所谓代理模式是指客户端并不直接调用实际的对象,而是通过调用代理,来间接的调用实际的对象。代理模式(Proxy Pattern)属于结构型模式。
你想喝奶茶,但是你不想自己去奶茶店买,而是找了外卖小哥送,这就是代理模式
package com.example.proxy;
/**
* 抽象对象角色 奶茶
*/
public interface BuyMilkyTea {
void buyMilkyTea();
}
package com.example.proxy;
/**
* 目标对象角色 我
*/
public class MyPeople implements BuyMilkyTea {
@Override
public void buyMilkyTea() {
System.out.println("我拿到奶茶");
}
}
package com.example.proxy;
/**
* 代理对象角色 外卖小哥
*/
public class TakeOutPeople implements BuyMilkyTea {
private BuyMilkyTea buyMilkyTea;
public TakeOutPeople(BuyMilkyTea buyMilkyTea) {
this.buyMilkyTea = buyMilkyTea;
}
@Override
public void buyMilkyTea() {
System.out.println("配送前操作,取奶茶");
buyMilkyTea.buyMilkyTea();
System.out.println("配送后操作,确认送达");
}
}
package com.example.proxy;
public class Test {
public static void main(String[] args) {
MyPeople myPeople = new MyPeople();
TakeOutPeople takeOutPeople = new TakeOutPeople(myPeople);
takeOutPeople.buyMilkyTea();
}
}
缺点: 代理类和委托类实现相同的接口,同时要实现相同的方法。这样就出现了大量的代码重复。如果接口增加一个方法,除了所有实现类需要实现这个方法外,所有代理类也需要实现此方法。增加了代码维护的复杂度。
动态代理有别于静态代理,是根据代理的对象,动态创建代理类。这样,就可以避免静态代理中代理类接口过多的问题。动态代理是实现方式,是通过反射来实现的,借助Java自带的java.lang.reflect.Proxy
,通过固定的规则生成。
其步骤如下:
InvocationHandler
接口,并重写该invoke
方法package com.example.dynamicproxy;
/**
* 抽象对象角色 奶茶
*/
public interface BuyMilkyTea {
void buyMilkyTea();
}
package com.example.dynamicproxy;
/**
* 目标对象角色 我
*/
public class MyPeople implements BuyMilkyTea {
@Override
public void buyMilkyTea() {
System.out.println("我拿到奶茶");
}
}
package com.example.dynamicproxy;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
/**
* 动态代理类
*/
public class DynamicTakeOutPeople implements InvocationHandler {
private Object object;
public DynamicTakeOutPeople(Object object) {
this.object = object;
}
@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
Object invoke = method.invoke(object, args);
return invoke;
}
}
package com.example.dynamicproxy;
import java.lang.reflect.Proxy;
public class Test {
public static void main(String[] args) {
MyPeople myPeople = new MyPeople();
DynamicTakeOutPeople dynamicTakeOutPeople = new DynamicTakeOutPeople(myPeople);
ClassLoader classLoader = dynamicTakeOutPeople.getClass().getClassLoader();
BuyMilkyTea buyMilkyTea = (BuyMilkyTea)Proxy.newProxyInstance(classLoader, new Class[]{BuyMilkyTea.class}, dynamicTakeOutPeople);
buyMilkyTea.buyMilkyTea();
}
}