java使用动态代理来实现AOP（日志记录）

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：

 1 /**
 2  * Created with IntelliJ IDEA.
 3  * Author: wangjie  email:[e-mail]
 4  * Date: 13-9-23
 5  * Time: 下午3:49
 6  */
 7 public interface BussinessService {
 8     public String login(String username, String password);
 9     public String find();
10 }
11 
12 public class BussinessServiceImpl implements BussinessService {
13     private Logger logger = Logger.getLogger(this.getClass().getSimpleName());
14 
15     @Override
16     public String login(String username, String password) {
17         return "login success";
18     }
19 
20     @Override
21     public String find() {
22         return "find success";
23     }
24 
25 }

 1 /**
 2  * Created with IntelliJ IDEA.
 3  * Author: wangjie  email:[e-mail]
 4  * Date: 13-9-24
 5  * Time: 上午10:27
 6  */
 7 public interface WorkService {
 8     public String work();
 9     public String sleep();
10 }
11 
12 public class WorkServiceImpl implements WorkService{
13     @Override
14     public String work() {
15         return "work success";
16     }
17 
18     @Override
19     public String sleep() {
20         return "sleep success";
21     }
22 }

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

 1 /**
 2  * Created with IntelliJ IDEA.
 3  * Author: wangjie  email:[e-mail]
 4  * Date: 13-9-23
 5  * Time: 下午3:47
 6  */
 7 public class LogInvoHandler implements InvocationHandler{
 8     private Logger logger = Logger.getLogger(this.getClass().getSimpleName());
 9 
10     private Object target; // 代理目标
11     private Object proxy; // 代理对象
12 
13     private static HashMap<Class<?>, LogInvoHandler> invoHandlers = new HashMap<Class<?>, LogInvoHandler>();
14 
15     private LogInvoHandler() {
16     }
17 
18     /**
19      * 通过Class来生成动态代理对象Proxy
20      * @param clazz
21      * @return
22      */
23     public synchronized static Object getProxyInstance(Class<?> clazz){
24         LogInvoHandler invoHandler = invoHandlers.get(clazz);
25 
26         if(null == invoHandler){
27             invoHandler = new LogInvoHandler();
28             try {
29                 Object tar = clazz.newInstance();
30                 invoHandler.setTarget(tar);
31                 invoHandler.setProxy(Proxy.newProxyInstance(tar.getClass().getClassLoader(),
32                         tar.getClass().getInterfaces(), invoHandler));
33             } catch (Exception e) {
34                 e.printStackTrace();
35             }
36             invoHandlers.put(clazz, invoHandler);
37 
38         }
39 
40         return invoHandler.getProxy();
41     }
42 
43     @Override
44     public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
45 
46         Object result = method.invoke(target, args); // 执行业务处理
47 
48         // 打印日志
49         logger.info("____invoke method: " + method.getName()
50                     + "; args: " + (null == args ? "null" : Arrays.asList(args).toString())
51                     + "; return: " + result);
52 
53 
54         return result;
55     }
56 
57     public Object getTarget() {
58         return target;
59     }
60 
61     public void setTarget(Object target) {
62         this.target = target;
63     }
64 
65     public Object getProxy() {
66         return proxy;
67     }
68 
69     public void setProxy(Object proxy) {
70         this.proxy = proxy;
71     }
72 }

然后编写一个Test类测试：

 1 /**
 2  * Created with IntelliJ IDEA.
 3  * Author: wangjie  email:[e-mail]
 4  * Date: 13-9-24
 5  * Time: 上午9:54
 6  */
 7 public class Test {
 8     public static Logger logger = Logger.getLogger(Test.class.getSimpleName());
 9     public static void main(String[] args) {
10 
11         BussinessService bs = (BussinessService)LogInvoHandler.getProxyInstance(BussinessServiceImpl.class);
12         bs.login("zhangsan", "123456");
13         bs.find();
14 
15         logger.info("--------------------------------------");
16 
17         WorkService ws = (WorkService)LogInvoHandler.getProxyInstance(WorkServiceImpl.class);
18         ws.work();
19         ws.sleep();
20 
21         logger.info("--------------------------------------");
22 
23         BussinessService bss = (BussinessService)LogInvoHandler.getProxyInstance(BussinessServiceImpl.class);
24         bss.login("lisi", "654321");
25         bss.find();
26 
27     }
28 }

以后需要添加新的业务逻辑XXXService，只需要调用

XXXService xs = (XXXService)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