9.5 dubbo事件通知机制

dubbo事件通知机制：http://dubbo.io/books/dubbo-user-book/demos/events-notify.html

一、使用方式

两个服务：

• DemoService：真正要调用的服务
• Notify：事件通知服务（用在consumer端）

provider：

1 package com.alibaba.dubbo.demo;
2 
3 public interface DemoService {
4     String sayHello(String name);
5 }

1 public class DemoServiceImpl implements DemoService {
2     @Override
3     public String sayHello(String name) {
4         throw new RpcException("ex, param: " + name);//测试onthrow方法
5 //        return "Hello " + name;//测试onreturn方法
6     }
7 }

consumer：

通知服务：Notify

1 package com.alibaba.dubbo.demo.consumer.eventnotify;
2 
3 public interface Notify {
4     void oninvoke(String name); // 调用之前
5     void onreturnWithoutParam(String result); // 调用之后
6     void onreturn(String result, String name); // 调用之后
7     void onthrow(Throwable ex, String name);  // 出现异常
8 }

 1 package com.alibaba.dubbo.demo.consumer.eventnotify;
 2 
 3 public class NotifyService implements Notify {
 4     @Override
 5     public void oninvoke(String name) {
 6         System.out.println("======oninvoke======, param: " + name);
 7     }
 8 
 9     @Override
10     public void onreturnWithoutParam(String result) {
11         System.out.println("======onreturn======, result: " + result);
12     }
13 
14     @Override
15     public void onreturn(String result, String name) {
16         System.out.println("======onreturn======, param: " + name + ", result: " + result);
17     }
18 
19     @Override
20     public void onthrow(Throwable ex, String name) {
21         System.out.println("======onthrow======, param: " + name + ", exception: " + ex.getMessage());
22     }
23 }

xml配置：

1     <bean id="notifyService"  class="com.alibaba.dubbo.demo.consumer.eventnotify.NotifyService"/>
2     <dubbo:reference id="demoService" check="false" interface="com.alibaba.dubbo.demo.DemoService">
3         <dubbo:method name="sayHello" timeout="60000" oninvoke="notifyService.oninvoke" onreturn="notifyService.onreturnWithoutParam" onthrow="notifyService.onthrow"/>
4     dubbo:reference>

之后就可以运行Consumer启动类，之后调用demoService.sayHello(String name)了。

注意：

• oninvoke方法：
  • 必须具有与真实的被调用方法sayHello相同的入参列表：例如，oninvoke(String name)
• onreturn方法：
  • 至少要有一个入参且第一个入参必须与sayHello的返回类型相同，接收返回结果：例如，onreturnWithoutParam(String result)
  • 可以有多个参数，多个参数的情况下，第一个后边的所有参数都是用来接收sayHello入参的：例如， onreturn(String result, String name)
• onthrow方法：
  • 至少要有一个入参且第一个入参类型为Throwable或其子类，接收返回结果；例如，onthrow(Throwable ex)
  • 可以有多个参数，多个参数的情况下，第一个后边的所有参数都是用来接收sayHello入参的：例如，onthrow(Throwable ex, String name)
• 如果是consumer在调用provider的过程中，出现异常时不会走onthrow方法的，onthrow方法只会在provider返回的RpcResult中含有Exception对象时，才会执行。（dubbo中下层服务的Exception会被放在响应RpcResult的exception对象中传递给上层服务）

 

二、源码解析

整个事件通知的逻辑都在FutureFilter中，来看一下源码：

  1 /**
  2  * EventFilter
  3  */
  4 @Activate(group = Constants.CONSUMER)
  5 public class FutureFilter implements Filter {
  6 
  7     protected static final Logger logger = LoggerFactory.getLogger(FutureFilter.class);
  8 
  9     public Result invoke(final Invoker invoker, final Invocation invocation) throws RpcException {
 10         final boolean isAsync = RpcUtils.isAsync(invoker.getUrl(), invocation);
 11 
 12         //1 调用服务之前：执行xxxService.oninvoke方法
 13         fireInvokeCallback(invoker, invocation);
 14         //2 调用服务
 15         Result result = invoker.invoke(invocation);
 16         //3 调用服务之后
 17         if (isAsync) {
 18             asyncCallback(invoker, invocation);
 19         } else {
 20             syncCallback(invoker, invocation, result);
 21         }
 22         //4 返回调用结果
 23         return result;
 24     }
 25 
 26     private void syncCallback(final Invoker invoker, final Invocation invocation, final Result result) {
 27         if (result.hasException()) {
 28             //3.1 调用服务之后：如果返回结果异常信息（注意：如果是consumer自己throw的异常，会在2的时候直接抛走，不会走到这里），直接执行xxxService.onthrow方法
 29             fireThrowCallback(invoker, invocation, result.getException());
 30         } else {
 31             //3.2 调用服务之后：如果返回值正常，执行xxxService.onreturn方法
 32             fireReturnCallback(invoker, invocation, result.getValue());
 33         }
 34     }
 35 
 36     private void asyncCallback(final Invoker invoker, final Invocation invocation) {
 37         Future f = RpcContext.getContext().getFuture();
 38         if (f instanceof FutureAdapter) {
 39             ResponseFuture future = ((FutureAdapter) f).getFuture();
 40             // 3.1 调用服务之后：设置回调ResponseCallback对象到DefaultFuture中，当provider返回响应时，执行DefaultFuture.doReceived方法，该方法会调用ResponseCallback对象的done或者caught方法
 41             future.setCallback(new ResponseCallback() {
 42                 public void done(Object rpcResult) {
 43                     if (rpcResult == null) {
 44                         logger.error(new IllegalStateException("invalid result value : null, expected " + Result.class.getName()));
 45                         return;
 46                     }
 47                     ///must be rpcResult
 48                     if (!(rpcResult instanceof Result)) {
 49                         logger.error(new IllegalStateException("invalid result type :" + rpcResult.getClass() + ", expected " + Result.class.getName()));
 50                         return;
 51                     }
 52                     Result result = (Result) rpcResult;
 53                     if (result.hasException()) {
 54                         fireThrowCallback(invoker, invocation, result.getException());
 55                     } else {
 56                         fireReturnCallback(invoker, invocation, result.getValue());
 57                     }
 58                 }
 59 
 60                 public void caught(Throwable exception) {
 61                     fireThrowCallback(invoker, invocation, exception);
 62                 }
 63             });
 64         }
 65     }
 66 
 67     /**
 68      * 反射执行xxxService.oninvoke方法：必须具有与真实的被调用方法sayHello相同的入参列表。
 69      */
 70     private void fireInvokeCallback(final Invoker invoker, final Invocation invocation) {
 71         final Method onInvokeMethod = (Method) StaticContext.getSystemContext().get(StaticContext.getKey(invoker.getUrl(), invocation.getMethodName(), Constants.ON_INVOKE_METHOD_KEY));
 72         final Object onInvokeInst = StaticContext.getSystemContext().get(StaticContext.getKey(invoker.getUrl(), invocation.getMethodName(), Constants.ON_INVOKE_INSTANCE_KEY));
 73 
 74         if (onInvokeMethod == null && onInvokeInst == null) {
 75             return;
 76         }
 77         if (onInvokeMethod == null || onInvokeInst == null) {
 78             throw new IllegalStateException("service:" + invoker.getUrl().getServiceKey() + " has a onreturn callback config , but no such " + (onInvokeMethod == null ? "method" : "instance") + " found. url:" + invoker.getUrl());
 79         }
 80         if (onInvokeMethod != null && !onInvokeMethod.isAccessible()) {
 81             onInvokeMethod.setAccessible(true);
 82         }
 83         // 获取真实方法sayHello传入的参数
 84         Object[] params = invocation.getArguments();
 85         try {
 86             onInvokeMethod.invoke(onInvokeInst, params);
 87         } catch (InvocationTargetException e) {
 88             fireThrowCallback(invoker, invocation, e.getTargetException());
 89         } catch (Throwable e) {
 90             fireThrowCallback(invoker, invocation, e);
 91         }
 92     }
 93 
 94     /**
 95      * 反射执行xxxService.onreturn方法：至少要有一个入参，接收返回结果
 96      */
 97     private void fireReturnCallback(final Invoker invoker, final Invocation invocation, final Object result) {
 98         final Method onReturnMethod = (Method) StaticContext.getSystemContext().get(StaticContext.getKey(invoker.getUrl(), invocation.getMethodName(), Constants.ON_RETURN_METHOD_KEY));
 99         final Object onReturnInst = StaticContext.getSystemContext().get(StaticContext.getKey(invoker.getUrl(), invocation.getMethodName(), Constants.ON_RETURN_INSTANCE_KEY));
100 
101         //not set onreturn callback
102         if (onReturnMethod == null && onReturnInst == null) {
103             return;
104         }
105 
106         if (onReturnMethod == null || onReturnInst == null) {
107             throw new IllegalStateException("service:" + invoker.getUrl().getServiceKey() + " has a onreturn callback config , but no such " + (onReturnMethod == null ? "method" : "instance") + " found. url:" + invoker.getUrl());
108         }
109         if (onReturnMethod != null && !onReturnMethod.isAccessible()) {
110             onReturnMethod.setAccessible(true);
111         }
112 
113         Object[] args = invocation.getArguments();
114         Object[] params;
115         Class[] rParaTypes = onReturnMethod.getParameterTypes();
116         if (rParaTypes.length > 1) {
117             // onreturn(xx, Object[]) 两个参数：第一个参数与真实方法sayHello方法返回结果类型相同，第二个接收所有的真实请求参数
118             if (rParaTypes.length == 2 && rParaTypes[1].isAssignableFrom(Object[].class)) {
119                 params = new Object[2];
120                 params[0] = result; // 真实方法的执行结果
121                 params[1] = args;   // 真实方法sayHello传入的参数
122             // onreturn(xx, Object... args) 多个参数：第一个参数与真实方法sayHello方法返回结果类型相同，后边几个接收所有的真实请求参数
123             } else {
124                 params = new Object[args.length + 1];
125                 params[0] = result; // 真实方法的执行结果
126                 System.arraycopy(args, 0, params, 1, args.length);
127             }
128         } else {
129             // onreturn(xx) 只有一个参数：接收返回执行结果
130             params = new Object[]{result}; // 执行结果
131         }
132         try {
133             onReturnMethod.invoke(onReturnInst, params);
134         } catch (InvocationTargetException e) {
135             fireThrowCallback(invoker, invocation, e.getTargetException());
136         } catch (Throwable e) {
137             fireThrowCallback(invoker, invocation, e);
138         }
139     }
140 
141     /**
142      * 反射执行xxxService.onthrow方法：至少要有一个入参且第一个入参类型为Throwable或其子类，接收返回结果
143      */
144     private void fireThrowCallback(final Invoker invoker, final Invocation invocation, final Throwable exception) {
145         final Method onthrowMethod = (Method) StaticContext.getSystemContext().get(StaticContext.getKey(invoker.getUrl(), invocation.getMethodName(), Constants.ON_THROW_METHOD_KEY));
146         final Object onthrowInst = StaticContext.getSystemContext().get(StaticContext.getKey(invoker.getUrl(), invocation.getMethodName(), Constants.ON_THROW_INSTANCE_KEY));
147 
148         //onthrow callback not configured
149         if (onthrowMethod == null && onthrowInst == null) {
150             return;
151         }
152         if (onthrowMethod == null || onthrowInst == null) {
153             throw new IllegalStateException("service:" + invoker.getUrl().getServiceKey() + " has a onthrow callback config , but no such " + (onthrowMethod == null ? "method" : "instance") + " found. url:" + invoker.getUrl());
154         }
155         if (onthrowMethod != null && !onthrowMethod.isAccessible()) {
156             onthrowMethod.setAccessible(true);
157         }
158         Class[] rParaTypes = onthrowMethod.getParameterTypes();
159         if (rParaTypes[0].isAssignableFrom(exception.getClass())) {
160             try {
161                 Object[] args = invocation.getArguments();
162                 Object[] params;
163 
164                 if (rParaTypes.length > 1) {
165                     // onthrow(xx, Object[]) 两个参数：第一个参数接收exception，第二个接收所有的真实请求参数
166                     if (rParaTypes.length == 2 && rParaTypes[1].isAssignableFrom(Object[].class)) {
167                         params = new Object[2];
168                         params[0] = exception;
169                         params[1] = args;
170                     // onthrow(xx, Object... args) 多个参数：第一个参数接收exception，后边几个接收所有的真实请求参数
171                     } else {
172                         params = new Object[args.length + 1];
173                         params[0] = exception;
174                         System.arraycopy(args, 0, params, 1, args.length);
175                     }
176                 } else {
177                     // onthrow(xx) 只有一个参数：接收exception
178                     params = new Object[]{exception};
179                 }
180                 onthrowMethod.invoke(onthrowInst, params);
181             } catch (Throwable e) {
182                 logger.error(invocation.getMethodName() + ".call back method invoke error . callback method :" + onthrowMethod + ", url:" + invoker.getUrl(), e);
183             }
184         } else {
185             logger.error(invocation.getMethodName() + ".call back method invoke error . callback method :" + onthrowMethod + ", url:" + invoker.getUrl(), exception);
186         }
187     }
188 }

从@Activate(group = Constants.CONSUMER)来看FutureFilter只用在consumer端；不管是同步调用还是异步调用，都会走FutureFilter。

原理：

• 首先走oninvoke(String name)方法；
• 然后走sayHello(String name)
• 最后根据同步还是异步分别走不同的逻辑。 

其中同步很简单，看sayHello(String name)的返回结果RpcResult中是否有exception对象，如果有，执行onthrow(Throwable ex, String name)；如果没有执行onreturnWithoutParam(String result)。

异步的操作：由于不知道provider什么时候回执行完毕，所以要添加回调等待provider端返回结果后，再执行onthrow(Throwable ex, String name)或者onreturnWithoutParam(String result)，这种模式很重要，这是统计异步方法调用时间的一种非常好的模式。

重点看一下异步！

 

三、异步回调模式

 1     private void asyncCallback(final Invoker invoker, final Invocation invocation) {
 2         Future f = RpcContext.getContext().getFuture();
 3         if (f instanceof FutureAdapter) {
 4             ResponseFuture future = ((FutureAdapter) f).getFuture();
 5             // 3.1 调用服务之后：设置回调ResponseCallback对象到DefaultFuture中，当provider返回响应时，执行DefaultFuture.doReceived方法，该方法会调用ResponseCallback对象的done或者caught方法
 6             future.setCallback(new ResponseCallback() {
 7                 public void done(Object rpcResult) {
 8                     if (rpcResult == null) {
 9                         logger.error(new IllegalStateException("invalid result value : null, expected " + Result.class.getName()));
10                         return;
11                     }
12                     ///must be rpcResult
13                     if (!(rpcResult instanceof Result)) {
14                         logger.error(new IllegalStateException("invalid result type :" + rpcResult.getClass() + ", expected " + Result.class.getName()));
15                         return;
16                     }
17                     Result result = (Result) rpcResult;
18                     if (result.hasException()) {
19                         fireThrowCallback(invoker, invocation, result.getException());
20                     } else {
21                         fireReturnCallback(invoker, invocation, result.getValue());
22                     }
23                 }
24 
25                 public void caught(Throwable exception) {
26                     fireThrowCallback(invoker, invocation, exception);
27                 }
28             });
29         }
30     }

上述的future对象是DefaultFuture，这里首先new了一个ResponseCallback回调函数，设置到了DefaultFuture的ResponseCallback callback属性中。来看一下DefaultFuture类：

 1     private volatile Response response;
 2     private volatile ResponseCallback callback;
 3 
 4     public boolean isDone() {
 5         return response != null;
 6     }
 7 
 8     public void setCallback(ResponseCallback callback) {
 9         if (isDone()) {
10             invokeCallback(callback);
11         } else {
12             boolean isdone = false;
13             lock.lock();
14             try {
15                 if (!isDone()) {
16                     this.callback = callback;
17                 } else {
18                     isdone = true;
19                 }
20             } finally {
21                 lock.unlock();
22             }
23             if (isdone) {
24                 invokeCallback(callback);
25             }
26         }
27     }

 1     private void invokeCallback(ResponseCallback c) {
 2         ResponseCallback callbackCopy = c;
 3         if (callbackCopy == null) {
 4             throw new NullPointerException("callback cannot be null.");
 5         }
 6         c = null;
 7         Response res = response;
 8         if (res == null) {
 9             throw new IllegalStateException("response cannot be null. url:" + channel.getUrl());
10         }
11 
12         if (res.getStatus() == Response.OK) {
13             try {
14                 // 返回正常，回调ResponseCallback回调函数的done方法
15                 callbackCopy.done(res.getResult());
16             } catch (Exception e) {
17                 logger.error("callback invoke error .reasult:" + res.getResult() + ",url:" + channel.getUrl(), e);
18             }
19         } else if (res.getStatus() == Response.CLIENT_TIMEOUT || res.getStatus() == Response.SERVER_TIMEOUT) {
20             try {
21                 TimeoutException te = new TimeoutException(res.getStatus() == Response.SERVER_TIMEOUT, channel, res.getErrorMessage());
22                 // 如果超时，回调ResponseCallback回调函数的caught方法
23                 callbackCopy.caught(te);
24             } catch (Exception e) {
25                 logger.error("callback invoke error ,url:" + channel.getUrl(), e);
26             }
27         } else {
28             try {
29                 RuntimeException re = new RuntimeException(res.getErrorMessage());
30                 // 其他异常，回调ResponseCallback回调函数的caught方法
31                 callbackCopy.caught(re);
32             } catch (Exception e) {
33                 logger.error("callback invoke error ,url:" + channel.getUrl(), e);
34             }
35         }
36     }

从setCallback(ResponseCallback callback)，如果此时provider端已经返回了响应（response!=null），则直接执行ResponseCallback回调函数中的done方法或者caught方法；否则，将上边创建的ResponseCallback实例赋值给DefaultFuture的ResponseCallback callback属性中。那么之后会在什么时候执行回调函数的方法呢？当consumer接收到provider的响应的时候！

 1     public static void received(Channel channel, Response response) {
 2         try {
 3             DefaultFuture future = FUTURES.remove(response.getId());
 4             if (future != null) {
 5                 future.doReceived(response);
 6             } else {
 7                 logger.warn("The timeout response finally returned at "
 8                         + (new SimpleDateFormat("yyyy-MM-dd HH:mm:ss.SSS").format(new Date()))
 9                         + ", response " + response
10                         + (channel == null ? "" : ", channel: " + channel.getLocalAddress()
11                         + " -> " + channel.getRemoteAddress()));
12             }
13         } finally {
14             CHANNELS.remove(response.getId());
15         }
16     }
17 
18     private void doReceived(Response res) {
19         lock.lock();
20         try {
21             response = res;
22             if (done != null) {
23                 done.signal();
24             }
25         } finally {
26             lock.unlock();
27         }
28         // 调用回调函数
29         if (callback != null) {
30             invokeCallback(callback);
31         }
32     }

当provider返回响应时，会调用DefaultFuture.received(Channel channel, Response response)方法（9.3 客户端接收响应信息(异步转同步的实现)），此时会执行回调函数。事件通知的源码就分析完了！最后看一个回调模式的使用场景：统计异步方法的调用时间。

 1     private void asyncCallback(final Invoker invoker, final Invocation invocation) {
 2         Future f = RpcContext.getContext().getFuture();
 3         final long start = System.currentTimeMillis();
 4         if (f instanceof FutureAdapter) {
 5             ResponseFuture future = ((FutureAdapter) f).getFuture();
 6             future.setCallback(new ResponseCallback() {
 7                 public void done(Object rpcResult) {
 8                     long cost = System.currentTimeMillis() - start;
 9                 }
10             });
11         }
12     }

上边的代码只是一个形式，实际上start时间需要在调用sayHello方法之前进行记录。