doubbo的参数回调

        参数回调实现了在客户端调用服务时，将回调方法做为参数传递给服务端。当服务端提供服务时会调用执行客户回调方法，从而执行客户端自定义的一些操作。

以下为具体实现方式：

服务端服务接口

public interface CallbackService {
    void addListener(String key, CallbackListener listener);
}

public interface CallbackListener {
    void changed(String msg);
}

 服务端接口实现

public class CallbackServiceImpl implements CallbackService {
     
    private final Map<String, CallbackListener> listeners = new ConcurrentHashMap<String, CallbackListener>();
  
    public CallbackServiceImpl() {
        Thread t = new Thread(new Runnable() {
            public void run() {
                while(true) {
                    try {
                        for(Map.Entry<String, CallbackListener> entry : listeners.entrySet()){
                           try {
                               entry.getValue().changed(getChanged(entry.getKey()));
                           } catch (Throwable t) {
                               listeners.remove(entry.getKey());
                           }
                        }
                        Thread.sleep(5000); // 定时触发变更通知
                    } catch (Throwable t) { // 防御容错
                        t.printStackTrace();
                    }
                }
            }
        });
        t.setDaemon(true);
        t.start();
    }
  
    public void addListener(String key, CallbackListener listener) {
        listeners.put(key, listener);
        listener.changed(getChanged(key)); // 发送变更通知
    }
     
    private String getChanged(String key) {
        return "Changed: " + new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(new Date());
    }
 
}

 服务端配置

<bean id="callbackService" class="com.callback.impl.CallbackServiceImpl" />
<dubbo:service interface="com.callback.CallbackService" ref="callbackService" connections="1" callbacks="1000" protocol="dubbo">
    <dubbo:method name="addListener">
        <dubbo:argument index="1" callback="true" />
        <!--也可以通过指定类型的方式-->
        <!--<dubbo:argument type="com.demo.CallbackListener" callback="true" />-->
    </dubbo:method>
</dubbo:service>

服务消费端配置

<dubbo:reference id="callbackService" interface="com.callback.CallbackService" />

 服务消费端调用

CallbackService callbackService = (CallbackService) context.getBean("callbackService");
 
callbackService.addListener("http://10.20.160.198/wiki/display/dubbo/foo.bar", new CallbackListener(){
    public void changed(String msg) {
        System.out.println("callback1:" + msg);
    }
});

 执行结果

callback1:Changed: 2016-06-17 14:15:05
callback2:Changed: 2016-06-17 14:15:05
callback2:Changed: 2016-06-17 14:15:06
callback1:Changed: 2016-06-17 14:15:06
callback2:Changed: 2016-06-17 14:15:11