java使用动态代理来实现AOP（日志记录）

以下内容为原创，转载时请注明链接地址：http://www.cnblogs.com/tiantianbyconan/p/3336627.html

AOP（面向方面）的思想，就是把项目共同的那部分功能分离开来，比如日志记录，避免在业务逻辑里面夹杂着跟业务逻辑无关的代码。

下面是一个AOP实现的简单例子：

首先定义一些业务方法：

/**
 * Created with IntelliJ IDEA.
 * Author: wangjie  email:tiantian.china.2@gmail.com
 * Date: 13-9-23
 * Time: 下午3:49
 */
public interface BussinessService {
    public String login(String username, String password);
    public String find();
}

public class BussinessServiceImpl implements BussinessService {
    private Logger logger = Logger.getLogger(this.getClass().getSimpleName());

    @Override
    public String login(String username, String password) {
        return "login success";
    }

    @Override
    public String find() {
        return "find success";
    }

}

/**
 * Created with IntelliJ IDEA.
 * Author: wangjie  email:tiantian.china.2@gmail.com
 * Date: 13-9-24
 * Time: 上午10:27
 */
public interface WorkService {
    public String work();
    public String sleep();
}

public class WorkServiceImpl implements WorkService{
    @Override
    public String work() {
        return "work success";
    }

    @Override
    public String sleep() {
        return "sleep success";
    }
}

实现InvocationHandler接口，使用map来存储不同的InvocationHandler对象，避免生成过多。

package com.wangjie.aoptest2.invohandler;

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.util.Arrays;
import java.util.HashMap;
import java.util.logging.Logger;

/**
 * Created with IntelliJ IDEA.
 * Author: wangjie  email:tiantian.china.2@gmail.com
 * Date: 13-9-23
 * Time: 下午3:47
 */
public class LogInvoHandler implements InvocationHandler{
    private Logger logger = Logger.getLogger(this.getClass().getSimpleName());

    private Object target; // 代理目标
    private Object proxy; // 代理对象

    private static HashMap<Class<?>, LogInvoHandler> invoHandlers = new HashMap<Class<?>, LogInvoHandler>();

    private LogInvoHandler() {
    }

    /**
     * 通过Class来生成动态代理对象Proxy
     * @param clazz
     * @return
     */
    public synchronized static<T> T getProxyInstance(Class<T> clazz){
        LogInvoHandler invoHandler = invoHandlers.get(clazz);

        if(null == invoHandler){
            invoHandler = new LogInvoHandler();
            try {
                T tar = clazz.newInstance();
                invoHandler.setTarget(tar);
                invoHandler.setProxy(Proxy.newProxyInstance(tar.getClass().getClassLoader(),
                        tar.getClass().getInterfaces(), invoHandler));
            } catch (Exception e) {
                e.printStackTrace();
            }
            invoHandlers.put(clazz, invoHandler);

        }

        return (T)invoHandler.getProxy();
    }

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

        Object result = method.invoke(target, args); // 执行业务处理

        // 打印日志
        logger.info("____invoke method: " + method.getName()
                    + "; args: " + (null == args ? "null" : Arrays.asList(args).toString())
                    + "; return: " + result);


        return result;
    }

    public Object getTarget() {
        return target;
    }

    public void setTarget(Object target) {
        this.target = target;
    }

    public Object getProxy() {
        return proxy;
    }

    public void setProxy(Object proxy) {
        this.proxy = proxy;
    }
}

然后编写一个Test类测试：

/**
 * Created with IntelliJ IDEA.
 * Author: wangjie  email:tiantian.china.2@gmail.com
 * Date: 13-9-24
 * Time: 上午9:54
 */
public class Test {
    public static Logger logger = Logger.getLogger(Test.class.getSimpleName());
    public static void main(String[] args) {

        BussinessService bs = LogInvoHandler.getProxyInstance(BussinessServiceImpl.class);
        bs.login("zhangsan", "123456");
        bs.find();

        logger.info("--------------------------------------");

        WorkService ws = LogInvoHandler.getProxyInstance(WorkServiceImpl.class);
        ws.work();
        ws.sleep();

        logger.info("--------------------------------------");

        BussinessService bss = LogInvoHandler.getProxyInstance(BussinessServiceImpl.class);
        bss.login("lisi", "654321");
        bss.find();

    }
}

以后需要添加新的业务逻辑XXXService，只需要调用

XXXService xs = LogInvoHandler.getProxyInstance(XXXServiceImpl.class);

即可。

也可以模仿Spring等框架的配置，把bean的类名配置在xml文件中，如：

<bean id="bussinessService" class="com.wangjie.aoptest2.service.impl.BussinessServiceImpl">

然后在java代码中解析xml，通过Class.forName("com.wangjie.aoptest2.service.impl.BussinessServiceImpl");获得Class对象

然后通过LogInvoHandler.getProxyInstance(Class.forName("com.wangjie.aoptest2.service.impl.BussinessServiceImpl"));获得代理对象Proxy

再使用反射去调用代理对象的方法。

运行结果如下：

九月 24, 2013 11:08:03 上午 com.wangjie.aoptest2.invohandler.LogInvoHandler invoke
INFO: ____invoke method: login; args: [zhangsan, 123456]; return: login success
九月 24, 2013 11:08:03 上午 com.wangjie.aoptest2.invohandler.LogInvoHandler invoke
INFO: ____invoke method: find; args: null; return: find success
九月 24, 2013 11:08:03 上午 com.wangjie.aoptest2.Test main
INFO: --------------------------------------
九月 24, 2013 11:08:03 上午 com.wangjie.aoptest2.invohandler.LogInvoHandler invoke
INFO: ____invoke method: work; args: null; return: work success
九月 24, 2013 11:08:03 上午 com.wangjie.aoptest2.invohandler.LogInvoHandler invoke
INFO: ____invoke method: sleep; args: null; return: sleep success
九月 24, 2013 11:08:03 上午 com.wangjie.aoptest2.Test main
INFO: --------------------------------------
九月 24, 2013 11:08:03 上午 com.wangjie.aoptest2.invohandler.LogInvoHandler invoke
INFO: ____invoke method: login; args: [lisi, 654321]; return: login success
九月 24, 2013 11:08:03 上午 com.wangjie.aoptest2.invohandler.LogInvoHandler invoke
INFO: ____invoke method: find; args: null; return: find success