Starting from 4.2, Spring annotations can be processed when used on Java 8 default methods as well. This allows for a lot of flexibility in creating complex bean implementations and configuration classes (the class with @Configuration). We can even take the advantage of Java 8 default method's multiple inheritance behavior pattern.

Let's see how to use Spring annotations on Java 8 default methods.

Example

An interface for bean

package com.logicbig.example;

import javax.annotation.PostConstruct;

public interface IMyBean {
  @PostConstruct
  default void init() {
      System.out.println("post construct: "+this.getClass().getSimpleName());
  }
}

The implementation

package com.logicbig.example;

public class MyBean implements IMyBean {

  public void showMessage(String msg) {
      System.out.println(msg);
  }
}

An interface for configuration

package com.logicbig.example;

import org.springframework.context.annotation.Bean;

public interface IMyConfig {
  @Bean
  default MyBean myBean() {
      return new MyBean();
  }
}

The implementation

package com.logicbig.example;

import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.annotation.Configuration;

@Configuration
public class MyConfig implements IMyConfig {
  public static void main(String[] args) {
      ApplicationContext context =
              new AnnotationConfigApplicationContext(MyConfig.class);
      MyBean bean = context.getBean(MyBean.class);
      bean.showMessage("a test message");
  }
}

Output

post construct: MyBean
a test message

Example Project

Dependencies and Technologies Used:

• spring-context 5.3.8: Spring Context. Version Compatibility: 4.2.0.RELEASE - 5.3.8 Version List
  ×

  Version compatibilities of spring-context with this example:

  • 4.2.0.RELEASE
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  Versions in green have been tested.

• JDK 8
• Maven 3.8.1