参数回调

通过参数回调从服务器端调用客户端逻辑

参数回调方式与调用本地 callback 或 listener 相同，只需要在 Spring 的配置文件中声明哪个参数是 callback 类型即可。Dubbo 将基于长连接生成反向代理，这样就可以从服务器端调用客户端逻辑。可以参考 dubbo 项目中的示例代码。

服务接口示例

CallbackService.java
  1. package com.callback;
  3. public interface CallbackService {
  4.     void addListener(String key, CallbackListener listener);
  5. }
CallbackListener.java
  1. package com.callback;
  3. public interface CallbackListener {
  4.     void changed(String msg);
  5. }

服务提供者接口实现示例

  1. package com.callback.impl;
  3. import java.text.SimpleDateFormat;
  4. import java.util.Date;
  5. import java.util.Map;
  6. import java.util.concurrent.ConcurrentHashMap;
  8. import com.callback.CallbackListener;
  9. import com.callback.CallbackService;
  11. public class CallbackServiceImpl implements CallbackService {
  13.     private final Map<String, CallbackListener> listeners = new ConcurrentHashMap<String, CallbackListener>();
  15.     public CallbackServiceImpl() {
  16.         Thread t = new Thread(new Runnable() {
  17.             public void run() {
  18.                 while(true) {
  19.                     try {
  20.                         for(Map.Entry<String, CallbackListener> entry : listeners.entrySet()){
  21.                            try {
  22.                                entry.getValue().changed(getChanged(entry.getKey()));
  23.                            } catch (Throwable t) {
  24.                                listeners.remove(entry.getKey());
  25.                            }
  26.                         }
  27.                         Thread.sleep(5000); // 定时触发变更通知
  28.                     } catch (Throwable t) { // 防御容错
  29.                         t.printStackTrace();
  30.                     }
  31.                 }
  32.             }
  33.         });
  34.         t.setDaemon(true);
  35.         t.start();
  36.     }
  38.     public void addListener(String key, CallbackListener listener) {
  39.         listeners.put(key, listener);
  40.         listener.changed(getChanged(key)); // 发送变更通知
  41.     }
  43.     private String getChanged(String key) {
  44.         return "Changed: " + new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(new Date());
  45.     }
  46. }

服务提供者配置示例

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

服务消费者配置示例

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

服务消费者调用示例

  1. ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("classpath:consumer.xml");
  2. context.start();
  4. CallbackService callbackService = (CallbackService) context.getBean("callbackService");
  6. callbackService.addListener("foo.bar", new CallbackListener(){
  7.     public void changed(String msg) {
  8.         System.out.println("callback1:" + msg);
  9.     }
  10. });

提示

2.0.6 及其以上版本支持

最后修改 September 21, 2021: Bug fix miss mialbox (#953) (57cf51b)