1. Spring Boot Application

This section includes topics relating directly to Spring Boot applications.

1.1. Create Your Own FailureAnalyzer

FailureAnalyzer is a great way to intercept an exception on startup and turn it into a human-readable message, wrapped in a FailureAnalysis. Spring Boot provides such an analyzer for application-context-related exceptions, JSR-303 validations, and more. You can also create your own.

AbstractFailureAnalyzer is a convenient extension of FailureAnalyzer that checks the presence of a specified exception type in the exception to handle. You can extend from that so that your implementation gets a chance to handle the exception only when it is actually present. If, for whatever reason, you cannot handle the exception, return null to give another implementation a chance to handle the exception.

FailureAnalyzer implementations must be registered in META-INF/spring.factories. The following example registers ProjectConstraintViolationFailureAnalyzer:

org.springframework.boot.diagnostics.FailureAnalyzer=\
com.example.ProjectConstraintViolationFailureAnalyzer
If you need access to the BeanFactory or the Environment, your FailureAnalyzer can simply implement BeanFactoryAware or EnvironmentAware respectively.

1.2. Troubleshoot Auto-configuration

The Spring Boot auto-configuration tries its best to “do the right thing”, but sometimes things fail, and it can be hard to tell why.

There is a really useful ConditionEvaluationReport available in any Spring Boot ApplicationContext. You can see it if you enable DEBUG logging output. If you use the spring-boot-actuator (see the Actuator chapter), there is also a conditions endpoint that renders the report in JSON. Use that endpoint to debug the application and see what features have been added (and which have not been added) by Spring Boot at runtime.

Many more questions can be answered by looking at the source code and the Javadoc. When reading the code, remember the following rules of thumb:

  • Look for classes called *AutoConfiguration and read their sources. Pay special attention to the @Conditional* annotations to find out what features they enable and when. Add --debug to the command line or a System property -Ddebug to get a log on the console of all the auto-configuration decisions that were made in your app. In a running Actuator app, look at the conditions endpoint (/actuator/conditions or the JMX equivalent) for the same information.

  • Look for classes that are @ConfigurationProperties (such as ServerProperties) and read from there the available external configuration options. The @ConfigurationProperties annotation has a name attribute that acts as a prefix to external properties. Thus, ServerProperties has prefix="server" and its configuration properties are server.port, server.address, and others. In a running Actuator app, look at the configprops endpoint.

  • Look for uses of the bind method on the Binder to pull configuration values explicitly out of the Environment in a relaxed manner. It is often used with a prefix.

  • Look for @Value annotations that bind directly to the Environment.

  • Look for @ConditionalOnExpression annotations that switch features on and off in response to SpEL expressions, normally evaluated with placeholders resolved from the Environment.

1.3. Customize the Environment or ApplicationContext Before It Starts

A SpringApplication has ApplicationListeners and ApplicationContextInitializers that are used to apply customizations to the context or environment. Spring Boot loads a number of such customizations for use internally from META-INF/spring.factories. There is more than one way to register additional customizations:

  • Programmatically, per application, by calling the addListeners and addInitializers methods on SpringApplication before you run it.

  • Declaratively, per application, by setting the context.initializer.classes or context.listener.classes properties.

  • Declaratively, for all applications, by adding a META-INF/spring.factories and packaging a jar file that the applications all use as a library.

The SpringApplication sends some special ApplicationEvents to the listeners (some even before the context is created) and then registers the listeners for events published by the ApplicationContext as well. See “spring-boot-features.html” in the ‘Spring Boot features’ section for a complete list.

It is also possible to customize the Environment before the application context is refreshed by using EnvironmentPostProcessor. Each implementation should be registered in META-INF/spring.factories, as shown in the following example:

org.springframework.boot.env.EnvironmentPostProcessor=com.example.YourEnvironmentPostProcessor

The implementation can load arbitrary files and add them to the Environment. For instance, the following example loads a YAML configuration file from the classpath:

public class EnvironmentPostProcessorExample implements EnvironmentPostProcessor {

    private final YamlPropertySourceLoader loader = new YamlPropertySourceLoader();

    @Override
    public void postProcessEnvironment(ConfigurableEnvironment environment,
            SpringApplication application) {
        Resource path = new ClassPathResource("com/example/myapp/config.yml");
        PropertySource<?> propertySource = loadYaml(path);
        environment.getPropertySources().addLast(propertySource);
    }

    private PropertySource<?> loadYaml(Resource path) {
        if (!path.exists()) {
            throw new IllegalArgumentException("Resource " + path + " does not exist");
        }
        try {
            return this.loader.load("custom-resource", path).get(0);
        }
        catch (IOException ex) {
            throw new IllegalStateException(
                    "Failed to load yaml configuration from " + path, ex);
        }
    }

}
The Environment has already been prepared with all the usual property sources that Spring Boot loads by default. It is therefore possible to get the location of the file from the environment. The preceding example adds the custom-resource property source at the end of the list so that a key defined in any of the usual other locations takes precedence. A custom implementation may define another order.
While using @PropertySource on your @SpringBootApplication may seem to be a convenient and easy way to load a custom resource in the Environment, we do not recommend it, because Spring Boot prepares the Environment before the ApplicationContext is refreshed. Any key defined with @PropertySource is loaded too late to have any effect on auto-configuration.

1.4. Build an ApplicationContext Hierarchy (Adding a Parent or Root Context)

You can use the ApplicationBuilder class to create parent/child ApplicationContext hierarchies. See “spring-boot-features.html” in the ‘Spring Boot features’ section for more information.

1.5. Create a Non-web Application

Not all Spring applications have to be web applications (or web services). If you want to execute some code in a main method but also bootstrap a Spring application to set up the infrastructure to use, you can use the SpringApplication features of Spring Boot. A SpringApplication changes its ApplicationContext class, depending on whether it thinks it needs a web application or not. The first thing you can do to help it is to leave server-related dependencies (e.g. servlet API) off the classpath. If you cannot do that (for example, you run two applications from the same code base) then you can explicitly call setWebApplicationType(WebApplicationType.NONE) on your SpringApplication instance or set the applicationContextClass property (through the Java API or with external properties). Application code that you want to run as your business logic can be implemented as a CommandLineRunner and dropped into the context as a @Bean definition.

2. Properties and Configuration

This section includes topics about setting and reading properties and configuration settings and their interaction with Spring Boot applications.

2.1. Automatically Expand Properties at Build Time

Rather than hardcoding some properties that are also specified in your project’s build configuration, you can automatically expand them by instead using the existing build configuration. This is possible in both Maven and Gradle.

2.1.1. Automatic Property Expansion Using Maven

You can automatically expand properties from the Maven project by using resource filtering. If you use the spring-boot-starter-parent, you can then refer to your Maven ‘project properties’ with @[email protected] placeholders, as shown in the following example:

Only production configuration is filtered that way (in other words, no filtering is applied on src/test/resources).
If you enable the addResources flag, the spring-boot:run goal can add src/main/resources directly to the classpath (for hot reloading purposes). Doing so circumvents the resource filtering and this feature. Instead, you can use the exec:java goal or customize the plugin’s configuration. See the plugin usage page for more details.

If you do not use the starter parent, you need to include the following element inside the <build/> element of your pom.xml:

<resources>
    <resource>
        <directory>src/main/resources</directory>
        <filtering>true</filtering>
    </resource>
</resources>

You also need to include the following element inside <plugins/>:

<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-resources-plugin</artifactId>
    <version>2.7</version>
    <configuration>
        <delimiters>
            <delimiter>@</delimiter>
        </delimiters>
        <useDefaultDelimiters>false</useDefaultDelimiters>
    </configuration>
</plugin>
The useDefaultDelimiters property is important if you use standard Spring placeholders (such as ${placeholder}) in your configuration. If that property is not set to false, these may be expanded by the build.

2.1.2. Automatic Property Expansion Using Gradle

You can automatically expand properties from the Gradle project by configuring the Java plugin’s processResources task to do so, as shown in the following example:

processResources {
    expand(project.properties)
}

You can then refer to your Gradle project’s properties by using placeholders, as shown in the following example:

app.name=${name}
app.description=${description}
Gradle’s expand method uses Groovy’s SimpleTemplateEngine, which transforms ${..} tokens. The ${..} style conflicts with Spring’s own property placeholder mechanism. To use Spring property placeholders together with automatic expansion, escape the Spring property placeholders as follows: \${..}.

2.2. Externalize the Configuration of SpringApplication

A SpringApplication has bean properties (mainly setters), so you can use its Java API as you create the application to modify its behavior. Alternatively, you can externalize the configuration by setting properties in spring.main.*. For example, in application.properties, you might have the following settings:

spring.main.web-application-type=none
spring.main.banner-mode=off

Then the Spring Boot banner is not printed on startup, and the application is not starting an embedded web server.

Properties defined in external configuration override the values specified with the Java API, with the notable exception of the sources used to create the ApplicationContext. Consider the following application:

new SpringApplicationBuilder()
    .bannerMode(Banner.Mode.OFF)
    .sources(demo.MyApp.class)
    .run(args);

Now consider the following configuration:

spring.main.sources=com.acme.Config,com.acme.ExtraConfig
spring.main.banner-mode=console

The actual application now shows the banner (as overridden by configuration) and uses three sources for the ApplicationContext (in the following order): demo.MyApp, com.acme.Config, and com.acme.ExtraConfig.

2.3. Change the Location of External Properties of an Application

By default, properties from different sources are added to the Spring Environment in a defined order (see “spring-boot-features.html” in the ‘Spring Boot features’ section for the exact order).

A nice way to augment and modify this ordering is to add @PropertySource annotations to your application sources. Classes passed to the SpringApplication static convenience methods and those added using setSources() are inspected to see if they have @PropertySources. If they do, those properties are added to the Environment early enough to be used in all phases of the ApplicationContext lifecycle. Properties added in this way have lower priority than any added by using the default locations (such as application.properties), system properties, environment variables, or the command line.

You can also provide the following System properties (or environment variables) to change the behavior:

  • spring.config.name (SPRING_CONFIG_NAME): Defaults to application as the root of the file name.

  • spring.config.location (SPRING_CONFIG_LOCATION): The file to load (such as a classpath resource or a URL). A separate Environment property source is set up for this document and it can be overridden by system properties, environment variables, or the command line.

No matter what you set in the environment, Spring Boot always loads application.properties as described above. By default, if YAML is used, then files with the ‘.yml’ extension are also added to the list.

Spring Boot logs the configuration files that are loaded at the DEBUG level and the candidates it has not found at TRACE level.

See ConfigFileApplicationListener for more detail.

2.4. Use ‘Short’ Command Line Arguments

Some people like to use (for example) --port=9000 instead of --server.port=9000 to set configuration properties on the command line. You can enable this behavior by using placeholders in application.properties, as shown in the following example:

server.port=${port:8080}
If you inherit from the spring-boot-starter-parent POM, the default filter token of the maven-resources-plugins has been changed from ${*} to @ (that is, @[email protected] instead of ${maven.token}) to prevent conflicts with Spring-style placeholders. If you have enabled Maven filtering for the application.properties directly, you may want to also change the default filter token to use other delimiters.
In this specific case, the port binding works in a PaaS environment such as Heroku or Cloud Foundry. In those two platforms, the PORT environment variable is set automatically and Spring can bind to capitalized synonyms for Environment properties.

2.5. Use YAML for External Properties

YAML is a superset of JSON and, as such, is a convenient syntax for storing external properties in a hierarchical format, as shown in the following example:

spring:
    application:
        name: cruncher
    datasource:
        driverClassName: com.mysql.jdbc.Driver
        url: jdbc:mysql://localhost/test
server:
    port: 9000

Create a file called application.yml and put it in the root of your classpath. Then add snakeyaml to your dependencies (Maven coordinates org.yaml:snakeyaml, already included if you use the spring-boot-starter). A YAML file is parsed to a Java Map<String,Object> (like a JSON object), and Spring Boot flattens the map so that it is one level deep and has period-separated keys, as many people are used to with Properties files in Java.

The preceding example YAML corresponds to the following application.properties file:

spring.application.name=cruncher
spring.datasource.driverClassName=com.mysql.jdbc.Driver
spring.datasource.url=jdbc:mysql://localhost/test
server.port=9000

See “spring-boot-features.html” in the ‘Spring Boot features’ section for more information about YAML.

2.6. Set the Active Spring Profiles

The Spring Environment has an API for this, but you would normally set a System property (spring.profiles.active) or an OS environment variable (SPRING_PROFILES_ACTIVE). Also, you can launch your application with a -D argument (remember to put it before the main class or jar archive), as follows:

$ java -jar -Dspring.profiles.active=production demo-0.0.1-SNAPSHOT.jar

In Spring Boot, you can also set the active profile in application.properties, as shown in the following example:

spring.profiles.active=production

A value set this way is replaced by the System property or environment variable setting but not by the SpringApplicationBuilder.profiles() method. Thus, the latter Java API can be used to augment the profiles without changing the defaults.

See “spring-boot-features.html” in the “Spring Boot features” section for more information.

2.7. Change Configuration Depending on the Environment

A YAML file is actually a sequence of documents separated by --- lines, and each document is parsed separately to a flattened map.

If a YAML document contains a spring.profiles key, then the profiles value (a comma-separated list of profiles) is fed into the Spring Environment.acceptsProfiles() method. If any of those profiles is active, that document is included in the final merge (otherwise, it is not), as shown in the following example:

server:
    port: 9000
---

spring:
    profiles: development
server:
    port: 9001

---

spring:
    profiles: production
server:
    port: 0

In the preceding example, the default port is 9000. However, if the Spring profile called ‘development’ is active, then the port is 9001. If ‘production’ is active, then the port is 0.

The YAML documents are merged in the order in which they are encountered. Later values override earlier values.

To do the same thing with properties files, you can use application-${profile}.properties to specify profile-specific values.

2.8. Discover Built-in Options for External Properties

Spring Boot binds external properties from application.properties (or .yml files and other places) into an application at runtime. There is not (and technically cannot be) an exhaustive list of all supported properties in a single location, because contributions can come from additional jar files on your classpath.

A running application with the Actuator features has a configprops endpoint that shows all the bound and bindable properties available through @ConfigurationProperties.

The appendix includes an application.properties example with a list of the most common properties supported by Spring Boot. The definitive list comes from searching the source code for @ConfigurationProperties and @Value annotations as well as the occasional use of Binder. For more about the exact ordering of loading properties, see "spring-boot-features.html".

3. Embedded Web Servers

Each Spring Boot web application includes an embedded web server. This feature leads to a number of how-to questions, including how to change the embedded server and how to configure the embedded server. This section answers those questions.

3.1. Use Another Web Server

Many Spring Boot starters include default embedded containers.

  • For servlet stack applications, the spring-boot-starter-web includes Tomcat by including spring-boot-starter-tomcat, but you can use spring-boot-starter-jetty or spring-boot-starter-undertow instead.

  • For reactive stack applications, the spring-boot-starter-webflux includes Reactor Netty by including spring-boot-starter-reactor-netty, but you can use spring-boot-starter-tomcat, spring-boot-starter-jetty, or spring-boot-starter-undertow instead.

When switching to a different HTTP server, you need to exclude the default dependencies in addition to including the one you need. Spring Boot provides separate starters for HTTP servers to help make this process as easy as possible.

The following Maven example shows how to exclude Tomcat and include Jetty for Spring MVC:

<properties>
    <servlet-api.version>3.1.0</servlet-api.version>
</properties>
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
    <exclusions>
        <!-- Exclude the Tomcat dependency -->
        <exclusion>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-tomcat</artifactId>
        </exclusion>
    </exclusions>
</dependency>
<!-- Use Jetty instead -->
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-jetty</artifactId>
</dependency>
The version of the Servlet API has been overridden as, unlike Tomcat 9 and Undertow 2.0, Jetty 9.4 does not support Servlet 4.0.

The following Gradle example shows how to exclude Netty and include Undertow for Spring WebFlux:

configurations {
    // exclude Reactor Netty
    compile.exclude module: 'spring-boot-starter-reactor-netty'
}

dependencies {
    compile 'org.springframework.boot:spring-boot-starter-webflux'
    // Use Undertow instead
    compile 'org.springframework.boot:spring-boot-starter-undertow'
    // ...
}
spring-boot-starter-reactor-netty is required to use the WebClient class, so you may need to keep a dependency on Netty even when you need to include a different HTTP server.

3.2. Disabling the Web Server

If your classpath contains the necessary bits to start a web server, Spring Boot will automatically start it. To disable this behaviour configure the WebApplicationType in your application.properties, as shown in the following example:

spring.main.web-application-type=none

3.3. Change the HTTP Port

In a standalone application, the main HTTP port defaults to 8080 but can be set with server.port (for example, in application.properties or as a System property). Thanks to relaxed binding of Environment values, you can also use SERVER_PORT (for example, as an OS environment variable).

To switch off the HTTP endpoints completely but still create a WebApplicationContext, use server.port=-1. (Doing so is sometimes useful for testing.)

For more details, see “spring-boot-features.html” in the ‘Spring Boot features’ section, or the ServerProperties source code.

3.4. Use a Random Unassigned HTTP Port

To scan for a free port (using OS natives to prevent clashes) use server.port=0.

3.5. Discover the HTTP Port at Runtime

You can access the port the server is running on from log output or from the ServletWebServerApplicationContext through its WebServer. The best way to get that and be sure that it has been initialized is to add a @Bean of type ApplicationListener<ServletWebServerInitializedEvent> and pull the container out of the event when it is published.

Tests that use @SpringBootTest(webEnvironment=WebEnvironment.RANDOM_PORT) can also inject the actual port into a field by using the @LocalServerPort annotation, as shown in the following example:

@RunWith(SpringJUnit4ClassRunner.class)
@SpringBootTest(webEnvironment=WebEnvironment.RANDOM_PORT)
public class MyWebIntegrationTests {

    @Autowired
    ServletWebServerApplicationContext server;

    @LocalServerPort
    int port;

    // ...

}

@LocalServerPort is a meta-annotation for @Value("${local.server.port}"). Do not try to inject the port in a regular application. As we just saw, the value is set only after the container has been initialized. Contrary to a test, application code callbacks are processed early (before the value is actually available).

3.6. Enable HTTP Response Compression

HTTP response compression is supported by Jetty, Tomcat, and Undertow. It can be enabled in application.properties, as follows:

server.compression.enabled=true

By default, responses must be at least 2048 bytes in length for compression to be performed. You can configure this behavior by setting the server.compression.min-response-size property.

By default, responses are compressed only if their content type is one of the following:

  • text/html

  • text/xml

  • text/plain

  • text/css

  • text/javascript

  • application/javascript

  • application/json

  • application/xml

You can configure this behavior by setting the server.compression.mime-types property.

3.7. Configure SSL

SSL can be configured declaratively by setting the various server.ssl.* properties, typically in application.properties or application.yml. The following example shows setting SSL properties in application.properties:

server.port=8443
server.ssl.key-store=classpath:keystore.jks
server.ssl.key-store-password=secret
server.ssl.key-password=another-secret

See Ssl for details of all of the supported properties.

Using configuration such as the preceding example means the application no longer supports a plain HTTP connector at port 8080. Spring Boot does not support the configuration of both an HTTP connector and an HTTPS connector through application.properties. If you want to have both, you need to configure one of them programmatically. We recommend using application.properties to configure HTTPS, as the HTTP connector is the easier of the two to configure programmatically. See the spring-boot-sample-tomcat-multi-connectors sample project for an example.

3.8. Configure HTTP/2

You can enable HTTP/2 support in your Spring Boot application with the server.http2.enabled configuration property. This support depends on the chosen web server and the application environment, since that protocol is not supported out-of-the-box by JDK8.

Spring Boot does not support h2c, the cleartext version of the HTTP/2 protocol. So you must configure SSL first.

3.8.1. HTTP/2 with Undertow

As of Undertow 1.4.0+, HTTP/2 is supported without any additional requirement on JDK8.

3.8.2. HTTP/2 with Jetty

As of Jetty 9.4.8, HTTP/2 is also supported with the Conscrypt library. To enable that support, your application needs to have two additional dependencies: org.eclipse.jetty:jetty-alpn-conscrypt-server and org.eclipse.jetty.http2:http2-server.

3.8.3. HTTP/2 with Tomcat

Spring Boot ships by default with Tomcat 9.0.x which supports HTTP/2 out of the box when using JDK 9 or later. Alternatively, HTTP/2 can be used on JDK 8 if the libtcnative library and its dependencies are installed on the host operating system.

The library folder must be made available, if not already, to the JVM library path. You can do so with a JVM argument such as -Djava.library.path=/usr/local/opt/tomcat-native/lib. More on this in the official Tomcat documentation.

Starting Tomcat 9.0.x on JDK 8 without that native support logs the following error:

ERROR 8787 --- [           main] o.a.coyote.http11.Http11NioProtocol      : The upgrade handler [org.apache.coyote.http2.Http2Protocol] for [h2] only supports upgrade via ALPN but has been configured for the ["https-jsse-nio-8443"] connector that does not support ALPN.

This error is not fatal, and the application still starts with HTTP/1.1 SSL support.

3.8.4. HTTP/2 with Reactor Netty

The spring-boot-webflux-starter is using by default Reactor Netty as a server. Reactor Netty can be configured for HTTP/2 using the JDK support with JDK 9 or later. For JDK 8 environments, or for optimal runtime performance, this server also supports HTTP/2 with native libraries. To enable that, your application needs to have an additional dependency.

Spring Boot manages the version for the io.netty:netty-tcnative-boringssl-static "uber jar", containing native libraries for all platforms. Developers can choose to import only the required dependencies using a classifier (see the Netty official documentation).

3.9. Configure the Web Server

Generally, you should first consider using one of the many available configuration keys and customize your web server by adding new entries in your application.properties (or application.yml, or environment, etc. see “Discover Built-in Options for External Properties”). The server.* namespace is quite useful here, and it includes namespaces like server.tomcat.*, server.jetty.* and others, for server-specific features. See the list of [common-application-properties].

The previous sections covered already many common use cases, such as compression, SSL or HTTP/2. However, if a configuration key doesn’t exist for your use case, you should then look at WebServerFactoryCustomizer. You can declare such a component and get access to the server factory relevant to your choice: you should select the variant for the chosen Server (Tomcat, Jetty, Reactor Netty, Undertow) and the chosen web stack (Servlet or Reactive).

The example below is for Tomcat with the spring-boot-starter-web (Servlet stack):

@Component
public class MyTomcatWebServerCustomizer
        implements WebServerFactoryCustomizer<TomcatServletWebServerFactory> {

    @Override
    public void customize(TomcatServletWebServerFactory factory) {
        // customize the factory here
    }
}

In addition Spring Boot provides:

Server Servlet stack Reactive stack

Tomcat

TomcatServletWebServerFactory

TomcatReactiveWebServerFactory

Jetty

JettyServletWebServerFactory

JettyReactiveWebServerFactory

Undertow

UndertowServletWebServerFactory

UndertowReactiveWebServerFactory

Reactor

N/A

NettyReactiveWebServerFactory

Once you’ve got access to a WebServerFactory, you can often add customizers to it to configure specific parts, like connectors, server resources, or the server itself - all using server-specific APIs.

As a last resort, you can also declare your own WebServerFactory component, which will override the one provided by Spring Boot. In this case, you can’t rely on configuration properties in the server namespace anymore.

3.10. Add a Servlet, Filter, or Listener to an Application

In a servlet stack application, i.e. with the spring-boot-starter-web, there are two ways to add Servlet, Filter, ServletContextListener, and the other listeners supported by the Servlet API to your application:

3.10.1. Add a Servlet, Filter, or Listener by Using a Spring Bean

To add a Servlet, Filter, or Servlet *Listener by using a Spring bean, you must provide a @Bean definition for it. Doing so can be very useful when you want to inject configuration or dependencies. However, you must be very careful that they do not cause eager initialization of too many other beans, because they have to be installed in the container very early in the application lifecycle. (For example, it is not a good idea to have them depend on your DataSource or JPA configuration.) You can work around such restrictions by initializing the beans lazily when first used instead of on initialization.

In the case of Filters and Servlets, you can also add mappings and init parameters by adding a FilterRegistrationBean or a ServletRegistrationBean instead of or in addition to the underlying component.

If no dispatcherType is specified on a filter registration, REQUEST is used. This aligns with the Servlet Specification’s default dispatcher type.

Like any other Spring bean, you can define the order of Servlet filter beans; please make sure to check the “spring-boot-features.html” section.

Disable Registration of a Servlet or Filter

As described earlier, any Servlet or Filter beans are registered with the servlet container automatically. To disable registration of a particular Filter or Servlet bean, create a registration bean for it and mark it as disabled, as shown in the following example:

@Bean
public FilterRegistrationBean registration(MyFilter filter) {
    FilterRegistrationBean registration = new FilterRegistrationBean(filter);
    registration.setEnabled(false);
    return registration;
}

3.10.2. Add Servlets, Filters, and Listeners by Using Classpath Scanning

@WebServlet, @WebFilter, and @WebListener annotated classes can be automatically registered with an embedded servlet container by annotating a @Configuration class with @ServletComponentScan and specifying the package(s) containing the components that you want to register. By default, @ServletComponentScan scans from the package of the annotated class.

3.11. Configure Access Logging

Access logs can be configured for Tomcat, Undertow, and Jetty through their respective namespaces.

For instance, the following settings log access on Tomcat with a custom pattern.

server.tomcat.basedir=my-tomcat
server.tomcat.accesslog.enabled=true
server.tomcat.accesslog.pattern=%t %a "%r" %s (%D ms)
The default location for logs is a logs directory relative to the Tomcat base directory. By default, the logs directory is a temporary directory, so you may want to fix Tomcat’s base directory or use an absolute path for the logs. In the preceding example, the logs are available in my-tomcat/logs relative to the working directory of the application.

Access logging for Undertow can be configured in a similar fashion, as shown in the following example:

server.undertow.accesslog.enabled=true
server.undertow.accesslog.pattern=%t %a "%r" %s (%D ms)

Logs are stored in a logs directory relative to the working directory of the application. You can customize this location by setting the server.undertow.accesslog.directory property.

Finally, access logging for Jetty can also be configured as follows:

server.jetty.accesslog.enabled=true
server.jetty.accesslog.filename=/var/log/jetty-access.log

By default, logs are redirected to System.err. For more details, see the Jetty documentation.

3.12. Running Behind a Front-end Proxy Server

Your application might need to send 302 redirects or render content with absolute links back to itself. When running behind a proxy, the caller wants a link to the proxy and not to the physical address of the machine hosting your app. Typically, such situations are handled through a contract with the proxy, which adds headers to tell the back end how to construct links to itself.

If the proxy adds conventional X-Forwarded-For and X-Forwarded-Proto headers (most proxy servers do so), the absolute links should be rendered correctly, provided server.use-forward-headers is set to true in your application.properties.

If your application runs in Cloud Foundry or Heroku, the server.use-forward-headers property defaults to true. In all other instances, it defaults to false.

3.12.1. Customize Tomcat’s Proxy Configuration

If you use Tomcat, you can additionally configure the names of the headers used to carry “forwarded” information, as shown in the following example:

server.tomcat.remote-ip-header=x-your-remote-ip-header
server.tomcat.protocol-header=x-your-protocol-header

Tomcat is also configured with a default regular expression that matches internal proxies that are to be trusted. By default, IP addresses in 10/8, 192.168/16, 169.254/16 and 127/8 are trusted. You can customize the valve’s configuration by adding an entry to application.properties, as shown in the following example:

server.tomcat.internal-proxies=192\\.168\\.\\d{1,3}\\.\\d{1,3}
The double backslashes are required only when you use a properties file for configuration. If you use YAML, single backslashes are sufficient, and a value equivalent to that shown in the preceding example would be 192\.168\.\d{1,3}\.\d{1,3}.
You can trust all proxies by setting the internal-proxies to empty (but do not do so in production).

You can take complete control of the configuration of Tomcat’s RemoteIpValve by switching the automatic one off (to do so, set server.use-forward-headers=false) and adding a new valve instance in a TomcatServletWebServerFactory bean.

3.13. Enable Multiple Connectors with Tomcat

You can add an org.apache.catalina.connector.Connector to the TomcatServletWebServerFactory, which can allow multiple connectors, including HTTP and HTTPS connectors, as shown in the following example:

@Bean
public ServletWebServerFactory servletContainer() {
    TomcatServletWebServerFactory tomcat = new TomcatServletWebServerFactory();
    tomcat.addAdditionalTomcatConnectors(createSslConnector());
    return tomcat;
}

private Connector createSslConnector() {
    Connector connector = new Connector("org.apache.coyote.http11.Http11NioProtocol");
    Http11NioProtocol protocol = (Http11NioProtocol) connector.getProtocolHandler();
    try {
        File keystore = new ClassPathResource("keystore").getFile();
        File truststore = new ClassPathResource("keystore").getFile();
        connector.setScheme("https");
        connector.setSecure(true);
        connector.setPort(8443);
        protocol.setSSLEnabled(true);
        protocol.setKeystoreFile(keystore.getAbsolutePath());
        protocol.setKeystorePass("changeit");
        protocol.setTruststoreFile(truststore.getAbsolutePath());
        protocol.setTruststorePass("changeit");
        protocol.setKeyAlias("apitester");
        return connector;
    }
    catch (IOException ex) {
        throw new IllegalStateException("can't access keystore: [" + "keystore"
                + "] or truststore: [" + "keystore" + "]", ex);
    }
}

3.14. Use Tomcat’s LegacyCookieProcessor

By default, the embedded Tomcat used by Spring Boot does not support "Version 0" of the Cookie format, so you may see the following error:

java.lang.IllegalArgumentException: An invalid character [32] was present in the Cookie value

If at all possible, you should consider updating your code to only store values compliant with later Cookie specifications. If, however, you cannot change the way that cookies are written, you can instead configure Tomcat to use a LegacyCookieProcessor. To switch to the LegacyCookieProcessor, use an WebServerFactoryCustomizer bean that adds a TomcatContextCustomizer, as shown in the following example:

@Bean
public WebServerFactoryCustomizer<TomcatServletWebServerFactory> cookieProcessorCustomizer() {
    return (factory) -> factory.addContextCustomizers(
            (context) -> context.setCookieProcessor(new LegacyCookieProcessor()));
}

3.15. Enable Multiple Listeners with Undertow

Add an UndertowBuilderCustomizer to the UndertowServletWebServerFactory and add a listener to the Builder, as shown in the following example:

@Bean
public UndertowServletWebServerFactory servletWebServerFactory() {
    UndertowServletWebServerFactory factory = new UndertowServletWebServerFactory();
    factory.addBuilderCustomizers(new UndertowBuilderCustomizer() {

        @Override
        public void customize(Builder builder) {
            builder.addHttpListener(8080, "0.0.0.0");
        }

    });
    return factory;
}

3.16. Create WebSocket Endpoints Using @ServerEndpoint

If you want to use @ServerEndpoint in a Spring Boot application that used an embedded container, you must declare a single ServerEndpointExporter @Bean, as shown in the following example:

@Bean
public ServerEndpointExporter serverEndpointExporter() {
    return new ServerEndpointExporter();
}

The bean shown in the preceding example registers any @ServerEndpoint annotated beans with the underlying WebSocket container. When deployed to a standalone servlet container, this role is performed by a servlet container initializer, and the ServerEndpointExporter bean is not required.

4. Spring MVC

Spring Boot has a number of starters that include Spring MVC. Note that some starters include a dependency on Spring MVC rather than include it directly. This section answers common questions about Spring MVC and Spring Boot.

4.1. Write a JSON REST Service

Any Spring @RestController in a Spring Boot application should render JSON response by default as long as Jackson2 is on the classpath, as shown in the following example:

@RestController
public class MyController {

    @RequestMapping("/thing")
    public MyThing thing() {
            return new MyThing();
    }

}

As long as MyThing can be serialized by Jackson2 (true for a normal POJO or Groovy object), then localhost:8080/thing serves a JSON representation of it by default. Note that, in a browser, you might sometimes see XML responses, because browsers tend to send accept headers that prefer XML.

4.2. Write an XML REST Service

If you have the Jackson XML extension (jackson-dataformat-xml) on the classpath, you can use it to render XML responses. The previous example that we used for JSON would work. To use the Jackson XML renderer, add the following dependency to your project:

<dependency>
    <groupId>com.fasterxml.jackson.dataformat</groupId>
    <artifactId>jackson-dataformat-xml</artifactId>
</dependency>

If Jackson’s XML extension is not available, JAXB (provided by default in the JDK) is used, with the additional requirement of having MyThing annotated as @XmlRootElement, as shown in the following example:

@XmlRootElement
public class MyThing {
    private String name;
    // .. getters and setters
}

To get the server to render XML instead of JSON, you might have to send an Accept: text/xml header (or use a browser).

4.3. Customize the Jackson ObjectMapper

Spring MVC (client and server side) uses HttpMessageConverters to negotiate content conversion in an HTTP exchange. If Jackson is on the classpath, you already get the default converter(s) provided by Jackson2ObjectMapperBuilder, an instance of which is auto-configured for you.

The ObjectMapper (or XmlMapper for Jackson XML converter) instance (created by default) has the following customized properties:

  • MapperFeature.DEFAULT_VIEW_INCLUSION is disabled

  • DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES is disabled

  • SerializationFeature.WRITE_DATES_AS_TIMESTAMPS is disabled

Spring Boot also has some features to make it easier to customize this behavior.

You can configure the ObjectMapper and XmlMapper instances by using the environment. Jackson provides an extensive suite of simple on/off features that can be used to configure various aspects of its processing. These features are described in six enums (in Jackson) that map onto properties in the environment:

Enum Property Values

com.fasterxml.jackson.databind.DeserializationFeature

spring.jackson.deserialization.<feature_name>

true, false

com.fasterxml.jackson.core.JsonGenerator.Feature

spring.jackson.generator.<feature_name>

true, false

com.fasterxml.jackson.databind.MapperFeature

spring.jackson.mapper.<feature_name>

true, false

com.fasterxml.jackson.core.JsonParser.Feature

spring.jackson.parser.<feature_name>

true, false

com.fasterxml.jackson.databind.SerializationFeature

spring.jackson.serialization.<feature_name>

true, false

com.fasterxml.jackson.annotation.JsonInclude.Include

spring.jackson.default-property-inclusion

always, non_null, non_absent, non_default, non_empty

For example, to enable pretty print, set spring.jackson.serialization.indent_output=true. Note that, thanks to the use of relaxed binding, the case of indent_output does not have to match the case of the corresponding enum constant, which is INDENT_OUTPUT.

This environment-based configuration is applied to the auto-configured Jackson2ObjectMapperBuilder bean and applies to any mappers created by using the builder, including the auto-configured ObjectMapper bean.

The context’s Jackson2ObjectMapperBuilder can be customized by one or more Jackson2ObjectMapperBuilderCustomizer beans. Such customizer beans can be ordered (Boot’s own customizer has an order of 0), letting additional customization be applied both before and after Boot’s customization.

Any beans of type com.fasterxml.jackson.databind.Module are automatically registered with the auto-configured Jackson2ObjectMapperBuilder and are applied to any ObjectMapper instances that it creates. This provides a global mechanism for contributing custom modules when you add new features to your application.

If you want to replace the default ObjectMapper completely, either define a @Bean of that type and mark it as @Primary or, if you prefer the builder-based approach, define a Jackson2ObjectMapperBuilder @Bean. Note that, in either case, doing so disables all auto-configuration of the ObjectMapper.

If you provide any @Beans of type MappingJackson2HttpMessageConverter, they replace the default value in the MVC configuration. Also, a convenience bean of type HttpMessageConverters is provided (and is always available if you use the default MVC configuration). It has some useful methods to access the default and user-enhanced message converters.

See the “Customize the @ResponseBody Rendering” section and the WebMvcAutoConfiguration source code for more details.

4.4. Customize the @ResponseBody Rendering

Spring uses HttpMessageConverters to render @ResponseBody (or responses from @RestController). You can contribute additional converters by adding beans of the appropriate type in a Spring Boot context. If a bean you add is of a type that would have been included by default anyway (such as MappingJackson2HttpMessageConverter for JSON conversions), it replaces the default value. A convenience bean of type HttpMessageConverters is provided and is always available if you use the default MVC configuration. It has some useful methods to access the default and user-enhanced message converters (For example, it can be useful if you want to manually inject them into a custom RestTemplate).

As in normal MVC usage, any WebMvcConfigurer beans that you provide can also contribute converters by overriding the configureMessageConverters method. However, unlike with normal MVC, you can supply only additional converters that you need (because Spring Boot uses the same mechanism to contribute its defaults). Finally, if you opt out of the Spring Boot default MVC configuration by providing your own @EnableWebMvc configuration, you can take control completely and do everything manually by using getMessageConverters from WebMvcConfigurationSupport.

See the WebMvcAutoConfiguration source code for more details.

4.5. Handling Multipart File Uploads

Spring Boot embraces the Servlet 3 javax.servlet.http.Part API to support uploading files. By default, Spring Boot configures Spring MVC with a maximum size of 1MB per file and a maximum of 10MB of file data in a single request. You may override these values, the location to which intermediate data is stored (for example, to the /tmp directory), and the threshold past which data is flushed to disk by using the properties exposed in the MultipartProperties class. For example, if you want to specify that files be unlimited, set the spring.servlet.multipart.max-file-size property to -1.

The multipart support is helpful when you want to receive multipart encoded file data as a @RequestParam-annotated parameter of type MultipartFile in a Spring MVC controller handler method.

See the MultipartAutoConfiguration source for more details.

It is recommended to use the container’s built-in support for multipart uploads rather than introducing an additional dependency such as Apache Commons File Upload.

4.6. Switch Off the Spring MVC DispatcherServlet

By default, all content is served from the root of your application (/). If you would rather map to a different path, you can configure one as follows:

spring.mvc.servlet.path=/acme

If you have additional servlets you can declare a @Bean of type Servlet or ServletRegistrationBean for each and Spring Boot will register them transparently to the container. Because servlets are registered that way, they can be mapped to a sub-context of the DispatcherServlet without invoking it.

Configuring the DispatcherServlet yourself is unusual but if you really need to do it, a @Bean of type DispatcherServletPath must be provided as well to provide the path of your custom DispatcherServlet.

4.7. Switch off the Default MVC Configuration

The easiest way to take complete control over MVC configuration is to provide your own @Configuration with the @EnableWebMvc annotation. Doing so leaves all MVC configuration in your hands.

4.8. Customize ViewResolvers

A ViewResolver is a core component of Spring MVC, translating view names in @Controller to actual View implementations. Note that ViewResolvers are mainly used in UI applications, rather than REST-style services (a View is not used to render a @ResponseBody). There are many implementations of ViewResolver to choose from, and Spring on its own is not opinionated about which ones you should use. Spring Boot, on the other hand, installs one or two for you, depending on what it finds on the classpath and in the application context. The DispatcherServlet uses all the resolvers it finds in the application context, trying each one in turn until it gets a result, so, if you add your own, you have to be aware of the order and in which position your resolver is added.

WebMvcAutoConfiguration adds the following ViewResolvers to your context:

  • An InternalResourceViewResolver named ‘defaultViewResolver’. This one locates physical resources that can be rendered by using the DefaultServlet (including static resources and JSP pages, if you use those). It applies a prefix and a suffix to the view name and then looks for a physical resource with that path in the servlet context (the defaults are both empty but are accessible for external configuration through spring.mvc.view.prefix and spring.mvc.view.suffix). You can override it by providing a bean of the same type.

  • A BeanNameViewResolver named ‘beanNameViewResolver’. This is a useful member of the view resolver chain and picks up any beans with the same name as the View being resolved. It should not be necessary to override or replace it.

  • A ContentNegotiatingViewResolver named ‘viewResolver’ is added only if there are actually beans of type View present. This is a ‘master’ resolver, delegating to all the others and attempting to find a match to the ‘Accept’ HTTP header sent by the client. There is a useful blog about ContentNegotiatingViewResolver that you might like to study to learn more, and you might also look at the source code for detail. You can switch off the auto-configured ContentNegotiatingViewResolver by defining a bean named ‘viewResolver’.

  • If you use Thymeleaf, you also have a ThymeleafViewResolver named ‘thymeleafViewResolver’. It looks for resources by surrounding the view name with a prefix and suffix. The prefix is spring.thymeleaf.prefix, and the suffix is spring.thymeleaf.suffix. The values of the prefix and suffix default to ‘classpath:/templates/’ and ‘.html’, respectively. You can override ThymeleafViewResolver by providing a bean of the same name.

  • If you use FreeMarker, you also have a FreeMarkerViewResolver named ‘freeMarkerViewResolver’. It looks for resources in a loader path (which is externalized to spring.freemarker.templateLoaderPath and has a default value of ‘classpath:/templates/’) by surrounding the view name with a prefix and a suffix. The prefix is externalized to spring.freemarker.prefix, and the suffix is externalized to spring.freemarker.suffix. The default values of the prefix and suffix are empty and ‘.ftl’, respectively. You can override FreeMarkerViewResolver by providing a bean of the same name.

  • If you use Groovy templates (actually, if groovy-templates is on your classpath), you also have a GroovyMarkupViewResolver named ‘groovyMarkupViewResolver’. It looks for resources in a loader path by surrounding the view name with a prefix and suffix (externalized to spring.groovy.template.prefix and spring.groovy.template.suffix). The prefix and suffix have default values of ‘classpath:/templates/’ and ‘.tpl’, respectively. You can override GroovyMarkupViewResolver by providing a bean of the same name.

For more detail, see the following sections:

5. Testing With Spring Security

Spring Security provides support for running tests as a specific user. For example, the test in the snippet below will run with an authenticated user that has the ADMIN role.

@Test
@WithMockUser(roles="ADMIN")
public void requestProtectedUrlWithUser() throws Exception {
    mvc
        .perform(get("/"))
        ...
}

Spring Security provides comprehensive integration with Spring MVC Test and this can also be used when testing controllers using the @WebMvcTest slice and MockMvc.

For additional details on Spring Security’s testing support, refer to Spring Security’s reference documentation).

6. Jersey

6.1. Secure Jersey endpoints with Spring Security

Spring Security can be used to secure a Jersey-based web application in much the same way as it can be used to secure a Spring MVC-based web application. However, if you want to use Spring Security’s method-level security with Jersey, you must configure Jersey to use setStatus(int) rather sendError(int). This prevents Jersey from committing the response before Spring Security has had an opportunity to report an authentication or authorization failure to the client.

The jersey.config.server.response.setStatusOverSendError property must be set to true on the application’s ResourceConfig bean, as shown in the following example:

@Component
public class JerseyConfig extends ResourceConfig {

    public JerseyConfig() {
        register(Endpoint.class);
        setProperties(Collections.singletonMap(
                "jersey.config.server.response.setStatusOverSendError", true));
    }

}

7. HTTP Clients

Spring Boot offers a number of starters that work with HTTP clients. This section answers questions related to using them.

7.1. Configure RestTemplate to Use a Proxy

As described in spring-boot-features.html, you can use a RestTemplateCustomizer with RestTemplateBuilder to build a customized RestTemplate. This is the recommended approach for creating a RestTemplate configured to use a proxy.

The exact details of the proxy configuration depend on the underlying client request factory that is being used. The following example configures HttpComponentsClientRequestFactory with an HttpClient that uses 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));
    }

}

8. Logging

Spring Boot has no mandatory logging dependency, except for the Commons Logging API, which is typically provided by Spring Framework’s spring-jcl module. To use Logback, you need to include it and spring-jcl on the classpath. The simplest way to do that is through the starters, which all depend on spring-boot-starter-logging. For a web application, you need only spring-boot-starter-web, since it depends transitively on the logging starter. If you use Maven, the following dependency adds logging for you:

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

Spring Boot has a LoggingSystem abstraction that attempts to configure logging based on the content of the classpath. If Logback is available, it is the first choice.

If the only change you need to make to logging is to set the levels of various loggers, you can do so in application.properties by using the "logging.level" prefix, as shown in the following example:

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

You can also set the location of a file to which to write the log (in addition to the console) by using "logging.file.name".

To configure the more fine-grained settings of a logging system, you need to use the native configuration format supported by the LoggingSystem in question. By default, Spring Boot picks up the native configuration from its default location for the system (such as classpath:logback.xml for Logback), but you can set the location of the config file by using the "logging.config" property.

8.1. Configure Logback for Logging

If you put a logback.xml in the root of your classpath, it is picked up from there (or from logback-spring.xml, to take advantage of the templating features provided by Boot). Spring Boot provides a default base configuration that you can include if you want to set levels, as shown in the following example:

<?xml version="1.0" encoding="UTF-8"?>
<configuration>
    <include resource="org/springframework/boot/logging/logback/base.xml"/>
    <logger name="org.springframework.web" level="DEBUG"/>
</configuration>

If you look at base.xml in the spring-boot jar, you can see that it uses some useful System properties that the LoggingSystem takes care of creating for you:

  • ${PID}: The current process ID.

  • ${LOG_FILE}: Whether logging.file.name was set in Boot’s external configuration.

  • ${LOG_PATH}: Whether logging.file.path (representing a directory for log files to live in) was set in Boot’s external configuration.

  • ${LOG_EXCEPTION_CONVERSION_WORD}: Whether logging.exception-conversion-word was set in Boot’s external configuration.

Spring Boot also provides some nice ANSI color terminal output on a console (but not in a log file) by using a custom Logback converter. See the default base.xml configuration for details.

If Groovy is on the classpath, you should be able to configure Logback with logback.groovy as well. If present, this setting is given preference.

8.1.1. Configure Logback for File-only Output

If you want to disable console logging and write output only to a file, you need a custom logback-spring.xml that imports file-appender.xml but not console-appender.xml, as shown in the following example:

<?xml version="1.0" encoding="UTF-8"?>
<configuration>
    <include resource="org/springframework/boot/logging/logback/defaults.xml" />
    <property name="LOG_FILE" value="${LOG_FILE:-${LOG_PATH:-${LOG_TEMP:-${java.io.tmpdir:-/tmp}}/}spring.log}"/>
    <include resource="org/springframework/boot/logging/logback/file-appender.xml" />
    <root level="INFO">
        <appender-ref ref="FILE" />
    </root>
</configuration>

You also need to add logging.file.name to your application.properties, as shown in the following example:

logging.file.name=myapplication.log

8.2. Configure Log4j for Logging

Spring Boot supports Log4j 2 for logging configuration if it is on the classpath. If you use the starters for assembling dependencies, you have to exclude Logback and then include log4j 2 instead. If you do not use the starters, you need to provide (at least) spring-jcl in addition to Log4j 2.

The simplest path is probably through the starters, even though it requires some jiggling with excludes. The following example shows how to set up the starters in Maven:

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter</artifactId>
    <exclusions>
        <exclusion>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-logging</artifactId>
        </exclusion>
    </exclusions>
</dependency>
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-log4j2</artifactId>
</dependency>

And the following example shows one way to set up the starters in Gradle:

dependencies {
    compile 'org.springframework.boot:spring-boot-starter-web'
    compile 'org.springframework.boot:spring-boot-starter-log4j2'
}

configurations {
    all {
        exclude group: 'org.springframework.boot', module: 'spring-boot-starter-logging'
    }
}
The Log4j starters gather together the dependencies for common logging requirements (such as having Tomcat use java.util.logging but configuring the output using Log4j 2). See the Actuator Log4j 2 samples for more detail and to see it in action.
To ensure that debug logging performed using java.util.logging is routed into Log4j 2, configure its JDK logging adapter by setting the java.util.logging.manager system property to org.apache.logging.log4j.jul.LogManager.

8.2.1. Use YAML or JSON to Configure Log4j 2

In addition to its default XML configuration format, Log4j 2 also supports YAML and JSON configuration files. To configure Log4j 2 to use an alternative configuration file format, add the appropriate dependencies to the classpath and name your configuration files to match your chosen file format, as shown in the following example:

Format Dependencies File names

YAML

com.fasterxml.jackson.core:jackson-databind
com.fasterxml.jackson.dataformat:jackson-dataformat-yaml

log4j2.yaml
log4j2.yml

JSON

com.fasterxml.jackson.core:jackson-databind

log4j2.json
log4j2.jsn

9. Data Access

Spring Boot includes a number of starters for working with data sources. This section answers questions related to doing so.

9.1. Configure a Custom DataSource

To configure your own DataSource, define a @Bean of that type in your configuration. Spring Boot reuses your DataSource anywhere one is required, including database initialization. If you need to externalize some settings, you can bind your DataSource to the environment (see “spring-boot-features.html”).

The following example shows how to define a data source in a bean:

@Bean
@ConfigurationProperties(prefix="app.datasource")
public DataSource dataSource() {
    return new FancyDataSource();
}

The following example shows how to define a data source by setting properties:

app.datasource.url=jdbc:h2:mem:mydb
app.datasource.username=sa
app.datasource.pool-size=30

Assuming that your FancyDataSource has regular JavaBean properties for the URL, the username, and the pool size, these settings are bound automatically before the DataSource is made available to other components. The regular database initialization also happens (so the relevant sub-set of spring.datasource.* can still be used with your custom configuration).

Spring Boot also provides a utility builder class, called DataSourceBuilder, that can be used to create one of the standard data sources (if it is on the classpath). The builder can detect the one to use based on what’s available on the classpath. It also auto-detects the driver based on the JDBC URL.

The following example shows how to create a data source by using a DataSourceBuilder:

@Bean
@ConfigurationProperties("app.datasource")
public DataSource dataSource() {
    return DataSourceBuilder.create().build();
}

To run an app with that DataSource, all you need is the connection information. Pool-specific settings can also be provided. Check the implementation that is going to be used at runtime for more details.

The following example shows how to define a JDBC data source by setting properties:

app.datasource.url=jdbc:mysql://localhost/test
app.datasource.username=dbuser
app.datasource.password=dbpass
app.datasource.pool-size=30

However, there is a catch. Because the actual type of the connection pool is not exposed, no keys are generated in the metadata for your custom DataSource and no completion is available in your IDE (because the DataSource interface exposes no properties). Also, if you happen to have Hikari on the classpath, this basic setup does not work, because Hikari has no url property (but does have a jdbcUrl property). In that case, you must rewrite your configuration as follows:

app.datasource.jdbc-url=jdbc:mysql://localhost/test
app.datasource.username=dbuser
app.datasource.password=dbpass
app.datasource.maximum-pool-size=30

You can fix that by forcing the connection pool to use and return a dedicated implementation rather than DataSource. You cannot change the implementation at runtime, but the list of options will be explicit.

The following example shows how create a HikariDataSource with DataSourceBuilder:

@Bean
@ConfigurationProperties("app.datasource")
public HikariDataSource dataSource() {
    return DataSourceBuilder.create().type(HikariDataSource.class).build();
}

You can even go further by leveraging what DataSourceProperties does for you — that is, by providing a default embedded database with a sensible username and password if no URL is provided. You can easily initialize a DataSourceBuilder from the state of any DataSourceProperties object, so you could also inject the DataSource that Spring Boot creates automatically. However, that would split your configuration into two namespaces: url, username, password, type, and driver on spring.datasource and the rest on your custom namespace (app.datasource). To avoid that, you can redefine a custom DataSourceProperties on your custom namespace, as shown in the following example:

@Bean
@Primary
@ConfigurationProperties("app.datasource")
public DataSourceProperties dataSourceProperties() {
    return new DataSourceProperties();
}

@Bean
@ConfigurationProperties("app.datasource.configuration")
public HikariDataSource dataSource(DataSourceProperties properties) {
    return properties.initializeDataSourceBuilder().type(HikariDataSource.class)
            .build();
}

This setup puts you in sync with what Spring Boot does for you by default, except that a dedicated connection pool is chosen (in code) and its settings are exposed in the app.datasource.configuration sub namespace. Because DataSourceProperties is taking care of the url/jdbcUrl translation for you, you can configure it as follows:

app.datasource.url=jdbc:mysql://localhost/test
app.datasource.username=dbuser
app.datasource.password=dbpass
app.datasource.configuration.maximum-pool-size=30
Spring Boot will expose Hikari-specific settings to spring.datasource.hikari. This example uses a more generic configuration sub namespace as the example does not support multiple datasource implementations.
Because your custom configuration chooses to go with Hikari, app.datasource.type has no effect. In practice, the builder is initialized with whatever value you might set there and then overridden by the call to .type().

See “spring-boot-features.html” in the “Spring Boot features” section and the DataSourceAutoConfiguration class for more details.

9.2. Configure Two DataSources

If you need to configure multiple data sources, you can apply the same tricks that are described in the previous section. You must, however, mark one of the DataSource instances as @Primary, because various auto-configurations down the road expect to be able to get one by type.

If you create your own DataSource, the auto-configuration backs off. In the following example, we provide the exact same feature set as the auto-configuration provides on the primary data source:

@Bean
@Primary
@ConfigurationProperties("app.datasource.first")
public DataSourceProperties firstDataSourceProperties() {
    return new DataSourceProperties();
}

@Bean
@Primary
@ConfigurationProperties("app.datasource.first.configuration")
public HikariDataSource firstDataSource() {
    return firstDataSourceProperties().initializeDataSourceBuilder()
            .type(HikariDataSource.class).build();
}

@Bean
@ConfigurationProperties("app.datasource.second")
public BasicDataSource secondDataSource() {
    return DataSourceBuilder.create().type(BasicDataSource.class).build();
}
firstDataSourceProperties has to be flagged as @Primary so that the database initializer feature uses your copy (if you use the initializer).

Both data sources are also bound for advanced customizations. For instance, you could configure them as follows:

app.datasource.first.url=jdbc:mysql://localhost/first
app.datasource.first.username=dbuser
app.datasource.first.password=dbpass
app.datasource.first.configuration.maximum-pool-size=30

app.datasource.second.url=jdbc:mysql://localhost/second
app.datasource.second.username=dbuser
app.datasource.second.password=dbpass
app.datasource.second.max-total=30

You can apply the same concept to the secondary DataSource as well, as shown in the following example:

@Bean
@Primary
@ConfigurationProperties("app.datasource.first")
public DataSourceProperties firstDataSourceProperties() {
    return new DataSourceProperties();
}

@Bean
@Primary
@ConfigurationProperties("app.datasource.first.configuration")
public HikariDataSource firstDataSource() {
    return firstDataSourceProperties().initializeDataSourceBuilder()
            .type(HikariDataSource.class).build();
}

@Bean
@ConfigurationProperties("app.datasource.second")
public DataSourceProperties secondDataSourceProperties() {
    return new DataSourceProperties();
}

@Bean
@ConfigurationProperties("app.datasource.second.configuration")
public BasicDataSource secondDataSource() {
    return secondDataSourceProperties().initializeDataSourceBuilder()
            .type(BasicDataSource.class).build();
}

The preceding example configures two data sources on custom namespaces with the same logic as Spring Boot would use in auto-configuration. Note that each configuration sub namespace provides advanced settings based on the chosen implementation.

9.3. Use Spring Data Repositories

Spring Data can create implementations of @Repository interfaces of various flavors. Spring Boot handles all of that for you, as long as those @Repositories are included in the same package (or a sub-package) of your @EnableAutoConfiguration class.

For many applications, all you need is to put the right Spring Data dependencies on your classpath (there is a spring-boot-starter-data-jpa for JPA and a spring-boot-starter-data-mongodb for Mongodb) and create some repository interfaces to handle your @Entity objects. Examples are in the JPA sample and the Mongodb sample.

Spring Boot tries to guess the location of your @Repository definitions, based on the @EnableAutoConfiguration it finds. To get more control, use the @EnableJpaRepositories annotation (from Spring Data JPA).

For more about Spring Data, see the Spring Data project page.

9.4. Separate @Entity Definitions from Spring Configuration

Spring Boot tries to guess the location of your @Entity definitions, based on the @EnableAutoConfiguration it finds. To get more control, you can use the @EntityScan annotation, as shown in the following example:

@Configuration
@EnableAutoConfiguration
@EntityScan(basePackageClasses=City.class)
public class Application {

    //...

}

9.5. Configure JPA Properties

Spring Data JPA already provides some vendor-independent configuration options (such as those for SQL logging), and Spring Boot exposes those options and a few more for Hibernate as external configuration properties. Some of them are automatically detected according to the context so you should not have to set them.

The spring.jpa.hibernate.ddl-auto is a special case, because, depending on runtime conditions, it has different defaults. If an embedded database is used and no schema manager (such as Liquibase or Flyway) is handling the DataSource, it defaults to create-drop. In all other cases, it defaults to none.

The dialect to use is also automatically detected based on the current DataSource, but you can set spring.jpa.database yourself if you want to be explicit and bypass that check on startup.

Specifying a database leads to the configuration of a well-defined Hibernate dialect. Several databases have more than one Dialect, and this may not suit your needs. In that case, you can either set spring.jpa.database to default to let Hibernate figure things out or set the dialect by setting the spring.jpa.database-platform property.

The most common options to set are shown in the following example:

spring.jpa.hibernate.naming.physical-strategy=com.example.MyPhysicalNamingStrategy
spring.jpa.show-sql=true

In addition, all properties in spring.jpa.properties.* are passed through as normal JPA properties (with the prefix stripped) when the local EntityManagerFactory is created.

If you need to apply advanced customization to Hibernate properties, consider registering a HibernatePropertiesCustomizer bean that will be invoked prior to creating the EntityManagerFactory. This takes precedence to anything that is applied by the auto-configuration.

9.6. Configure Hibernate Naming Strategy

Hibernate uses two different naming strategies to map names from the object model to the corresponding database names. The fully qualified class name of the physical and the implicit strategy implementations can be configured by setting the spring.jpa.hibernate.naming.physical-strategy and spring.jpa.hibernate.naming.implicit-strategy properties, respectively. Alternatively, if ImplicitNamingStrategy or PhysicalNamingStrategy beans are available in the application context, Hibernate will be automatically configured to use them.

By default, Spring Boot configures the physical naming strategy with SpringPhysicalNamingStrategy. This implementation provides the same table structure as Hibernate 4: all dots are replaced by underscores and camel casing is replaced by underscores as well. By default, all table names are generated in lower case, but it is possible to override that flag if your schema requires it.

For example, a TelephoneNumber entity is mapped to the telephone_number table.

If you prefer to use Hibernate 5’s default instead, set the following property:

spring.jpa.hibernate.naming.physical-strategy=org.hibernate.boot.model.naming.PhysicalNamingStrategyStandardImpl

Alternatively, you can configure the following bean:

@Bean
public PhysicalNamingStrategy physicalNamingStrategy() {
    return new PhysicalNamingStrategyStandardImpl();
}

9.7. Configure Hibernate Second-Level Caching

Hibernate second-level cache can be configured for a range of cache providers. Rather than configuring Hibernate to lookup the cache provider again, it is better to provide the one that is available in the context whenever possible.

If you’re using JCache, this is pretty easy. First, make sure that org.hibernate:hibernate-jcache is available on the classpath. Then, add a HibernatePropertiesCustomizer bean as shown in the following example:

@Configuration
public class HibernateSecondLevelCacheExample {

    @Bean
    public HibernatePropertiesCustomizer hibernateSecondLevelCacheCustomizer(
            JCacheCacheManager cacheManager) {
        return (properties) -> properties.put(ConfigSettings.CACHE_MANAGER,
                cacheManager.getCacheManager());

    }

}

This customizer will configure Hibernate to use the same CacheManager as the one that the application uses. It is also possible to use separate CacheManager instances. For details, refer to the Hibernate user guide.

9.8. Use Dependency Injection in Hibernate Components

By default, Spring Boot registers a BeanContainer implementation that uses the BeanFactory so that converters and entity listeners can use regular dependency injection.

You can disable or tune this behaviour by registering a HibernatePropertiesCustomizer that removes or changes the hibernate.resource.beans.container property.

9.9. Use a Custom EntityManagerFactory

To take full control of the configuration of the EntityManagerFactory, you need to add a @Bean named ‘entityManagerFactory’. Spring Boot auto-configuration switches off its entity manager in the presence of a bean of that type.

9.10. Use Two EntityManagers

Even if the default EntityManagerFactory works fine, you need to define a new one. Otherwise, the presence of the second bean of that type switches off the default. To make it easy to do, you can use the convenient EntityManagerBuilder provided by Spring Boot. Alternatively, you can just the LocalContainerEntityManagerFactoryBean directly from Spring ORM, as shown in the following example:

// add two data sources configured as above

@Bean
public LocalContainerEntityManagerFactoryBean customerEntityManagerFactory(
        EntityManagerFactoryBuilder builder) {
    return builder
            .dataSource(customerDataSource())
            .packages(Customer.class)
            .persistenceUnit("customers")
            .build();
}

@Bean
public LocalContainerEntityManagerFactoryBean orderEntityManagerFactory(
        EntityManagerFactoryBuilder builder) {
    return builder
            .dataSource(orderDataSource())
            .packages(Order.class)
            .persistenceUnit("orders")
            .build();
}

The configuration above almost works on its own. To complete the picture, you need to configure TransactionManagers for the two EntityManagers as well. If you mark one of them as @Primary, it could be picked up by the default JpaTransactionManager in Spring Boot. The other would have to be explicitly injected into a new instance. Alternatively, you might be able to use a JTA transaction manager that spans both.

If you use Spring Data, you need to configure @EnableJpaRepositories accordingly, as shown in the following example:

@Configuration
@EnableJpaRepositories(basePackageClasses = Customer.class,
        entityManagerFactoryRef = "customerEntityManagerFactory")
public class CustomerConfiguration {
    ...
}

@Configuration
@EnableJpaRepositories(basePackageClasses = Order.class,
        entityManagerFactoryRef = "orderEntityManagerFactory")
public class OrderConfiguration {
    ...
}

9.11. Use a Traditional persistence.xml File

Spring Boot will not search for or use a META-INF/persistence.xml by default. If you prefer to use a traditional persistence.xml, you need to define your own @Bean of type LocalEntityManagerFactoryBean (with an ID of ‘entityManagerFactory’) and set the persistence unit name there.

See JpaBaseConfiguration for the default settings.

9.12. Use Spring Data JPA and Mongo Repositories

Spring Data JPA and Spring Data Mongo can both automatically create Repository implementations for you. If they are both present on the classpath, you might have to do some extra configuration to tell Spring Boot which repositories to create. The most explicit way to do that is to use the standard Spring Data @EnableJpaRepositories and @EnableMongoRepositories annotations and provide the location of your Repository interfaces.

There are also flags (spring.data.*.repositories.enabled and spring.data.*.repositories.type) that you can use to switch the auto-configured repositories on and off in external configuration. Doing so is useful, for instance, in case you want to switch off the Mongo repositories and still use the auto-configured MongoTemplate.

The same obstacle and the same features exist for other auto-configured Spring Data repository types (Elasticsearch, Solr, and others). To work with them, change the names of the annotations and flags accordingly.

9.13. Customize Spring Data’s Web Support

Spring Data provides web support that simplifies the use of Spring Data repositories in a web application. Spring Boot provides properties in the spring.data.web namespace for customizing its configuration. Note that if you are using Spring Data REST, you must use the properties in the spring.data.rest namespace instead.

9.14. Expose Spring Data Repositories as REST Endpoint

Spring Data REST can expose the Repository implementations as REST endpoints for you, provided Spring MVC has been enabled for the application.

Spring Boot exposes a set of useful properties (from the spring.data.rest namespace) that customize the RepositoryRestConfiguration. If you need to provide additional customization, you should use a RepositoryRestConfigurer bean.

If you do not specify any order on your custom RepositoryRestConfigurer, it runs after the one Spring Boot uses internally. If you need to specify an order, make sure it is higher than 0.

9.15. Configure a Component that is Used by JPA

If you want to configure a component that JPA uses, then you need to ensure that the component is initialized before JPA. When the component is auto-configured, Spring Boot takes care of this for you. For example, when Flyway is auto-configured, Hibernate is configured to depend upon Flyway so that Flyway has a chance to initialize the database before Hibernate tries to use it.

If you are configuring a component yourself, you can use an EntityManagerFactoryDependsOnPostProcessor subclass as a convenient way of setting up the necessary dependencies. For example, if you use Hibernate Search with Elasticsearch as its index manager, any EntityManagerFactory beans must be configured to depend on the elasticsearchClient bean, as shown in the following example:

/**
 * {@link EntityManagerFactoryDependsOnPostProcessor} that ensures that
 * {@link EntityManagerFactory} beans depend on the {@code elasticsearchClient} bean.
 */
@Configuration
static class ElasticsearchJpaDependencyConfiguration
        extends EntityManagerFactoryDependsOnPostProcessor {

    ElasticsearchJpaDependencyConfiguration() {
        super("elasticsearchClient");
    }

}

9.16. Configure jOOQ with Two DataSources

If you need to use jOOQ with multiple data sources, you should create your own DSLContext for each one. Refer to JooqAutoConfiguration for more details.

In particular, JooqExceptionTranslator and SpringTransactionProvider can be reused to provide similar features to what the auto-configuration does with a single DataSource.

10. Database Initialization

An SQL database can be initialized in different ways depending on what your stack is. Of course, you can also do it manually, provided the database is a separate process. It is recommended to use a single mechanism for schema generation.

10.1. Initialize a Database Using JPA

JPA has features for DDL generation, and these can be set up to run on startup against the database. This is controlled through two external properties:

  • spring.jpa.generate-ddl (boolean) switches the feature on and off and is vendor independent.

  • spring.jpa.hibernate.ddl-auto (enum) is a Hibernate feature that controls the behavior in a more fine-grained way. This feature is described in more detail later in this guide.

10.2. Initialize a Database Using Hibernate

You can set spring.jpa.hibernate.ddl-auto explicitly and the standard Hibernate property values are none, validate, update, create, and create-drop. Spring Boot chooses a default value for you based on whether it thinks your database is embedded. It defaults to create-drop if no schema manager has been detected or none in all other cases. An embedded database is detected by looking at the Connection type. hsqldb, h2, and derby are embedded, and others are not. Be careful when switching from in-memory to a ‘real’ database that you do not make assumptions about the existence of the tables and data in the new platform. You either have to set ddl-auto explicitly or use one of the other mechanisms to initialize the database.

You can output the schema creation by enabling the org.hibernate.SQL logger. This is done for you automatically if you enable the debug mode.

In addition, a file named import.sql in the root of the classpath is executed on startup if Hibernate creates the schema from scratch (that is, if the ddl-auto property is set to create or create-drop). This can be useful for demos and for testing if you are careful but is probably not something you want to be on the classpath in production. It is a Hibernate feature (and has nothing to do with Spring).

10.3. Initialize a Database

Spring Boot can automatically create the schema (DDL scripts) of your DataSource and initialize it (DML scripts). It loads SQL from the standard root classpath locations: schema.sql and data.sql, respectively. In addition, Spring Boot processes the schema-${platform}.sql and data-${platform}.sql files (if present), where platform is the value of spring.datasource.platform. This allows you to switch to database-specific scripts if necessary. For example, you might choose to set it to the vendor name of the database (hsqldb, h2, oracle, mysql, postgresql, and so on).

Spring Boot automatically creates the schema of an embedded DataSource. This behaviour can be customized by using the spring.datasource.initialization-mode property. For instance, if you want to always initialize the DataSource regardless of its type:

spring.datasource.initialization-mode=always

By default, Spring Boot enables the fail-fast feature of the Spring JDBC initializer. This means that, if the scripts cause exceptions, the application fails to start. You can tune that behavior by setting spring.datasource.continue-on-error.

In a JPA-based app, you can choose to let Hibernate create the schema or use schema.sql, but you cannot do both. Make sure to disable spring.jpa.hibernate.ddl-auto if you use schema.sql.

10.4. Initialize a Spring Batch Database

If you use Spring Batch, it comes pre-packaged with SQL initialization scripts for most popular database platforms. Spring Boot can detect your database type and execute those scripts on startup. If you use an embedded database, this happens by default. You can also enable it for any database type, as shown in the following example:

spring.batch.initialize-schema=always

You can also switch off the initialization explicitly by setting spring.batch.initialize-schema=never.

10.5. Use a Higher-level Database Migration Tool

Spring Boot supports two higher-level migration tools: Flyway and Liquibase.

10.5.1. Execute Flyway Database Migrations on Startup

To automatically run Flyway database migrations on startup, add the org.flywaydb:flyway-core to your classpath.

The migrations are scripts in the form V<VERSION>__<NAME>.sql (with <VERSION> an underscore-separated version, such as ‘1’ or ‘2_1’). By default, they are in a folder called classpath:db/migration, but you can modify that location by setting spring.flyway.locations. This is a comma-separated list of one or more classpath: or filesystem: locations. For example, the following configuration would search for scripts in both the default classpath location and the /opt/migration directory:

spring.flyway.locations=classpath:db/migration,filesystem:/opt/migration

You can also add a special {vendor} placeholder to use vendor-specific scripts. Assume the following:

spring.flyway.locations=classpath:db/migration/{vendor}

Rather than using db/migration, the preceding configuration sets the folder to use according to the type of the database (such as db/migration/mysql for MySQL). The list of supported databases is available in DatabaseDriver.

FlywayProperties provides most of Flyway’s settings and a small set of additional properties that can be used to disable the migrations or switch off the location checking. If you need more control over the configuration, consider registering a FlywayConfigurationCustomizer bean.

Spring Boot calls Flyway.migrate() to perform the database migration. If you would like more control, provide a @Bean that implements FlywayMigrationStrategy.

Flyway supports SQL and Java callbacks. To use SQL-based callbacks, place the callback scripts in the classpath:db/migration folder. To use Java-based callbacks, create one or more beans that implement Callback. Any such beans are automatically registered with Flyway. They can be ordered by using @Order or by implementing Ordered. Beans that implement the deprecated FlywayCallback interface can also be detected, however they cannot be used alongside Callback beans.

By default, Flyway autowires the (@Primary) DataSource in your context and uses that for migrations. If you like to use a different DataSource, you can create one and mark its @Bean as @FlywayDataSource. If you do so and want two data sources, remember to create another one and mark it as @Primary. Alternatively, you can use Flyway’s native DataSource by setting spring.flyway.[url,user,password] in external properties. Setting either spring.flyway.url or spring.flyway.user is sufficient to cause Flyway to use its own DataSource. If any of the three properties has not be set, the value of its equivalent spring.datasource property will be used.

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

You can also use Flyway to provide data for specific scenarios. For example, you can place test-specific migrations in src/test/resources and they are run only when your application starts for testing. Also, you can use profile-specific configuration to customize spring.flyway.locations so that certain migrations run only when a particular profile is active. For example, in application-dev.properties, you might specify the following setting:

spring.flyway.locations=classpath:/db/migration,classpath:/dev/db/migration

With that setup, migrations in dev/db/migration run only when the dev profile is active.

10.5.2. Execute Liquibase Database Migrations on Startup

To automatically run Liquibase database migrations on startup, add the org.liquibase:liquibase-core to your classpath.

By default, the master change log is read from db/changelog/db.changelog-master.yaml, but you can change the location by setting spring.liquibase.change-log. In addition to YAML, Liquibase also supports JSON, XML, and SQL change log formats.

By default, Liquibase autowires the (@Primary) DataSource in your context and uses that for migrations. If you need to use a different DataSource, you can create one and mark its @Bean as @LiquibaseDataSource. If you do so and you want two data sources, remember to create another one and mark it as @Primary. Alternatively, you can use Liquibase’s native DataSource by setting spring.liquibase.[url,user,password] in external properties. Setting either spring.liquibase.url or spring.liquibase.user is sufficient to cause Liquibase to use its own DataSource. If any of the three properties has not be set, the value of its equivalent spring.datasource property will be used.

See LiquibaseProperties for details about available settings such as contexts, the default schema, and others.

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

11. Messaging

Spring Boot offers a number of starters that include messaging. This section answers questions that arise from using messaging with Spring Boot.

11.1. Disable Transacted JMS Session

If your JMS broker does not support transacted sessions, you have to disable the support of transactions altogether. If you create your own JmsListenerContainerFactory, there is nothing to do, since, by default it cannot be transacted. If you want to use the DefaultJmsListenerContainerFactoryConfigurer to reuse Spring Boot’s default, you can disable transacted sessions, as follows:

@Bean
public DefaultJmsListenerContainerFactory jmsListenerContainerFactory(
        ConnectionFactory connectionFactory,
        DefaultJmsListenerContainerFactoryConfigurer configurer) {
    DefaultJmsListenerContainerFactory listenerFactory =
            new DefaultJmsListenerContainerFactory();
    configurer.configure(listenerFactory, connectionFactory);
    listenerFactory.setTransactionManager(null);
    listenerFactory.setSessionTransacted(false);
    return listenerFactory;
}

The preceding example overrides the default factory, and it should be applied to any other factory that your application defines, if any.

12. Batch Applications

This section answers questions that arise from using Spring Batch with Spring Boot.

By default, batch applications require a DataSource to store job details. If you want to deviate from that, you need to implement BatchConfigurer. See The Javadoc of @EnableBatchProcessing for more details.

For more about Spring Batch, see the Spring Batch project page.

12.1. Execute Spring Batch Jobs on Startup

Spring Batch auto-configuration is enabled by adding @EnableBatchProcessing (from Spring Batch) somewhere in your context.

By default, it executes all Jobs in the application context on startup (see JobLauncherCommandLineRunner for details). You can narrow down to a specific job or jobs by specifying spring.batch.job.names (which takes a comma-separated list of job name patterns).

Specifying job parameters on the command line

Unlike command line option arguments that set properties in the Environment (i.e. by starting with --, such as --my-property=value), job parameters have to be specified on the command line without dashes (e.g. jobParam=value).

If the application context includes a JobRegistry, the jobs in spring.batch.job.names are looked up in the registry instead of being autowired from the context. This is a common pattern with more complex systems, where multiple jobs are defined in child contexts and registered centrally.

13. Actuator

Spring Boot includes the Spring Boot Actuator. This section answers questions that often arise from its use.

13.1. Change the HTTP Port or Address of the Actuator Endpoints

In a standalone application, the Actuator HTTP port defaults to the same as the main HTTP port. To make the application listen on a different port, set the external property: management.server.port. To listen on a completely different network address (such as when you have an internal network for management and an external one for user applications), you can also set management.server.address to a valid IP address to which the server is able to bind.

For more detail, see the ManagementServerProperties source code and “production-ready-features.html” in the “Production-ready features” section.

13.2. Customize the ‘whitelabel’ Error Page

Spring Boot installs a ‘whitelabel’ error page that you see in a browser client if you encounter a server error (machine clients consuming JSON and other media types should see a sensible response with the right error code).

Set server.error.whitelabel.enabled=false to switch the default error page off. Doing so restores the default of the servlet container that you are using. Note that Spring Boot still tries to resolve the error view, so you should probably add your own error page rather than disabling it completely.

Overriding the error page with your own depends on the templating technology that you use. For example, if you use Thymeleaf, you can add an error.html template. If you use FreeMarker, you can add an error.ftl template. In general, you need a View that resolves with a name of error or a @Controller that handles the /error path. Unless you replaced some of the default configuration, you should find a BeanNameViewResolver in your ApplicationContext, so a @Bean named error would be a simple way of doing that. See ErrorMvcAutoConfiguration for more options.

See also the section on “Error Handling” for details of how to register handlers in the servlet container.

13.3. Sanitize sensible values

Information returned by the env and configprops endpoints can be somewhat sensitive so keys matching a certain pattern are sanitized by default (i.e. their values are replaced by ******).

Spring Boot uses sensible defaults for such keys: for instance, any key ending with the word "password", "secret", "key" or "token" is sanitized. It is also possible to use a regular expression instead, such as *credentials.* to sanitize any key that holds the word credentials as part of the key.

The patterns to use can be customized using the management.endpoint.env.keys-to-sanitize and management.endpoint.configprops.keys-to-sanitize respectively.

14. Security

This section addresses questions about security when working with Spring Boot, including questions that arise from using Spring Security with Spring Boot.

For more about Spring Security, see the Spring Security project page.

14.1. Switch off the Spring Boot Security Configuration

If you define a @Configuration with a WebSecurityConfigurerAdapter in your application, it switches off the default webapp security settings in Spring Boot.

14.2. Change the UserDetailsService and Add User Accounts

If you provide a @Bean of type AuthenticationManager, AuthenticationProvider, or UserDetailsService, the default @Bean for InMemoryUserDetailsManager is not created, so you have the full feature set of Spring Security available (such as various authentication options).

The easiest way to add user accounts is to provide your own UserDetailsService bean.

14.3. Enable HTTPS When Running behind a Proxy Server

Ensuring that all your main endpoints are only available over HTTPS is an important chore for any application. If you use Tomcat as a servlet container, then Spring Boot adds Tomcat’s own RemoteIpValve automatically if it detects some environment settings, and you should be able to rely on the HttpServletRequest to report whether it is secure or not (even downstream of a proxy server that handles the real SSL termination). The standard behavior is determined by the presence or absence of certain request headers (x-forwarded-for and x-forwarded-proto), whose names are conventional, so it should work with most front-end proxies. You can switch on the valve by adding some entries to application.properties, as shown in the following example:

server.tomcat.remote-ip-header=x-forwarded-for
server.tomcat.protocol-header=x-forwarded-proto

(The presence of either of those properties switches on the valve. Alternatively, you can add the RemoteIpValve by adding a TomcatServletWebServerFactory bean.)

To configure Spring Security to require a secure channel for all (or some) requests, consider adding your own WebSecurityConfigurerAdapter that adds the following HttpSecurity configuration:

@Configuration
public class SslWebSecurityConfigurerAdapter extends WebSecurityConfigurerAdapter {

    @Override
    protected void configure(HttpSecurity http) throws Exception {
        // Customize the application security
        http.requiresChannel().anyRequest().requiresSecure();
    }

}

15. Hot Swapping

Spring Boot supports hot swapping. This section answers questions about how it works.

15.1. Reload Static Content

There are several options for hot reloading. The recommended approach is to use spring-boot-devtools, as it provides additional development-time features, such as support for fast application restarts and LiveReload as well as sensible development-time configuration (such as template caching). Devtools works by monitoring the classpath for changes. This means that static resource changes must be "built" for the change to take affect. By default, this happens automatically in Eclipse when you save your changes. In IntelliJ IDEA, the Make Project command triggers the necessary build. Due to the default restart exclusions, changes to static resources do not trigger a restart of your application. They do, however, trigger a live reload.

Alternatively, running in an IDE (especially with debugging on) is a good way to do development (all modern IDEs allow reloading of static resources and usually also allow hot-swapping of Java class changes).

Finally, the Maven and Gradle plugins can be configured (see the addResources property) to support running from the command line with reloading of static files directly from source. You can use that with an external css/js compiler process if you are writing that code with higher-level tools.

15.2. Reload Templates without Restarting the Container

Most of the templating technologies supported by Spring Boot include a configuration option to disable caching (described later in this document). If you use the spring-boot-devtools module, these properties are automatically configured for you at development time.

15.2.1. Thymeleaf Templates

If you use Thymeleaf, set spring.thymeleaf.cache to false. See ThymeleafAutoConfiguration for other Thymeleaf customization options.

15.2.2. FreeMarker Templates

If you use FreeMarker, set spring.freemarker.cache to false. See FreeMarkerAutoConfiguration for other FreeMarker customization options.

15.2.3. Groovy Templates

If you use Groovy templates, set spring.groovy.template.cache to false. See GroovyTemplateAutoConfiguration for other Groovy customization options.

15.3. Fast Application Restarts

The spring-boot-devtools module includes support for automatic application restarts. While not as fast as technologies such as JRebel it is usually significantly faster than a “cold start”. You should probably give it a try before investigating some of the more complex reload options discussed later in this document.

For more details, see the using-spring-boot.html section.

15.4. Reload Java Classes without Restarting the Container

Many modern IDEs (Eclipse, IDEA, and others) support hot swapping of bytecode. Consequently, if you make a change that does not affect class or method signatures, it should reload cleanly with no side effects.

16. Build

Spring Boot includes build plugins for Maven and Gradle. This section answers common questions about these plugins.

16.1. Generate Build Information

Both the Maven plugin and the Gradle plugin allow generating build information containing the coordinates, name, and version of the project. The plugins can also be configured to add additional properties through configuration. When such a file is present, Spring Boot auto-configures a BuildProperties bean.

To generate build information with Maven, add an execution for the build-info goal, as shown in the following example:

<build>
    <plugins>
        <plugin>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-maven-plugin</artifactId>
            <version>2.2.0.BUILD-SNAPSHOT</version>
            <executions>
                <execution>
                    <goals>
                        <goal>build-info</goal>
                    </goals>
                </execution>
            </executions>
        </plugin>
    </plugins>
</build>
See the Spring Boot Maven Plugin documentation for more details.

The following example does the same with Gradle:

springBoot {
    buildInfo()
}
See the Spring Boot Gradle Plugin documentation for more details.

16.2. Generate Git Information

Both Maven and Gradle allow generating a git.properties file containing information about the state of your git source code repository when the project was built.

For Maven users, the spring-boot-starter-parent POM includes a pre-configured plugin to generate a git.properties file. To use it, add the following declaration to your POM:

<build>
    <plugins>
        <plugin>
            <groupId>pl.project13.maven</groupId>
            <artifactId>git-commit-id-plugin</artifactId>
        </plugin>
    </plugins>
</build>

Gradle users can achieve the same result by using the gradle-git-properties plugin, as shown in the following example:

plugins {
    id "com.gorylenko.gradle-git-properties" version "1.5.1"
}
The commit time in git.properties is expected to match the following format: yyyy-MM-dd’T’HH:mm:ssZ. This is the default format for both plugins listed above. Using this format lets the time be parsed into a Date and its format, when serialized to JSON, to be controlled by Jackson’s date serialization configuration settings.

16.3. Customize Dependency Versions

If you use a Maven build that inherits directly or indirectly from spring-boot-dependencies (for instance, spring-boot-starter-parent) but you want to override a specific third-party dependency, you can add appropriate <properties> elements. Browse the spring-boot-dependencies POM for a complete list of properties. For example, to pick a different slf4j version, you would add the following property:

<properties>
    <slf4j.version>1.7.5<slf4j.version>
</properties>
Doing so only works if your Maven project inherits (directly or indirectly) from spring-boot-dependencies. If you have added spring-boot-dependencies in your own dependencyManagement section with <scope>import</scope>, you have to redefine the artifact yourself instead of overriding the property.
Each Spring Boot release is designed and tested against this specific set of third-party dependencies. Overriding versions may cause compatibility issues.

To override dependency versions in Gradle, see this section of the Gradle plugin’s documentation.

16.4. Create an Executable JAR with Maven

The spring-boot-maven-plugin can be used to create an executable “fat” JAR. If you use the spring-boot-starter-parent POM, you can declare the plugin and your jars are repackaged as follows:

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

If you do not use the parent POM, you can still use the plugin. However, you must additionally add an <executions> section, as follows:

<build>
    <plugins>
        <plugin>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-maven-plugin</artifactId>
            <version>2.2.0.BUILD-SNAPSHOT</version>
            <executions>
                <execution>
                    <goals>
                        <goal>repackage</goal>
                    </goals>
                </execution>
            </executions>
        </plugin>
    </plugins>
</build>

See the plugin documentation for full usage details.

16.5. Use a Spring Boot Application as a Dependency

Like a war file, a Spring Boot application is not intended to be used as a dependency. If your application contains classes that you want to share with other projects, the recommended approach is to move that code into a separate module. The separate module can then be depended upon by your application and other projects.

If you cannot rearrange your code as recommended above, Spring Boot’s Maven and Gradle plugins must be configured to produce a separate artifact that is suitable for use as a dependency. The executable archive cannot be used as a dependency as the executable jar format packages application classes in BOOT-INF/classes. This means that they cannot be found when the executable jar is used as a dependency.

To produce the two artifacts, one that can be used as a dependency and one that is executable, a classifier must be specified. This classifier is applied to the name of the executable archive, leaving the default archive for use as a dependency.

To configure a classifier of exec in Maven, you can use the following configuration:

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

16.6. Extract Specific Libraries When an Executable Jar Runs

Most nested libraries in an executable jar do not need to be unpacked in order to run. However, certain libraries can have problems. For example, JRuby includes its own nested jar support, which assumes that the jruby-complete.jar is always directly available as a file in its own right.

To deal with any problematic libraries, you can flag that specific nested jars should be automatically unpacked when the executable jar first runs. Such nested jars are written beneath the temporary directory identified by the java.io.tmpdir system property.

Care should be taken to ensure that your operating system is configured so that it will not delete the jars that have been unpacked to the temporary directory while the application is still running.

For example, to indicate that JRuby should be flagged for unpacking by using the Maven Plugin, you would add the following configuration:

<build>
    <plugins>
        <plugin>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-maven-plugin</artifactId>
            <configuration>
                <requiresUnpack>
                    <dependency>
                        <groupId>org.jruby</groupId>
                        <artifactId>jruby-complete</artifactId>
                    </dependency>
                </requiresUnpack>
            </configuration>
        </plugin>
    </plugins>
</build>

16.7. Create a Non-executable JAR with Exclusions

Often, if you have an executable and a non-executable jar as two separate build products, the executable version has additional configuration files that are not needed in a library jar. For example, the application.yml configuration file might by excluded from the non-executable JAR.

In Maven, the executable jar must be the main artifact and you can add a classified jar for the library, as follows:

<build>
    <plugins>
        <plugin>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-maven-plugin</artifactId>
        </plugin>
        <plugin>
            <artifactId>maven-jar-plugin</artifactId>
            <executions>
                <execution>
                    <id>lib</id>
                    <phase>package</phase>
                    <goals>
                        <goal>jar</goal>
                    </goals>
                    <configuration>
                        <classifier>lib</classifier>
                        <excludes>
                            <exclude>application.yml</exclude>
                        </excludes>
                    </configuration>
                </execution>
            </executions>
        </plugin>
    </plugins>
</build>

16.8. Remote Debug a Spring Boot Application Started with Maven

To attach a remote debugger to a Spring Boot application that was started with Maven, you can use the jvmArguments property of the maven plugin.

See this example for more details.

16.9. Build an Executable Archive from Ant without Using spring-boot-antlib

To build with Ant, you need to grab dependencies, compile, and then create a jar or war archive. To make it executable, you can either use the spring-boot-antlib module or you can follow these instructions:

  1. If you are building a jar, package the application’s classes and resources in a nested BOOT-INF/classes directory. If you are building a war, package the application’s classes in a nested WEB-INF/classes directory as usual.

  2. Add the runtime dependencies in a nested BOOT-INF/lib directory for a jar or WEB-INF/lib for a war. Remember not to compress the entries in the archive.

  3. Add the provided (embedded container) dependencies in a nested BOOT-INF/lib directory for a jar or WEB-INF/lib-provided for a war. Remember not to compress the entries in the archive.

  4. Add the spring-boot-loader classes at the root of the archive (so that the Main-Class is available).

  5. Use the appropriate launcher (such as JarLauncher for a jar file) as a Main-Class attribute in the manifest and specify the other properties it needs as manifest entries — principally, by setting a Start-Class property.

The following example shows how to build an executable archive with Ant:

<target name="build" depends="compile">
    <jar destfile="target/${ant.project.name}-${spring-boot.version}.jar" compress="false">
        <mappedresources>
            <fileset dir="target/classes" />
            <globmapper from="*" to="BOOT-INF/classes/*"/>
        </mappedresources>
        <mappedresources>
            <fileset dir="src/main/resources" erroronmissingdir="false"/>
            <globmapper from="*" to="BOOT-INF/classes/*"/>
        </mappedresources>
        <mappedresources>
            <fileset dir="${lib.dir}/runtime" />
            <globmapper from="*" to="BOOT-INF/lib/*"/>
        </mappedresources>
        <zipfileset src="${lib.dir}/loader/spring-boot-loader-jar-${spring-boot.version}.jar" />
        <manifest>
            <attribute name="Main-Class" value="org.springframework.boot.loader.JarLauncher" />
            <attribute name="Start-Class" value="${start-class}" />
        </manifest>
    </jar>
</target>

The Ant Sample has a build.xml file with a manual task that should work if you run it with the following command:

$ ant -lib <folder containing ivy-2.2.jar> clean manual

Then you can run the application with the following command:

$ java -jar target/*.jar

17. Traditional Deployment

Spring Boot supports traditional deployment as well as more modern forms of deployment. This section answers common questions about traditional deployment.

17.1. Create a Deployable War File

Because Spring WebFlux does not strictly depend on the Servlet API and applications are deployed by default on an embedded Reactor Netty server, War deployment is not supported for WebFlux applications.

The first step in producing a deployable war file is to provide a SpringBootServletInitializer subclass and override its configure method. Doing so makes use of Spring Framework’s Servlet 3.0 support and lets you configure your application when it is launched by the servlet container. Typically, you should update your application’s main class to extend SpringBootServletInitializer, as shown in the following example:

@SpringBootApplication
public class Application extends SpringBootServletInitializer {

    @Override
    protected SpringApplicationBuilder configure(SpringApplicationBuilder application) {
        return application.sources(Application.class);
    }

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

}

The next step is to update your build configuration such that your project produces a war file rather than a jar file. If you use Maven and spring-boot-starter-parent (which configures Maven’s war plugin for you), all you need to do is to modify pom.xml to change the packaging to war, as follows:

<packaging>war</packaging>

If you use Gradle, you need to modify build.gradle to apply the war plugin to the project, as follows:

apply plugin: 'war'

The final step in the process is to ensure that the embedded servlet container does not interfere with the servlet container to which the war file is deployed. To do so, you need to mark the embedded servlet container dependency as being provided.

If you use Maven, the following example marks the servlet container (Tomcat, in this case) as being provided:

<dependencies>
    <!-- … -->
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-tomcat</artifactId>
        <scope>provided</scope>
    </dependency>
    <!-- … -->
</dependencies>

If you use Gradle, the following example marks the servlet container (Tomcat, in this case) as being provided:

dependencies {
    // …
    providedRuntime 'org.springframework.boot:spring-boot-starter-tomcat'
    // …
}
providedRuntime is preferred to Gradle’s compileOnly configuration. Among other limitations, compileOnly dependencies are not on the test classpath, so any web-based integration tests fail.

If you use the Spring Boot build tools, marking the embedded servlet container dependency as provided produces an executable war file with the provided dependencies packaged in a lib-provided directory. This means that, in addition to being deployable to a servlet container, you can also run your application by using java -jar on the command line.

Take a look at Spring Boot’s sample applications for a Maven-based example of the previously described configuration.

17.2. Convert an Existing Application to Spring Boot

For a non-web application, it should be easy to convert an existing Spring application to a Spring Boot application. To do so, throw away the code that creates your ApplicationContext and replace it with calls to SpringApplication or SpringApplicationBuilder. Spring MVC web applications are generally amenable to first creating a deployable war application and then migrating it later to an executable war or jar. See the Getting Started Guide on Converting a jar to a war.

To create a deployable war by extending SpringBootServletInitializer (for example, in a class called Application) and adding the Spring Boot @SpringBootApplication annotation, use code similar to that shown in the following example:

@SpringBootApplication
public class Application extends SpringBootServletInitializer {

    @Override
    protected SpringApplicationBuilder configure(SpringApplicationBuilder application) {
        // Customize the application or call application.sources(...) to add sources
        // Since our example is itself a @Configuration class (via @SpringBootApplication)
        // we actually don't need to override this method.
        return application;
    }

}

Remember that, whatever you put in the sources is merely a Spring ApplicationContext. Normally, anything that already works should work here. There might be some beans you can remove later and let Spring Boot provide its own defaults for them, but it should be possible to get something working before you need to do that.

Static resources can be moved to /public (or /static or /resources or /META-INF/resources) in the classpath root. The same applies to messages.properties (which Spring Boot automatically detects in the root of the classpath).

Vanilla usage of Spring DispatcherServlet and Spring Security should require no further changes. If you have other features in your application (for instance, using other servlets or filters), you may need to add some configuration to your Application context, by replacing those elements from the web.xml, as follows:

  • A @Bean of type Servlet or ServletRegistrationBean installs that bean in the container as if it were a <servlet/> and <servlet-mapping/> in web.xml.

  • A @Bean of type Filter or FilterRegistrationBean behaves similarly (as a <filter/> and <filter-mapping/>).

  • An ApplicationContext in an XML file can be added through an @ImportResource in your Application. Alternatively, simple cases where annotation configuration is heavily used already can be recreated in a few lines as @Bean definitions.

Once the war file is working, you can make it executable by adding a main method to your Application, as shown in the following example:

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

If you intend to start your application as a war or as an executable application, you need to share the customizations of the builder in a method that is both available to the SpringBootServletInitializer callback and in the main method in a class similar to the following:

@SpringBootApplication
public class Application extends SpringBootServletInitializer {

    @Override
    protected SpringApplicationBuilder configure(SpringApplicationBuilder builder) {
        return configureApplication(builder);
    }

    public static void main(String[] args) {
        configureApplication(new SpringApplicationBuilder()).run(args);
    }

    private static SpringApplicationBuilder configureApplication(SpringApplicationBuilder builder) {
        return builder.sources(Application.class).bannerMode(Banner.Mode.OFF);
    }

}

Applications can fall into more than one category:

  • Servlet 3.0+ applications with no web.xml.

  • Applications with a web.xml.

  • Applications with a context hierarchy.

  • Applications without a context hierarchy.

All of these should be amenable to translation, but each might require slightly different techniques.

Servlet 3.0+ applications might translate pretty easily if they already use the Spring Servlet 3.0+ initializer support classes. Normally, all the code from an existing WebApplicationInitializer can be moved into a SpringBootServletInitializer. If your existing application has more than one ApplicationContext (for example, if it uses AbstractDispatcherServletInitializer) then you might be able to combine all your context sources into a single SpringApplication. The main complication you might encounter is if combining does not work and you need to maintain the context hierarchy. See the entry on building a hierarchy for examples. An existing parent context that contains web-specific features usually needs to be broken up so that all the ServletContextAware components are in the child context.

Applications that are not already Spring applications might be convertible to Spring Boot applications, and the previously mentioned guidance may help. However, you may yet encounter problems. In that case, we suggest asking questions on Stack Overflow with a tag of spring-boot.

17.3. Deploying a WAR to WebLogic

To deploy a Spring Boot application to WebLogic, you must ensure that your servlet initializer directly implements WebApplicationInitializer (even if you extend from a base class that already implements it).

A typical initializer for WebLogic should resemble the following example:

import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.web.servlet.support.SpringBootServletInitializer;
import org.springframework.web.WebApplicationInitializer;

@SpringBootApplication
public class MyApplication extends SpringBootServletInitializer implements WebApplicationInitializer {

}

If you use Logback, you also need to tell WebLogic to prefer the packaged version rather than the version that was pre-installed with the server. You can do so by adding a WEB-INF/weblogic.xml file with the following contents:

<?xml version="1.0" encoding="UTF-8"?>
<wls:weblogic-web-app
    xmlns:wls="http://xmlns.oracle.com/weblogic/weblogic-web-app"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
        http://java.sun.com/xml/ns/javaee/ejb-jar_3_0.xsd
        http://xmlns.oracle.com/weblogic/weblogic-web-app
        http://xmlns.oracle.com/weblogic/weblogic-web-app/1.4/weblogic-web-app.xsd">
    <wls:container-descriptor>
        <wls:prefer-application-packages>
            <wls:package-name>org.slf4j</wls:package-name>
        </wls:prefer-application-packages>
    </wls:container-descriptor>
</wls:weblogic-web-app>

17.4. Use Jedis Instead of Lettuce

By default, the Spring Boot starter (spring-boot-starter-data-redis) uses Lettuce. You need to exclude that dependency and include the Jedis one instead. Spring Boot manages these dependencies to help make this process as easy as possible.

The following example shows how to do so in Maven:

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-data-redis</artifactId>
    <exclusions>
        <exclusion>
            <groupId>io.lettuce</groupId>
            <artifactId>lettuce-core</artifactId>
        </exclusion>
    </exclusions>
</dependency>
<dependency>
    <groupId>redis.clients</groupId>
    <artifactId>jedis</artifactId>
</dependency>

The following example shows how to do so in Gradle:

configurations {
    compile.exclude module: "lettuce"
}

dependencies {
    compile("redis.clients:jedis")
    // ...
}