《设计模式之禅》--代理扩展：动态代理

public interface Subject {
    //业务操作
    public void doSomething(String str);
}

public class RealSubject implements Subject {
    //业务操作
    public void doSomething(String str) {
        System.out.println("do something!---->" + str);
    }
}

public class MyInvocationHandler implements InvocationHandler {
    //被代理的对象
    private Object target = null;

    //通过构造函数传递一个对象
    public MyInvocationHandler(Object _obj) {
        this.target = _obj;
    }

    //代理方法
    public Object invoke(Object proxy, Method method, Object[] args)
            throws Throwable {
        //执行被代理的方法
        return method.invoke(this.target, args);
    }
}

public class DynamicProxy<T> {
    public static <T> T newProxyInstance(ClassLoader loader, Class<?>[] interfaces, InvocationHandler h) {
        //寻找JoinPoint连接点，AOP框架使用元数据定义
        if (true) {
            //执行一个前置通知
            (new BeforeAdvice()).exec();
        }
        //执行目标，并返回结果
        return (T) Proxy.newProxyInstance(loader, interfaces, h);
    }
}

public interface IAdvice {
    //通知只有一个方法，执行即可
    public void exec();
}

public class BeforeAdvice implements IAdvice {
    public void exec() {
        System.out.println("我是前置通知，我被执行了！");
    }
}

public class Client {
    public static void main(String[] args) {
        //定义一个主题
        Subject subject = new RealSubject();
        //定义一个Handler
        InvocationHandler handler = new MyInvocationHandler(subject);
        //定义主题的代理
        Subject proxy = DynamicProxy.newProxyInstance(subject.getClass().
                getClassLoader(), subject.getClass().getInterfaces(), handler);
        //代理的行为
        proxy.doSomething("Finish");
    }
}

我是前置通知，我被执行了！
do something!---->Finish

public class SubjectDynamicProxy extends DynamicProxy {
    public static <T> T newProxyInstance(Subject subject) {
        //获得ClassLoader
        ClassLoader loader = subject.getClass().getClassLoader();
        //获得接口数组
        Class<?>[] classes = subject.getClass().getInterfaces();
        //获得handler
        InvocationHandler handler = new MyInvocationHandler(subject);
        return newProxyInstance(loader, classes, handler);
    }
}

public class Client {
    public static void main(String[] args) {
        //定义一个主题
        Subject subject = new RealSubject();
        //定义主题的代理
        Subject proxy = SubjectDynamicProxy.newProxyInstance(subject);
        //代理的行为
        proxy.doSomething("Finish");
    }
}