简介

代理模式给某一个对象提供一个代理对象，并由代理对象控制对原对象的引用

实际应用场景

买火车票不一定在火车站买，也可以去代售点

UML

1、静态代理

2、动态代理

代码实现

/**
 * @author liuyongtao
 * @since 2021-3-15 12:00
 */
public interface Image {

    void display();
}

/**
 * @author liuyongtao
 * @since 2021-3-15 12:10
 */
public class PathImage implements Image {
    @Override
    public void display() {
        System.out.println(PathImage.class.getName());
    }
}

/**
 * @author liuyongtao
 * @since 2021-3-15 12:01
 */
public class RealImage implements Image {
    @Override
    public void display() {
        System.out.println(RealImage.class.getName());
    }
}

1、静态代理

/**
 * @author liuyongtao
 * @since 2021-3-15 12:02
 */
public class ProxyImage implements Image {

    private Image image;

    public ProxyImage(Image image) {
        this.image = image;
    }

    @Override
    public void display() {
        System.out.println(image.getClass().getName() + " 执行之前。。。");
        image.display();
        System.out.println(image.getClass().getName() + " 执行之后。。。");
    }

}

/**
 * @author liuyongtao
 * @since 2021-3-15 12:06
 */
public class Main {

    public static void main(String[] args) {
        ProxyImage proxyImage = new ProxyImage(new RealImage());
        proxyImage.display();
        System.out.println("==========");
        proxyImage = new ProxyImage(new PathImage());
        proxyImage.display();
    }
}

2、动态代理(JDK)

/**
 * @author liuyongtao
 * @since 2021-3-15 14:01
 */
public class DynamicProxyHandler<T> implements InvocationHandler {

    private T obj;

    public DynamicProxyHandler(T obj) {
        this.obj = obj;
    }

    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        System.out.println(obj.getClass().getName() + " 执行之前。。。");
        Object invoke = method.invoke(obj, args);
        System.out.println(obj.getClass().getName() + " 执行之后。。。");
        return invoke;
    }

    /**
     * 获取代码对象
     *
     * @return {@link T}
     * @author liuyongtao
     * @since 2021-3-15 14:16
     */
    public T proxy() {
        return (T) Proxy.newProxyInstance(obj.getClass().getClassLoader(), 
        obj.getClass().getInterfaces(), this);
    }
}

/**
 * @author liuyongtao
 * @since 2021-3-15 14:11
 */
public class Main {

    public static void main(String[] args) {
        DynamicProxyHandler<Image> proxyHandler= new DynamicProxyHandler<>(new RealImage());
        proxyHandler.proxy().display();
        System.out.println("==========");
        proxyHandler= new DynamicProxyHandler<>(new PathImage());
        proxyHandler.proxy().display();
    }
}