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) throws Exception {
		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'
	// …
}

	Tip
	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.

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

Older Servlet containers do not have support for the ServletContextInitializer bootstrap process used in Servlet 3.0. You can still use Spring and Spring Boot in these containers, but you are going to need to add a web.xml to your application and configure it to load an ApplicationContext via a DispatcherServlet.

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:

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);
}

Note

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:

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.

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>

Spring Boot uses Servlet 3.0 APIs to initialize the ServletContext (register Servlets and so on), so you cannot use the same application in a Servlet 2.5 container. It is, however, possible to run a Spring Boot application on an older container with some special tools. If you include org.springframework.boot:spring-boot-legacy as a dependency (maintained separately to the core of Spring Boot and currently available at 1.1.0.RELEASE), all you need to do is create a web.xml and declare a context listener to create the application context and your filters and servlets. The context listener is a special purpose one for Spring Boot, but the rest of it is normal for a Spring application in Servlet 2.5. The following Maven example shows how to set up a Spring Boot project to run in a Servlet 2.5 container:

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.5" xmlns="http://java.sun.com/xml/ns/javaee"
	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/web-app_2_5.xsd">

	<context-param>
		<param-name>contextConfigLocation</param-name>
		<param-value>demo.Application</param-value>
	</context-param>

	<listener>
		<listener-class>org.springframework.boot.legacy.context.web.SpringBootContextLoaderListener</listener-class>
	</listener>

	<filter>
		<filter-name>metricsFilter</filter-name>
		<filter-class>org.springframework.web.filter.DelegatingFilterProxy</filter-class>
	</filter>

	<filter-mapping>
		<filter-name>metricsFilter</filter-name>
		<url-pattern>/*</url-pattern>
	</filter-mapping>

	<servlet>
		<servlet-name>appServlet</servlet-name>
		<servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
		<init-param>
			<param-name>contextAttribute</param-name>
			<param-value>org.springframework.web.context.WebApplicationContext.ROOT</param-value>
		</init-param>
		<load-on-startup>1</load-on-startup>
	</servlet>

	<servlet-mapping>
		<servlet-name>appServlet</servlet-name>
		<url-pattern>/</url-pattern>
	</servlet-mapping>

</web-app>

In the preceding example, we use a single application context (the one created by the context listener) and attach it to the DispatcherServlet by using an init parameter. This is normal in a Spring Boot application (you normally only have one application context).

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")
	// ...
}