S07 代理模式 示例（二） JDK动态代理

概述

• JDK 动态代理只能代理实现了接口的类；

动态代理代码

import designpattern.structural.proxy.Order;
import designpattern.structural.proxy.db.DataSourceContextHolder;

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

public class OrderServiceDynamicProxy implements InvocationHandler {

    private Object target;

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

    public Object bind(){
        Class cls = target.getClass();
        return Proxy.newProxyInstance(
                cls.getClassLoader(),
                cls.getInterfaces(),
                this);
    }

    @Override
    public Object invoke(Object proxy,
                         Method method,
                         Object[] args) throws Throwable {
        Object argObject = args[0];
        beforeMethod(argObject);
        Object object = method.invoke(target, args);
        afterMethod();
        return object;
    }

    private void beforeMethod(Object obj){
        int userId = 0;
        System.out.println("动态代理 before code");
        if(obj instanceof Order){
            Order order = (Order)obj;
            userId = order.getUserId();
        }
        int dbRouter = userId % 2;
        System.out.println("动态代理分配到【db" + dbRouter+"】处理数据");

        //todo 设置dataSource;
        DataSourceContextHolder.setDBType("db" + String.valueOf(dbRouter));
    }

    private void afterMethod(){
        System.out.println("动态代理 after code");
    }

}

public class Test {
    public static void main(String[] args) {
        Order order = new Order();
//        order.setUserId(2);
        order.setUserId(1);

        IOrderService orderServiceDynamicProxy =
                (IOrderService)
                        new OrderServiceDynamicProxy(new OrderServiceImpl())
                                .bind();
        orderServiceDynamicProxy.saveOrder(order);
    }
}

输出：

动态代理 before code
动态代理分配到【db1】处理数据
Service层调用Dao层添加Order
Dao层添加Order成功
动态代理 after code