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 [^1]。可以参考 dubbo 项目中的示例代码。
package com.callback; public interface CallbackService { void addListener(String key, CallbackListener listener); }
package com.callback; public interface CallbackListener { void changed(String msg); }
package com.callback.impl; import java.text.SimpleDateFormat; import java.util.Date; import java.util.Map; import java.util.concurrent.ConcurrentHashMap; import com.callback.CallbackListener; import com.callback.CallbackService; 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()); } }
<bean id="callbackService" class="com.callback.impl.CallbackServiceImpl" /> <dubbo:service interface="com.callback.CallbackService" ref="callbackService" connections="1" callbacks="1000"> <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>
<dubbo:reference id="callbackService" interface="com.callback.CallbackService" />
ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("classpath:consumer.xml"); context.start(); 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); } });
[^1]: 2.0.6
及其以上版本支持