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其他网址

注解设值/取值

简介

属性可以是单个对象，也可以是数组

可以设值属性为枚举类型；

实例 

package org.example.a;import java.lang.annotation.*;import java.lang.reflect.Field;import java.util.ArrayList;import java.util.List;@Retention(RetentionPolicy.RUNTIME)@Target({ElementType.FIELD})@Documented@interface Parent {    Color[] value() default {};}@Retention(RetentionPolicy.RUNTIME)@Target({ElementType.FIELD})@Documented@interface Bottom {    String name() default "";}enum Color {    RED,    @Bottom(name = "浅红色")    @Parent({RED})    LIGHT_RED,    @Bottom(name = "深红色")    @Parent({RED, LIGHT_RED})    DARK_RED;    List
    
      childrens = new ArrayList<>();    static List
     
       bottoms = new ArrayList<>();    static {        for (Color value : Color.values()) {            try {                Field field = Color.class.getField(value.name());                if (field.isAnnotationPresent(Bottom.class)) {                    bottoms.add(value);                }                Parent parent = field.getAnnotation(Parent.class);                if (parent != null) {                    for (Color color : parent.value()) {                        color.childrens.add(value);                    }                }            } catch (NoSuchFieldException e) {                e.printStackTrace();            }        }    }}public class Demo {    public static void main(String[] args) {        System.out.println("Color.RED.childrens:         " + Color.RED.childrens);        System.out.println("Color.LIGHT_RED.childrens:   " + Color.LIGHT_RED.childrens);        System.out.println("Color.bottoms:               " + Color.bottoms);        try {            Field field = Color.class.getField(Color.LIGHT_RED.name());            if (field.isAnnotationPresent(Bottom.class)) {                System.out.println("Color.LIGHT_RED的注解属性名： " +                        field.getAnnotation(Bottom.class).name());            }        } catch (NoSuchFieldException e) {            e.printStackTrace();        }    }}
     
    

执行结果

Color.RED.childrens:         [LIGHT_RED, DARK_RED]Color.LIGHT_RED.childrens:   [DARK_RED]Color.bottoms:               [LIGHT_RED, DARK_RED]Color.LIGHT_RED的注解属性名： 浅红色

Annotation+反射 实现工厂模式

其他网址

简介

需求：

代码 

package org.example.a;import java.lang.annotation.ElementType;import java.lang.annotation.Retention;import java.lang.annotation.RetentionPolicy;import java.lang.annotation.Target;import java.lang.reflect.InvocationHandler;import java.lang.reflect.Method;import java.lang.reflect.Proxy;//业务接口interface IMessage{    public void send(String msg);}//业务接口实现子类class IMessageImpl1 implements IMessage{    @Override    public void send(String msg) {        System.out.println("send(IMessageImpl1): " + msg);    }}//业务接口实现子类class IMessageImpl2 implements IMessage{    @Override    public void send(String msg) {        System.out.println("send(IMessageImpl2): " + msg);    }}class Factory{    private Factory() {}    public static 
    
      T getInstance(Class
     
       clazz) {        try {    //利用反射获取实例化对象            return (T) new MessageProxy().bind(clazz.getDeclaredConstructor().newInstance());        } catch (Exception e) {            return null;        }    }}class MessageProxy implements InvocationHandler {    private Object target;    public Object bind(Object target) {        this.target = target;        return Proxy.newProxyInstance(target.getClass().getClassLoader(), target.getClass().getInterfaces(), this);    }    public boolean connect() {        System.out.println("connect(proxy)");        return true;    }    public void close() {        System.out.println("close(proxy)");    }    @Override    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {        try {            if(this.connect()) {                return method.invoke(this.target, args);//代理调用            }else {                throw new Exception("cannont send");            }        } finally {            this.close();        }    }}@Target({ElementType.TYPE, ElementType.METHOD}) //只能用在类和方法上@Retention(RetentionPolicy.RUNTIME)@interface UseMessage{    //定义要使用的类型    public Class
       clazz();}//Annotation定义使用类。红色部分可以修改为其他实现类，实现调用不同类输出。@UseMessage(clazz = IMessageImpl1.class)class MessageService{    private IMessage message;        //定义业务处理    public MessageService() {        UseMessage use = MessageService.class.getAnnotation(UseMessage.class);        this.message = (IMessage) Factory.getInstance(use.clazz());    //通过Annotation获取    }    public void send(String msg) {        this.message.send(msg);    }}public class Demo {    public static void main(String[] args) {        MessageService messageService = new MessageService();        messageService.send("www.sina.com.cn");    }}
     
    

输出结果

connect(proxy)

send(IMessageImpl1): www.sina.com.cn

close(proxy)

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