The @SpringBootApplication annotation explained

Posted On January 1, 2021March 28, 2021

In this article, I will be explaining the @SpringBootApplication annotation.

What is the @SpringBootApplication annotation

The @SpringBootApplication annotation is a convenience annotation that combines the @EnableAutoConfiguration, @Configuration and the @ComponentScan annotations in a Spring Boot application. These annotations do the following:

@EnableAutoConfiguration – This enables Spring Boot’s autoconfiguration mechanism. Auto-configuration refers to creating beans automatically by scanning the classpath.

@ComponentScan – Typically, in a Spring application, annotations like @Component, @Configuration, @Service, @Repository are specified on classes to mark them as Spring beans. The @ComponentScan annotation basically tells Spring Boot to scan the current package and its sub-packages in order to identify annotated classes and configure them as Spring beans. Thus, it designates the current package as the root package for component scanning.

@Configuration – Designates the class as a configuration class for Java configuration. In addition to beans configured via component scanning, an application may desire to configure some additional beans via the @Bean annotation as demonstrated here. Thus, the return value of methods having the @Bean annotation in this class are registered as beans.

How to use the @SpringBootApplication annotation

In order to run a Spring Boot application, it needs to have a class with the @SpringBootApplication annotation. The following code demonstrates this:

package demo;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class Main {

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

}

• The Main class has the @SpringBootApplication annotation
• It simply invokes the SpringApplication.run method. This starts the Spring application as a standalone application, runs the embedded servers and loads the beans.
• Normally, such a main class is placed in a root package above other packages. This enables component scanning to scan all the sub-packages for beans.
• For a complete working example of a simple Spring Boot application you can refer to this article.

Conclusion

So, in this article, we learnt how the @SpringBootApplication annotation works and how to use it in a Spring Boot application.