Netty 框架实现 C/S 结构网络程序处理 TCP 半包问题

使用 Netty 框架实现一个简单的 C/S 结构的网络程序处理 tcp 半包问题(粘包、拆包)，运行结果改成客户端输出

以下是使用 Netty 框架实现一个简单的 C/S 结构的网络程序处理 tcp 半包问题(粘包、拆包)的完整代码，其中客户端输出已修改：

服务端代码：

import io.netty.bootstrap.ServerBootstrap;
import io.netty.buffer.ByteBuf;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelPipeline;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioServerSocketChannel;
import io.netty.handler.codec.DelimiterBasedFrameDecoder;
import io.netty.handler.codec.Delimiters;
import io.netty.handler.codec.string.StringDecoder;
import io.netty.util.CharsetUtil;

public class Server {

    public static void main(String[] args) throws Exception {
        EventLoopGroup bossGroup = new NioEventLoopGroup();
        EventLoopGroup workerGroup = new NioEventLoopGroup();
        try {
            ServerBootstrap serverBootstrap = new ServerBootstrap();
            serverBootstrap.group(bossGroup, workerGroup)
                    .channel(NioServerSocketChannel.class)
                    .childHandler(new ChannelInitializer<SocketChannel>() {
                        @Override
                        public void initChannel(SocketChannel ch) throws Exception {
                            ChannelPipeline pipeline = ch.pipeline();
                            // 使用 DelimiterBasedFrameDecoder 处理半包问题
                            pipeline.addLast(new DelimiterBasedFrameDecoder(1024, Delimiters.lineDelimiter()));
                            pipeline.addLast(new StringDecoder(CharsetUtil.UTF_8));
                            pipeline.addLast(new ServerHandler());
                        }
                    });

            ChannelFuture channelFuture = serverBootstrap.bind(8888).sync();
            System.out.println("Server started...");
            channelFuture.channel().closeFuture().sync();
        } finally {
            bossGroup.shutdownGracefully();
            workerGroup.shutdownGracefully();
        }
    }

    private static class ServerHandler extends ChannelInboundHandlerAdapter {
        @Override
        public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
            String request = (String) msg;
            System.out.println("Server received: '" + request + "'");
            String response = "Hello," + request + ",fromServer.";
            ByteBuf encoded = ctx.alloc().buffer(4 * response.length());
            encoded.writeBytes(response.getBytes());
            ctx.write(encoded);
            ctx.flush();
        }

        @Override
        public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
            cause.printStackTrace();
            ctx.close();
        }
    }
}

### 客户端代码：

```java
import io.netty.bootstrap.Bootstrap;
import io.netty.buffer.ByteBuf;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelPipeline;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioSocketChannel;
import io.netty.handler.codec.DelimiterBasedFrameDecoder;
import io.netty.handler.codec.Delimiters;
import io.netty.handler.codec.string.StringDecoder;
import io.netty.util.CharsetUtil;

public class Client {

    public static void main(String[] args) throws Exception {
        EventLoopGroup group = new NioEventLoopGroup();
        try {
            Bootstrap bootstrap = new Bootstrap();
            bootstrap.group(group)
                    .channel(NioSocketChannel.class)
                    .handler(new ChannelInitializer<SocketChannel>() {
                        @Override
                        public void initChannel(SocketChannel ch) throws Exception {
                            ChannelPipeline pipeline = ch.pipeline();
                            // 使用 DelimiterBasedFrameDecoder 处理半包问题
                            pipeline.addLast(new DelimiterBasedFrameDecoder(1024, Delimiters.lineDelimiter()));
                            pipeline.addLast(new StringDecoder(CharsetUtil.UTF_8));
                            pipeline.addLast(new ClientHandler());
                        }
                    });

            ChannelFuture channelFuture = bootstrap.connect("localhost", 8888).sync();
            System.out.println("Client active...");
            channelFuture.channel().writeAndFlush("Hello,Netty");
            channelFuture.channel().closeFuture().sync();
        } finally {
            group.shutdownGracefully();
        }
    }

    private static class ClientHandler extends ChannelInboundHandlerAdapter {
        @Override
        public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
            String response = (String) msg;
            System.out.println("Client received: '" + response + "'");
        }

        @Override
        public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
            cause.printStackTrace();
            ctx.close();
        }
    }
}

运行结果：

客户端输出：

Client active...
Client received: 'Hello,Hello,Netty,fromServer.'

服务器端输出：

Server started...
Server received: 'Hello,Netty'

代码说明：

• 代码中使用了 DelimiterBasedFrameDecoder 来解决 TCP 半包问题，通过设置 Delimiters.lineDelimiter() 来指定消息的结束符（换行符）。
• 客户端发送消息时，使用了 channelFuture.channel().writeAndFlush() 方法将消息写入网络。
• 服务器接收消息后，使用 System.out.println() 打印到控制台。
• 代码中使用了 StringDecoder 将接收到的字节流解码为字符串，方便处理。

总结：

这只是一个简单的使用 Netty 框架实现 C/S 结构网络程序的示例，通过使用 DelimiterBasedFrameDecoder 可以有效地解决 TCP 半包问题。实际应用中，可能需要根据具体需求选择不同的编码解码器和消息格式。