Java 动态代理

什么是代理模式：

在类的定义与调用之间加入一个中间件，代替该类向外实现功能

 

 

有一个图书类，实现了将书给用户的操作，而 BookStore 作为 Book 的代理类，在其中实现了用户付款的逻辑，用户实际是通过 BookStore 来对 Book 类的方法进行调用

 

Java 中实现动态代理主要用两种方式：基于 jdk 的动态代理与基于 cglib 的动态代理

jdk 基于接口实现

cglib 基于继承实现

cglib 的效率由于 jdk 的效率

基于 jdk 的动态代理

Book

package com.example.j2eedemo.proxy.jdk.saleBook;

public interface Book {

    public void sale();

}

BookImpl

package com.example.j2eedemo.proxy.jdk.saleBook;

public class BookImpl implements Book {
    @Override
    public void sale() {
        System.out.println("已将图书交给用户");
    }
}

BookStore

package com.example.j2eedemo.proxy.jdk.saleBook;

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


public class BookStore implements InvocationHandler {

    // 被代理对象
    private Object target;

    public Object createProxyObject(Object target){
        this.target = target;

        return Proxy.newProxyInstance(target.getClass().getClassLoader(), target.getClass().getInterfaces(), this);
    }

    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {

        Object result;

        System.out.println("用户已付款");
        result = method.invoke(target, args);
        System.out.println("结束购买");

        return result;
    }
}

User

package com.example.j2eedemo.proxy.jdk.saleBook;


public class User {

    public static void main(String[] args) {

        BookStore store = new BookStore();

        Book book = (Book) store.createProxyObject(new BookImpl());

        book.sale();
    }

}

User 类运行结果

 

基于 cglib 的动态代理

Book

package com.example.j2eedemo.proxy.cglib.saleBook;


public class Book {

    public void sale(){
        System.out.println("已将图书交给用户");
    }

}

BookStore

package com.example.j2eedemo.proxy.cglib.saleBook;

import org.springframework.cglib.proxy.Enhancer;
import org.springframework.cglib.proxy.MethodInterceptor;
import org.springframework.cglib.proxy.MethodProxy;

import java.lang.reflect.Method;


public class BookStore implements MethodInterceptor {

    private Object target;

    public Object createBookProxy(Object target){
        this.target = target;

        Enhancer enhancer = new Enhancer();

        // 设置代理目标
        enhancer.setSuperclass(target.getClass());

        enhancer.setCallback(this);

        return enhancer.create();
    }

    @Override
    public Object intercept(Object o, Method method, Object[] objects, MethodProxy methodProxy) throws Throwable {
        Object result;

        System.out.println("用户已付款");
        result = method.invoke(target, objects);
        System.out.println("结束购买");

        return result;
    }
}

User

package com.example.j2eedemo.proxy.cglib.saleBook;


public class User {

    public static void main(String[] args) {
        BookStore store = new BookStore();

        Book book = (Book) store.createBookProxy(new Book());

        book.sale();
    }

}

运行结果