参数回调 callbacks

效果：Consumer调用Provider方法，在Provider方法中回调Consumer提供的方法。

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。

服务接口示例

CallbackService.java

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

CallbackListener.java

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

服务提供者接口实现示例

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 (InterruptedException e) {
e.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());
}
}

服务提供者配置示例

<bean id="callbackService" class="com.ssmp.serviceImpl.CallbackServiceImpl" />
<dubbo:service interface="com.ssmp.service.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>

服务消费者配置示例

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

服务消费者调用示例

ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("classpath:META-INF/spring/user-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);
}
});
System.in.read();