Spring Boot configuration method (java configuration and annotation configuration)

Java Configuration
Starting with Spring 3.x, Spring provides the ability to configure Java. Java configuration is the configuration method recommended by Spring 4.x, which can completely replace xml configuration; Java configuration is also the configuration method recommended by Spring Boot.

Java configuration is achieved through @Configuration and @Bean .
1. @Configuration declares that the current class is a configuration class, which is equivalent to a Spring-configured xml file
. 2. The @Bean annotation is on the method, declaring that the return value of the current method is a Bean.

@Configuration
public class JavaConfig {

    @Bean
    public TestService TestService(){
         return new TestService();
    }
}

Annotation configuration
In the Spring 2.x era, with the annotation support brought by JDK 1.5, Spring provides annotations for declaring beans (such as @Service, @Component), which greatly reduces the amount of configuration. Compared with using XML, Spring uses annotations to describe the configuration of beans. Because class annotations are in the source code of a class, it can obtain the benefits of type safety checking and can support refactoring well.

@Service
public class TestService {

    public TestService(){
        System.out.println("TestService.TestService()");
    }

    public void SayHello(){
        System.out.println("Hello World!");
    }
}

Summary
When to use Java configuration or annotation configuration? The main principles are: use Java configuration (such as database-related configuration, MVC-related configuration) for global configuration, and use annotation configuration for business bean configuration.