin = amqpAdmin;
		this.amqpTemplate = amqpTemplate;
	}

	// ...

}
[Note]Note

RabbitMessagingTemplate can be injected in a similar manner. If a MessageConverter bean is defined, it is associated automatically to the auto-configured AmqpTemplate.

If necessary, any org.springframework.amqp.core.Queue that is defined as a bean is automatically used to declare a corresponding queue on the RabbitMQ instance.

To retry operations, you can enable retries on the AmqpTemplate (for example, in the event that the broker connection is lost). Retries are disabled by default.

32.2.3 Receiving a Message

When the Rabbit infrastructure is present, any bean can be annotated with @RabbitListener to create a listener endpoint. If no RabbitListenerContainerFactory has been defined, a default SimpleRabbitListenerContainerFactory is automatically configured and you can switch to a direct container using the spring.rabbitmq.listener.type property. If a MessageConverter or a MessageRecoverer bean is defined, it is automatically associated with the default factory.

The following sample component creates a listener endpoint on the someQueue queue:

@Component
public class MyBean {

	@RabbitListener(queues = "someQueue")
	public void processMessage(String content) {
		// ...
	}

}
[Tip]Tip

See the Javadoc of @EnableRabbit for more details.

If you need to create more RabbitListenerContainerFactory instances or if you want to override the default, Spring Boot provides a SimpleRabbitListenerContainerFactoryConfigurer and a DirectRabbitListenerContainerFactoryConfigurer that you can use to initialize a SimpleRabbitListenerContainerFactory and a DirectRabbitListenerContainerFactory with the same settings as the factories used by the auto-configuration.

[Tip]Tip

It does not matter which container type you chose. Those two beans are exposed by the auto-configuration.

For instance, the following configuration class exposes another factory that uses a specific MessageConverter:

@Configuration
static class RabbitConfiguration {

	@Bean
	public SimpleRabbitListenerContainerFactory myFactory(
			SimpleRabbitListenerContainerFactoryConfigurer configurer) {
		SimpleRabbitListenerContainerFactory factory =
				new SimpleRabbitListenerContainerFactory();
		configurer.configure(factory, connectionFactory);
		factory.setMessageConverter(myMessageConverter());
		return factory;
	}

}

Then you can use the factory in any @RabbitListener-annotated method, as follows:

@Component
public class MyBean {

	@RabbitListener(queues = "someQueue", containerFactory="myFactory")
	public void processMessage(String content) {
		// ...
	}

}

You can enable retries to handle situations where your listener throws an exception. By default, RejectAndDontRequeueRecoverer is used, but you can define a MessageRecoverer of your own. When retries are exhausted, the message is rejected and either dropped or routed to a dead-letter exchange if the broker is configured to do so. By default, retries are disabled.

[Important]Important

By default, if retries are disabled and the listener throws an exception, the delivery is retried indefinitely. You can modify this behavior in two ways: Set the defaultRequeueRejected property to false so that zero re-deliveries are attempted or throw an AmqpRejectAndDontRequeueException to signal the message should be rejected. The latter is the mechanism used when retries are enabled and the maximum number of delivery attempts is reached.

32.3 Apache Kafka Support

Apache Kafka is supported by providing auto-configuration of the spring-kafka project.

Kafka configuration is controlled by external configuration properties in spring.kafka.*. For example, you might declare the following section in application.properties:

spring.kafka.bootstrap-servers=localhost:9092
spring.kafka.consumer.group-id=myGroup
[Tip]Tip

To create a topic on startup, add a bean of type NewTopic. If the topic already exists, the bean is ignored.

See KafkaProperties for more supported options.

32.3.1 Sending a Message

Spring’s KafkaTemplate is auto-configured, and you can autowire it directly in your own beans, as shown in the following example:

@Component
public class MyBean {

	private final KafkaTemplate kafkaTemplate;

	@Autowired
	public MyBean(KafkaTemplate kafkaTemplate) {
		this.kafkaTemplate = kafkaTemplate;
	}

	// ...

}
[Note]Note

If a RecordMessageConverter bean is defined, it is automatically associated to the auto-configured KafkaTemplate.

32.3.2 Receiving a Message

When the Apache Kafka infrastructure is present, any bean can be annotated with @KafkaListener to create a listener endpoint. If no KafkaListenerContainerFactory has been defined, a default one is automatically configured with keys defined in spring.kafka.listener.*. Also, if a RecordMessageConverter bean is defined, it is automatically associated to the default factory.

The following component creates a listener endpoint on the someTopic topic:

@Component
public class MyBean {

	@KafkaListener(topics = "someTopic")
	public void processMessage(String content) {
		// ...
	}

}

32.3.3 Additional Kafka Properties

The properties supported by auto configuration are shown in Appendix A, Common application properties. Note that, for the most part, these properties (hyphenated or camelCase) map directly to the Apache Kafka dotted properties. Refer to the Apache Kafka documentation for details.

The first few of these properties apply to both producers and consumers but can be specified at the producer or consumer level if you wish to use different values for each. Apache Kafka designates properties with an importance of HIGH, MEDIUM, or LOW. Spring Boot auto-configuration supports all HIGH importance properties, some selected MEDIUM and LOW properties, and any properties that do not have a default value.

Only a subset of the properties supported by Kafka are available through the KafkaProperties class. If you wish to configure the producer or consumer with additional properties that are not directly supported, use the following properties:

spring.kafka.properties.prop.one=first
spring.kafka.admin.properties.prop.two=second
spring.kafka.consumer.properties.prop.three=third
spring.kafka.producer.properties.prop.four=fourth

This sets the common prop.one Kafka property to first (applies to producers, consumers and admins), the prop.two admin property to second, the prop.three consumer property to third and the prop.four producer property to fourth.

You can also configure the Spring Kafka JsonDeserializer as follows:

spring.kafka.consumer.value-deserializer=org.springframework.kafka.support.serializer.JsonDeserializer
spring.kafka.consumer.properties.spring.json.value.default.type=com.example.Invoice
spring.kafka.consumer.properties.spring.json.trusted.packages=com.example,org.acme

Similarly, you can disable the JsonSerializer default behavior of sending type information in headers:

spring.kafka.producer.value-serializer=org.springframework.kafka.support.serializer.JsonSerializer
spring.kafka.producer.properties.spring.json.add.type.headers=false
[Important]Important

Properties set in this way override any configuration item that Spring Boot explicitly supports.

33. Calling REST Services with RestTemplate

If you need to call remote REST services from your application, you can use the Spring Framework’s RestTemplate class. Since RestTemplate instances often need to be customized before being used, Spring Boot does not provide any single auto-configured RestTemplate bean. It does, however, auto-configure a RestTemplateBuilder, which can be used to create RestTemplate instances when needed. The auto-configured RestTemplateBuilder ensures that sensible HttpMessageConverters are applied to RestTemplate instances.

The following code shows a typical example:

@Service
public class MyService {

	private final RestTemplate restTemplate;

	public MyService(RestTemplateBuilder restTemplateBuilder) {
		this.restTemplate = restTemplateBuilder.build();
	}

	public Details someRestCall(String name) {
		return this.restTemplate.getForObject("/{name}/details", Details.class, name);
	}

}
[Tip]Tip

RestTemplateBuilder includes a number of useful methods that can be used to quickly configure a RestTemplate. For example, to add BASIC auth support, you can use builder.basicAuthorization("user", "password").build().

33.1 RestTemplate Customization

There are three main approaches to RestTemplate customization, depending on how broadly you want the customizations to apply.

To make the scope of any customizations as narrow as possible, inject the auto-configured RestTemplateBuilder and then call its methods as required. Each method call returns a new RestTemplateBuilder instance, so the customizations only affect this use of the builder.

To make an application-wide, additive customization, use a RestTemplateCustomizer bean. All such beans are automatically registered with the auto-configured RestTemplateBuilder and are applied to any templates that are built with it.

The following example shows a customizer that configures the use of a proxy for all hosts except 192.168.0.5:

static class ProxyCustomizer implements RestTemplateCustomizer {

	@Override
	public void customize(RestTemplate restTemplate) {
		HttpHost proxy = new HttpHost("proxy.example.com");
		HttpClient httpClient = HttpClientBuilder.create()
				.setRoutePlanner(new DefaultProxyRoutePlanner(proxy) {

					@Override
					public HttpHost determineProxy(HttpHost target,
							HttpRequest request, HttpContext context)
							throws HttpException {
						if (target.getHostName().equals("192.168.0.5")) {
							return null;
						}
						return super.determineProxy(target, request, context);
					}

				}).build();
		restTemplate.setRequestFactory(
				new HttpComponentsClientHttpRequestFactory(httpClient));
	}

}

Finally, the most extreme (and rarely used) option is to create your own RestTemplateBuilder bean. Doing so switches off the auto-configuration of a RestTemplateBuilder and prevents any RestTemplateCustomizer beans from being used.

34. Calling REST Services with WebClient

If you have Spring WebFlux on your classpath, you can also choose to use WebClient to call remote REST services. Compared to RestTemplate, this client has a more functional feel and is fully reactive. You can create your own client instance with the builder, WebClient.create(). See the relevant section on WebClient.

Spring Boot creates and pre-configures such a builder for you. For example, client HTTP codecs are configured in the same fashion as the server ones (see WebFlux HTTP codecs auto-configuration).

The following code shows a typical example:

@Service
public class MyService {

	private final WebClient webClient;

	public MyService(WebClient.Builder webClientBuilder) {
		this.webClient = webClientBuilder.baseUrl("http://example.org").build();
	}

	public Mono<Details> someRestCall(String name) {
		return this.webClient.get().url("/{name}/details", name)
						.retrieve().bodyToMono(Details.class);
	}

}

34.1 WebClient Customization

There are three main approaches to WebClient customization, depending on how broadly you want the customizations to apply.

To make the scope of any customizations as narrow as possible, inject the auto-configured WebClient.Builder and then call its methods as required. WebClient.Builder instances are stateful: Any change on the builder is reflected in all clients subsequently created with it. If you want to create several clients with the same builder, you can also consider cloning the builder with WebClient.Builder other = builder.clone();.

To make an application-wide, additive customization to all WebClient.Builder instances, you can declare WebClientCustomizer beans and change the WebClient.Builder locally at the point of injection.

Finally, you can fall back to the original API and use WebClient.create(). In that case, no auto-configuration or WebClientCustomizer is applied.

35. Validation

The method validation feature supported by Bean Validation 1.1 is automatically enabled as long as a JSR-303 implementation (such as Hibernate validator) is on the classpath. This lets bean methods be annotated with javax.validation constraints on their parameters and/or on their return value. Target classes with such annotated methods need to be annotated with the @Validated annotation at the type level for their methods to be searched for inline constraint annotations.

For instance, the following service triggers the validation of the first argument, making sure its size is between 8 and 10:

@Service
@Validated
public class MyBean {

	public Archive findByCodeAndAuthor(@Size(min = 8, max = 10) String code,
			Author author) {
		...
	}

}

36. Sending Email

The Spring Framework provides an easy abstraction for sending email by using the JavaMailSender interface, and Spring Boot provides auto-configuration for it as well as a starter module.

[Tip]Tip

See the reference documentation for a detailed explanation of how you can use JavaMailSender.

If spring.mail.host and the relevant libraries (as defined by spring-boot-starter-mail) are available, a default JavaMailSender is created if none exists. The sender can be further customized by configuration items from the spring.mail namespace. See MailProperties for more details.

In particular, certain default timeout values are infinite, and you may want to change that to avoid having a thread blocked by an unresponsive mail server, as shown in the following example:

spring.mail.properties.mail.smtp.connectiontimeout=5000
spring.mail.properties.mail.smtp.timeout=3000
spring.mail.properties.mail.smtp.writetimeout=5000

It is also possible to configure a JavaMailSender with an existing Session from JNDI:

spring.mail.jndi-name=mail/Session

When a jndi-name is set, it takes precedence over all other Session-related settings.

37. Distributed Transactions with JTA

Spring Boot supports distributed JTA transactions across multiple XA resources by using either an Atomikos or Bitronix embedded transaction manager. JTA transactions are also supported when deploying to a suitable Java EE Application Server.

When a JTA environment is detected, Spring’s JtaTransactionManager is used to manage transactions. Auto-configured JMS, DataSource, and JPA beans are upgraded to support XA transactions. You can use standard Spring idioms, such as @Transactional, to participate in a distributed transaction. If you are within a JTA environment and still want to use local transactions, you can set the spring.jta.enabled property to false to disable the JTA auto-configuration.

37.1 Using an Atomikos Transaction Manager

Atomikos is a popular open source transaction manager which can be embedded into your Spring Boot application. You can use the spring-boot-starter-jta-atomikos Starter to pull in the appropriate Atomikos libraries. Spring Boot auto-configures Atomikos and ensures that appropriate depends-on settings are applied to your Spring beans for correct startup and shutdown ordering.

By default, Atomikos transaction logs are written to a transaction-logs directory in your application’s home directory (the directory in which your application jar file resides). You can customize the location of this directory by setting a spring.jta.log-dir property in your application.properties file. Properties starting with spring.jta.atomikos.properties can also be used to customize the Atomikos UserTransactionServiceImp. See the AtomikosProperties Javadoc for complete details.

[Note]Note

To ensure that multiple transaction managers can safely coordinate the same resource managers, each Atomikos instance must be configured with a unique ID. By default, this ID is the IP address of the machine on which Atomikos is running. To ensure uniqueness in production, you should configure the spring.jta.transaction-manager-id property with a different value for each instance of your application.

37.2 Using a Bitronix Transaction Manager

Bitronix is a popular open-source JTA transaction manager implementation. You can use the spring-boot-starter-jta-bitronix starter to add the appropriate Bitronix dependencies to your project. As with Atomikos, Spring Boot automatically configures Bitronix and post-processes your beans to ensure that startup and shutdown ordering is correct.

By default, Bitronix transaction log files (part1.btm and part2.btm) are written to a transaction-logs directory in your application home directory. You can customize the location of this directory by setting the spring.jta.log-dir property. Properties starting with spring.jta.bitronix.properties are also bound to the bitronix.tm.Configuration bean, allowing for complete customization. See the Bitronix documentation for details.

[Note]Note

To ensure that multiple transaction managers can safely coordinate the same resource managers, each Bitronix instance must be configured with a unique ID. By default, this ID is the IP address of the machine on which Bitronix is running. To ensure uniqueness in production, you should configure the spring.jta.transaction-manager-id property with a different value for each instance of your application.

37.3 Using a Narayana Transaction Manager

Narayana is a popular open source JTA transaction manager implementation supported by JBoss. You can use the spring-boot-starter-jta-narayana starter to add the appropriate Narayana dependencies to your project. As with Atomikos and Bitronix, Spring Boot automatically configures Narayana and post-processes your beans to ensure that startup and shutdown ordering is correct.

By default, Narayana transaction logs are written to a transaction-logs directory in your application home directory (the directory in which your application jar file resides). You can customize the location of this directory by setting a spring.jta.log-dir property in your application.properties file. Properties starting with spring.jta.narayana.properties can also be used to customize the Narayana configuration. See the NarayanaProperties Javadoc for complete details.

[Note]Note

To ensure that multiple transaction managers can safely coordinate the same resource managers, each Narayana instance must be configured with a unique ID. By default, this ID is set to 1. To ensure uniqueness in production, you should configure the spring.jta.transaction-manager-id property with a different value for each instance of your application.

37.4 Using a Java EE Managed Transaction Manager

If you package your Spring Boot application as a war or ear file and deploy it to a Java EE application server, you can use your application server’s built-in transaction manager. Spring Boot tries to auto-configure a transaction manager by looking at common JNDI locations (java:comp/UserTransaction, java:comp/TransactionManager, and so on). If you use a transaction service provided by your application server, you generally also want to ensure that all resources are managed by the server and exposed over JNDI. Spring Boot tries to auto-configure JMS by looking for a ConnectionFactory at the JNDI path (java:/JmsXA or java:/XAConnectionFactory), and you can use the spring.datasource.jndi-name property to configure your DataSource.

37.5 Mixing XA and Non-XA JMS Connections

When using JTA, the primary JMS ConnectionFactory bean is XA-aware and participates in distributed transactions. In some situations, you might want to process certain JMS messages by using a non-XA ConnectionFactory. For example, your JMS processing logic might take longer than the XA timeout.

If you want to use a non-XA ConnectionFactory, you can inject the nonXaJmsConnectionFactory bean rather than the @Primary jmsConnectionFactory bean. For consistency, the jmsConnectionFactory bean is also provided by using the bean alias xaJmsConnectionFactory.

The following example shows how to inject ConnectionFactory instances:

// Inject the primary (XA aware) ConnectionFactory
@Autowired
private ConnectionFactory defaultConnectionFactory;

// Inject the XA aware ConnectionFactory (uses the alias and injects the same as above)
@Autowired
@Qualifier("xaJmsConnectionFactory")
private ConnectionFactory xaConnectionFactory;

// Inject the non-XA aware ConnectionFactory
@Autowired
@Qualifier("nonXaJmsConnectionFactory")
private ConnectionFactory nonXaConnectionFactory;

37.6 Supporting an Alternative Embedded Transaction Manager

The XAConnectionFactoryWrapper and XADataSourceWrapper interfaces can be used to support alternative embedded transaction managers. The interfaces are responsible for wrapping XAConnectionFactory and XADataSource beans and exposing them as regular ConnectionFactory and DataSource beans, which transparently enroll in the distributed transaction. DataSource and JMS auto-configuration use JTA variants, provided you have a JtaTransactionManager bean and appropriate XA wrapper beans registered within your ApplicationContext.

The BitronixXAConnectionFactoryWrapper and BitronixXADataSourceWrapper provide good examples of how to write XA wrappers.

38. Hazelcast

If Hazelcast is on the classpath and a suitable configuration is found, Spring Boot auto-configures a HazelcastInstance that you can inject in your application.

If you define a com.hazelcast.config.Config bean, Spring Boot uses that. If your configuration defines an instance name, Spring Boot tries to locate an existing instance rather than creating a new one.

You could also specify the hazelcast.xml configuration file to use through configuration, as shown in the following example:

spring.hazelcast.config=classpath:config/my-hazelcast.xml

Otherwise, Spring Boot tries to find the Hazelcast configuration from the default locations: hazelcast.xml in the working directory or at the root of the classpath. We also check if the hazelcast.config system property is set. See the Hazelcast documentation for more details.

If hazelcast-client is present on the classpath, Spring Boot first attempts to create a client by checking the following configuration options:

  • The presence of a com.hazelcast.client.config.ClientConfig bean.
  • A configuration file defined by the spring.hazelcast.config property.
  • The presence of the hazelcast.client.config system property.
  • A hazelcast-client.xml in the working directory or at the root of the classpath.
[Note]Note

Spring Boot also has explicit caching support for Hazelcast. If caching is enabled, the HazelcastInstance is automatically wrapped in a CacheManager implementation.

39. Quartz Scheduler

Spring Boot offers several conveniences for working with the Quartz scheduler, including the spring-boot-starter-quartz “Starter”. If Quartz is available, a Scheduler is auto-configured (through the SchedulerFactoryBean abstraction).

Beans of the following types are automatically picked up and associated with the Scheduler:

  • JobDetail: defines a particular Job. JobDetail instances can be built with the JobBuilder API.
  • Calendar.
  • Trigger: defines when a particular job is triggered.

By default, an in-memory JobStore is used. However, it is possible to configure a JDBC-based store if a DataSource bean is available in your application and if the spring.quartz.job-store-type property is configured accordingly, as shown in the following example:

spring.quartz.job-store-type=jdbc

When the JDBC store is used, the schema can be initialized on startup, as shown in the following example:

spring.quartz.jdbc.initialize-schema=always
[Note]Note

By default, the database is detected and initialized by using the standard scripts provided with the Quartz library. It is also possible to provide a custom script by setting the spring.quartz.jdbc.schema property.

Quartz Scheduler configuration can be customized by using Quartz configuration properties ()spring.quartz.properties.*) and SchedulerFactoryBeanCustomizer beans, which allow programmatic SchedulerFactoryBean customization.

[Note]Note

In particular, an Executor bean is not associated with the scheduler as Quartz offers a way to configure the scheduler via spring.quartz.properties. If you need to customize the task executor, consider implementing SchedulerFactoryBeanCustomizer.

Jobs can define setters to inject data map properties. Regular beans can also be injected in a similar manner, as shown in the following example:

public class SampleJob extends QuartzJobBean {

	private MyService myService;

	private String name;

	// Inject "MyService" bean
	public void setMyService(MyService myService) { ... }

	// Inject the "name" job data property
	public void setName(String name) { ... }

	@Override
	protected void executeInternal(JobExecutionContext context)
			throws JobExecutionException {
		...
	}

}

40. Spring Integration

Spring Boot offers several conveniences for working with Spring Integration, including the spring-boot-starter-integration “Starter”. Spring Integration provides abstractions over messaging and also other transports such as HTTP, TCP, and others. If Spring Integration is available on your classpath, it is initialized through the @EnableIntegration annotation.

Spring Boot also configures some features that are triggered by the presence of additional Spring Integration modules. If spring-integration-jmx is also on the classpath, message processing statistics are published over JMX . If spring-integration-jdbc is available, the default database schema can be created on startup, as shown in the following line:

spring.integration.jdbc.initialize-schema=always

See the IntegrationAutoConfiguration and IntegrationProperties classes for more details.

By default, if a Micrometer meterRegistry bean is present, Spring Integration metrics will be managed by Micrometer. If you wish to use legacy Spring Integration metrics, add a DefaultMetricsFactory bean to the application context.

41. Spring Session

Spring Boot provides Spring Session auto-configuration for a wide range of data stores. When building a Servlet web application, the following stores can be auto-configured:

  • JDBC
  • Redis
  • Hazelcast
  • MongoDB

When building a reactive web application, the following stores can be auto-configured:

  • Redis
  • MongoDB

If a single Spring Session module is present on the classpath, Spring Boot uses that store implementation automatically. If you have more than one implementation, you must choose the StoreType that you wish to use to store the sessions. For instance, to use JDBC as the back-end store, you can configure your application as follows:

spring.session.store-type=jdbc
[Tip]Tip

You can disable Spring Session by setting the store-type to none.

Each store has specific additional settings. For instance, it is possible to customize the name of the table for the JDBC store, as shown in the following example:

spring.session.jdbc.table-name=SESSIONS

For setting the timeout of the session you can use the spring.session.timeout property. If that property is not set, the auto-configuration falls back to the value of server.servlet.session.timeout.

42. Monitoring and Management over JMX

Java Management Extensions (JMX) provide a standard mechanism to monitor and manage applications. By default, Spring Boot creates an MBeanServer bean with an ID of mbeanServer and exposes any of your beans that are annotated with Spring JMX annotations (@ManagedResource, @ManagedAttribute, or @ManagedOperation).

See the JmxAutoConfiguration class for more details.

43. Testing

Spring Boot provides a number of utilities and annotations to help when testing your application. Test support is provided by two modules: spring-boot-test contains core items, and spring-boot-test-autoconfigure supports auto-configuration for tests.

Most developers use the spring-boot-starter-test “Starter”, which imports both Spring Boot test modules as well as JUnit, AssertJ, Hamcrest, and a number of other useful libraries.

43.1 Test Scope Dependencies

The spring-boot-starter-test “Starter” (in the test scope) contains the following provided libraries:

  • JUnit: The de-facto standard for unit testing Java applications.
  • Spring Test & Spring Boot Test: Utilities and integration test support for Spring Boot applications.
  • AssertJ: A fluent assertion library.
  • Hamcrest: A library of matcher objects (also known as constraints or predicates).
  • Mockito: A Java mocking framework.
  • JSONassert: An assertion library for JSON.
  • JsonPath: XPath for JSON.

We generally find these common libraries to be useful when writing tests. If these libraries do not suit your needs, you can add additional test dependencies of your own.

43.2 Testing Spring Applications

One of the major advantages of dependency injection is that it should make your code easier to unit test. You can instantiate objects by using the new operator without even involving Spring. You can also use mock objects instead of real dependencies.

Often, you need to move beyond unit testing and start integration testing (with a Spring ApplicationContext). It is useful to be able to perform integration testing without requiring deployment of your application or needing to connect to other infrastructure.

The Spring Framework includes a dedicated test module for such integration testing. You can declare a dependency directly to org.springframework:spring-test or use the spring-boot-starter-test “Starter” to pull it in transitively.

If you have not used the spring-test module before, you should start by reading the relevant section of the Spring Framework reference documentation.

43.3 Testing Spring Boot Applications

A Spring Boot application is a Spring ApplicationContext, so nothing very special has to be done to test it beyond what you would normally do with a vanilla Spring context.

[Note]Note

External properties, logging, and other features of Spring Boot are installed in the context by default only if you use SpringApplication to create it.

Spring Boot provides a @SpringBootTest annotation, which can be used as an alternative to the standard spring-test @ContextConfiguration annotation when you need Spring Boot features. The annotation works by creating the ApplicationContext used in your tests through SpringApplication. In addition to @SpringBootTest a number of other annotations are also provided for testing more specific slices of an application.

[Tip]Tip

Don’t forget to also add @RunWith(SpringRunner.class) to your test, otherwise the annotations will be ignored.

You can use the webEnvironment attribute of @SpringBootTest to further refine how your tests run:

  • MOCK: Loads a WebApplicationContext and provides a mock servlet environment. Embedded servlet containers are not started when using this annotation. If servlet APIs are not on your classpath, this mode transparently falls back to creating a regular non-web ApplicationContext. It can be used in conjunction with @AutoConfigureMockMvc for MockMvc-based testing of your application.
  • RANDOM_PORT: Loads an ServletWebServerApplicationContext and provides a real servlet environment. Embedded servlet containers are started and listen on a random port.
  • DEFINED_PORT: Loads a ServletWebServerApplicationContext and provides a real servlet environment. Embedded servlet containers are started and listen on a defined port (from your application.properties or on the default port of 8080).
  • NONE: Loads an ApplicationContext by using SpringApplication but does not provide any servlet environment (mock or otherwise).
[Note]Note

If your test is @Transactional, it rolls back the transaction at the end of each test method by default. However, as using this arrangement with either RANDOM_PORT or DEFINED_PORT implicitly provides a real servlet environment, the HTTP client and server run in separate threads and, thus, in separate transactions. Any transaction initiated on the server does not roll back in this case.

43.3.1 Detecting Web Application Type

If Spring MVC is available, a regular MVC-based application context is configured. If you have only Spring WebFlux, we’ll detect that and configure a WebFlux-based application context instead.

If both are present, Spring MVC takes precedence. If you want to test a reactive web application in this scenario, you must set the spring.main.web-application-type property:

@RunWith(SpringRunner.class)
@SpringBootTest(properties = "spring.main.web-application-type=reactive")
public class MyWebFluxTests { ... }

43.3.2 Detecting Test Configuration

If you are familiar with the Spring Test Framework, you may be used to using @ContextConfiguration(classes=…​) in order to specify which Spring @Configuration to load. Alternatively, you might have often used nested @Configuration classes within your test.

When testing Spring Boot applications, this is often not required. Spring Boot’s @*Test annotations search for your primary configuration automatically whenever you do not explicitly define one.

The search algorithm works up from the package that contains the test until it finds a class annotated with @SpringBootApplication or @SpringBootConfiguration. As long as you structured your code in a sensible way, your main configuration is usually found.

[Note]Note

If you use a test annotation to test a more specific slice of your application, you should avoid adding configuration settings that are specific to a particular area on the main method’s application class.

The underlying component scan configuration of @SpringBootApplication defines exclude filters that are used to make sure slicing works as expected. If you are using an explicit @ComponentScan directive on your @SpringBootApplication-annoted class, be aware that those filters will be disabled. If you are using slicing, you should define them again.

If you want to customize the primary configuration, you can use a nested @TestConfiguration class. Unlike a nested @Configuration class, which would be used instead of your application’s primary configuration, a nested @TestConfiguration class is used in addition to your application’s primary configuration.

[Note]Note

Spring’s test framework caches application contexts between tests. Therefore, as long as your tests share the same configuration (no matter how it is discovered), the potentially time-consuming process of loading the context happens only once.

43.3.3 Excluding Test Configuration

If your application uses component scanning (for example, if you use @SpringBootApplication or @ComponentScan), you may find top-level configuration classes that you created only for specific tests accidentally get picked up everywhere.

As we have seen earlier, @TestConfiguration can be used on an inner class of a test to customize the primary configuration. When placed on a top-level class, @TestConfiguration indicates that classes in src/test/java should not be picked up by scanning. You can then import that class explicitly where it is required, as shown in the following example:

@RunWith(SpringRunner.class)
@SpringBootTest
@Import(MyTestsConfiguration.class)
public class MyTests {

	@Test
	public void exampleTest() {
		...
	}

}
[Note]Note

If you directly use @ComponentScan (that is, not through @SpringBootApplication) you need to register the TypeExcludeFilter with it. See the Javadoc for details.

43.3.4 Testing with a running server

If you need to start a full running server, we recommend that you use random ports. If you use @SpringBootTest(webEnvironment=WebEnvironment.RANDOM_PORT), an available port is picked at random each time your test runs.

The @LocalServerPort annotation can be used to inject the actual port used into your test. For convenience, tests that need to make REST calls to the started server can additionally @Autowire a WebTestClient, which resolves relative links to the running server and comes with a dedicated API for verifying responses, as shown in the following example:

import org.junit.Test;
import org.junit.runner.RunWith;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.boot.test.context.SpringBootTest.WebEnvironment;
import org.springframework.test.context.junit4.SpringRunner;
import org.springframework.test.web.reactive.server.WebTestClient;

@RunWith(SpringRunner.class)
@SpringBootTest(webEnvironment = WebEnvironment.RANDOM_PORT)
public class RandomPortWebTestClientExampleTests {

	@Autowired
	private WebTestClient webClient;

	@Test
	public void exampleTest() {
		this.webClient.get().uri("/").exchange().expectStatus().isOk()
				.expectBody(String.class).isEqualTo("Hello World");
	}

}

Spring Boot also provides a TestRestTemplate facility:

import org.junit.Test;
import org.junit.runner.RunWith;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.boot.test.context.SpringBootTest.WebEnvironment;
import org.springframework.boot.test.web.client.TestRestTemplate;
import org.springframework.test.context.junit4.SpringRunner;

import static org.assertj.core.api.Assertions.assertThat;

@RunWith(SpringRunner.class)
@SpringBootTest(webEnvironment = WebEnvironment.RANDOM_PORT)
public class RandomPortTestRestTemplateExampleTests {

	@Autowired
	private TestRestTemplate restTemplate;

	@Test
	public void exampleTest() {
		String body = this.restTemplate.getForObject("/", String.class);
		assertThat(body).isEqualTo("Hello World");
	}

}

43.3.5 Using JMX

As the test context framework caches context, JMX is disabled by default to prevent identical components to register on the same domain. If such test needs access to an MBeanServer, consider marking it dirty as well:

@RunWith(SpringRunner.class)
@SpringBootTest(properties = "spring.jmx.enabled=true")
@DirtiesContext
public class SampleJmxTests {

	@Autowired
	private MBeanServer mBeanServer;

	@Test
	public void exampleTest() {
		// ...
	}

}

43.3.6 Mocking and Spying Beans

When running tests, it is sometimes necessary to mock certain components within your application context. For example, you may have a facade over some remote service that is unavailable during development. Mocking can also be useful when you want to simulate failures that might be hard to trigger in a real environment.

Spring Boot includes a @MockBean annotation that can be used to define a Mockito mock for a bean inside your ApplicationContext. You can use the annotation to add new beans or replace a single existing bean definition. The annotation can be used directly on test classes, on fields within your test, or on @Configuration classes and fields. When used on a field, the instance of the created mock is also injected. Mock beans are automatically reset after each test method.

[Note]Note

If your test uses one of Spring Boot’s test annotations (such as @SpringBootTest), this feature is automatically enabled. To use this feature with a different arrangement, a listener must be explicitly added, as shown in the following example:

@TestExecutionListeners(MockitoTestExecutionListener.class)

The following example replaces an existing RemoteService bean with a mock implementation:

import org.junit.*;
import org.junit.runner.*;
import org.springframework.beans.factory.annotation.*;
import org.springframework.boot.test.context.*;
import org.springframework.boot.test.mock.mockito.*;
import org.springframework.test.context.junit4.*;

import static org.assertj.core.api.Assertions.*;
import static org.mockito.BDDMockito.*;

@RunWith(SpringRunner.class)
@SpringBootTest
public class MyTests {

	@MockBean
	private RemoteService remoteService;

	@Autowired
	private Reverser reverser;

	@Test
	public void exampleTest() {
		// RemoteService has been injected into the reverser bean
		given(this.remoteService.someCall()).willReturn("mock");
		String reverse = reverser.reverseSomeCall();
		assertThat(reverse).isEqualTo("kcom");
	}

}

Additionally, you can use @SpyBean to wrap any existing bean with a Mockito spy. See the Javadoc for full details.

[Note]Note

While Spring’s test framework caches application contexts between tests and reuses a context for tests sharing the same configuration, the use of @MockBean or @SpyBean influences the cache key, which will most likely increase the number of contexts.

43.3.7 Auto-configured Tests

Spring Boot’s auto-configuration system works well for applications but can sometimes be a little too much for tests. It often helps to load only the parts of the configuration that are required to test a “slice” of your application. For example, you might want to test that Spring MVC controllers are mapping URLs correctly, and you do not want to involve database calls in those tests, or you might want to test JPA entities, and you are not interested in the web layer when those tests run.

The spring-boot-test-autoconfigure module includes a number of annotations that can be used to automatically configure such “slices”. Each of them works in a similar way, providing a @…​Test annotation that loads the ApplicationContext and one or more @AutoConfigure…​ annotations that can be used to customize auto-configuration settings.

[Note]Note

Each slice loads a very restricted set of auto-configuration classes. If you need to exclude one of them, most @…​Test annotations provide an excludeAutoConfiguration attribute. Alternatively, you can use @ImportAutoConfiguration#exclude.

[Tip]Tip

It is also possible to use the @AutoConfigure…​ annotations with the standard @SpringBootTest annotation. You can use this combination if you are not interested in “slicing” your application but you want some of the auto-configured test beans.

43.3.8 Auto-configured JSON Tests

To test that object JSON serialization and deserialization is working as expected, you can use the @JsonTest annotation. @JsonTest auto-configures the available supported JSON mapper, which can be one of the following libraries:

  • Jackson ObjectMapper, any @JsonComponent beans and any Jackson Modules
  • Gson
  • Jsonb

If you need to configure elements of the auto-configuration, you can use the @AutoConfigureJsonTesters annotation.

Spring Boot includes AssertJ-based helpers that work with the JSONassert and JsonPath libraries to check that JSON appears as expected. The JacksonTester, GsonTester, JsonbTester, and BasicJsonTester classes can be used for Jackson, Gson, Jsonb, and Strings respectively. Any helper fields on the test class can be @Autowired when using @JsonTest. The following example shows a test class for Jackson:

import org.junit.*;
import org.junit.runner.*;
import org.springframework.beans.factory.annotation.*;
import org.springframework.boot.test.autoconfigure.json.*;
import org.springframework.boot.test.context.*;
import org.springframework.boot.test.json.*;
import org.springframework.test.context.junit4.*;

import static org.assertj.core.api.Assertions.*;

@RunWith(SpringRunner.class)
@JsonTest
public class MyJsonTests {

	@Autowired
	private JacksonTester<VehicleDetails> json;

	@Test
	public void testSerialize() throws Exception {
		VehicleDetails details = new VehicleDetails("Honda", "Civic");
		// Assert against a `.json` file in the same package as the test
		assertThat(this.json.write(details)).isEqualToJson("expected.json");
		// Or use JSON path based assertions
		assertThat(this.json.write(details)).hasJsonPathStringValue("@.make");
		assertThat(this.json.write(details)).extractingJsonPathStringValue("@.make")
				.isEqualTo("Honda");
	}

	@Test
	public void testDeserialize() throws Exception {
		String content = "{\"make\":\"Ford\",\"model\":\"Focus\"}";
		assertThat(this.json.parse(content))
				.isEqualTo(new VehicleDetails("Ford", "Focus"));
		assertThat(this.json.parseObject(content).getMake()).isEqualTo("Ford");
	}

}
[Note]Note

JSON helper classes can also be used directly in standard unit tests. To do so, call the initFields method of the helper in your @Before method if you do not use @JsonTest.

A list of the auto-configuration that is enabled by @JsonTest can be found in the appendix.

43.3.9 Auto-configured Spring MVC Tests

To test whether Spring MVC controllers are working as expected, use the @WebMvcTest annotation. @WebMvcTest auto-configures the Spring MVC infrastructure and limits scanned beans to @Controller, @ControllerAdvice, @JsonComponent, Converter, GenericConverter, Filter, WebMvcConfigurer, and HandlerMethodArgumentResolver. Regular @Component beans are not scanned when using this annotation.

[Tip]Tip

If you need to register extra components, such as the Jackson Module, you can import additional configuration classes by using @Import on your test.

Often, @WebMvcTest is limited to a single controller and is used in combination with @MockBean to provide mock implementations for required collaborators.

@WebMvcTest also auto-configures MockMvc. Mock MVC offers a powerful way to quickly test MVC controllers without needing to start a full HTTP server.

[Tip]Tip

You can also auto-configure MockMvc in a non-@WebMvcTest (such as @SpringBootTest) by annotating it with @AutoConfigureMockMvc. The following example uses MockMvc:

import org.junit.*;
import org.junit.runner.*;
import org.springframework.beans.factory.annotation.*;
import org.springframework.boot.test.autoconfigure.web.servlet.*;
import org.springframework.boot.test.mock.mockito.*;

import static org.assertj.core.api.Assertions.*;
import static org.mockito.BDDMockito.*;
import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.*;
import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.*;

@RunWith(SpringRunner.class)
@WebMvcTest(UserVehicleController.class)
public class MyControllerTests {

	@Autowired
	private MockMvc mvc;

	@MockBean
	private UserVehicleService userVehicleService;

	@Test
	public void testExample() throws Exception {
		given(this.userVehicleService.getVehicleDetails("sboot"))
				.willReturn(new VehicleDetails("Honda", "Civic"));
		this.mvc.perform(get("/sboot/vehicle").accept(MediaType.TEXT_PLAIN))
				.andExpect(status().isOk()).andExpect(content().string("Honda Civic"));
	}

}
[Tip]Tip

If you need to configure elements of the auto-configuration (for example, when servlet filters should be applied) you can use attributes in the @AutoConfigureMockMvc annotation.

If you use HtmlUnit or Selenium, auto-configuration also provides an HTMLUnit WebClient bean and/or a WebDriver bean. The following example uses HtmlUnit:

import com.gargoylesoftware.htmlunit.*;
import org.junit.*;
import org.junit.runner.*;
import org.springframework.beans.factory.annotation.*;
import org.springframework.boot.test.autoconfigure.web.servlet.*;
import org.springframework.boot.test.mock.mockito.*;

import static org.assertj.core.api.Assertions.*;
import static org.mockito.BDDMockito.*;

@RunWith(SpringRunner.class)
@WebMvcTest(UserVehicleController.class)
public class MyHtmlUnitTests {

	@Autowired
	private WebClient webClient;

	@MockBean
	private UserVehicleService userVehicleService;

	@Test
	public void testExample() throws Exception {
		given(this.userVehicleService.getVehicleDetails("sboot"))
				.willReturn(new VehicleDetails("Honda", "Civic"));
		HtmlPage page = this.webClient.getPage("/sboot/vehicle.html");
		assertThat(page.getBody().getTextContent()).isEqualTo("Honda Civic");
	}

}
[Note]Note

By default, Spring Boot puts WebDriver beans in a special “scope” to ensure that the driver exits after each test and that a new instance is injected. If you do not want this behavior, you can add @Scope("singleton") to your WebDriver @Bean definition.

A list of the auto-configuration settings that are enabled by @WebMvcTest can be found in the appendix.

[Tip]Tip

Sometimes writing Spring MVC tests is not enough; Spring Boot can help you run full end-to-end tests with an actual server.

43.3.10 Auto-configured Spring WebFlux Tests

To test that Spring WebFlux controllers are working as expected, you can use the @WebFluxTest annotation. @WebFluxTest auto-configures the Spring WebFlux infrastructure and limits scanned beans to @Controller, @ControllerAdvice, @JsonComponent, Converter, GenericConverter, and WebFluxConfigurer. Regular @Component beans are not scanned when the @WebFluxTest annotation is used.

[Tip]Tip

If you need to register extra components, such as Jackson Module, you can import additional configuration classes using @Import on your test.

Often, @WebFluxTest is limited to a single controller and used in combination with the @MockBean annotation to provide mock implementations for required collaborators.

@WebFluxTest also auto-configures WebTestClient, which offers a powerful way to quickly test WebFlux controllers without needing to start a full HTTP server.

[Tip]Tip

You can also auto-configure WebTestClient in a non-@WebFluxTest (such as @SpringBootTest) by annotating it with @AutoConfigureWebTestClient. The following example shows a class that uses both @WebFluxTest and a WebTestClient:

import org.junit.Test;
import org.junit.runner.RunWith;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.autoconfigure.web.reactive.WebFluxTest;
import org.springframework.http.MediaType;
import org.springframework.test.context.junit4.SpringRunner;
import org.springframework.test.web.reactive.server.WebTestClient;

@RunWith(SpringRunner.class)
@WebFluxTest(UserVehicleController.class)
public class MyControllerTests {

	@Autowired
	private WebTestClient webClient;

	@MockBean
	private UserVehicleService userVehicleService;

	@Test
	public void testExample() throws Exception {
		given(this.userVehicleService.getVehicleDetails("sboot"))
				.willReturn(new VehicleDetails("Honda", "Civic"));
		this.webClient.get().uri("/sboot/vehicle").accept(MediaType.TEXT_PLAIN)
				.exchange()
				.expectStatus().isOk()
				.expectBody(String.class).isEqualTo("Honda Civic");
	}

}
[Tip]Tip

This setup is only supported by WebFlux applications as using WebTestClient in a mocked web application only works with WebFlux at the moment.

A list of the auto-configuration that is enabled by @WebFluxTest can be found in the appendix.

[Note]Note

@WebFluxTest cannot detect routes registered via the functional web framework. For testing RouterFunction beans in the context, consider importing your RouterFunction yourself via @Import or using @SpringBootTest.

[Tip]Tip

Sometimes writing Spring WebFlux tests is not enough; Spring Boot can help you run full end-to-end tests with an actual server.

43.3.11 Auto-configured Data JPA Tests

You can use the @DataJpaTest annotation to test JPA applications. By default, it configures an in-memory embedded database, scans for @Entity classes, and configures Spring Data JPA repositories. Regular @Component beans are not loaded into the ApplicationContext.

By default, data JPA tests are transactional and roll back at the end of each test. See the relevant section in the Spring Framework Reference Documentation for more details. If that is not what you want, you can disable transaction management for a test or for the whole class as follows:

import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.boot.test.autoconfigure.orm.jpa.DataJpaTest;
import org.springframework.test.context.junit4.SpringRunner;
import org.springframework.transaction.annotation.Propagation;
import org.springframework.transaction.annotation.Transactional;

@RunWith(SpringRunner.class)
@DataJpaTest
@Transactional(propagation = Propagation.NOT_SUPPORTED)
public class ExampleNonTransactionalTests {

}

Data JPA tests may also inject a TestEntityManager bean, which provides an alternative to the standard JPA EntityManager that is specifically designed for tests. If you want to use TestEntityManager outside of @DataJpaTest instances, you can also use the @AutoConfigureTestEntityManager annotation. A JdbcTemplate is also available if you need that. The following example shows the @DataJpaTest annotation in use:

import org.junit.*;
import org.junit.runner.*;
import org.springframework.boot.test.autoconfigure.orm.jpa.*;

import static org.assertj.core.api.Assertions.*;

@RunWith(SpringRunner.class)
@DataJpaTest
public class ExampleRepositoryTests {

	@Autowired
	private TestEntityManager entityManager;

	@Autowired
	private UserRepository repository;

	@Test
	public void testExample() throws Exception {
		this.entityManager.persist(new User("sboot", "1234"));
		User user = this.repository.findByUsername("sboot");
		assertThat(user.getUsername()).isEqualTo("sboot");
		assertThat(user.getVin()).isEqualTo("1234");
	}

}

In-memory embedded databases generally work well for tests, since they are fast and do not require any installation. If, however, you prefer to run tests against a real database you can use the @AutoConfigureTestDatabase annotation, as shown in the following example:

@RunWith(SpringRunner.class)
@DataJpaTest
@AutoConfigureTestDatabase(replace=Replace.NONE)
public class ExampleRepositoryTests {

	// ...

}

A list of the auto-configuration settings that are enabled by @DataJpaTest can be found in the appendix.

43.3.12 Auto-configured JDBC Tests

@JdbcTest is similar to @DataJpaTest but is for pure JDBC-related tests. By default, it also configures an in-memory embedded database and a JdbcTemplate. Regular @Component beans are not loaded into the ApplicationContext.

By default, JDBC tests are transactional and roll back at the end of each test. See the relevant section in the Spring Framework Reference Documentation for more details. If that is not what you want, you can disable transaction management for a test or for the whole class, as follows:

import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.boot.test.autoconfigure.jdbc.JdbcTest;
import org.springframework.test.context.junit4.SpringRunner;
import org.springframework.transaction.annotation.Propagation;
import org.springframework.transaction.annotation.Transactional;

@RunWith(SpringRunner.class)
@JdbcTest
@Transactional(propagation = Propagation.NOT_SUPPORTED)
public class ExampleNonTransactionalTests {

}

If you prefer your test to run against a real database, you can use the @AutoConfigureTestDatabase annotation in the same way as for DataJpaTest. (See "Section 43.3.11, “Auto-configured Data JPA Tests”".)

A list of the auto-configuration that is enabled by @JdbcTest can be found in the appendix.

43.3.13 Auto-configured jOOQ Tests

You can use @JooqTest in a similar fashion as @JdbcTest but for jOOQ-related tests. As jOOQ relies heavily on a Java-based schema that corresponds with the database schema, the existing DataSource is used. If you want to replace it with an in-memory database, you can use @AutoConfigureTestDatabase to override those settings. (For more about using jOOQ with Spring Boot, see "Section 29.5, “Using jOOQ”", earlier in this chapter.)

@JooqTest configures a DSLContext. Regular @Component beans are not loaded into the ApplicationContext. The following example shows the @JooqTest annotation in use:

import org.jooq.DSLContext;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.boot.test.autoconfigure.jooq.JooqTest;
import org.springframework.test.context.junit4.SpringRunner;

@RunWith(SpringRunner.class)
@JooqTest
public class ExampleJooqTests {

	@Autowired
	private DSLContext dslContext;
}

JOOQ tests are transactional and roll back at the end of each test by default. If that is not what you want, you can disable transaction management for a test or for the whole test class as shown in the JDBC example.

A list of the auto-configuration that is enabled by @JooqTest can be found in the appendix.

43.3.14 Auto-configured Data MongoDB Tests

You can use @DataMongoTest to test MongoDB applications. By default, it configures an in-memory embedded MongoDB (if available), configures a MongoTemplate, scans for @Document classes, and configures Spring Data MongoDB repositories. Regular @Component beans are not loaded into the ApplicationContext. (For more about using MongoDB with Spring Boot, see "Section 30.2, “MongoDB”", earlier in this chapter.)

The following class shows the @DataMongoTest annotation in use:

import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.autoconfigure.data.mongo.DataMongoTest;
import org.springframework.data.mongodb.core.MongoTemplate;
import org.springframework.test.context.junit4.SpringRunner;

@RunWith(SpringRunner.class)
@DataMongoTest
public class ExampleDataMongoTests {

	@Autowired
	private MongoTemplate mongoTemplate;

	//
}

In-memory embedded MongoDB generally works well for tests, since it is fast and does not require any developer installation. If, however, you prefer to run tests against a real MongoDB server, you should exclude the embedded MongoDB auto-configuration, as shown in the following example:

import org.junit.runner.RunWith;
 import org.springframework.boot.autoconfigure.mongo.embedded.EmbeddedMongoAutoConfiguration;
import org.springframework.boot.test.autoconfigure.data.mongo.DataMongoTest;
import org.springframework.test.context.junit4.SpringRunner;

@RunWith(SpringRunner.class)
@DataMongoTest(excludeAutoConfiguration = EmbeddedMongoAutoConfiguration.class)
public class ExampleDataMongoNonEmbeddedTests {

}

A list of the auto-configuration settings that are enabled by @DataMongoTest can be found in the appendix.

43.3.15 Auto-configured Data Neo4j Tests

You can use @DataNeo4jTest to test Neo4j applications. By default, it uses an in-memory embedded Neo4j (if the embedded driver is available), scans for @NodeEntity classes, and configures Spring Data Neo4j repositories. Regular @Component beans are not loaded into the ApplicationContext. (For more about using Neo4J with Spring Boot, see "Section 30.3, “Neo4j”", earlier in this chapter.)

The following example shows a typical setup for using Neo4J tests in Spring Boot:

import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.autoconfigure.data.neo4j.DataNeo4jTest;
import org.springframework.test.context.junit4.SpringRunner;

@RunWith(SpringRunner.class)
@DataNeo4jTest
public class ExampleDataNeo4jTests {

	@Autowired
	private YourRepository repository;

	//
}

By default, Data Neo4j tests are transactional and roll back at the end of each test. See the relevant section in the Spring Framework Reference Documentation for more details. If that is not what you want, you can disable transaction management for a test or for the whole class, as follows:

import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.boot.test.autoconfigure.data.neo4j.DataNeo4jTest;
import org.springframework.test.context.junit4.SpringRunner;
import org.springframework.transaction.annotation.Propagation;
import org.springframework.transaction.annotation.Transactional;

@RunWith(SpringRunner.class)
@DataNeo4jTest
@Transactional(propagation = Propagation.NOT_SUPPORTED)
public class ExampleNonTransactionalTests {

}

A list of the auto-configuration settings that are enabled by @DataNeo4jTest can be found in the appendix.

43.3.16 Auto-configured Data Redis Tests

You can use @DataRedisTest to test Redis applications. By default, it scans for @RedisHash classes and configures Spring Data Redis repositories. Regular @Component beans are not loaded into the ApplicationContext. (For more about using Redis with Spring Boot, see "Section 30.1, “Redis”", earlier in this chapter.)

The following example shows the @DataRedisTest annotation in use:

import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.autoconfigure.data.redis.DataRedisTest;
import org.springframework.test.context.junit4.SpringRunner;

@RunWith(SpringRunner.class)
@DataRedisTest
public class ExampleDataRedisTests {

	@Autowired
	private YourRepository repository;

	//
}

A list of the auto-configuration settings that are enabled by @DataRedisTest can be found in the appendix.

43.3.17 Auto-configured Data LDAP Tests

You can use @DataLdapTest to test LDAP applications. By default, it configures an in-memory embedded LDAP (if available), configures an LdapTemplate, scans for @Entry classes, and configures Spring Data LDAP repositories. Regular @Component beans are not loaded into the ApplicationContext. (For more about using LDAP with Spring Boot, see "Section 30.9, “LDAP”", earlier in this chapter.)

The following example shows the @DataLdapTest annotation in use:

import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.autoconfigure.data.ldap.DataLdapTest;
import org.springframework.ldap.core.LdapTemplate;
import org.springframework.test.context.junit4.SpringRunner;

@RunWith(SpringRunner.class)
@DataLdapTest
public class ExampleDataLdapTests {

	@Autowired
	private LdapTemplate ldapTemplate;

	//
}

In-memory embedded LDAP generally works well for tests, since it is fast and does not require any developer installation. If, however, you prefer to run tests against a real LDAP server, you should exclude the embedded LDAP auto-configuration, as shown in the following example:

import org.junit.runner.RunWith;
import org.springframework.boot.autoconfigure.ldap.embedded.EmbeddedLdapAutoConfiguration;
import org.springframework.boot.test.autoconfigure.data.ldap.DataLdapTest;
import org.springframework.test.context.junit4.SpringRunner;

@RunWith(SpringRunner.class)
@DataLdapTest(excludeAutoConfiguration = EmbeddedLdapAutoConfiguration.class)
public class ExampleDataLdapNonEmbeddedTests {

}

A list of the auto-configuration settings that are enabled by @DataLdapTest can be found in the appendix.

43.3.18 Auto-configured REST Clients

You can use the @RestClientTest annotation to test REST clients. By default, it auto-configures Jackson, GSON, and Jsonb support, configures a RestTemplateBuilder, and adds support for MockRestServiceServer. The specific beans that you want to test should be specified by using the value or components attribute of @RestClientTest, as shown in the following example:

@RunWith(SpringRunner.class)
@RestClientTest(RemoteVehicleDetailsService.class)
public class ExampleRestClientTest {

	@Autowired
	private RemoteVehicleDetailsService service;

	@Autowired
	private MockRestServiceServer server;

	@Test
	public void getVehicleDetailsWhenResultIsSuccessShouldReturnDetails()
			throws Exception {
		this.server.expect(requestTo("/greet/details"))
				.andRespond(withSuccess("hello", MediaType.TEXT_PLAIN));
		String greeting = this.service.callRestService();
		assertThat(greeting).isEqualTo("hello");
	}

}

A list of the auto-configuration settings that are enabled by @RestClientTest can be found in the appendix.

43.3.19 Auto-configured Spring REST Docs Tests

You can use the @AutoConfigureRestDocs annotation to use Spring REST Docs in your tests with Mock MVC or REST Assured. It removes the need for the JUnit rule in Spring REST Docs.

@AutoConfigureRestDocs can be used to override the default output directory (target/generated-snippets if you are using Maven or build/generated-snippets if you are using Gradle). It can also be used to configure the host, scheme, and port that appears in any documented URIs.

Auto-configured Spring REST Docs Tests with Mock MVC

@AutoConfigureRestDocs customizes the MockMvc bean to use Spring REST Docs. You can inject it by using @Autowired and use it in your tests as you normally would when using Mock MVC and Spring REST Docs, as shown in the following example:

import org.junit.Test;
import org.junit.runner.RunWith;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.autoconfigure.web.servlet.WebMvcTest;
import org.springframework.http.MediaType;
import org.springframework.test.context.junit4.SpringRunner;
import org.springframework.test.web.servlet.MockMvc;

import static org.springframework.restdocs.mockmvc.MockMvcRestDocumentation.document;
import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.get;
import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.*;

@RunWith(SpringRunner.class)
@WebMvcTest(UserController.class)
@AutoConfigureRestDocs
public class UserDocumentationTests {

	@Autowired
	private MockMvc mvc;

	@Test
	public void listUsers() throws Exception {
		this.mvc.perform(get("/users").accept(MediaType.TEXT_PLAIN))
				.andExpect(status().isOk())
				.andDo(document("list-users"));
	}

}

If you require more control over Spring REST Docs configuration than offered by the attributes of @AutoConfigureRestDocs, you can use a RestDocsMockMvcConfigurationCustomizer bean, as shown in the following example:

@TestConfiguration
static class CustomizationConfiguration
		implements RestDocsMockMvcConfigurationCustomizer {

	@Override
	public void customize(MockMvcRestDocumentationConfigurer configurer) {
		configurer.snippets().withTemplateFormat(TemplateFormats.markdown());
	}

}

If you want to make use of Spring REST Docs support for a parameterized output directory, you can create a RestDocumentationResultHandler bean. The auto-configuration calls alwaysDo with this result handler, thereby causing each MockMvc call to automatically generate the default snippets. The following example shows a RestDocumentationResultHandler being defined:

@TestConfiguration
static class ResultHandlerConfiguration {

	@Bean
	public RestDocumentationResultHandler restDocumentation() {
		return MockMvcRestDocumentation.document("{method-name}");
	}

}

Auto-configured Spring REST Docs Tests with REST Assured

@AutoConfigureRestDocs makes a RequestSpecification bean, preconfigured to use Spring REST Docs, available to your tests. You can inject it by using @Autowired and use it in your tests as you normally would when using REST Assured and Spring REST Docs, as shown in the following example:

import io.restassured.specification.RequestSpecification;
import org.junit.Test;
import org.junit.runner.RunWith;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.autoconfigure.restdocs.AutoConfigureRestDocs;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.boot.test.context.SpringBootTest.WebEnvironment;
import org.springframework.boot.web.server.LocalServerPort;
import org.springframework.test.context.junit4.SpringRunner;

import static io.restassured.RestAssured.given;
import static org.hamcrest.CoreMatchers.is;
import static org.springframework.restdocs.restassured3.RestAssuredRestDocumentation.document;

@RunWith(SpringRunner.class)
@SpringBootTest(webEnvironment = WebEnvironment.RANDOM_PORT)
@AutoConfigureRestDocs
public class UserDocumentationTests {

	@LocalServerPort
	private int port;

	@Autowired
	private RequestSpecification documentationSpec;

	@Test
	public void listUsers() {
		given(this.documentationSpec).filter(document("list-users")).when()
				.port(this.port).get("/").then().assertThat().statusCode(is(200));
	}

}

If you require more control over Spring REST Docs configuration than offered by the attributes of @AutoConfigureRestDocs, a RestDocsRestAssuredConfigurationCustomizer bean can be used, as shown in the following example:

@TestConfiguration
public static class CustomizationConfiguration
		implements RestDocsRestAssuredConfigurationCustomizer {

	@Override
	public void customize(RestAssuredRestDocumentationConfigurer configurer) {
		configurer.snippets().withTemplateFormat(TemplateFormats.markdown());
	}

}

43.3.20 User Configuration and Slicing

If you structure your code in a sensible way, your @SpringBootApplication class is used by default as the configuration of your tests.

It then becomes important not to litter the application’s main class with configuration settings that are specific to a particular area of its functionality.

Assume that you are using Spring Batch and you rely on the auto-configuration for it. You could define your @SpringBootApplication as follows:

@SpringBootApplication
@EnableBatchProcessing
public class SampleApplication { ... }

Because this class is the source configuration for the test, any slice test actually tries to start Spring Batch, which is definitely not what you want to do. A recommended approach is to move that area-specific configuration to a separate @Configuration class at the same level as your application, as shown in the following example:

@Configuration
@EnableBatchProcessing
public class BatchConfiguration { ... }
[Note]Note

Depending on the complexity of your application, you may either have a single @Configuration class for your customizations or one class per domain area. The latter approach lets you enable it in one of your tests, if necessary, with the @Import annotation.

Another source of confusion is classpath scanning. Assume that, while you structured your code in a sensible way, you need to scan an additional package. Your application may resemble the following code:

@SpringBootApplication
@ComponentScan({ "com.example.app", "org.acme.another" })
public class SampleApplication { ... }

Doing so effectively overrides the default component scan directive with the side effect of scanning those two packages regardless of the slice that you chose. For instance, a @DataJpaTest seems to suddenly scan components and user configurations of your application. Again, moving the custom directive to a separate class is a good way to fix this issue.

[Tip]Tip

If this is not an option for you, you can create a @SpringBootConfiguration somewhere in the hierarchy of your test so that it is used instead. Alternatively, you can specify a source for your test, which disables the behavior of finding a default one.

43.3.21 Using Spock to Test Spring Boot Applications

If you wish to use Spock to test a Spring Boot application, you should add a dependency on Spock’s spock-spring module to your application’s build. spock-spring integrates Spring’s test framework into Spock. It is recommended that you use Spock 1.1 or later to benefit from a number of improvements to Spock’s Spring Framework and Spring Boot integration. See the documentation for Spock’s Spring module for further details.

43.4 Test Utilities

A few test utility classes that are generally useful when testing your application are packaged as part of spring-boot.

43.4.1 ConfigFileApplicationContextInitializer

ConfigFileApplicationContextInitializer is an ApplicationContextInitializer that you can apply to your tests to load Spring Boot application.properties files. You can use it when you do not need the full set of features provided by @SpringBootTest, as shown in the following example:

@ContextConfiguration(classes = Config.class,
	initializers = ConfigFileApplicationContextInitializer.class)
[Note]Note

Using ConfigFileApplicationContextInitializer alone does not provide support for @Value("${…​}") injection. Its only job is to ensure that application.properties files are loaded into Spring’s Environment. For @Value support, you need to either additionally configure a PropertySourcesPlaceholderConfigurer or use @SpringBootTest, which auto-configures one for you.

43.4.2 TestPropertyValues

TestPropertyValues lets you quickly add properties to a ConfigurableEnvironment or ConfigurableApplicationContext. You can call it with key=value strings, as follows:

TestPropertyValues.of("org=Spring", "name=Boot").applyTo(env);

43.4.3 OutputCapture

OutputCapture is a JUnit Rule that you can use to capture System.out and System.err output. You can declare the capture as a @Rule and then use toString() for assertions, as follows:

import org.junit.Rule;
import org.junit.Test;
import org.springframework.boot.test.rule.OutputCapture;

import static org.hamcrest.Matchers.*;
import static org.junit.Assert.*;

public class MyTest {

	@Rule
	public OutputCapture capture = new OutputCapture();

	@Test
	public void testName() throws Exception {
		System.out.println("Hello World!");
		assertThat(capture.toString(), containsString("World"));
	}

}

43.4.4 TestRestTemplate

[Tip]Tip

Spring Framework 5.0 provides a new WebTestClient that works for WebFlux integration tests and both WebFlux and MVC end-to-end testing. It provides a fluent API for assertions, unlike TestRestTemplate.

TestRestTemplate is a convenience alternative to Spring’s RestTemplate that is useful in integration tests. You can get a vanilla template or one that sends Basic HTTP authentication (with a username and password). In either case, the template behaves in a test-friendly way by not throwing exceptions on server-side errors. It is recommended, but not mandatory, to use the Apache HTTP Client (version 4.3.2 or better). If you have that on your classpath, the TestRestTemplate responds by configuring the client appropriately. If you do use Apache’s HTTP client, some additional test-friendly features are enabled:

  • Redirects are not followed (so you can assert the response location).
  • Cookies are ignored (so the template is stateless).

TestRestTemplate can be instantiated directly in your integration tests, as shown in the following example:

public class MyTest {

	private TestRestTemplate template = new TestRestTemplate();

	@Test
	public void testRequest() throws Exception {
		HttpHeaders headers = this.template.getForEntity(
				"http://myhost.example.com/example", String.class).getHeaders();
		assertThat(headers.getLocation()).hasHost("other.example.com");
	}

}

Alternatively, if you use the @SpringBootTest annotation with WebEnvironment.RANDOM_PORT or WebEnvironment.DEFINED_PORT, you can inject a fully configured TestRestTemplate and start using it. If necessary, additional customizations can be applied through the RestTemplateBuilder bean. Any URLs that do not specify a host and port automatically connect to the embedded server, as shown in the following example:

@RunWith(SpringRunner.class)
@SpringBootTest(webEnvironment = WebEnvironment.RANDOM_PORT)
public class SampleWebClientTests {

	@Autowired
	private TestRestTemplate template;

	@Test
	public void testRequest() {
		HttpHeaders headers = this.template.getForEntity("/example", String.class)
				.getHeaders();
		assertThat(headers.getLocation()).hasHost("other.example.com");
	}

	@TestConfiguration
	static class Config {

		@Bean
		public RestTemplateBuilder restTemplateBuilder() {
			return new RestTemplateBuilder().setConnectTimeout(1000).setReadTimeout(1000);
		}

	}

}

44. WebSockets

Spring Boot provides WebSockets auto-configuration for embedded Tomcat 8.5, Jetty 9, and Undertow. If you deploy a war file to a standalone container, Spring Boot assumes that the container is responsible for the configuration of its WebSocket support.

Spring Framework provides rich WebSocket support that can be easily accessed through the spring-boot-starter-websocket module.

45. Web Services

Spring Boot provides Web Services auto-configuration so that all you must do is define your Endpoints.

The Spring Web Services features can be easily accessed with the spring-boot-starter-webservices module.

SimpleWsdl11Definition and SimpleXsdSchema beans can be automatically created for your WSDLs and XSDs respectively. To do so, configure their location, as shown in the following example:

spring.webservices.wsdl-locations=classpath:/wsdl

46. Creating Your Own Auto-configuration

If you work in a company that develops shared libraries, or if you work on an open-source or commercial library, you might want to develop your own auto-configuration. Auto-configuration classes can be bundled in external jars and still be picked-up by Spring Boot.

Auto-configuration can be associated to a “starter” that provides the auto-configuration code as well as the typical libraries that you would use with it. We first cover what you need to know to build your own auto-configuration and then we move on to the typical steps required to create a custom starter.

[Tip]Tip

A demo project is available to showcase how you can create a starter step-by-step.

46.1 Understanding Auto-configured Beans

Under the hood, auto-configuration is implemented with standard @Configuration classes. Additional @Conditional annotations are used to constrain when the auto-configuration should apply. Usually, auto-configuration classes use @ConditionalOnClass and @ConditionalOnMissingBean annotations. This ensures that auto-configuration applies only when relevant classes are found and when you have not declared your own @Configuration.

You can browse the source code of spring-boot-autoconfigure to see the @Configuration classes that Spring provides (see the META-INF/spring.factories file).

46.2 Locating Auto-configuration Candidates

Spring Boot checks for the presence of a META-INF/spring.factories file within your published jar. The file should list your configuration classes under the EnableAutoConfiguration key, as shown in the following example:

org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
com.mycorp.libx.autoconfigure.LibXAutoConfiguration,\
com.mycorp.libx.autoconfigure.LibXWebAutoConfiguration

You can use the @AutoConfigureAfter or @AutoConfigureBefore annotations if your configuration needs to be applied in a specific order. For example, if you provide web-specific configuration, your class may need to be applied after WebMvcAutoConfiguration.

If you want to order certain auto-configurations that should not have any direct knowledge of each other, you can also use @AutoConfigureOrder. That annotation has the same semantic as the regular @Order annotation but provides a dedicated order for auto-configuration classes.

[Note]Note

Auto-configurations must be loaded that way only. Make sure that they are defined in a specific package space and that, in particular, they are never the target of component scanning.

46.3 Condition Annotations

You almost always want to include one or more @Conditional annotations on your auto-configuration class. The @ConditionalOnMissingBean annotation is one common example that is used to allow developers to override auto-configuration if they are not happy with your defaults.

Spring Boot includes a number of @Conditional annotations that you can reuse in your own code by annotating @Configuration classes or individual @Bean methods. These annotations include:

46.3.1 Class Conditions

The @ConditionalOnClass and @ConditionalOnMissingClass annotations let configuration be included based on the presence or absence of specific classes. Due to the fact that annotation metadata is parsed by using ASM, you can use the value attribute to refer to the real class, even though that class might not actually appear on the running application classpath. You can also use the name attribute if you prefer to specify the class name by using a String value.

[Tip]Tip

If you use @ConditionalOnClass or @ConditionalOnMissingClass as a part of a meta-annotation to compose your own composed annotations, you must use name as referring to the class in such a case is not handled.

46.3.2 Bean Conditions

The @ConditionalOnBean and @ConditionalOnMissingBean annotations let a bean be included based on the presence or absence of specific beans. You can use the value attribute to specify beans by type or name to specify beans by name. The search attribute lets you limit the ApplicationContext hierarchy that should be considered when searching for beans.

When placed on a @Bean method, the target type defaults to the return type of the method, as shown in the following example:

@Configuration
public class MyAutoConfiguration {

	@Bean
	@ConditionalOnMissingBean
	public MyService myService() { ... }

}

In the preceding example, the myService bean is going to be created if no bean of type MyService is already contained in the ApplicationContext.

[Tip]Tip

You need to be very careful about the order in which bean definitions are added, as these conditions are evaluated based on what has been processed so far. For this reason, we recommend using only @ConditionalOnBean and @ConditionalOnMissingBean annotations on auto-configuration classes (since these are guaranteed to load after any user-defined bean definitions have been added).

[Note]Note

@ConditionalOnBean and @ConditionalOnMissingBean do not prevent @Configuration classes from being created. Using these conditions at the class level is equivalent to marking each contained @Bean method with the annotation.

46.3.3 Property Conditions

The @ConditionalOnProperty annotation lets configuration be included based on a Spring Environment property. Use the prefix and name attributes to specify the property that should be checked. By default, any property that exists and is not equal to false is matched. You can also create more advanced checks by using the havingValue and matchIfMissing attributes.

46.3.4 Resource Conditions

The @ConditionalOnResource annotation lets configuration be included only when a specific resource is present. Resources can be specified by using the usual Spring conventions, as shown in the following example: file:/home/user/test.dat.

46.3.5 Web Application Conditions

The @ConditionalOnWebApplication and @ConditionalOnNotWebApplication annotations let configuration be included depending on whether the application is a “web application”. A web application is any application that uses a Spring WebApplicationContext, defines a session scope, or has a StandardServletEnvironment.

46.3.6 SpEL Expression Conditions

The @ConditionalOnExpression annotation lets configuration be included based on the result of a SpEL expression.

46.4 Testing your Auto-configuration

An auto-configuration can be affected by many factors: user configuration (@Bean definition and Environment customization), condition evaluation (presence of a particular library), and others. Concretely, each test should create a well defined ApplicationContext that represents a combination of those customizations. ApplicationContextRunner provides a great way to achieve that.

ApplicationContextRunner is usually defined as a field of the test class to gather the base, common configuration. The following example makes sure that UserServiceAutoConfiguration is always invoked:

private final ApplicationContextRunner contextRunner = new ApplicationContextRunner()
		.withConfiguration(AutoConfigurations.of(UserServiceAutoConfiguration.class));
[Tip]Tip

If multiple auto-configurations have to be defined, there is no need to order their declarations as they are invoked in the exact same order as when running the application.

Each test can use the runner to represent a particular use case. For instance, the sample below invokes a user configuration (UserConfiguration) and checks that the auto-configuration backs off properly. Invoking run provides a callback context that can be used with Assert4J.

@Test
public void defaultServiceBacksOff() {
	this.contextRunner.withUserConfiguration(UserConfiguration.class)
			.run((context) -> {
				assertThat(context).hasSingleBean(UserService.class);
				assertThat(context.getBean(UserService.class)).isSameAs(
						context.getBean(UserConfiguration.class).myUserService());
			});
}

@Configuration
static class UserConfiguration {

	@Bean
	public UserService myUserService() {
		return new UserService("mine");
	}

}

It is also possible to easily customize the Environment, as shown in the following example:

@Test
public void serviceNameCanBeConfigured() {
	this.contextRunner.withPropertyValues("user.name=test123").run((context) -> {
		assertThat(context).hasSingleBean(UserService.class);
		assertThat(context.getBean(UserService.class).getName()).isEqualTo("test123");
	});
}

46.4.1 Simulating a Web Context

If you need to test an auto-configuration that only operates in a Servlet or Reactive web application context, use the WebApplicationContextRunner or ReactiveWebApplicationContextRunner respectively.

46.4.2 Overriding the Classpath

It is also possible to test what happens when a particular class and/or package is not present at runtime. Spring Boot ships with a FilteredClassLoader that can easily be used by the runner. In the following example, we assert that if UserService is not present, the auto-configuration is properly disabled:

@Test
public void serviceIsIgnoredIfLibraryIsNotPresent() {
	this.contextRunner.withClassLoader(new FilteredClassLoader(UserService.class))
			.run((context) -> assertThat(context).doesNotHaveBean("userService"));
}

46.5 Creating Your Own Starter

A full Spring Boot starter for a library may contain the following components:

  • The autoconfigure module that contains the auto-configuration code.
  • The starter module that provides a dependency to the autoconfigure module as well as the library and any additional dependencies that are typically useful. In a nutshell, adding the starter should provide everything needed to start using that library.
[Tip]Tip

You may combine the auto-configuration code and the dependency management in a single module if you do not need to separate those two concerns.

46.5.1 Naming

You should make sure to provide a proper namespace for your starter. Do not start your module names with spring-boot, even if you use a different Maven groupId. We may offer official support for the thing you auto-configure in the future.

As a rule of thumb, you should name a combined module after the starter. For example, assume that you are creating a starter for "acme" and that you name the auto-configure module acme-spring-boot-autoconfigure and the starter acme-spring-boot-starter. If you only have one module that combines the two, name it acme-spring-boot-starter.

Also, if your starter provides configuration keys, use a unique namespace for them. In particular, do not include your keys in the namespaces that Spring Boot uses (such as server, management, spring, and so on). If you use the same namespace, we may modify these namespaces in the future in ways that break your modules.

Make sure to trigger meta-data generation so that IDE assistance is available for your keys as well. You may want to review the generated meta-data (META-INF/spring-configuration-metadata.json) to make sure your keys are properly documented.

46.5.2 autoconfigure Module

The autoconfigure module contains everything that is necessary to get started with the library. It may also contain configuration key definitions (such as @ConfigurationProperties) and any callback interface that can be used to further customize how the components are initialized.

[Tip]Tip

You should mark the dependencies to the library as optional so that you can include the autoconfigure module in your projects more easily. If you do it that way, the library is not provided and, by default, Spring Boot backs off.

Spring Boot uses an annotation processor to collect the conditions on auto-configurations in a metadata file (META-INF/spring-autoconfigure-metadata.properties). If that file is present, it is used to eagerly filter auto-configurations that do not match, which will improve startup time. It is recommended to add the following dependency in a module that contains auto-configurations:

<dependency>
	<groupId>org.springframework.boot</groupId>
	<artifactId>spring-boot-autoconfigure-processor</artifactId>
	<optional>true</optional>
</dependency>

With Gradle 4.5 and earlier, the dependency should be declared in the compileOnly configuration, as shown in the following example:

dependencies {
	compileOnly "org.springframework.boot:spring-boot-autoconfigure-processor"
}

With Gradle 4.6 and later, the dependency should be declared in the annotationProcessor configuration, as shown in the following example:

dependencies {
	annotationProcessor "org.springframework.boot:spring-boot-autoconfigure-processor"
}

46.5.3 Starter Module

The starter is really an empty jar. Its only purpose is to provide the necessary dependencies to work with the library. You can think of it as an opinionated view of what is required to get started.

Do not make assumptions about the project in which your starter is added. If the library you are auto-configuring typically requires other starters, mention them as well. Providing a proper set of default dependencies may be hard if the number of optional dependencies is high, as you should avoid including dependencies that are unnecessary for a typical usage of the library. In other words, you should not include optional dependencies.

[Note]Note

Either way, your starter must reference the core Spring Boot starter (spring-boot-starter) directly or indirectly (i.e. no need to add it if your starter relies on another starter). If a project is created with only your custom starter, Spring Boot’s core features will be honoured by the presence of the core starter.

47. Kotlin support

Kotlin is a statically-typed language targeting the JVM (and other platforms) which allows writing concise and elegant code while providing interoperability with existing libraries written in Java.

Spring Boot provides Kotlin support by leveraging the support in other Spring projects such as Spring Framework, Spring Data, and Reactor. See the Spring Framework Kotlin support documentation for more information.

The easiest way to start with Spring Boot and Kotlin is to follow this comprehensive tutorial. You can create new Kotlin projects via start.spring.io. Feel free to join the #spring channel of Kotlin Slack or ask a question with spring and kotlin tags on Stack Overflow if you need support.

47.1 Requirements

Spring Boot supports Kotlin 1.2.x. To use Kotlin, org.jetbrains.kotlin:kotlin-stdlib and org.jetbrains.kotlin:kotlin-reflect must be present on the classpath. The kotlin-stdlib variants kotlin-stdlib-jdk7 and kotlin-stdlib-jdk8 can also be used.

Since Kotlin classes are final by default, you are likely to want to configure kotlin-spring plugin in order to automatically open Spring-annotated classes so that they can be proxied.

Jackson’s Kotlin module is required for serializing / deserializing JSON data in Kotlin. It is automatically registered when found on the classpath. A warning message is logged if Jackson and Kotlin are present but the Jackson Kotlin module is not.

[Tip]Tip

These dependencies and plugins are provided by default if one bootstraps a Kotlin project on start.spring.io.

47.2 Null-safety

One of Kotlin’s key features is null-safety. It deals with null values at compile time rather than deferring the problem to runtime and encountering a NullPointerException. This helps to eliminate a common source of bugs without paying the cost of wrappers like Optional. Kotlin also allows using functional constructs with nullable values as described in this comprehensive guide to null-safety in Kotlin.

Although Java does not allow one to express null-safety in its type system, Spring Framework, Spring Data, and Reactor now provide null-safety of their API via tooling-friendly annotations. By default, types from Java APIs used in Kotlin are recognized as platform types for which null-checks are relaxed. Kotlin’s support for JSR 305 annotations combined with nullability annotations provide null-safety for the related Spring API in Kotlin.

The JSR 305 checks can be configured by adding the -Xjsr305 compiler flag with the following options: -Xjsr305={strict|warn|ignore}. The default behavior is the same as -Xjsr305=warn. The strict value is required to have null-safety taken in account in Kotlin types inferred from Spring API but should be used with the knowledge that Spring API nullability declaration could evolve even between minor releases and more checks may be added in the future).

WARN: Generic type arguments, varargs and array elements nullability are not yet supported. See SPR-15942 for up-to-date information. Also be aware that Spring Boot’s own API is not yet annotated.

47.3 Kotlin API

47.3.1 runApplication

Spring Boot provides an idiomatic way to run an application with runApplication<MyApplication>(*args) as shown in the following example:

import org.springframework.boot.autoconfigure.SpringBootApplication
import org.springframework.boot.runApplication

@SpringBootApplication
class MyApplication

fun main(args: Array<String>) {
	runApplication<MyApplication>(*args)
}

This is a drop-in replacement for SpringApplication.run(MyApplication::class.java, *args). It also allows customization of the application as shown in the following example:

runApplication<MyApplication>(*args) {
	setBannerMode(OFF)
}

47.3.2 Extensions

Kotlin extensions provide the ability to extend existing classes with additional functionality. The Spring Boot Kotlin API makes use of these extensions to add new Kotlin specific conveniences to existing APIs.

TestRestTemplate extensions, similar to those provided by Spring Framework for RestOperations in Spring Framework, are provided. Among other things, the extensions make it possible to take advantage of Kotlin reified type parameters.

47.4 Dependency management

In order to avoid mixing different version of Kotlin dependencies on the classpath, dependency management of the following Kotlin dependencies is provided:

  • kotlin-reflect
  • kotlin-runtime
  • kotlin-stdlib
  • kotlin-stdlib-jdk7
  • kotlin-stdlib-jdk8
  • kotlin-stdlib-jre7
  • kotlin-stdlib-jre8

With Maven, the Kotlin version can be customized via the kotlin.version property and plugin management is provided for kotlin-maven-plugin. With Gradle, the Spring Boot plugin automatically aligns the kotlin.version with the version of the Kotlin plugin.

47.5 @ConfigurationProperties

@ConfigurationProperties currently only works with lateinit or nullable var properties (the former is recommended), since immutable classes initialized by constructors are not yet supported.

@ConfigurationProperties("example.kotlin")
class KotlinExampleProperties {

	lateinit var name: String

	lateinit var description: String

	val myService = MyService()

	class MyService {

		lateinit var apiToken: String

		lateinit var uri: URI

	}

}
[Tip]Tip

To generate your own metadata using the annotation processor, kapt should be configured with the spring-boot-configuration-processor dependency.

47.6 Testing

While it is possible to use JUnit 4 (the default provided by spring-boot-starter-test) to test Kotlin code, JUnit 5 is recommended. JUnit 5 enables a test class to be instantiated once and reused for all of the class’s tests. This makes it possible to use @BeforeAll and @AfterAll annotations on non-static methods, which is a good fit for Kotlin.

To use JUnit 5, exclude junit:junit dependency from spring-boot-starter-test, add JUnit 5 dependencies, and configure the Maven or Gradle plugin accordingly. See the JUnit 5 documentation for more details. You also need to switch test instance lifecycle to "per-class".

47.7 Resources

47.7.2 Examples

48. What to Read Next

If you want to learn more about any of the classes discussed in this section, you can check out the Spring Boot API documentation or you can browse the source code directly. If you have specific questions, take a look at the how-to section.

If you are comfortable with Spring Boot’s core features, you can continue on and read about production-ready features.

Part V. Spring Boot Actuator: Production-ready features

Spring Boot includes a number of additional features to help you monitor and manage your application when you push it to production. You can choose to manage and monitor your application by using HTTP endpoints or with JMX. Auditing, health, and metrics gathering can also be automatically applied to your application.

49. Enabling Production-ready Features

The spring-boot-actuator module provides all of Spring Boot’s production-ready features. The simplest way to enable the features is to add a dependency to the spring-boot-starter-actuator ‘Starter’.

To add the actuator to a Maven based project, add the following ‘Starter’ dependency:

<dependencies>
	<dependency>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-actuator</artifactId>
	</dependency>
</dependencies>

For Gradle, use the following declaration:

dependencies {
	compile("org.springframework.boot:spring-boot-starter-actuator")
}

50. Endpoints

Actuator endpoints let you monitor and interact with your application. Spring Boot includes a number of built-in endpoints and lets you add your own. For example, the health endpoint provides basic application health information.

Each individual endpoint can be enabled or disabled. This controls whether or not the endpoint is created and its bean exists in the application context. To be remotely accessible an endpoint also has to be exposed via JMX or HTTP. Most applications choose HTTP, where the ID of the endpoint along with a prefix of /actuator is mapped to a URL. For example, by default, the health endpoint is mapped to /actuator/health.

The following technology-agnostic endpoints are available:

IDDescriptionEnabled by default

auditevents

Exposes audit events information for the current application.

Yes

beans

Displays a complete list of all the Spring beans in your application.

Yes

conditions

Shows the conditions that were evaluated on configuration and auto-configuration classes and the reasons why they did or did not match.

Yes

configprops

Displays a collated list of all @ConfigurationProperties.

Yes

env

Exposes properties from Spring’s ConfigurableEnvironment.

Yes

flyway

Shows any Flyway database migrations that have been applied.

Yes

health

Shows application health information.

Yes

httptrace

Displays HTTP trace information (by default, the last 100 HTTP request-response exchanges).

Yes

info

Displays arbitrary application info.

Yes

loggers

Shows and modifies the configuration of loggers in the application.

Yes

liquibase

Shows any Liquibase database migrations that have been applied.

Yes

metrics

Shows ‘metrics’ information for the current application.

Yes

mappings

Displays a collated list of all @RequestMapping paths.

Yes

scheduledtasks

Displays the scheduled tasks in your application.

Yes

sessions

Allows retrieval and deletion of user sessions from a Spring Session-backed session store. Not available when using Spring Session’s support for reactive web applications.

Yes

shutdown

Lets the application be gracefully shutdown.

No

threaddump

Performs a thread dump.

Yes

If your application is a web application (Spring MVC, Spring WebFlux, or Jersey), you can use the following additional endpoints:

IDDescriptionEnabled by default

heapdump

Returns a GZip compressed hprof heap dump file.

Yes

jolokia

Exposes JMX beans over HTTP (when Jolokia is on the classpath, not available for WebFlux).

Yes

logfile

Returns the contents of the logfile (if logging.file or logging.path properties have been set). Supports the use of the HTTP Range header to retrieve part of the log file’s content.

Yes

prometheus

Exposes metrics in a format that can be scraped by a Prometheus server.

Yes

To learn more about the Actuator’s endpoints and their request and response formats, please refer to the separate API documentation (HTML or PDF).

50.1 Enabling Endpoints

By default, all endpoints except for shutdown are enabled. To configure the enablement of an endpoint, use its management.endpoint.<id>.enabled property. The following example enables the shutdown endpoint:

management.endpoint.shutdown.enabled=true

If you prefer endpoint enablement to be opt-in rather than opt-out, set the management.endpoints.enabled-by-default property to false and use individual endpoint enabled properties to opt back in. The following example enables the info endpoint and disables all other endpoints:

management.endpoints.enabled-by-default=false
management.endpoint.info.enabled=true
[Note]Note

Disabled endpoints are removed entirely from the application context. If you want to change only the technologies over which an endpoint is exposed, use the include and exclude properties instead.

50.2 Exposing Endpoints

Since Endpoints may contain sensitive information, careful consideration should be given about when to expose them. The following table shows the default exposure for the built-in endpoints:

IDJMXWeb

auditevents

Yes

No

beans

Yes

No

conditions

Yes

No

configprops

Yes

No

env

Yes

No

flyway

Yes

No

health

Yes

Yes

heapdump

N/A

No

httptrace

Yes

No

info

Yes

Yes

jolokia

N/A

No

logfile

N/A

No

loggers

Yes

No

liquibase

Yes

No

metrics

Yes

No

mappings

Yes

No

prometheus

N/A

No

scheduledtasks

Yes

No

sessions

Yes

No

shutdown

Yes

No

threaddump

Yes

No

To change which endpoints are exposed, use the following technology-specific include and exclude properties:

PropertyDefault

management.endpoints.jmx.exposure.exclude

 

management.endpoints.jmx.exposure.include

*

management.endpoints.web.exposure.exclude

 

management.endpoints.web.exposure.include

info, health

The include property lists the IDs of the endpoints that are exposed. The exclude property lists the IDs of the endpoints that should not be exposed. The exclude property takes precedence over the include property. Both include and exclude properties can be configured with a list of endpoint IDs.

For example, to stop exposing all endpoints over JMX and only expose the health and info endpoints, use the following property:

management.endpoints.jmx.exposure.include=health,info

* can be used to select all endpoints. For example, to expose everything over HTTP except the env and beans endpoints, use the following properties:

management.endpoints.web.exposure.include=*
management.endpoints.web.exposure.exclude=env,beans
[Note]Note

* has a special meaning in YAML, so be sure to add quotes if you want to include (or exclude) all endpoints, as shown in the following example:

management:
	endpoints:
		web:
			exposure:
				include: "*"
[Note]Note

If your application is exposed publicly, we strongly recommend that you also secure your endpoints.

[Tip]Tip

If you want to implement your own strategy for when endpoints are exposed, you can register an EndpointFilter bean.

50.3 Securing HTTP Endpoints

You should take care to secure HTTP endpoints in the same way that you would any other sensitive URL. If Spring Security is present, endpoints are secured by default using Spring Security’s content-negotiation strategy. If you wish to configure custom security for HTTP endpoints, for example, only allow users with a certain role to access them, Spring Boot provides some convenient RequestMatcher objects that can be used in combination with Spring Security.

A typical Spring Security configuration might look something like the following example:

@Configuration
public class ActuatorSecurity extends WebSecurityConfigurerAdapter {

	@Override
	protected void configure(HttpSecurity http) throws Exception {
		http.requestMatcher(EndpointRequest.toAnyEndpoint()).authorizeRequests()
				.anyRequest().hasRole("ENDPOINT_ADMIN")
				.and()
			.httpBasic();
	}

}

The preceding example uses EndpointRequest.toAnyEndpoint() to match a request to any endpoint and then ensures that all have the ENDPOINT_ADMIN role. Several other matcher methods are also available on EndpointRequest. See the API documentation (HTML or PDF) for details.

If you deploy applications behind a firewall, you may prefer that all your actuator endpoints can be accessed without requiring authentication. You can do so by changing the management.endpoints.web.exposure.include property, as follows:

application.properties. 

management.endpoints.web.exposure.include=*

Additionally, if Spring Security is present, you would need to add custom security configuration that allows unauthenticated access to the endpoints as shown in the following example:

@Configuration
public class ActuatorSecurity extends WebSecurityConfigurerAdapter {

	@Override
	protected void configure(HttpSecurity http) throws Exception {
		http.requestMatcher(EndpointRequest.toAnyEndpoint()).authorizeRequests()
			.anyRequest().permitAll();
	}

}

50.4 Configuring Endpoints

Endpoints automatically cache responses to read operations that do not take any parameters. To configure the amount of time for which an endpoint will cache a response, use its cache.time-to-live property. The following example sets the time-to-live of the beans endpoint’s cache to 10 seconds:

application.properties. 

management.endpoint.beans.cache.time-to-live=10s

[Note]Note

The prefix management.endpoint.<name> is used to uniquely identify the endpoint that is being configured.

[Note]Note

When making an authenticated HTTP request, the Principal is considered as input to the endpoint and, therefore, the response will not be cached.

50.5 Hypermedia for Actuator Web Endpoints

A “discovery page” is added with links to all the endpoints. The “discovery page” is available on /actuator by default.

When a custom management context path is configured, the “discovery page” automatically moves from /actuator to the root of the management context. For example, if the management context path is /management, then the discovery page is available from /management. When the management context path is set to /, the discovery page is disabled to prevent the possibility of a clash with other mappings.

50.6 Actuator Web Endpoint Paths

By default, endpoints are exposed over HTTP under the /actuator path by using the ID of the endpoint. For example, the beans endpoint is exposed under /actuator/beans. If you want to map endpoints to a different path, you can use the management.endpoints.web.path-mapping property. Also, if you want change the base path, you can use management.endpoints.web.base-path.

The following example remaps /actuator/health to /healthcheck:

application.properties. 

management.endpoints.web.base-path=/
management.endpoints.web.path-mapping.health=healthcheck

50.7 CORS Support

Cross-origin resource sharing (CORS) is a W3C specification that lets you specify in a flexible way what kind of cross-domain requests are authorized. If you use Spring MVC or Spring WebFlux, Actuator’s web endpoints can be configured to support such scenarios.

CORS support is disabled by default and is only enabled once the management.endpoints.web.cors.allowed-origins property has been set. The following configuration permits GET and POST calls from the example.com domain:

management.endpoints.web.cors.allowed-origins=http://example.com
management.endpoints.web.cors.allowed-methods=GET,POST
[Tip]Tip

See CorsEndpointProperties for a complete list of options.

50.8 Implementing Custom Endpoints

If you add a @Bean annotated with @Endpoint, any methods annotated with @ReadOperation, @WriteOperation, or @DeleteOperation are automatically exposed over JMX and, in a web application, over HTTP as well. Endpoints can be exposed over HTTP using Jersey, Spring MVC, or Spring WebFlux.

You can also write technology-specific endpoints by using @JmxEndpoint or @WebEndpoint. These endpoints are restricted to their respective technologies. For example, @WebEndpoint is exposed only over HTTP and not over JMX.

You can write technology-specific extensions by using @EndpointWebExtension and @EndpointJmxExtension. These annotations let you provide technology-specific operations to augment an existing endpoint.

Finally, if you need access to web-framework-specific functionality, you can implement Servlet or Spring @Controller and @RestController endpoints at the cost of them not being available over JMX or when using a different web framework.

50.8.1 Receiving Input

Operations on an endpoint receive input via their parameters. When exposed via the web, the values for these parameters are taken from the URL’s query parameters and from the JSON request body. When exposed via JMX, the parameters are mapped to the parameters of the MBean’s operations. Parameters are required by default. They can be made optional by annotating them with @org.springframework.lang.Nullable.

[Note]Note

To allow the input to be mapped to the operation method’s parameters, Java code implementing an endpoint should be compiled with -parameters, and Kotlin code implementing an endpoint should be compiled with -java-parameters. This will happen automatically if you are using Spring Boot’s Gradle plugin or if you are using Maven and spring-boot-starter-parent.

Input type conversion

The parameters passed to endpoint operation methods are, if necessary, automatically converted to the required type. Before calling an operation method, the input received via JMX or an HTTP request is converted to the required types using an instance of ApplicationConversionService.

50.8.2 Custom Web Endpoints

Operations on an @Endpoint, @WebEndpoint, or @WebEndpointExtension are automatically exposed over HTTP using Jersey, Spring MVC, or Spring WebFlux.

Web Endpoint Request Predicates

A request predicate is automatically generated for each operation on a web-exposed endpoint.

Path

The path of the predicate is determined by the ID of the endpoint and the base path of web-exposed endpoints. The default base path is /actuator. For example, an endpoint with the ID sessions will use /actuator/sessions as its path in the predicate.

The path can be further customized by annotating one or more parameters of the operation method with @Selector. Such a parameter is added to the path predicate as a path variable. The variable’s value is passed into the operation method when the endpoint operation is invoked.

HTTP method

The HTTP method of the predicate is determined by the operation type, as shown in the following table:

OperationHTTP method

@ReadOperation

GET

@WriteOperation

POST

@DeleteOperation

DELETE

Consumes

For a @WriteOperation (HTTP POST) that uses the request body, the consumes clause of the predicate is application/vnd.spring-boot.actuator.v2+json, application/json. For all other operations the consumes clause is empty.

Produces

The produces clause of the predicate can be determined by the produces attribute of the @DeleteOperation, @ReadOperation, and @WriteOperation annotations. The attribute is optional. If it is not used, the produces clause is determined automatically.

If the operation method returns void or Void the produces clause is empty. If the operation method returns a org.springframework.core.io.Resource, the produces clause is application/octet-stream. For all other operations the produces clause is application/vnd.spring-boot.actuator.v2+json, application/json.

Web Endpoint Response Status

The default response status for an endpoint operation depends on the operation type (read, write, or delete) and what, if anything, the operation returns.

A @ReadOperation returns a value, the response status will be 200 (OK). If it does not return a value, the response status will be 404 (Not Found).

If a @WriteOperation or @DeleteOperation returns a value, the response status will be 200 (OK). If it does not return a value the response status will be 204 (No Content).

If an operation is invoked without a required parameter, or with a parameter that cannot be converted to the required type, the operation method will not be called and the response status will be 400 (Bad Request).

Web Endpoint Range Requests

An HTTP range request can be used to request part of an HTTP resource. When using Spring MVC or Spring Web Flux, operations that return a org.springframework.core.io.Resource automatically support range requests.

[Note]Note

Range requests are not supported when using Jersey.

Web Endpoint Security

An operation on a web endpoint or a web-specific endpoint extension can receive the current java.security.Principal or org.springframework.boot.actuate.endpoint.SecurityContext as a method parameter. The former is typically used in conjunction with @Nullable to provide different behaviour for authenticated and unauthenticated users. The latter is typically used to perform authorization checks using its isUserInRole(String) method.

50.8.3 Servlet endpoints

A Servlet can be exposed as an endpoint by implementing a class annotated with @ServletEndpoint that also implements Supplier<EndpointServlet>. Servlet endpoints provide deeper integration with the Servlet container but at the expense of portability. They are intended to be used to expose an existing Servlet as an endpoint. For new endpoints, the @Endpoint and @WebEndpoint annotations should be preferred whenever possible.

50.8.4 Controller endpoints

@ControllerEndpoint and @RestControllerEndpoint can be used to implement an endpoint that is only exposed by Spring MVC or Spring WebFlux. Methods are mapped using the standard annotations for Spring MVC and Spring WebFlux such as @RequestMapping and @GetMapping, with the endpoint’s ID being used as a prefix for the path. Controller endpoints provide deeper integration with Spring’s web frameworks but at the expense of portability. The @Endpoint and @WebEndpoint annotations should be preferred whenever possible.

50.9 Health Information

You can use health information to check the status of your running application. It is often used by monitoring software to alert someone when a production system goes down. The information exposed by the health endpoint depends on the management.endpoint.health.show-details property which can be configured with one of the following values:

NameDescription

never

Details are never shown.

when-authorized

Details are only shown to authorized users. Authorized roles can be configured using management.endpoint.health.roles.

always

Details are shown to all users.

The default value is never. A user is considered to be authorized when they are in one or more of the endpoint’s roles. If the endpoint has no configured roles (the default) all authenticated users are considered to be authorized. The roles can be configured using the management.endpoint.health.roles property.

[Note]Note

If you have secured your application and wish to use always, your security configuration must permit access to the health endpoint for both authenticated and unauthenticated users.

Health information is collected from all HealthIndicator beans defined in your ApplicationContext. Spring Boot includes a number of auto-configured HealthIndicators, and you can also write your own. By default, the final system state is derived by the HealthAggregator, which sorts the statuses from each HealthIndicator based on an ordered list of statuses. The first status in the sorted list is used as the overall health status. If no HealthIndicator returns a status that is known to the HealthAggregator, an UNKNOWN status is used.

50.9.1 Auto-configured HealthIndicators

The following HealthIndicators are auto-configured by Spring Boot when appropriate:

NameDescription

CassandraHealthIndicator

Checks that a Cassandra database is up.

DiskSpaceHealthIndicator

Checks for low disk space.

DataSourceHealthIndicator

Checks that a connection to DataSource can be obtained.

ElasticsearchHealthIndicator

Checks that an Elasticsearch cluster is up.

InfluxDbHealthIndicator

Checks that an InfluxDB server is up.

JmsHealthIndicator

Checks that a JMS broker is up.

MailHealthIndicator

Checks that a mail server is up.

MongoHealthIndicator

Checks that a Mongo database is up.

Neo4jHealthIndicator

Checks that a Neo4j server is up.

RabbitHealthIndicator

Checks that a Rabbit server is up.

RedisHealthIndicator

Checks that a Redis server is up.

SolrHealthIndicator

Checks that a Solr server is up.

[Tip]Tip

You can disable them all by setting the management.health.defaults.enabled property.

50.9.2 Writing Custom HealthIndicators

To provide custom health information, you can register Spring beans that implement the HealthIndicator interface. You need to provide an implementation of the health() method and return a Health response. The Health response should include a status and can optionally include additional details to be displayed. The following code shows a sample HealthIndicator implementation:

import org.springframework.boot.actuate.health.Health;
import org.springframework.boot.actuate.health.HealthIndicator;
import org.springframework.stereotype.Component;

@Component
public class MyHealthIndicator implements HealthIndicator {

	@Override
	public Health health() {
		int errorCode = check(); // perform some specific health check
		if (errorCode != 0) {
			return Health.down().withDetail("Error Code", errorCode).build();
		}
		return Health.up().build();
	}

}
[Note]Note

The identifier for a given HealthIndicator is the name of the bean without the HealthIndicator suffix, if it exists. In the preceding example, the health information is available in an entry named my.

In addition to Spring Boot’s predefined Status types, it is also possible for Health to return a custom Status that represents a new system state. In such cases, a custom implementation of the HealthAggregator interface also needs to be provided, or the default implementation has to be configured by using the management.health.status.order configuration property.

For example, assume a new Status with code FATAL is being used in one of your HealthIndicator implementations. To configure the severity order, add the following property to your application properties:

management.health.status.order=FATAL, DOWN, OUT_OF_SERVICE, UNKNOWN, UP

The HTTP status code in the response reflects the overall health status (for example, UP maps to 200, while OUT_OF_SERVICE and DOWN map to 503). You might also want to register custom status mappings if you access the health endpoint over HTTP. For example, the following property maps FATAL to 503 (service unavailable):

management.health.status.http-mapping.FATAL=503
[Tip]Tip

If you need more control, you can define your own HealthStatusHttpMapper bean.

The following table shows the default status mappings for the built-in statuses:

StatusMapping

DOWN

SERVICE_UNAVAILABLE (503)

OUT_OF_SERVICE

SERVICE_UNAVAILABLE (503)

UP

No mapping by default, so http status is 200

UNKNOWN

No mapping by default, so http status is 200

50.9.3 Reactive Health Indicators

For reactive applications, such as those using Spring WebFlux, ReactiveHealthIndicator provides a non-blocking contract for getting application health. Similar to a traditional HealthIndicator, health information is collected from all ReactiveHealthIndicator beans defined in your ApplicationContext. Regular HealthIndicator beans that do not check against a reactive API are included and executed on the elastic scheduler.

To provide custom health information from a reactive API, you can register Spring beans that implement the ReactiveHealthIndicator interface. The following code shows a sample ReactiveHealthIndicator implementation:

@Component
public class MyReactiveHealthIndicator implements ReactiveHealthIndicator {

	@Override
	public Mono<Health> health() {
		return doHealthCheck() //perform some specific health check that returns a Mono<Health>
			.onErrorResume(ex -> Mono.just(new Health.Builder().down(ex).build())));
	}

}
[Tip]Tip

To handle the error automatically, consider extending from AbstractReactiveHealthIndicator.

50.9.4 Auto-configured ReactiveHealthIndicators

The following ReactiveHealthIndicators are auto-configured by Spring Boot when appropriate:

NameDescription

MongoReactiveHealthIndicator

Checks that a Mongo database is up.

RedisReactiveHealthIndicator

Checks that a Redis server is up.

[Tip]Tip

If necessary, reactive indicators replace the regular ones. Also, any HealthIndicator that is not handled explicitly is wrapped automatically.

50.10 Application Information

Application information exposes various information collected from all InfoContributor beans defined in your ApplicationContext. Spring Boot includes a number of auto-configured InfoContributor beans, and you can write your own.

50.10.1 Auto-configured InfoContributors

The following InfoContributor beans are auto-configured by Spring Boot, when appropriate:

NameDescription

EnvironmentInfoContributor

Exposes any key from the Environment under the info key.

GitInfoContributor

Exposes git information if a git.properties file is available.

BuildInfoContributor

Exposes build information if a META-INF/build-info.properties file is available.

[Tip]Tip

It is possible to disable them all by setting the management.info.defaults.enabled property.

50.10.2 Custom Application Information

You can customize the data exposed by the info endpoint by setting info.* Spring properties. All Environment properties under the info key are automatically exposed. For example, you could add the following settings to your application.properties file:

info.app.encoding=UTF-8
info.app.java.source=1.8
info.app.java.target=1.8
[Tip]Tip

Rather than hardcoding those values, you could also expand info properties at build time.

Assuming you use Maven, you could rewrite the preceding example as follows:

info.app.encoding[email protected]@
info.app.java.source[email protected]@
info.app.java.target[email protected]@

50.10.3 Git Commit Information

Another useful feature of the info endpoint is its ability to publish information about the state of your git source code repository when the project was built. If a GitProperties bean is available, the git.branch, git.commit.id, and git.commit.time properties are exposed.

[Tip]Tip

A GitProperties bean is auto-configured if a git.properties file is available at the root of the classpath. See "Generate git information" for more details.

If you want to display the full git information (that is, the full content of git.properties), use the management.info.git.mode property, as follows:

management.info.git.mode=full

50.10.4 Build Information

If a BuildProperties bean is available, the info endpoint can also publish information about your build. This happens if a META-INF/build-info.properties file is available in the classpath.

[Tip]Tip

The Maven and Gradle plugins can both generate that file. See "Generate build information" for more details.

50.10.5 Writing Custom InfoContributors

To provide custom application information, you can register Spring beans that implement the InfoContributor interface.

The following example contributes an example entry with a single value:

import java.util.Collections;

import org.springframework.boot.actuate.info.Info;
import org.springframework.boot.actuate.info.InfoContributor;
import org.springframework.stereotype.Component;

@Component
public class ExampleInfoContributor implements InfoContributor {

	@Override
	public void contribute(Info.Builder builder) {
		builder.withDetail("example",
				Collections.singletonMap("key", "value"));
	}

}

If you reach the info endpoint, you should see a response that contains the following additional entry:

{
	"example": {
		"key" : "value"
	}
}

51. Monitoring and Management over HTTP

If you are developing a web application, Spring Boot Actuator auto-configures all enabled endpoints to be exposed over HTTP. The default convention is to use the id of the endpoint with a prefix of /actuator as the URL path. For example, health is exposed as /actuator/health.

[Tip]Tip

Actuator is supported natively with Spring MVC, Spring WebFlux, and Jersey.

51.1 Customizing the Management Endpoint Paths

Sometimes, it is useful to customize the prefix for the management endpoints. For example, your application might already use /actuator for another purpose. You can use the management.endpoints.web.base-path property to change the prefix for your management endpoint, as shown in the following example:

management.endpoints.web.base-path=/manage

The preceding application.properties example changes the endpoint from /actuator/{id} to /manage/{id} (for example, /manage/info).

[Note]Note

Unless the management port has been configured to expose endpoints by using a different HTTP port, management.endpoints.web.base-path is relative to server.servlet.context-path. If management.server.port is configured, management.endpoints.web.base-path is relative to management.server.servlet.context-path.

51.2 Customizing the Management Server Port

Exposing management endpoints by using the default HTTP port is a sensible choice for cloud-based deployments. If, however, your application runs inside your own data center, you may prefer to expose endpoints by using a different HTTP port.

You can set the management.server.port property to change the HTTP port, as shown in the following example:

management.server.port=8081

51.3 Configuring Management-specific SSL

When configured to use a custom port, the management server can also be configured with its own SSL by using the various management.server.ssl.* properties. For example, doing so lets a management server be available over HTTP while the main application uses HTTPS, as shown in the following property settings:

server.port=8443
server.ssl.enabled=true
server.ssl.key-store=classpath:store.jks
server.ssl.key-password=secret
management.server.port=8080
management.server.ssl.enabled=false

Alternatively, both the main server and the management server can use SSL but with different key stores, as follows:

server.port=8443
server.ssl.enabled=true
server.ssl.key-store=classpath:main.jks
server.ssl.key-password=secret
management.server.port=8080
management.server.ssl.enabled=true
management.server.ssl.key-store=classpath:management.jks
management.server.ssl.key-password=secret

51.4 Customizing the Management Server Address

You can customize the address that the management endpoints are available on by setting the management.server.address property. Doing so can be useful if you want to listen only on an internal or ops-facing network or to listen only for connections from localhost.

[Note]Note

You can listen on a different address only when the port differs from the main server port.

The following example application.properties does not allow remote management connections:

management.server.port=8081
management.server.address=127.0.0.1

51.5 Disabling HTTP Endpoints

If you do not want to expose endpoints over HTTP, you can set the management port to -1, as shown in the following example:

management.server.port=-1

52. Monitoring and Management over JMX

Java Management Extensions (JMX) provide a standard mechanism to monitor and manage applications. By default, Spring Boot exposes management endpoints as JMX MBeans under the org.springframework.boot domain.

52.1 Customizing MBean Names

The name of the MBean is usually generated from the id of the endpoint. For example, the health endpoint is exposed as org.springframework.boot:type=Endpoint,name=Health.

If your application contains more than one Spring ApplicationContext, you may find that names clash. To solve this problem, you can set the management.endpoints.jmx.unique-names property to true so that MBean names are always unique.

You can also customize the JMX domain under which endpoints are exposed. The following settings show an example of doing so in application.properties:

management.endpoints.jmx.domain=com.example.myapp
management.endpoints.jmx.unique-names=true

52.2 Disabling JMX Endpoints

If you do not want to expose endpoints over JMX, you can set the management.endpoints.jmx.exposure.exclude property to *, as shown in the following example:

management.endpoints.jmx.exposure.exclude=*

52.3 Using Jolokia for JMX over HTTP

Jolokia is a JMX-HTTP bridge that provides an alternative method of accessing JMX beans. To use Jolokia, include a dependency to org.jolokia:jolokia-core. For example, with Maven, you would add the following dependency:

<dependency>
	<groupId>org.jolokia</groupId>
	<artifactId>jolokia-core</artifactId>
	</dependency>

The Jolokia endpoint can then be exposed by adding jolokia or * to the management.endpoints.web.exposure.include property. You can then access it by using /actuator/jolokia on your management HTTP server.

52.3.1 Customizing Jolokia

Jolokia has a number of settings that you would traditionally configure by setting servlet parameters. With Spring Boot, you can use your application.properties file. To do so, prefix the parameter with management.endpoint.jolokia.config., as shown in the following example:

management.endpoint.jolokia.config.debug=true

52.3.2 Disabling Jolokia

If you use Jolokia but do not want Spring Boot to configure it, set the management.endpoint.jolokia.enabled property to false, as follows:

management.endpoint.jolokia.enabled=false

53. Loggers

Spring Boot Actuator includes the ability to view and configure the log levels of your application at runtime. You can view either the entire list or an individual logger’s configuration, which is made up of both the explicitly configured logging level as well as the effective logging level given to it by the logging framework. These levels can be one of:

  • TRACE
  • DEBUG
  • INFO
  • WARN
  • ERROR
  • FATAL
  • OFF
  • null

null indicates that there is no explicit configuration.

53.1 Configure a Logger

To configure a given logger, POST a partial entity to the resource’s URI, as shown in the following example:

{
	"configuredLevel": "DEBUG"
}
[Tip]Tip

To “reset” the specific level of the logger (and use the default configuration instead), you can pass a value of null as the configuredLevel.

54. Metrics

Spring Boot Actuator provides dependency management and auto-configuration for Micrometer, an application metrics facade that supports numerous monitoring systems, including:

[Tip]Tip

To learn more about Micrometer’s capabilities, please refer to its reference documentation, in particular the concepts section.

54.1 Getting started

Spring Boot auto-configures a composite MeterRegistry and adds a registry to the composite for each of the supported implementations that it finds on the classpath. Having a dependency on micrometer-registry-{system} in your runtime classpath is enough for Spring Boot to configure the registry.

Most registries share common features. For instance, you can disable a particular registry even if the Micrometer registry implementation is on the classpath. For instance, to disable Datadog:

management.metrics.export.datadog.enabled=false

Spring Boot will also add any auto-configured registries to the global static composite registry on the Metrics class unless you explicitly tell it not to:

management.metrics.use-global-registry=false

You can register any number of MeterRegistryCustomizer beans to further configure the registry, such as applying common tags, before any meters are registered with the registry:

@Bean
MeterRegistryCustomizer<MeterRegistry> metricsCommonTags() {
	return registry -> registry.config().commonTags("region", "us-east-1");
}

You can apply customizations to particular registry implementations by being more specific about the generic type:

@Bean
MeterRegistryCustomizer<GraphiteMeterRegistry> graphiteMetricsNamingConvention() {
	return registry -> registry.config().namingConvention(MY_CUSTOM_CONVENTION);
}

With that setup in place you can inject MeterRegistry in your components and register metrics:

@Component
public class SampleBean {

	private final Counter counter;

	public SampleBean(MeterRegistry registry) {
		this.counter = registry.counter("received.messages");
	}

	public void handleMessage(String message) {
		this.counter.increment();
		// handle message implementation
	}

}

Spring Boot also configures built-in instrumentation (i.e. MeterBinder implementations) that you can control via configuration or dedicated annotation markers.

54.2 Supported monitoring systems

54.2.1 Atlas

By default, metrics are exported to Atlas running on your local machine. The location of the Atlas server to use can be provided using:

management.metrics.export.atlas.uri=http://atlas.example.com:7101/api/v1/publish

54.2.2 Datadog

Datadog registry pushes metrics to datadoghq periodically. To export metrics to Datadog, your API key must be provided:

management.metrics.export.datadog.api-key=YOUR_KEY

You can also change the interval at which metrics are sent to Datadog:

management.metrics.export.datadog.step=30s

54.2.3 Ganglia

By default, metrics are exported to Ganglia running on your local machine. The Ganglia server host and port to use can be provided using:

management.metrics.export.ganglia.host=ganglia.example.com
management.metrics.export.ganglia.port=9649

54.2.4 Graphite

By default, metrics are exported to Graphite running on your local machine. The Graphite server host and port to use can be provided using:

management.metrics.export.graphite.host=graphite.example.com
management.metrics.export.graphite.port=9004

Micrometer provides a default HierarchicalNameMapper that governs how a dimensional meter id is mapped to flat hierarchical names.

[Tip]Tip

To take control over this behaviour, define your GraphiteMeterRegistry and supply your own HierarchicalNameMapper. An auto-configured GraphiteConfig and Clock beans are provided unless you define your own:

@Bean
public GraphiteMeterRegistry graphiteMeterRegistry(GraphiteConfig config, Clock clock) {
	return new GraphiteMeterRegistry(config, clock, MY_HIERARCHICAL_MAPPER);
}

54.2.5 Influx

By default, metrics are exported to Influx running on your local machine. The location of the Influx server to use can be provided using:

management.metrics.export.influx.uri=http://influx.example.com:8086

54.2.6 JMX

Micrometer provides a hierarchical mapping to JMX, primarily as a cheap and portable way to view metrics locally.By default, metrics are exported to the metrics JMX domain. The domain to use can be provided provided using:

management.metrics.export.jmx.domain=com.example.app.metrics

Micrometer provides a default HierarchicalNameMapper that governs how a dimensional meter id is mapped to flat hierarchical names.

[Tip]Tip

To take control over this behaviour, define your JmxMeterRegistry and supply your own HierarchicalNameMapper. An auto-configured JmxConfig and Clock beans are provided unless you define your own:

@Bean
public JmxMeterRegistry jmxMeterRegistry(JmxConfig config, Clock clock) {
	return new JmxMeterRegistry(config, clock, MY_HIERARCHICAL_MAPPER);
}

54.2.7 New Relic

New Relic registry pushes metrics to New Relic periodically. To export metrics to New Relic, your API key and account id must be provided:

management.metrics.export.newrelic.api-key=YOUR_KEY
management.metrics.export.newrelic.account-id=YOUR_ACCOUNT_ID

You can also change the interval at which metrics are sent to New Relic:

management.metrics.export.newrelic.step=30s

54.2.8 Prometheus

Prometheus expects to scrape or poll individual app instances for metrics. Spring Boot provides an actuator endpoint available at /actuator/prometheus to present a Prometheus scrape with the appropriate format.

[Tip]Tip

The endpoint is not available by default and must be exposed, see exposing endpoints for more details.

Here is an example scrape_config to add to prometheus.yml:

scrape_configs:
  - job_name: 'spring'
	metrics_path: '/actuator/prometheus'
	static_configs:
	  - targets: ['HOST:PORT']

54.2.9 SignalFx

SignalFx registry pushes metrics to SignalFx periodically. To export metrics to SignalFx, your access token must be provided:

management.metrics.export.signalfx.access-token=YOUR_ACCESS_TOKEN

You can also change the interval at which metrics are sent to SignalFx:

management.metrics.export.signalfx.step=30s

54.2.10 Simple

Micrometer ships with a simple, in-memory backend that is automatically used as a fallback if no other registry is configured. This allows you to see what metrics are collected in the metrics endpoint.

The in-memory backend disables itself as soon as you’re using any of the other available backend. You can also disable it explicitly:

management.metrics.export.simple.enabled=false

54.2.11 StatsD

The StatsD registry pushes metrics over UDP to a StatsD agent eagerly. By default, metrics are exported to a StatsD agent running on your local machine. The StatsD agent host and port to use can be provided using:

management.metrics.export.statsd.host=statsd.example.com
management.metrics.export.statsd.port=9125

You can also change the StatsD line protocol to use (default to Datadog):

management.metrics.export.statsd.flavor=etsy

54.2.12 Wavefront

Wavefront registry pushes metrics to Wavefront periodically. If you are exporting metrics to Wavefront directly, your API token must be provided:

management.metrics.export.wavefront.api-token=YOUR_API_TOKEN

Alternatively, you may use a Wavefront sidecar or an internal proxy set up in your environment that forwards metrics data to the Wavefront API host:

management.metrics.export.wavefront.uri=proxy://localhost:2878
[Tip]Tip

If publishing metrics to a Wavefront proxy (as described in the documentation), the host must be in the proxy://HOST:PORT format.

You can also change the interval at which metrics are sent to Wavefront:

management.metrics.export.wavefront.step=30s

54.3 Supported Metrics

Spring Boot registers the following core metrics when applicable:

  • JVM metrics, report utilization of:

    • Various memory and buffer pools
    • Statistics related to garbage collection
    • Threads utilization
    • Number of classes loaded/unloaded
  • CPU metrics
  • File descriptor metrics
  • Logback metrics: record the number of events logged to Logback at each level
  • Uptime metrics: report a gauge for uptime and a fixed gauge representing the application’s absolute start time
  • Tomcat metrics
  • Spring Integration metrics

54.3.1 Spring MVC Metrics

Auto-configuration enables the instrumentation of requests handled by Spring MVC. When management.metrics.web.server.auto-time-requests is true, this instrumentation occurs for all requests. Alternatively, when set to false, you can enable instrumentation by adding @Timed to a request-handling method:

@RestController
@Timed 1
public class MyController {

	@GetMapping("/api/people")
	@Timed(extraTags = { "region", "us-east-1" }) 2
	@Timed(value = "all.people", longTask = true) 3
	public List<Person> listPeople() { ... }

}

1

A controller class to enable timings on every request handler in the controller.

2

A method to enable for an individual endpoint. This is not necessary if you have it on the class, but can be used to further customize the timer for this particular endpoint.

3

A method with longTask = true to enable a long task timer for the method. Long task timers require a separate metric name, and can be stacked with a short task timer.

By default, metrics are generated with the name, http.server.requests. The name can be customized by setting the management.metrics.web.server.requests-metric-name property.

By default, Spring MVC-related metrics are tagged with the following information:

  • method, the request’s method (for example, GET or POST).
  • uri, the request’s URI template prior to variable substitution, if possible (for example, /api/person/{id}).
  • status, the response’s HTTP status code (for example, 200 or 500).
  • exception, the simple class name of any exception that was thrown while handling the request.

To customize the tags, provide a @Bean that implements WebMvcTagsProvider.

54.3.2 Spring WebFlux Metrics

Auto-configuration enables the instrumentation of all requests handled by WebFlux controllers and functional handlers.

By default, metrics are generated with the name http.server.requests. You can customize the name by setting the management.metrics.web.server.requests-metric-name property.

By default, WebFlux-related metrics are tagged with the following information:

  • method, the request’s method (for example, GET or POST).
  • uri, the request’s URI template prior to variable substitution, if possible (for example, /api/person/{id}).
  • status, the response’s HTTP status code (for example, 200 or 500).
  • exception, the simple class name of any exception that was thrown while handling the request.

To customize the tags, provide a @Bean that implements WebFluxTagsProvider.

54.3.3 RestTemplate Metrics

The instrumentation of any RestTemplate created using the auto-configured RestTemplateBuilder is enabled. It is also possible to apply MetricsRestTemplateCustomizer manually.

By default, metrics are generated with the name, http.client.requests. The name can be customized by setting the management.metrics.web.client.requests-metric-name property.

By default, metrics generated by an instrumented RestTemplate are tagged with the following information:

  • method, the request’s method (for example, GET or POST).
  • uri, the request’s URI template prior to variable substitution, if possible (for example, /api/person/{id}).
  • status, the response’s HTTP status code (for example, 200 or 500).
  • clientName, the host portion of the URI.

To customize the tags, provide a @Bean that implements RestTemplateExchangeTagsProvider. There are convenience static functions in RestTemplateExchangeTags.

54.3.4 Cache Metrics

Auto-configuration enables the instrumentation of all available Caches on startup with metrics prefixed with cache. Cache instrumentation is standardized for a basic set of metrics. Additional, cache-specific metrics are also available.

The following cache libraries are supported:

  • Caffeine
  • EhCache 2
  • Hazelcast
  • Any compliant JCache (JSR-107) implementation

Metrics are tagged by the name of the cache and by the name of the CacheManager that is derived from the bean name.

[Note]Note

Only caches that are available on startup are bound to the registry. For caches created on-the-fly or programmatically after the startup phase, an explicit registration is required. A CacheMetricsRegistrar bean is made available to make that process easier.

54.3.5 DataSource Metrics

Auto-configuration enables the instrumentation of all available DataSource objects with a metric named jdbc. Data source instrumentation results in gauges representing the currently active, maximum allowed, and minimum allowed connections in the pool. Each of these gauges has a name that is prefixed by jdbc.

Metrics are also tagged by the name of the DataSource computed based on the bean name.

[Tip]Tip

By default, Spring Boot provides metadata for all supported data sources; you can add additional DataSourcePoolMetadataProvider beans if your favorite data source isn’t supported out of the box. See DataSourcePoolMetadataProvidersConfiguration for examples.

Also, Hikari-specific metrics are exposed with a hikaricp prefix. Each metric is tagged by the name of the Pool (can be controlled with spring.datasource.name).

54.3.6 RabbitMQ Metrics

Auto-configuration will enable the instrumentation of all available RabbitMQ connection factories with a metric named rabbitmq.

54.4 Registering custom metrics

To register custom metrics, inject MeterRegistry into your component, as shown in the following example:

class Dictionary {

	private final List<String> words = new CopyOnWriteArrayList<>();

	Dictionary(MeterRegistry registry) {
		registry.gaugeCollectionSize("dictionary.size", Tags.empty(), this.words);
	}

	// …

}

If you find that you repeatedly instrument a suite of metrics across components or applications, you may encapsulate this suite in a MeterBinder implementation. By default, metrics from all MeterBinder beans will be automatically bound to the Spring-managed MeterRegistry.

54.5 Customizing individual metrics

If you need to apply customizations to specific Meter instances you can use the io.micrometer.core.instrument.config.MeterFilter interface. By default, all MeterFilter beans will be automatically applied to the micrometer MeterRegistry.Config.

For example, if you want to rename the mytag.region tag to mytag.area for all meter IDs beginning with com.example, you can do the following:

@Bean
public MeterFilter renameRegionTagMeterFilter() {
	return MeterFilter.renameTag("com.example", "mytag.region", "mytag.area");
}

54.5.1 Per-meter properties

In addition to MeterFilter beans, it’s also possible to apply a limited set of customization on a per-meter basis using properties. Per-meter customizations apply to any all meter IDs that start with the given name. For example, the following will disable any meters that have an ID starting with example.remote

management.metrics.enable.example.remote=false

The following properties allow per-meter customization:

Table 54.1. Per-meter customizations

PropertyDescription

management.metrics.enable

Whether to deny meters from emitting any metrics.

management.metrics.distribution.percentiles-histogram

Whether to publish a histogram suitable for computing aggregable (across dimension) percentile approximations.

management.metrics.distribution.percentiles

Publish percentile