The @SpringBootApplication annotation explained

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

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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;@SpringBootApplicationpublic 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.

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Conclusion

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

 

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