使用Tomcat的shutdown，会报以下错误，这个是什么原因？

[shine4net]

Nov 16, 2015 4:39:37 AM org.apache.catalina.loader.WebappClassLoaderBase clearReferencesThreads
SEVERE: The web application [/shh-gateway] appears to have started a thread named [DubboClientReconnectTimer-thread-1] but has failed to stop it. This is very likely to create a memory leak.
Nov 16, 2015 4:39:37 AM org.apache.catalina.loader.WebappClassLoaderBase clearReferencesThreads
SEVERE: The web application [/shh-gateway] appears to have started a thread named [NettyClientBoss-thread-1] but has failed to stop it. This is very likely to create a memory leak.
Nov 16, 2015 4:39:37 AM org.apache.catalina.loader.WebappClassLoaderBase clearReferencesThreads
SEVERE: The web application [/shh-gateway] appears to have started a thread named [New I/O client worker #1-1] but has failed to stop it. This is very likely to create a memory leak.
Nov 16, 2015 4:39:37 AM org.apache.catalina.loader.WebappClassLoaderBase clearReferencesThreads
SEVERE: The web application [/shh-gateway] appears to have started a thread named [dubbo-remoting-client-heartbeat-thread-1] but has failed to stop it. This is very likely to create a memory leak.
Nov 16, 2015 4:39:37 AM org.apache.catalina.loader.WebappClassLoaderBase clearReferencesThreads
SEVERE: The web application [/shh-gateway] appears to have started a thread named [DubboClientReconnectTimer-thread-2] but has failed to stop it. This is very likely to create a memory leak.
Nov 16, 2015 4:39:37 AM org.apache.catalina.loader.WebappClassLoaderBase clearReferencesThreads
SEVERE: The web application [/shh-gateway] appears to have started a thread named [DubboSharedHandler-thread-1] but has failed to stop it. This is very likely to create a memory leak.
Nov 16, 2015 4:39:37 AM org.apache.coyote.AbstractProtocol stop
INFO: Stopping ProtocolHandler ["http-bio-8080"]
Nov 16, 2015 4:39:37 AM org.apache.coyote.AbstractProtocol stop
INFO: Stopping ProtocolHandler ["ajp-bio-8009"]
Nov 16, 2015 4:39:37 AM org.apache.coyote.AbstractProtocol destroy
INFO: Destroying ProtocolHandler ["http-bio-8080"]
Nov 16, 2015 4:39:37 AM org.apache.coyote.AbstractProtocol destroy
INFO: Destroying ProtocolHandler ["ajp-bio-8009"]
Nov 16, 2015 4:39:37 AM org.apache.catalina.loader.WebappClassLoaderBase loadClass
INFO: Illegal access: this web application instance has been stopped already.  Could not load com.alibaba.dubbo.registry.support.AbstractRegistryFactory.  The eventual following stack trace is caused by an error thrown for debugging purposes as well as to attempt to terminate the thread which caused the illegal access, and has no functional impact.
java.lang.IllegalStateException
    at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1745)
    at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1703)
    at com.alibaba.dubbo.config.ProtocolConfig.destroyAll(ProtocolConfig.java:429)
    at com.alibaba.dubbo.config.AbstractConfig$1.run(AbstractConfig.java:452)
    at java.lang.Thread.run(Thread.java:745)

Exception in thread "DubboShutdownHook" java.lang.NoClassDefFoundError: com/alibaba/dubbo/registry/support/AbstractRegistryFactory
    at com.alibaba.dubbo.config.ProtocolConfig.destroyAll(ProtocolConfig.java:429)
    at com.alibaba.dubbo.config.AbstractConfig$1.run(AbstractConfig.java:452)
    at java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.ClassNotFoundException: com.alibaba.dubbo.registry.support.AbstractRegistryFactory
    at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1854)
    at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1703)
    ... 3 more

[duoduobabi]

看一下你的ZooKeeper版本是不是3.3.3。升级一下ZooKeeper版本试试。我用的是3.4.5。

[ralf0131]

Related issue #1665

[ralf0131]

This is because Dubbo is not shut down cleanly. This issue has been fix from 2.6.3 onwards.