An exceptionCaught() event was fired, and it reached at the tail of the pipeline. It usually means

警告: An exceptionCaught() event was fired, and it reached at the tail of the pipeline. It usually means the last handler in the pipeline did not handle the exception.
java.io.IOException: 远程主机强迫关闭了一个现有的连接。
at sun.nio.ch.SocketDispatcher.read0(Native Method)
at sun.nio.ch.SocketDispatcher.read(Unknown Source)
at sun.nio.ch.IOUtil.readIntoNativeBuffer(Unknown Source)
at sun.nio.ch.IOUtil.read(Unknown Source)
at sun.nio.ch.SocketChannelImpl.read(Unknown Source)
at io.netty.buffer.UnpooledUnsafeDirectByteBuf.setBytes(UnpooledUnsafeDirectByteBuf.java:446)
at io.netty.buffer.AbstractByteBuf.writeBytes(AbstractByteBuf.java:871)
at io.netty.channel.socket.nio.NioSocketChannel.doReadBytes(NioSocketChannel.java:208)
at io.netty.channel.nio.AbstractNioByteChannel$NioByteUnsafe.read(AbstractNioByteChannel.java:119)
at io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:485)
at io.netty.channel.nio.NioEventLoop.processSelectedKeysOptimized(NioEventLoop.java:452)
at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:346)
at io.netty.util.concurrent.SingleThreadEventExecutor$5.run(SingleThreadEventExecutor.java:794)
at java.lang.Thread.run(Unknown Source)

@Override
public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
super.exceptionCaught(ctx, cause);
Channel channel = ctx.channel();
//……
if(channel.isActive())ctx.close();
}