Documentation

Event Notify

Before calling, after calling, when an exception occurs,will trigger oninvoke, onreturn, onthrow events.You can configure which method to notify when an event occurs.

Service Interface

interface IDemoService {
    public Person get(int id);
}

Service provider implement the service.

class NormalDemoService implements IDemoService {
    public Person get(int id) {
        return new Person(id, "charles`son", 4);
    }
}

Service provider configure the service which it provided.

<dubbo:application name="rpc-callback-demo" />
<dubbo:registry address="zookeeper://127.0.0.1:2181"/>
<bean id="demoService" class="org.apache.dubbo.callback.implicit.NormalDemoService" />
<dubbo:service interface="org.apache.dubbo.callback.implicit.IDemoService" ref="demoService" version="1.0.0" group="cn"/>

Declare the Callback interface at service consumer-side.

interface Notify {
    public void onreturn(Person msg, Integer id);
    public void onthrow(Throwable ex, Integer id);
}

Implement the Callback at service consumer-side.

class NotifyImpl implements Notify {
    public Map<Integer, Person>    ret    = new HashMap<Integer, Person>();
    public Map<Integer, Throwable> errors = new HashMap<Integer, Throwable>();

    public void onreturn(Person msg, Integer id) {
        System.out.println("onreturn:" + msg);
        ret.put(id, msg);
    }

    public void onthrow(Throwable ex, Integer id) {
        errors.put(id, ex);
    }
}

Configure the Callback at service consumer-side.

<bean id ="demoCallback" class = "org.apache.dubbo.callback.implicit.NofifyImpl" />
<dubbo:reference id="demoService" interface="org.apache.dubbo.callback.implicit.IDemoService" version="1.0.0" group="cn" >
      <dubbo:method name="get" async="true" onreturn = "demoCallback.onreturn" onthrow="demoCallback.onthrow" />
</dubbo:reference>

callback andasync functions are orthogonally decomposed. async = true means that the result is returned immediately.onreturn means that a callback is required.

There are several situations with the tow attributes[^2].

  • Asynchronous callback mode:async=true onreturn="xxx"
  • Synchronous callback mode:async=false onreturn="xxx"
  • Asynchronous no callback:async=true
  • Synchronous no callback:async=true

Testing code

IDemoService demoService = (IDemoService) context.getBean("demoService");
NofifyImpl notify = (NofifyImpl) context.getBean("demoCallback");
int requestId = 2;
Person ret = demoService.get(requestId);
Assert.assertEquals(null, ret);
//for Test:Just used to illustrate the normal callback callback, the specific business decisions.
for (int i = 0; i < 10; i++) {
    if (!notify.ret.containsKey(requestId)) {
        Thread.sleep(200);
    } else {
        break;
    }
}
Assert.assertEquals(requestId, notify.ret.get(requestId).getId());

NOTE2.0.7+ version,async=false is default.