Dog类：

package com.nick.ref;

@MyComponent
public class Dog extends Animal {
    @MyValue("2")
    private Integer id;
    @MyValue("旺财")
    private String name;

    void shout(){
        System.out.println("Dog shout");
    }
}

 

类的自定义注解MyComponent：

package com.nick.ref;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

@Retention(RetentionPolicy.RUNTIME) //意思是注解什么时候生效
@Target(ElementType.TYPE) //意思是给谁加注解，类or字段
public @interface MyComponent {
}

 

字段的自定义注解MyValue：

package com.nick.ref;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;


@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.FIELD)
public @interface MyValue {
    String value();
}

 

注解的反射用法：

package com.nick.ref;

import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.util.Arrays;

public class TestAnnotation {
    public static void main(String[] args) throws Exception {
        Class<Dog> dogClass = Dog.class;
        MyComponent annotation = dogClass.getAnnotation(MyComponent.class);
        if (null != annotation){
            //创建对象
            Constructor<Dog> constructor = dogClass.getConstructor(null);
            Dog dog = constructor.newInstance(null);
            //开始赋值
            Field[] fields = dogClass.getDeclaredFields();
            for (Field field : fields) {
                MyValue valueAnnotation = field.getAnnotation(MyValue.class);
                if (null != valueAnnotation){
                    field.setAccessible(true);
                    String value = valueAnnotation.value();
                    String typeName = field.getType().getName();
                    if (typeName.equals("java.lang.Integer")){
                        field.set(dog, Integer.parseInt(value));
                    }else {
                        field.set(dog, value);
                    }
                }
            }
            printObject(dog);
        }

    }

    public static void printObject(Object ob) {
        Field[] fields = ob.getClass().getDeclaredFields();//获取所有属性
        String s = ob.getClass().getName();
        System.out.print( s.substring( s.lastIndexOf(".")+1 )+ " {");
        Arrays.stream(fields).forEach(field -> {
            //获取是否可访问
            boolean flag = field.isAccessible();
            try {
                //设置该属性总是可访问
                field.setAccessible(true);
                System.out.print( field.getName() + "=" + field.get(ob) + ", ");
            } catch (IllegalAccessException e) {
                e.printStackTrace();
            }
            //还原可访问权限
            field.setAccessible(flag);
        });
        System.out.println("}");
    }

}