Why do I need main method if I develop web app as war using Spring Boot?

Question

I am developing web app using Spring Boot. My typical deployment is generating war and place it in webapps folder in Tomcat directory.

I noticed with SpringBoot, I will need a main method. I am wondering why this is needed. If there is a way to avoid it, what would that be?

@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);
    }

}

Answer 1

Main method is not required for the typical deployment scenario of building a war and placing it in webapps folder of Tomcat. All you need is:

public class Application extends SpringBootServletInitializer {

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

However, if you want to be able to launch the app from within an IDE (e.g. with Eclipse's Run As -> Java Application) while developing or build an executable jar or a war that can run standalone with Spring Boot's embedded tomcat by just java -jar myapp.war command, an entry point class with a main method might be helpful.

Answer 2

To run in a separate web container

You don't need the main method, all you need is to do is to extend SpringBootServletInitializer as Kryger mentioned.

@SpringBootApplication
public class Application extends SpringBootServletInitializer {

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

To run in the command line as a standalone application

Here you need the main method, so that you can run it using java -jar from the command line.

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

Source: https://spring.io/guides/gs/convert-jar-to-war/