[JAVA] Differences between Spring Initializr packaging JAR and WAR

Generate web application with Spring Initializr

Generate a Web application template with the following settings in Spring Initializr.

• Project: Gradle Project
• Language: Java
• Spring Boot: 2.2.1
• Java: 8
• Dependencies: Spring Web

I generated the Packaging items as Jar and War, respectively, and took the difference with the diff command.

Difference between Jar and War

$ diff -r jar war
diff -r jar/demo/build.gradle war/demo/build.gradle
4a5
> 	id 'war'
16a18
> 	providedRuntime 'org.springframework.boot:spring-boot-starter-tomcat'
Only in war/demo/src/main/java/com/example/demo: ServletInitializer.java

Gradle War Plugin

Gradle's War Plugin has been added to the War application.

id 'war'

War Plugin is a plugin that adds a task to generate a war file.

Reference: The War Plugin

Spring Boot Tomcat Starter

Spring Boot Tomcat Starter is specified in providedRuntime for War applications.

providedRuntime 'org.springframework.boot:spring-boot-starter-tomcat'

This uses the embedded Tomcat when running in the local environment, but by specifying providedRuntime, the embedded Tomcat is not included when the war file is generated. Reference: Maven Repository: org \ .springframework \ .boot »spring \ -boot \ -starter \ -tomcat

ServletInitializer

A ServletInitializer has been added to the War application.

package com.example.demo;

import org.springframework.boot.builder.SpringApplicationBuilder;
import org.springframework.boot.web.servlet.support.SpringBootServletInitializer;

public class ServletInitializer extends SpringBootServletInitializer {

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

}

This will be a class that implements the WebApplicationInitializer interface required in the environment where the war file is deployed and operated. Reference: [SpringBootServletInitializer \ (Spring Boot Docs 2 \ .2 \ .1 \ .RELEASE API )](https://docs.spring.io/spring-boot/docs/2.2.1.RELEASE/api/org/ springframework / boot / web / servlet / support / SpringBootServletInitializer.html)