dubbo的rpc服务如果使用的是长连接的协议，如dubbo协议，tcp长连接本身升双向异步的，dubbo内部通过监听返回结果，来实现方法调用的同步，所以性能上是有牺牲的；

在某些场景可以通过异步提升性能

 

服务消费者Callback接口及实现：

consumer.xml

 

 

注意点：因为是回调异步，异步处理的时候有时候需要，当时调用时候的一些对象，所有你可以

自己写个子类，继承入参，在新类里设置需要的内容，回调就可以带过来，（但新子类必须都实现序列号接口，不然回调不成功）；

 

详细参考：

com.alibaba.dubbo.rpc.protocol.dubbo.filter.FutureFilter

异常只有在onreturn的时候发生发生异常（返回异常，这里onreturn调用也是异常的），才调用

private void fireInvokeCallback(final Invoker
     invoker, final Invocation invocation) {        final Method onInvokeMethod = (Method)StaticContext.getSystemContext().get(StaticContext.getKey(invoker.getUrl(), invocation.getMethodName(), Constants.ON_INVOKE_METHOD_KEY));        final Object onInvokeInst = StaticContext.getSystemContext().get(StaticContext.getKey(invoker.getUrl(), invocation.getMethodName(), Constants.ON_INVOKE_INSTANCE_KEY));                if (onInvokeMethod == null  &&  onInvokeInst == null ){            return ;        }        if (onInvokeMethod == null  ||  onInvokeInst == null ){            throw new IllegalStateException("service:" + invoker.getUrl().getServiceKey() +" has a onreturn callback config , but no such "+(onInvokeMethod == null ? "method" : "instance")+" found. url:"+invoker.getUrl());        }        if (onInvokeMethod != null && ! onInvokeMethod.isAccessible()) {            onInvokeMethod.setAccessible(true);        }                Object[] params = invocation.getArguments();        try {            onInvokeMethod.invoke(onInvokeInst, params);        } catch (InvocationTargetException e) {            fireThrowCallback(invoker, invocation, e.getTargetException());        } catch (Throwable e) {            fireThrowCallback(invoker, invocation, e);        }    }

public class Test {    public static void main(String[] args) {        DubboParam p = new DubboParam();        DubboServiceManager dubboServiceManager = new DubboServiceManager(p);                RetrunNotify notify=new RetrunNotify();                ReferenceConfig
    
      ref=dubboServiceManager.getChatHisServiceReference();                List
     
        list=new ArrayList
      
       ();        MethodConfig methodConfig=new MethodConfig();        methodConfig.setName("insert");        methodConfig.setAsync(true);        methodConfig.setOnreturn(notify);        methodConfig.setOnreturnMethod("onreturn");        methodConfig.setOnthrow(notify);        methodConfig.setOnthrowMethod("onthrow");        list.add(methodConfig);                                ref.setMethods(list);                                ChatHisDTONotify his = new ChatHisDTONotify();         Random r = new Random();        try {            his.setSenderId(r.nextLong());            his.setMsg(" msg" + r.nextInt());            his.setReceiverId(r.nextLong());            his.setDomainId(1L);            his.setA(100);            his.setC(new Date());            ResponseDTO
       
         a = ref.get().insert(his);                       System.out.println("onreturn:" + a);        } catch (Exception e) {            // TODO: handle exception        }      }        public static class ChatHisDTONotify extends ChatHisDTO{                Object c;                int a;        public int getA() {            return a;        }        public void setA(int a) {            this.a = a;        }        @Override        public String toString() {            return "ChatHisDTONotify [c=" + c + ", a=" + a + "]";        }        public Object getC() {            return c;        }        public void setC(Object c) {            this.c = c;        }            }        public static class RetrunNotify{           private int maxSize=20000;           Map
        
          map=new ConcurrentHashMap
         
          (); public void onreturn(ResponseDTO
          
            a,ChatHisDTONotify msg) { System.out.println(a.getDataResult()); System.out.println("onreturn:" + msg); throw new RuntimeException("xxxxx"); } public void onthrow(Throwable ex,ChatHisDTONotify msg ){ System.out.println(msg.getA()); } }}
          
         
        
       
      
     
    

问题：

 dubbo的异步调用发现个问题

A -----[异步]-->    B   --[同步调用]-->C B同步dubbo调用C，就好直接返回null

如果B下一步还有同步调用D，就会正确；

待调查