简单谈谈java自定义注解

package com.sam.annotation;
import java.lang.annotation.*;

/**
 * @author sam
 * @since 2017/7/13
 */
@Target({ElementType.METHOD, ElementType.FIELD})
@Retention(RetentionPolicy.RUNTIME)
@Inherited
@Documented
public @interface MyMessage {

  String name() default "sam";

  int num() default 0;

  String desc();

}

package com.sam.annotation;
/**
 * @author sam
 * @since 2017/7/13
 */
public class AnnotationTest {

  @MyMessage(num = 10, desc = "参数a")
  private static int a;


  @MyMessage(name = "Sam test", desc = "测试方法test")
  public void test() {
    System.out.println("test");
  }

}

package com.sam.annotation;

import java.lang.reflect.Field;
import java.lang.reflect.Method;

/**
 * 使用反射处理注解
 *
 * @author sam
 * @since 2017/7/13
 */
public class MyMessageProcessor {

  public static void main(String[] args) {

    try {

      //加载annotationTest.class类
      Class clazz = MyMessageProcessor.class.getClassLoader().loadClass("com.sam.annotation.AnnotationTest");

      //获取属性
      Field[] fields = clazz.getDeclaredFields();
      //遍历属性
      for (Field field : fields) {
        MyMessage myMessage = field.getAnnotation(MyMessage.class);
        System.out.println("name:" + myMessage.name() + " num:" + myMessage.num() + " desc:" + myMessage.desc());
      }

      //获取类中的方法
      Method[] methods = clazz.getMethods();
      //遍历方法
      for (Method method : methods) {

        //判断方法是否带有MyMessage注解
        if (method.isAnnotationPresent(MyMessage.class)) {
          // 获取所有注解 method.getDeclaredAnnotations();
          // 获取MyMessage注解
          MyMessage myMessage = method.getAnnotation(MyMessage.class);
          System.out.println("name:" + myMessage.name() + " num:" + myMessage.num() + " desc:" + myMessage.desc());
        }
      }

    } catch (ClassNotFoundException e) {
      e.printStackTrace();
    }
  }

}

name:sam num:10 desc:参数a
name:Sam test num:0 desc:测试方法test

Process finished with exit code 0