最近在学习Dubbo时，遇到了“java.lang.IllegalStateException: Failed to subscribe consumer://192.168.238.1/com.alibaba.dubbo.registry.RegistryService”错误信息。Dubbo采用Zookeeper作为注册中心。具体错误堆栈信息如下：
Exception in thread "main" java.lang.IllegalStateException: Failed to subscribe consumer://192.168.238.1/com.alibaba.dubbo.registry.RegistryService?application=demo-provider&callbacks=10000&connect.timeout=10000&dubbo=2.5.3&interface=com.alibaba.dubbo.registry.RegistryService&lazy=true&methods=lookup,unsubscribe,subscribe,unregister,register&pid=304200&reconnect=false&sticky=true&subscribe.1.callback=true&timeout=10000×tamp=1555682409594&unsubscribe.1.callback=false, cause: Failed to invoke the method subscribe in the service com.alibaba.dubbo.registry.RegistryService. Tried 3 times of the providers [127.0.0.1:2181] (1/1) from the registry 127.0.0.1:2181 on the consumer 192.168.238.1 using the dubbo version 2.5.3. Last error is: Invoke remote method timeout. at com.alibaba.dubbo.registry.support.FailbackRegistry.subscribe(FailbackRegistry.java:206) at com.alibaba.dubbo.registry.integration.RegistryDirectory.subscribe(RegistryDirectory.java:133) at com.alibaba.dubbo.registry.dubbo.DubboRegistryFactory.createRegistry(DubboRegistryFactory.java:80) at com.alibaba.dubbo.registry.support.AbstractRegistryFactory.getRegistry(AbstractRegistryFactory.java:94) at com.alibaba.dubbo.registry.RegistryFactory$Adpative.getRegistry(RegistryFactory$Adpative.java) at com.alibaba.dubbo.registry.integration.RegistryProtocol.getRegistry(RegistryProtocol.java:190) at com.alibaba.dubbo.registry.integration.RegistryProtocol.export(RegistryProtocol.java:109) at com.alibaba.dubbo.rpc.protocol.ProtocolFilterWrapper.export(ProtocolFilterWrapper.java:53) at com.alibaba.dubbo.rpc.protocol.ProtocolListenerWrapper.export(ProtocolListenerWrapper.java:54) at com.alibaba.dubbo.rpc.Protocol$Adpative.export(Protocol$Adpative.java) at com.alibaba.dubbo.config.ServiceConfig.doExportUrlsFor1Protocol(ServiceConfig.java:485) at com.alibaba.dubbo.config.ServiceConfig.doExportUrls(ServiceConfig.java:281) at com.alibaba.dubbo.config.ServiceConfig.doExport(ServiceConfig.java:242) at com.alibaba.dubbo.config.ServiceConfig.export(ServiceConfig.java:143) at com.alibaba.dubbo.config.spring.ServiceBean.onApplicationEvent(ServiceBean.java:109) at org.springframework.context.event.SimpleApplicationEventMulticaster.invokeListener(SimpleApplicationEventMulticaster.java:163) at org.springframework.context.event.SimpleApplicationEventMulticaster.multicastEvent(SimpleApplicationEventMulticaster.java:136) at org.springframework.context.support.AbstractApplicationContext.publishEvent(AbstractApplicationContext.java:381) at org.springframework.context.support.AbstractApplicationContext.publishEvent(AbstractApplicationContext.java:335) at org.springframework.context.support.AbstractApplicationContext.finishRefresh(AbstractApplicationContext.java:855) at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:541) at org.springframework.context.support.ClassPathXmlApplicationContext.<init>(ClassPathXmlApplicationContext.java:139) at org.springframework.context.support.ClassPathXmlApplicationContext.<init>(ClassPathXmlApplicationContext.java:93) at com.huangx.dubbo.provider.Provider.main(Provider.java:11) Caused by: com.alibaba.dubbo.rpc.RpcException: Failed to invoke the method subscribe in the service com.alibaba.dubbo.registry.RegistryService. Tried 3 times of the providers [127.0.0.1:2181] (1/1) from the registry 127.0.0.1:2181 on the consumer 192.168.238.1 using the dubbo version 2.5.3. Last error is: Invoke remote method timeout. method: subscribe, provider: dubbo://127.0.0.1:2181/com.alibaba.dubbo.registry... at com.alibaba.dubbo.rpc.cluster.support.FailoverClusterInvoker.doInvoke(FailoverClusterInvoker.java:101) at com.alibaba.dubbo.rpc.cluster.support.AbstractClusterInvoker.invoke(AbstractClusterInvoker.java:227) at com.alibaba.dubbo.rpc.cluster.support.wrapper.MockClusterInvoker.invoke(MockClusterInvoker.java:72) at com.alibaba.dubbo.rpc.proxy.InvokerInvocationHandler.invoke(InvokerInvocationHandler.java:52) at com.alibaba.dubbo.common.bytecode.proxy0.subscribe(proxy0.java) at com.alibaba.dubbo.registry.dubbo.DubboRegistry.doSubscribe(DubboRegistry.java:138) at com.alibaba.dubbo.registry.support.FailbackRegistry.subscribe(FailbackRegistry.java:189) ... 23 more Caused by: com.alibaba.dubbo.remoting.TimeoutException: Waiting server-side response timeout. start time: 2019-04-19 22:00:34.555, end time: 2019-04-19 22:00:44.568, client elapsed: 10 ms, server elapsed: 10002 ms, timeout: 10000 ms, request: Request [id=4, version=2.0.0, twoway=true, event=false, broken=false, data=RpcInvocation [methodName=subscribe, ... at com.alibaba.dubbo.remoting.exchange.support.DefaultFuture.get(DefaultFuture.java:107) at com.alibaba.dubbo.remoting.exchange.support.DefaultFuture.get(DefaultFuture.java:84) at com.alibaba.dubbo.rpc.protocol.dubbo.DubboInvoker.doInvoke(DubboInvoker.java:96) at com.alibaba.dubbo.rpc.protocol.AbstractInvoker.invoke(AbstractInvoker.java:144) at com.alibaba.dubbo.monitor.support.MonitorFilter.invoke(MonitorFilter.java:75) at com.alibaba.dubbo.rpc.protocol.ProtocolFilterWrapper$1.invoke(ProtocolFilterWrapper.java:91) at com.alibaba.dubbo.rpc.protocol.dubbo.filter.FutureFilter.invoke(FutureFilter.java:53) at com.alibaba.dubbo.rpc.protocol.ProtocolFilterWrapper$1.invoke(ProtocolFilterWrapper.java:91) at com.alibaba.dubbo.rpc.filter.ConsumerContextFilter.invoke(ConsumerContextFilter.java:48) at com.alibaba.dubbo.rpc.protocol.ProtocolFilterWrapper$1.invoke(ProtocolFilterWrapper.java:91) at com.alibaba.dubbo.rpc.listener.ListenerInvokerWrapper.invoke(ListenerInvokerWrapper.java:74) at com.alibaba.dubbo.rpc.protocol.InvokerWrapper.invoke(InvokerWrapper.java:53) at com.alibaba.dubbo.rpc.cluster.support.FailoverClusterInvoker.doInvoke(FailoverClusterInvoker.java:77) ... 29 more
根据上面的日志得知时订阅失败，等待服务响应超时。
解决思路如下：
（1）查看是不是ZooKeeper出现了问题，打开Zookeeper终端，出现下面日志：
2019-04-19 22:00:23,883 [myid:] - WARN [NIOServerCxn.Factory:0.0.0.0/0.0.0.0:2181:NIOServerCnxn@383] - Exception causing close of session 0x0: Len error -625229312 2019-04-19 22:00:23,885 [myid:] - INFO [NIOServerCxn.Factory:0.0.0.0/0.0.0.0:2181:NIOServerCnxn@1040] - Closed socket connection for client /192.168.238.1:1723 (no session established for client) 2019-04-19 22:00:28,710 [myid:] - INFO [NIOServerCxn.Factory:0.0.0.0/0.0.0.0:2181:NIOServerCnxnFactory@215] - Accepted socket connection from /192.168.238.1:1728 2019-04-19 22:00:28,833 [myid:] - WARN [NIOServerCxn.Factory:0.0.0.0/0.0.0.0:2181:NIOServerCnxn@383] - Exception causing close of session 0x0: Len error -625229312 2019-04-19 22:00:28,836 [myid:] - INFO [NIOServerCxn.Factory:0.0.0.0/0.0.0.0:2181:NIOServerCnxn@1040] - Closed socket connection for client /192.168.238.1:1728 (no session established for client) 2019-04-19 22:00:34,556 [myid:] - INFO [NIOServerCxn.Factory:0.0.0.0/0.0.0.0:2181:NIOServerCnxnFactory@215] - Accepted socket connection from /192.168.238.1:1734
Zookeeper拒绝连接。解决办法：关闭zookeeper，删除zk的dataDir配置的目录中的数据。然后重启ZK，使用ZKClient去连接ZK。我这里可以连接到ZK，说明ZK没有问题。
（2）仔细检查我们的配置文件，如下:
<?xml version="1.0" encoding="UTF-8"?> <beans xmlns:xsi="https://www.w3.org/2001/XMLSchema-instance" xmlns:dubbo="https://code.alibabatech.com/schema/dubbo" xmlns="https://www.springframework.org/schema/beans" xsi:schemaLocation="https://www.springframework.org/schema/beans https://www.springframework.org/schema/beans/spring-beans-4.3.xsd https://code.alibabatech.com/schema/dubbo https://code.alibabatech.com/schema/dubbo/dubbo.xsd"> <!-- 应用名称 --> <dubbo:application name="demo-consumer"/> <!-- 注册中心 --> <dubbo:registry protocol="dubbo" address="127.0.0.1:2181" /> <!-- 服务使用 dubbo 协议调用 --> <dubbo:reference id="helloServiceDubbo" interface="com.huangx.dubbo.service.HelloService" protocol="dubbo" /> <!-- 服务使用 rmi 协议调用 --> <dubbo:reference id="helloServiceRMI" interface="com.huangx.dubbo.service.HelloService" protocol="rmi" /> <!-- 服务使用 hessian 协议调用 --> <dubbo:reference id="helloServiceHessian" interface="com.huangx.dubbo.service.HelloService" protocol="hessian" /> </beans>
我们主要查看注册中心的配置，参考 https://dubbo.apache.org/zh-cn/docs/user/references/xml/dubbo-registry.html 地址，该地址是Dubbo官网文档，如下：
| protocol | <protocol> | string | 可选 | dubbo | 服务发现 | 注册中心地址协议，支持dubbo, http, local三种协议，分别表示：dubbo地址、http地址、本地注册中心 | 2.0.0以上版本 |
根据官网的描述，上面配置没有错误啊。但是就是不能运行，于是参考了 https://dubbo.apache.org/zh-cn/docs/user/references/registry/zookeeper.html 官网关于注册中心配置的教程，发现我的配置存在问题。应该配置如下：
<!-- 注册中心 --> <dubbo:registry protocol="zookeeper" address="127.0.0.1:2181" /> <!-- 或者 --> <dubbo:registry address="zookeeper://127.0.0.1:2181" />
这样问题就解决了！！！
总结：自己注册中心的协议配置错误。应该把 dubbo 改为 zookeeper。
疑问？
官网 https://dubbo.apache.org/zh-cn/docs/user/references/xml/dubbo-registry.html 中关于<dubbo:register> 中 protocol 文档描述是不是有问题哦。。。
