在 spring cloud 或 spring boot 项目中，服务依赖 zookeeper，又通过 apache curator 客户端连接 zk 时，如果版本匹配不一致，会出现兼容性问题，导致服务启动失败。
报错信息
org.apache.zookeeper.KeeperException$UnimplementedException: KeeperErrorCode = Unimplemented for /spring-cloud-services/knowledgedict/7f610178-bfa4-41f7-abbe-7653740fd35c
at org.apache.zookeeper.KeeperException.create(KeeperException.java:103) ~[zookeeper-3.5.3-beta.jar:3.5.3-beta-8ce24f9e675cbefffb8f21a47e06b42864475a60]
at org.apache.zookeeper.KeeperException.create(KeeperException.java:51) ~[zookeeper-3.5.3-beta.jar:3.5.3-beta-8ce24f9e675cbefffb8f21a47e06b42864475a60]
at org.apache.zookeeper.ZooKeeper.create(ZooKeeper.java:1525) ~[zookeeper-3.5.3-beta.jar:3.5.3-beta-8ce24f9e675cbefffb8f21a47e06b42864475a60]
at org.apache.curator.framework.imps.CreateBuilderImpl$17.call(CreateBuilderImpl.java:1181) ~[curator-framework-4.0.1.jar:4.0.1]
at org.apache.curator.framework.imps.CreateBuilderImpl$17.call(CreateBuilderImpl.java:1158) ~[curator-framework-4.0.1.jar:4.0.1]
at org.apache.curator.connection.StandardConnectionHandlingPolicy.callWithRetry(StandardConnectionHandlingPolicy.java:64) ~[curator-client-4.0.1.jar:na]
at org.apache.curator.RetryLoop.callWithRetry(RetryLoop.java:100) ~[curator-client-4.0.1.jar:na]
at org.apache.curator.framework.imps.CreateBuilderImpl.pathInForeground(CreateBuilderImpl.java:1155) ~[curator-framework-4.0.1.jar:4.0.1]
at org.apache.curator.framework.imps.CreateBuilderImpl.protectedPathInForeground(CreateBuilderImpl.java:605) ~[curator-framework-4.0.1.jar:4.0.1]
at org.apache.curator.framework.imps.CreateBuilderImpl.forPath(CreateBuilderImpl.java:595) ~[curator-framework-4.0.1.jar:4.0.1]
at org.apache.curator.framework.imps.CreateBuilderImpl.forPath(CreateBuilderImpl.java:49) ~[curator-framework-4.0.1.jar:4.0.1]
at org.apache.curator.x.discovery.details.ServiceDiscoveryImpl.internalRegisterService(ServiceDiscoveryImpl.java:236) ~[curator-x-discovery-4.0.1.jar:na]
at org.apache.curator.x.discovery.details.ServiceDiscoveryImpl.reRegisterServices(ServiceDiscoveryImpl.java:456) ~[curator-x-discovery-4.0.1.jar:na]
at org.apache.curator.x.discovery.details.ServiceDiscoveryImpl.access$100(ServiceDiscoveryImpl.java:58) ~[curator-x-discovery-4.0.1.jar:na]
at org.apache.curator.x.discovery.details.ServiceDiscoveryImpl$1.stateChanged(ServiceDiscoveryImpl.java:78) ~[curator-x-discovery-4.0.1.jar:na]
at org.apache.curator.framework.state.ConnectionStateManager$2.apply(ConnectionStateManager.java:274) [curator-framework-4.0.1.jar:4.0.1]
at org.apache.curator.framework.state.ConnectionStateManager$2.apply(ConnectionStateManager.java:270) [curator-framework-4.0.1.jar:4.0.1]
at org.apache.curator.framework.listen.ListenerContainer$1.run(ListenerContainer.java:93) [curator-framework-4.0.1.jar:4.0.1]
at org.apache.curator.shaded.com.google.common.util.concurrent.MoreExecutors$DirectExecutor.execute(MoreExecutors.java:435) [curator-client-4.0.1.jar:na]
at org.apache.curator.framework.listen.ListenerContainer.forEach(ListenerContainer.java:85) [curator-framework-4.0.1.jar:4.0.1]
at org.apache.curator.framework.state.ConnectionStateManager.processEvents(ConnectionStateManager.java:268) [curator-framework-4.0.1.jar:4.0.1]
at org.apache.curator.framework.state.ConnectionStateManager.access$000(ConnectionStateManager.java:44) [curator-framework-4.0.1.jar:4.0.1]
at org.apache.curator.framework.state.ConnectionStateManager$1.call(ConnectionStateManager.java:120) [curator-framework-4.0.1.jar:4.0.1]
at java.util.concurrent.FutureTask.run(FutureTask.java:266) [na:1.8.0_241]
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) [na:1.8.0_241]
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) [na:1.8.0_241]
at java.lang.Thread.run(Thread.java:748) [na:1.8.0_241]
笔者直接用 spring cloud 对应大版本的依赖关系，zookeeper 是 3.5.3-beta 版本，curator 是 4.0.1 版本，但是 zookeeper 服务端版本是 3.4.x 版本。
报错原因
curator 和 zookeeper 版本之前有如下兼容关系：
Curator 官网说明如下：
第一种情况：
Curator 2.x.x
compatible with both ZooKeeper 3.4.x and ZooKeeper 3.5.x
Curator 3.x.x
compatible only with ZooKeeper 3.5.x and includes support for new features such as dynamic reconfiguration, etc.
第二种情况：
ZooKeeper 3.5.x
Curator 4.0 has a hard dependency on ZooKeeper 3.5.x
If you are using ZooKeeper 3.5.x there's nothing additional to do - just use Curator 4.0
ZooKeeper 3.4.x
Curator 4.0 supports ZooKeeper 3.4.x ensembles in a soft-compatibility mode. To use this mode you must exclude ZooKeeper when adding Curator to your dependency management tool.
解决方法
针对笔者的问题，由于 zookeeper 服务器是 3.4.x 版本，curator 是 4.0.1 版本，将 curator 强依赖的 zookeeper 3.5.x 版本显性指定为 3.4.x 即可。
以 gradle 配置示例：
dependencies {
xxxxxx
compile group: 'org.apache.zookeeper', name: 'zookeeper', version: '3.4.13'
xxxxxx
}
maven 示例如下：
<dependencies>
......
<dependency>
<groupId>org.apache.zookeeper</groupId>
<artifactId>zookeeper</artifactId>
<version>3.4.13</version>
</dependency>
......
</dependencies>