• I have searched the issues of this repository and believe that this is not a duplicate.
• I have checked the FAQ of this repository and believe that this is not a duplicate.

Environment

• Dubbo version: 2.7.3
• Operating System version: Linux iZwz9b62gfds6u2rpy623tZ 3.10.0-514.26.2.el7.x86_64 不同的group应该是不同的注册中心 #1 SMP Tue Jul 4 15:04:05 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux
• Java version: 1.8

Steps to reproduce this issue

Pls. provide [GitHub address] to reproduce this issue.

Expected Result

What do you expected from the above steps？

Actual Result

在同一个机器上部署了zk, 服务提供者， 服务消费者（web）,
在tomcat正常启动一段时间后，抛异常，zk连接不上了，
但是服务提供者与zk的心跳是正常的。

If there is an exception, please attach the exception trace:
[WEB_MOBILE] [localhost-startStop-1-SendThread(iZwz9b62gfds6u2rpy623tZ:2181)] 2019-10-17 17:19:13 [ INFO] (org.apache.zookeeper.ClientCnxn$SendThread:1029) | Opening socket connection to server iZwz9b62gfds6u2rpy623tZ/10.81.249.56:2181. Will not attempt to authenticate using SASL (unknown error)
[WEB_MOBILE] [localhost-startStop-1-SendThread(iZwz9b62gfds6u2rpy623tZ:2181)] 2019-10-17 17:19:13 [ INFO] (org.apache.zookeeper.ClientCnxn$SendThread:879) | Socket connection established to iZwz9b62gfds6u2rpy623tZ/10.81.249.56:2181, initiating session
[WEB_MOBILE] [localhost-startStop-1-SendThread(iZwz9b62gfds6u2rpy623tZ:2181)] 2019-10-17 17:19:13 [ WARN] (org.apache.zookeeper.ClientCnxn$SendThread:1168) | Session 0x10637dcf99d0049 for server iZwz9b62gfds6u2rpy623tZ/10.81.249.56:2181, unexpected error, closing socket connection and attempting reconnect
java.lang.NoClassDefFoundError: org/apache/zookeeper/proto/SetWatches
at org.apache.zookeeper.ClientCnxn$SendThread.primeConnection(ClientCnxn.java:929)
at org.apache.zookeeper.ClientCnxnSocketNIO.doTransport(ClientCnxnSocketNIO.java:363)
at org.apache.zookeeper.ClientCnxn$SendThread.run(ClientCnxn.java:1145)
[WEB_MOBILE] [NettyClientWorker-1-2] 2019-10-17 17:19:14 [ WARN] (io.netty.util.internal.logging.Slf4JLogger:151) | Unexpected exception in the selector loop.
java.lang.NoClassDefFoundError: io/netty/channel/AdaptiveRecvByteBufAllocator$HandleImpl
at io.netty.channel.AdaptiveRecvByteBufAllocator.newHandle(AdaptiveRecvByteBufAllocator.java:196)
at io.netty.channel.AbstractChannel$AbstractUnsafe.recvBufAllocHandle(AbstractChannel.java:438)
at io.netty.channel.nio.AbstractNioByteChannel$NioByteUnsafe.read(AbstractNioByteChannel.java:140)
at io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:647)
at io.netty.channel.nio.NioEventLoop.processSelectedKeysOptimized(NioEventLoop.java:582)
at io.netty.channel.nio.NioEventLoop.processSelectedKeys(NioEventLoop.java:499)
at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:461)
at io.netty.util.concurrent.SingleThreadEventExecutor$5.run(SingleThreadEventExecutor.java:884)
at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30)
at java.lang.Thread.run(Thread.java:748)
[WEB_MOBILE] [NettyClientWorker-1-4] 2019-10-17 17:19:14 [ WARN] (io.netty.util.internal.logging.Slf4JLogger:151) | Unexpected exception in the selector loop.
java.lang.NoClassDefFoundError: io/netty/channel/AdaptiveRecvByteBufAllocator$HandleImpl
at io.netty.channel.AdaptiveRecvByteBufAllocator.newHandle(AdaptiveRecvByteBufAllocator.java:196)
at io.netty.channel.AbstractChannel$AbstractUnsafe.recvBufAllocHandle(AbstractChannel.java:438)
at io.netty.channel.nio.AbstractNioByteChannel$NioByteUnsafe.read(AbstractNioByteChannel.java:140)
at io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:647)
at io.netty.channel.nio.NioEventLoop.processSelectedKeysOptimized(NioEventLoop.java:582)
at io.netty.channel.nio.NioEventLoop.processSelectedKeys(NioEventLoop.java:499)
at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:461)
at io.netty.util.concurrent.SingleThreadEventExecutor$5.run(SingleThreadEventExecutor.java:884)
at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30)
at java.lang.Thread.run(Thread.java:748)
[WEB_MOBILE] [NettyClientWorker-1-5] 2019-10-17 17:19:14 [ WARN] (io.netty.util.internal.logging.Slf4JLogger:151) | Unexpected exception in the selector loop.
java.lang.NoClassDefFoundError: io/netty/channel/AdaptiveRecvByteBufAllocator$HandleImpl
at io.netty.channel.AdaptiveRecvByteBufAllocator.newHandle(AdaptiveRecvByteBufAllocator.java:196)
at io.netty.channel.AbstractChannel$AbstractUnsafe.recvBufAllocHandle(AbstractChannel.java:438)
at io.netty.channel.nio.AbstractNioByteChannel$NioByteUnsafe.read(AbstractNioByteChannel.java:140)
at io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:647)
at io.netty.channel.nio.NioEventLoop.processSelectedKeysOptimized(NioEventLoop.java:582)
at io.netty.channel.nio.NioEventLoop.processSelectedKeys(NioEventLoop.java:499)
at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:461)
at io.netty.util.concurrent.SingleThreadEventExecutor$5.run(SingleThreadEventExecutor.java:884)
at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30)
at java.lang.Thread.run(Thread.java:748)
[WEB_MOBILE] [NettyClientWorker-1-1] 2019-10-17 17:19:14 [ WARN] (io.netty.util.internal.logging.Slf4JLogger:151) | Unexpected exception in the selector loop.
java.lang.NoClassDefFoundError: io/netty/channel/AdaptiveRecvByteBufAllocator$HandleImpl
at io.netty.channel.AdaptiveRecvByteBufAllocator.newHandle(AdaptiveRecvByteBufAllocator.java:196)
at io.netty.channel.AbstractChannel$AbstractUnsafe.recvBufAllocHandle(AbstractChannel.java:438)
at io.netty.channel.nio.AbstractNioByteChannel$NioByteUnsafe.read(AbstractNioByteChannel.java:140)
at io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:647)
at io.netty.channel.nio.NioEventLoop.processSelectedKeysOptimized(NioEventLoop.java:582)
at io.netty.channel.nio.NioEventLoop.processSelectedKeys(NioEventLoop.java:499)
at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:461)
at io.netty.util.concurrent.SingleThreadEventExecutor$5.run(SingleThreadEventExecutor.java:884)
at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30)
at java.lang.Thread.run(Thread.java:748)
[WEB_MOBILE] [NettyClientWorker-1-3] 2019-10-17 17:19:14 [ WARN] (io.netty.util.internal.logging.Slf4JLogger:151) | Unexpected exception in the selector loop.
java.lang.NoClassDefFoundError: io/netty/channel/AdaptiveRecvByteBufAllocator$HandleImpl
at io.netty.channel.AdaptiveRecvByteBufAllocator.newHandle(AdaptiveRecvByteBufAllocator.java:196)
at io.netty.channel.AbstractChannel$AbstractUnsafe.recvBufAllocHandle(AbstractChannel.java:438)
at io.netty.channel.nio.AbstractNioByteChannel$NioByteUnsafe.read(AbstractNioByteChannel.java:140)
at io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:647)
at io.netty.channel.nio.NioEventLoop.processSelectedKeysOptimized(NioEventLoop.java:582)
at io.netty.channel.nio.NioEventLoop.processSelectedKeys(NioEventLoop.java:499)
at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:461)
at io.netty.util.concurrent.SingleThreadEventExecutor$5.run(SingleThreadEventExecutor.java:884)
at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30)
at java.lang.Thread.run(Thread.java:748)

Just put your stack trace here!