组合注解和元注解

从 spring 2.0 开始为了响应 jdk1.5推出的注解功能, spring 开始大量加入注解来替代xml 配置.

元注解:即可注解到其他注解的注解.

组合注解:即被注解的注解.

示例:

组合注解:

package com.pangu.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
@ComponentScan
public @interface CustomeConfiguration {
    
    String[] value() default {}; //覆盖 value 参数.
    
}

service:

package com.pangu.annotation;

import org.springframework.stereotype.Service;

@Service
public class DemoService {

    public void outputResult(){
        System.out.println("从组合注解中照样获取 bean.");
    }
    
}

配置类(使用组合注解):

package com.pangu.annotation;

/**
 * @ClassName: DemoConfig
 * @Description: TODO 新的配置类
 * @author etfox
 * @date 2018年9月28日 下午11:45:19
 *
 * @Copyright: 2018 www.etfox.com Inc. All rights reserved.
 */
@CustomeConfiguration
public class DemoConfig {

}

测试:

package com.pangu.annotation;

import org.junit.Test;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;

public class Main {

    @Test
    public void test() {
        AnnotationConfigApplicationContext context = 
                new AnnotationConfigApplicationContext(DemoConfig.class);
        
        DemoService demoService = context.getBean(DemoService.class);
        
        demoService.outputResult();
        
        context.close();
        
    }

}

结果:

九月 28, 2018 11:46:36 下午 org.springframework.context.support.AbstractApplicationContext prepareRefresh
信息: Refreshing org.springframework.context.annotation.AnnotationConfigApplicationContext@75828a0f: startup date [Fri Sep 28 23:46:36 CST 2018]; root of context hierarchy
从组合注解中照样获取 bean.
九月 28, 2018 11:46:36 下午 org.springframework.context.support.AbstractApplicationContext doClose
信息: Closing org.springframework.context.annotation.AnnotationConfigApplicationContext@75828a0f: startup date [Fri Sep 28 23:46:36 CST 2018]; root of context hierarchy

组合注解和元注解

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