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

The older version say 4.1.9.RELEASE will end up in the following exception:

Exception in thread "main" org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type [com.logicbig.example.MyBean] is defined
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.getBean(DefaultListableBeanFactory.java:371)
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.getBean(DefaultListableBeanFactory.java:331)
	at org.springframework.context.support.AbstractApplicationContext.getBean(AbstractApplicationContext.java:975)
	at com.logicbig.example.MyConfig.main(MyConfig.java:13)

Example Project

Dependencies and Technologies Used:

• spring-context 4.2.0.RELEASE: Spring Context.
• JDK 1.8
• Maven 3.3.9