代理模式

公用接口和实现

public interface Calculator {
    public Integer add(Integer num1, Integer num2);
    public Integer minus(Integer num1, Integer num2);
}

public class CalculatorImpl implements Calculator {
 
    @Override
    public Integer add(Integer num1, Integer num2) {
        int ret = num1 + num2;
        System.out.println("in calculatorImpl, res: " + ret);
        return ret;
    }
     
    @Override
    public Integer minus(Integer num1, Integer num2) {
        int ret = num1 - num2;
        System.out.println("int calculatorImpl, res: " + ret);
        return ret;
    }
}

静态代理

public class StaticCalculatorProxy implements Calculator {
    Calculator obj;
     
    public StaticCalculatorProxy(Calculator obj) {
        this.obj = obj; 
    }
 
    @Override
    public Integer add(Integer num1, Integer num2) {
        System.out.println("in StaticCalculatorProxy, before invocation");
        Integer ret = obj.add(num1, num2);
        System.out.println("in StaticCalculatorProxy, after invocation");
        return ret;
    }
 
    @Override
    public Integer minus(Integer num1, Integer num2) {
        System.out.println("in StaticCalculatorProxy, before invocation");
        Integer ret = obj.minus(num1, num2);
        System.out.println("in StaticCalculatorProxy, after invocation");
        return ret;
    }
 
}

测试代码：

public static void staticProxy() {
        CalculatorImpl calculator = new CalculatorImpl();
        StaticCalculatorProxy calculatorProxy = new StaticCalculatorProxy(calculator);
        calculatorProxy.add(1, 2);
        calculatorProxy.minus(2, 1);
    }

动态代理

public class CalculatorHandler implements InvocationHandler {
     
    private Object obj; //被代理类
    public CalculatorHandler(Object obj) {
        this.obj = obj;
    }
 
    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        System.out.println("in calculatorhandler, before invocation");
        Object ret = method.invoke(obj, args);  //执行被代理类方法
        System.out.println("in calculationhandler, after invocation");
        return ret;
    }
}

测试代码：

public static void dynamicProxy() {
        CalculatorImpl calculatorImpl = new CalculatorImpl();//被代理类
        CalculatorHandler calculatorHandler = new CalculatorHandler(calculatorImpl);
        Calculator calculator = (Calculator) Proxy.newProxyInstance(
                calculatorImpl.getClass().getClassLoader(),
                calculatorImpl.getClass().getInterfaces(), calculatorHandler);
        calculator.add(1, 2);
        calculator.minus(1, 2);
    }

动态代理的好处

无论calculator中包含多少函数，动态代理只需实现一次，实际工程中，System.out.println(“in calculatorhandler, before invocation”)可能是加缓存，打日志等操作。

代理模式和装饰器模式的区别

• 装饰器模式关注于在一个对象上动态的添加方法，然而代理模式关注于控制对对象的访问；
• 使用代理模式，代理和真实对象之间的的关系通常在编译时就已经确定了，而装饰者能够在运行时递归地被构造；

代理器模式在插件化中的应用

Android插件化原理解析——Hook机制之动态代理
动态加载APK原理分享

参考文章

JAVA 动态代理