Spring的组合注解和元注解原理与用法详解

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Component
public @interface Configuration {
  String value() default "";
}

package com.wisely.highlight_spring4.ch3.annotation;
import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Configuration //组合@Configuration元注解
@ComponentScan //组合@ComponentScan元注解
public @interface WiselyConfiguration {
  String[] value() default {}; //覆盖value参数
}

package com.wisely.highlight_spring4.ch3.annotation;
import org.springframework.stereotype.Service;
@Service
public class DemoService {
   public void outputResult(){
     System.out.println("从组合注解配置照样获得的bean");
   }
}

package com.wisely.highlight_spring4.ch3.annotation;
@WiselyConfiguration("com.wisely.highlight_spring4.ch3.annotation")
public class DemoConfig {
}

package com.wisely.highlight_spring4.ch3.annotation;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
public class Main {
   public static void main(String[] args) {
     AnnotationConfigApplicationContext context =
        new AnnotationConfigApplicationContext(DemoConfig.class);
     DemoService demoService = context.getBean(DemoService.class);
     demoService.outputResult();
     context.close();
   }
}