Netty：ChannelHandler抛出异常，对应的channel被关闭

说明

使用Netty框架构建的socket服务端在处理客户端请求时，每接到一个客户端的连接请求，服务端会分配一个channel处理跟该客户端的交互。如果处理该channel数据的ChannelHandler抛出异常没有捕获，那么该channel会关闭。但服务端和其它客户端的通信不受影响。

代码示例

该示例验证场景：
服务端和客户端建立了正常的连接，服务端给该客户端分配了一个channel。从该channel读取数据的ChannelHandler抛出异常，没有被捕获，导致该channel被关闭，服务端和该客户端的通信中断。但服务端和其它客户端的通信不受影响。

服务端代码片段

package com.thb.power.server;import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelOption;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.nio.NioServerSocketChannel;
import io.netty.handler.logging.LogLevel;
import io.netty.handler.logging.LoggingHandler;/*** 服务端的主函数* @author thb**/
public class MainStation {private static final Logger logger = LogManager.getLogger();static final int PORT = Integer.parseInt(System.getProperty("port", "22335"));public static void main(String[] args) throws Exception {logger.traceEntry();// 配置服务器EventLoopGroup bossGroup = new NioEventLoopGroup();EventLoopGroup workerGroup = new NioEventLoopGroup();try {ServerBootstrap b =  new ServerBootstrap();b.group(bossGroup, workerGroup).channel(NioServerSocketChannel.class).option(ChannelOption.SO_BACKLOG, 100).handler(new LoggingHandler(LogLevel.INFO)).childHandler(new MainStationInitializer());// 启动服务端ChannelFuture f = b.bind(PORT).sync();// 等待直到server socket关闭f.channel().closeFuture().sync();} finally {// 关闭所有event loops以便终止所有的线程bossGroup.shutdownGracefully();workerGroup.shutdownGracefully();}logger.traceExit();}}

package com.thb.power.server;import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;import com.thb.power.constant.PowerConstants;
import com.thb.power.handler.VerifyChecksumHandler;import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelPipeline;
import io.netty.channel.socket.SocketChannel;
import io.netty.handler.codec.DelimiterBasedFrameDecoder;
import io.netty.handler.logging.LogLevel;
import io.netty.handler.logging.LoggingHandler;public class MainStationInitializer extends ChannelInitializer<SocketChannel> {private static final Logger logger = LogManager.getLogger();@Overridepublic void initChannel(SocketChannel ch) throws Exception {logger.traceEntry();ChannelPipeline p = ch.pipeline();		 p.addLast(new LoggingHandler(LogLevel.INFO));// 用报文开头的字符、结尾的字符作为分隔符，解析成完整的报文	p.addLast(new DelimiterBasedFrameDecoder(PowerConstants.SOCKET_MAX_BYTES_PER_PACKET, true, Unpooled.wrappedBuffer(new byte[] {PowerConstants.SOCKET_END_MARK}),Unpooled.wrappedBuffer(new byte[] {PowerConstants.SOCKET_START_MARK})));	p.addLast(new VerifyChecksumHandler());logger.traceExit();}
}

package com.thb.power.handler;import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;import io.netty.buffer.ByteBuf;
import io.netty.buffer.ByteBufUtil;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;
import io.netty.handler.codec.CorruptedFrameException;
import io.netty.util.ReferenceCounted;/*** 验证接收的报文的校验和* @author thb**/
public class VerifyChecksumHandler extends ChannelInboundHandlerAdapter {private static final Logger logger = LogManager.getLogger();@Overridepublic void channelRead(ChannelHandlerContext ctx, Object msg) {logger.traceEntry();		if (msg instanceof ByteBuf) {ByteBuf m = (ByteBuf)msg;logger.info("msg reference count: {}", m.refCnt());// 此处人为构造场景，以便验证抛出异常的情况。将引用计数减少1，执行后，引用计数变为0，读数据会抛异常m.release();m.readByte();logger.info("readableBytes: " + m.readableBytes());		// 将收到的报文的每个字节转换为十六进制打印出来			logger.info(ByteBufUtil.prettyHexDump(m));			} else {// 这个数据不需要向后传递，因为数据已经错误了// 传入的对象msg如果实现了ReferenceCounted接口，那么显式就释放if (msg instanceof ReferenceCounted) {((ReferenceCounted)msg).release();}throw new CorruptedFrameException("received illegal data: not ByteBuf type");}logger.traceExit();}@Overridepublic void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {cause.printStackTrace();ctx.close();}
}

package com.thb.power.constant;/*** 保存了一些常数* @author thb**/
public final class PowerConstants {/*** 定义了私有构造函数，防止被外部实例化*/private PowerConstants() {}/*** 通信报文的起始符*/public static final byte SOCKET_START_MARK = (byte)0x68;/*** 通信报文的的结束符*/public static final byte SOCKET_END_MARK = (byte)0x16;/*** 每个报文的最大字节数*/public static final short SOCKET_MAX_BYTES_PER_PACKET = 1024;
}

启动服务端

启动客户端，并向服务端发送数据

服务端的ChannelHandler处理数据时抛出了异常，断开了和该客户端的连接

从输出可以看出，服务端处理客户端channel数据的ChannelHandler抛出了异常，服务端终止了和该客户端的连接。

观察客户端的输出

从输出可以看出，客户端终止了和服务端的连接。

服务端可以继续接受新的客户端连接

从输出可以看出，服务端可以正常接受新的客户端的连接