LineBasedFrameDecoder的使用

为了解决TCP粘包/拆包导致的半包读写问题，Netty默认提供了多种编解码器用于处理该类问题，本例程将展示Netty中LineBasedFrameDecoder的使用。

代码的关键部分在于：

ch.pipeline().addLast(new LineBasedFrameDecoder(1024));
ch.pipeline().addLast(new StringDecoder());
ch.pipeline().addLast(new LineTimeClientHandler());

package learn.netty.linebasedframedecoder;

import io.netty.bootstrap.Bootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelOption;
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.LineBasedFrameDecoder;
import io.netty.handler.codec.string.StringDecoder;

/**
 * @author stone
 * @date 2019/7/29 16:24
 */
public class LineTimeClient {
    public void connect(int port, String host) {
        EventLoopGroup group = new NioEventLoopGroup();
        try {
            Bootstrap b = new Bootstrap();
            b.group(group)
                    .channel(NioSocketChannel.class)
                    .option(ChannelOption.TCP_NODELAY, true)
                    .handler(new ChannelInitializer<SocketChannel>() {
                        @Override
                        protected void initChannel(SocketChannel ch) throws Exception {
                            // 代码的关键部分，添加行解析器，添加stringDecoder，再添加业务类
                            ch.pipeline().addLast(new LineBasedFrameDecoder(1024));
                            ch.pipeline().addLast(new StringDecoder());
                            ch.pipeline().addLast(new LineTimeClientHandler());
                        }
                    });
            // 发起异步连接操作
            ChannelFuture f = b.connect(host, port).sync();
            // 等待链路关闭
            f.channel().closeFuture().sync();
        } catch (Exception e) {

        } finally {
            group.shutdownGracefully();
        }
    }

    public static void main(String[] args) {
        int port = 8080;
        if (null != args && args.length > 0) {
            try {
                port = Integer.valueOf(args[0]);
            } catch (Exception e) {

            }
        }
        new LineTimeClient().connect(port,"127.0.0.1");
    }
}

package learn.netty.linebasedframedecoder;

import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;
import io.netty.util.ReferenceCountUtil;

import java.util.logging.Logger;

/**
 * @author stone
 * @date 2019/7/29 16:29
 */
public class LineTimeClientHandler extends ChannelInboundHandlerAdapter {
    private static final Logger logger = Logger.getLogger(LineTimeClientHandler.class.getName());

    private int counter;
    private byte[] req;

    public LineTimeClientHandler() {
        req = ("QUERY TIME ORDER" + System.getProperty("line.separator")).getBytes();
    }

    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        ByteBuf message = null;
        for (int i = 0; i < 100; i++) {
            message = Unpooled.buffer(req.length);
            message.writeBytes(req);
            ctx.writeAndFlush(message);
        }
    }

    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        String body = (String) msg;
        System.out.println("Now is:" + body + "; the counter is:" + (++counter));
        ReferenceCountUtil.release(msg);
    }

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        logger.warning("Unexcepted exception from downstream:" + cause.getMessage());
        ctx.close();
    }
}

package learn.netty.linebasedframedecoder;

import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelOption;
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.LineBasedFrameDecoder;
import io.netty.handler.codec.string.StringDecoder;

/**
 * @author stone
 * @date 2019/7/29 15:44
 */
public class LineTimeServer {
    public void bind(int port) {
        // 配置服务端的NIO线程组
        EventLoopGroup bossGroup = new NioEventLoopGroup();
        EventLoopGroup workerGroup = new NioEventLoopGroup();
        try {
            ServerBootstrap b = new ServerBootstrap();
            // 配置线程组及参数
            b.group(bossGroup, workerGroup)
                    .channel(NioServerSocketChannel.class)
                    .option(ChannelOption.SO_BACKLOG, 128)
                    .childHandler(new ChannelInitializer<SocketChannel>() { // 接收客户端channel的后续处理
                        @Override
                        protected void initChannel(SocketChannel ch) throws Exception {
                            // 解决tcp粘包拆包问题
                            ch.pipeline().addLast(new LineBasedFrameDecoder(1024));
                            ch.pipeline().addLast(new StringDecoder());
                            ch.pipeline().addLast(new  LineTimeServerHandler());
                        }
                    });
            ChannelFuture f = b.bind(port).sync();
            System.out.println("服务已经启动：" + port);
            f.channel().closeFuture().sync();

        } catch (Exception e) {

        } finally {
            bossGroup.shutdownGracefully();
            workerGroup.shutdownGracefully();
        }
    }

    public static void main(String[] args) {
        int port = 8080;
        if (null != args && args.length > 0) {
            try {
                port = Integer.valueOf(args[0]);
            } catch (Exception e) {

            }
        }
        new LineTimeServer().bind(port);
    }
}

package learn.netty.linebasedframedecoder;

import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;
import io.netty.util.ReferenceCountUtil;

import java.util.Date;

/**
 * @author stone
 * @date 2019/7/29 16:10
 */
public class LineTimeServerHandler extends ChannelInboundHandlerAdapter {
    private int counter;

    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        String body = (String) msg;
        System.out.println("The time server receive order:" + body + ";the counter is:" + (++counter));
        String currentTime = "QUERY TIME ORDER".equalsIgnoreCase(body) ? new Date(System.currentTimeMillis()).toString()
                : "BAD ORDER";
        currentTime = currentTime + System.getProperty("line.separator");
        ByteBuf resp = Unpooled.copiedBuffer(currentTime.getBytes());
        ctx.write(resp);
        ReferenceCountUtil.release(msg);
    }

    @Override
    public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {
        ctx.flush();
    }

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