Java自定义注解

元注解：注解的注解。

项目结构

定义FruitName注解

package com.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;

/*
 * 水果名称注解
 */
@Target(ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface FruitName {
    String value() default "";
}

定义FruitColor注解

package com.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;

/*
 * 水果颜色注解
 */
@Target(ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface FruitColor {
    public enum Color {红色,绿色,蓝色};
    Color color() default Color.红色;
}

定义FruitProvider注解

package com.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;


/*
 * 水果供应商注解
 */
@Target(ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface FruitProvider {
    String name() default "";
    String address() default "";
}

定义Apple类

package com.fruit;

import com.annotation.FruitColor;
import com.annotation.FruitName;
import com.annotation.FruitProvider;
import com.annotation.FruitColor.Color;

public class Apple {
    @FruitName("红富士")
    private String name;
    @FruitColor(color=Color.红色)
    private String color;
    @FruitProvider(name="烟台果品",address="烟台市芝罘区幸福中路")
    private String provider;
}

定义Test类

package com.test;

import java.lang.reflect.Field;

import com.annotation.FruitColor;
import com.annotation.FruitName;
import com.annotation.FruitProvider;
import com.fruit.Apple;

public class Test {
    public static void main(String[] args) {
        Field[] fields = Apple.class.getDeclaredFields();
        for(Field field : fields){
            if(field.isAnnotationPresent(FruitName.class)){
                FruitName fruitName = field.getAnnotation(FruitName.class);
                System.out.println("水果名称："+fruitName.value());
            }else if(field.isAnnotationPresent(FruitColor.class)){
                FruitColor fruitColor = field.getAnnotation(FruitColor.class);
                System.out.println("水果颜色："+fruitColor.color());
            }else if(field.isAnnotationPresent(FruitProvider.class)){
                FruitProvider provider = field.getAnnotation(FruitProvider.class);
                System.out.println("供货商："+provider.name()+"（"+provider.address()+"）");
            }
        }
    }
}

运行结果

水果名称：红富士
水果颜色：红色
供货商：烟台果品（烟台市芝罘区幸福中路）