SpringBootServletInitializer Example

By Arvind Rai, December 03, 2021

On this page we will learn using SpringBootServletInitializer class.
1. The SpringBootServletInitializer class is the implementation of WebApplicationInitializer interface.
2. The SpringBootServletInitializer is used to run SpringApplication from a traditional WAR deployment.
3. The SpringBootServletInitializer binds Servlet, Filter and ServletContextInitializer beans from the application context to the server.
4. By default we run Spring Boot application by creating an executable JAR with embedded server. To run WAR file of Spring Boot application from a standalone web server, we need to use SpringBootServletInitializer.
5. To use it, the main class annotated with @SpringBootApplication extends SpringBootServletInitializer.

@SpringBootApplication
public class SpringBootDemo extends SpringBootServletInitializer {
  public static void main(String[] args) {
	SpringApplication.run(SpringBootDemo.class, args);
  }
}

Now the WAR file created by this application can run in standalone web server.
6. The class extending SpringBootServletInitializer should either override its configure method or make the initializer class itself a @Configuration class.
Find the configure method from Spring doc.

SpringApplicationBuilder configure(SpringApplicationBuilder builder)

7. To use SpringBootServletInitializer in combination with other WebApplicationInitializers, we might need to add an @Ordered annotation to configure a specific startup order.

Using SpringBootServletInitializer

pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
	<modelVersion>4.0.0</modelVersion>
	<groupId>com.concretepage</groupId>
	<artifactId>soap-ws</artifactId>
	<version>0.0.1-SNAPSHOT</version>
	<packaging>war</packaging>
	<name>spring-demo</name>
	<description>Spring Demo Application</description>
	<parent>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-parent</artifactId>
		<version>2.6.1</version>
		<relativePath />
	</parent>
	<properties>
		<java.version>16</java.version>
		<context.path>spring-app</context.path>
	</properties>
	<dependencies>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-web</artifactId>
		</dependency>
	</dependencies>
	<build>
		<plugins>
			<plugin>
				<groupId>org.apache.maven.plugins</groupId>
				<artifactId>maven-war-plugin</artifactId>
				<version>3.2.0</version>
				<configuration>
					<warName>${context.path}</warName>
				</configuration>
			</plugin>
		</plugins>
	</build>
</project>

MyController.java

package com.concretepage;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class MyController {
   @GetMapping(value="hello")
   public String hello() {
      return "Hello World!";
   }
}

SpringBootDemo.java

package com.concretepage;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.web.servlet.support.SpringBootServletInitializer;

@SpringBootApplication
public class SpringBootDemo extends SpringBootServletInitializer {
  public static void main(String[] args) {
	SpringApplication.run(SpringBootDemo.class, args);
  }
}

The @SpringBootApplication annotation is the combination of @Configuration, @EnableAutoConfiguration and @ComponentScan annotations.
Now run application from a traditional WAR deployment.
1. Create WAR using below command.