动态代理

要理解动态代理首先要理解代理或者说代理模式。

代理模式

屏幕快照 2020-04-09 下午2.39.14.png

代理模式非常简单，被代理类和代理类实现同一个接口，并且在代理类的中有被代理类的实例。

举一个实际的例子

[IWork.java]

public interface IWork {
    void work();
}

[Actor.java]

public class Actor implements IWork {
    @Override
    public void work() {
        System.out.println("Actor must act movie!'");
    }
}

[Agent.java]

public class Agent implements IWork {
    private Actor mActor;

    public Agent(Actor actor) {
        mActor = actor;
    }

    @Override
    public void work() {
        System.out.println("Agent receive job and money!'");
        mActor.work();
    }
}

[ProxyPattern.java]

public class ProxyPattern {
    public static void main(String[] args) {
        Agent agent = new Agent(new Actor());

        agent.work();
    }
}

动态代理

代理模式明白了之后，动态代理其实就很简单了，Java中通过自带的特性，可以动态生成一个实例的的代理实例，在代理实例的回调方法中进行业务的处理。下面我们通过实际例子实现上面静态代理的功能。

[IWork.java]

public interface IWork {
    void work();
}

[Actor.java]

public class Actor implements IWork {
    @Override
    public void work() {
        System.out.println("Actor must act movie!'");
    }
}

[DynamicProxyHandler.java]

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;

public class DynamicProxyHandler implements InvocationHandler {
    private Object target;

    public DynamicProxyHandler(Object target) {
        this.target = target;
    }

    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        if (method.getName().equals("work")) {
            System.out.println("Agent receive job and money!'");
        }

        method.invoke(target, args);
        return null;
    }

    public static void main(String[] args) {
        Actor actor = new Actor();
        DynamicProxyHandler dynamicProxyHandler = new DynamicProxyHandler(actor);

        IWork worker = (IWork) Proxy.newProxyInstance(
                IWork.class.getClassLoader(),
                new Class[] {IWork.class},
                dynamicProxyHandler);

        worker.work();
    }
}