[网络协议]Netty实现WebSocket长连接

????????WebSocket协议是使用单个TCP连接进行全双工通信的协议，浏览器与服务器使用一个长连接，可以双向数据传输，且服务器可以主动给浏览器推送数据。Netty是通过给通道绑定的管道，添加一个WebSocketServerProtocleHandler处理器，将http协议升级为WebSocket协议的，数据传输采用帧WebSocketFrame的形式，比如常用的文本帧TextWebSocketFrame传输文本数据。

服务器

package com.tech.netty.netty.websocket;

import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelPipeline;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioServerSocketChannel;
import io.netty.handler.codec.http.HttpObjectAggregator;
import io.netty.handler.codec.http.HttpServerCodec;
import io.netty.handler.codec.http.websocketx.WebSocketServerProtocolHandler;
import io.netty.handler.logging.LogLevel;
import io.netty.handler.logging.LoggingHandler;
import io.netty.handler.stream.ChunkedWriteHandler;

/**
 * @author lw
 * @since 2021/8/20
 */
public class MyServer {
    public static void main(String[] args) throws InterruptedException {
        //创建2个线程组
        NioEventLoopGroup bossGroup = new NioEventLoopGroup(1);
        NioEventLoopGroup workerGroup = new NioEventLoopGroup();
        try{
            ServerBootstrap serverBootstrap = new ServerBootstrap();
            serverBootstrap.group(bossGroup,workerGroup)
                    .channel(NioServerSocketChannel.class)
                    .handler(new LoggingHandler(LogLevel.INFO))
                    .childHandler(new ChannelInitializer<SocketChannel>() {
                        @Override
                        protected void initChannel(SocketChannel ch) throws Exception {
                            ChannelPipeline pipeline = ch.pipeline();
                            //因为基于http协议 使用http的编码器和解码器
                            pipeline.addLast("HttpServerCodec",new HttpServerCodec())
                                    //以块方式写 添加ChunkedWriteHandler处理器
                                    .addLast("ChunkedWriteHandler", new ChunkedWriteHandler())
                                    //http传输过程中会分段 HttpObjectAggregator可以将多个段聚合
                                    //这就是为什么，当浏览器发送大量数据时，就会发多次http请求
                                    .addLast("HttpObjectAggregator",new HttpObjectAggregator(8192))
                                    //对应websocket 它的数据是以帧(WebSocketFrame)形式传递
                                    //浏览器请求时ws://localhost:7000/hello表示请求的uri
                                    //WebSocketServerProtocolHandler的核心功能是将http协议升级为ws协议 并保持长连接
                                    //是通过一个状态码 101
                                    .addLast("WebSocketServerProtocolHandler",new WebSocketServerProtocolHandler("/hello"))
                                    //自定义的handler做业务逻辑处理
                                    .addLast(new MyTextWebSocketFrameHandler());
                        }
                    });
            //启动服务器
            ChannelFuture channelFuture = serverBootstrap.bind(7000).sync();
            channelFuture.channel().closeFuture().sync();
        }finally {
            bossGroup.shutdownGracefully();
            workerGroup.shutdownGracefully();
        }
    }
}

package com.tech.netty.netty.websocket;

import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.SimpleChannelInboundHandler;
import io.netty.handler.codec.http.websocketx.TextWebSocketFrame;

import java.time.LocalDateTime;

/**
 * @author lw
 * @since 2021/8/20
 */
//TextWebSocketFrame表示一个文本帧
public class MyTextWebSocketFrameHandler extends SimpleChannelInboundHandler<TextWebSocketFrame> {
    @Override
    protected void channelRead0(ChannelHandlerContext ctx, TextWebSocketFrame msg) throws Exception {
        System.out.println("服务端接收到消息"+msg.text());
        //回复消息
        ctx.channel().writeAndFlush(new TextWebSocketFrame("服务器时间 "+ LocalDateTime.now()+" "+msg.text()));
    }

    //当web客户端连接后触发该方法
    @Override
    public void handlerAdded(ChannelHandlerContext ctx) throws Exception {
        System.out.println("handlerAdded 被调用 "+ctx.channel().id().asLongText());
        System.out.println("handlerAdded 被调用 "+ctx.channel().id().asShortText());
    }

    @Override
    public void handlerRemoved(ChannelHandlerContext ctx) throws Exception {
        //id表示唯一 longText是唯一的 shortText不是惟一的
        System.out.println("handlerRemoved 被调用 "+ctx.channel().id().asLongText());
        System.out.println("handlerRemoved 被调用 "+ctx.channel().id().asShortText());
    }

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        System.out.println("异常发生 "+cause.getMessage());
        //关闭连接
        ctx.close();
    }
}

客户端

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<script>
    var socket;
    //判断当前浏览器是否支持websocket
    if(window.WebSocket) {
        //go on
        socket = new WebSocket("ws://localhost:7000/hello");
        //相当于channelReado, ev 收到服务器端回送的消息
        socket.onmessage = function (ev) {
            var rt = document.getElementById("responseText");
            rt.value = rt.value + "\n" + ev.data;
        }

        //相当于连接开启(感知到连接开启)
        socket.onopen = function (ev) {
            var rt = document.getElementById("responseText");
            rt.value = "连接开启了.."
        }

        //相当于连接关闭(感知到连接关闭)
        socket.onclose = function (ev) {

            var rt = document.getElementById("responseText");
            rt.value = rt.value + "\n" + "连接关闭了.."
        }
    } else {
        alert("当前浏览器不支持websocket")
    }

    //发送消息到服务器
    function send(message) {
        if(!window.socket) { //先判断socket是否创建好
            return;
        }
        if(socket.readyState == WebSocket.OPEN) {
            //通过socket 发送消息
            socket.send(message)
        } else {
            alert("连接没有开启");
        }
    }
</script>
    <form onsubmit="return false">
        <textarea name="message" style="height: 300px; width: 300px"></textarea>
        <input type="button" value="发生消息" onclick="send(this.form.message.value)">
        <textarea id="responseText" style="height: 300px; width: 300px"></textarea>
        <input type="button" value="清空内容" onclick="document.getElementById('responseText').value=''">
    </form>
</body>
</html>

程序运行后 测试效果如下：

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