java-netty知识点笔记和注意事项

1. 如何获取ctx的id
   使用ctx.ctx.toString()就可以了

    public void channelRead(ChannelHandlerContext ctx, Object msg) {
        //传来的消息包装成字节缓冲区
        String byteBuf = (String) msg;
//        ByteBuf byteBuf = (ByteBuf) msg;
        //Netty提供了字节缓冲区的toString方法，并且可以设置参数为编码格式：CharsetUtil.UTF_8
        System.out.println("客户端读取服务返回的数据：" + byteBuf+" and ctx is "+ctx.toString());
        ctxOut=ctx;
        RESPSTR=byteBuf;

    }

结果如下

客户端读取服务返回的数据：0 and ctx is ChannelHandlerContext(NettyClientHandlerInner#0, [id: 0x59510140, L:/127.0.0.1:54769 - R:/127.0.0.1:1003])

2. 阻塞执行问题
   在启动了连接server后，如果是封装到一个方法里，程序是不能往下执行的，如下
   如果把nettyClientHandlerInner.sendMSG(“write:0”);放在了client.connectToServer(nettyClientHandlerInner);后面，程序是执行到connectToServer就不会往下执行了

            NettyClientHandlerInner nettyClientHandlerInner=new NettyClientHandlerInner();
            new Thread(new Runnable() {
                @Override
                public void run() {
                    nettyClientQA client = new nettyClientQA();
                    nettyClientHandlerInner.sendMSG("write:0");
                    client.connectToServer(nettyClientHandlerInner);
                }
            }).start();

上面代码执行到sendMSG的时候，会报错，因为还没有通道激活初始化，因此，解决暂时方法是，应该还有更好的解决方法，等后面想到了再更新

            NettyClientHandlerInner nettyClientHandlerInner=new NettyClientHandlerInner();
            nettyClientQA client = new nettyClientQA();
            new Thread(new Runnable() {
                @Override
                public void run() {
                    new Thread(new Runnable() {
                        @Override
                        public void run() {
                            try {
                                Thread.sleep(5000);
                            } catch (InterruptedException e) {
                                e.printStackTrace();
                            }
                            nettyClientHandlerInner.sendMSG("write:0");
                        }
                    }).start();

                    client.connectToServer(nettyClientHandlerInner);
                }
            }).start();

3. 如何捕获client handler的异常
   加个内部类即可

package sample.appfunction.netty;

import io.netty.bootstrap.Bootstrap;
import io.netty.buffer.Unpooled;
import io.netty.channel.*;
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;
import io.netty.util.CharsetUtil;

import java.io.IOException;
import java.util.Scanner;
import java.util.concurrent.TimeUnit;

public class nettyClientQA {
    public  void connectToServer(NettyClientHandlerInner nettyClientHandler){
        EventLoopGroup workerGroup = new NioEventLoopGroup();

        try {
            Bootstrap b = new Bootstrap(); // (1)
            b.group(workerGroup); // (2)
            b.channel(NioSocketChannel.class); // (3)
            b.option(ChannelOption.SO_KEEPALIVE, true); // (4)
            b.handler(new ChannelInitializer<SocketChannel>() {
                @Override
                public void initChannel(SocketChannel ch) throws Exception {
                    ch.pipeline().addLast(new LineBasedFrameDecoder(1024));
                    ch.pipeline().addLast(new StringDecoder());
                    ch.pipeline().addLast(nettyClientHandler);
                    ch.pipeline().addLast(new ExceptionHandlingChannelHandler());
                }
            });

            // Start the client.
            ChannelFuture f = b.connect("127.0.0.1", 1003).sync(); // (5)
            f.addListener(new ChannelFutureListener() {
                @Override
                public void operationComplete(ChannelFuture future) {
                    if (future.isSuccess()) {
                        // 连接成功，无需重连
                        System.out.println("connect to server success");
                    } else {
                        // 连接失败，进行重连
                        System.out.println("connect to server failed,try it again");
                        future.channel().eventLoop().schedule(new Runnable() {
                            @Override
                            public void run() {
                                b.connect(); // 重新连接服务端
                            }
                        }, 1, TimeUnit.SECONDS); // 1秒后进行重连
                    }
                }
            });

            // Wait until the connection is closed.
            f.channel().closeFuture().sync();
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            workerGroup.shutdownGracefully();
        }
    }

    public class ExceptionHandlingChannelHandler extends ChannelInboundHandlerAdapter {
        @Override
        public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {
            cause.printStackTrace(); // 打印异常堆栈跟踪
            System.out.println("发生异常");
        }
    }
}

4. 在server handler的异常如何捕捉

    @ChannelHandler.Sharable
    public  class NettyServerHandler extends ChannelInboundHandlerAdapter { // (1)

        @Override
        public void channelRead(ChannelHandlerContext ctx, Object msg) throws IOException { // (2)
            String byteBuf = (String) msg;
            pubMSG=byteBuf;
//            System.out.println("客户端发来的消息是：" + byteBuf);

            System.out.println("收到连接的原信息 "+pubMSG);
            if(byteBuf.contains("write:")){
                currentValue=Integer.parseInt(byteBuf.split(":")[1]);
                System.out.println("收到写入请求 "+currentValue);
            }
            if(byteBuf.contains("read")){
                ctx.writeAndFlush(Unpooled.copiedBuffer(currentValue+"\r\n", CharsetUtil.UTF_8));
                System.out.println("收到读取请求 "+currentValue);
            }
        }

        //数据读取完毕事件
        public void channelReadComplete(ChannelHandlerContext ctx) throws IOException, InterruptedException {
            //数据读取完毕，将信息包装成一个Buffer传递给下一个Handler，Unpooled.copiedBuffer会返回一个Buffer
            //调用的是事件处理器的上下文对象的writeAndFlush方法
            //意思就是说将  你好  传递给了下一个handler
//            ctx.writeAndFlush(Unpooled.copiedBuffer("服务端已经读取消息完成!"+pubMSG+"\r\n", CharsetUtil.UTF_8));
        }

        @Override
        public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) { // (4)
            // Close the connection when an exception is raised.
//            cause.printStackTrace();
            Channel channel = ctx.channel();
            if(channel.isActive())ctx.close();


            System.out.println(cause.getCause());
            System.out.println(cause.getMessage());

        }
    }```