一、websockt简介

一直以来，网络都是围绕着http协议进行开发的。然而，http会有一些固有的问题，所以websocket被引入。

（一）http缺点

1. HTTP是半双工协议，也就是说，数据可在客户端和服务端两个方向上传输，但是，不能同时传输。
2. HTTP消息冗长繁琐，HTTP消息包括请求头、消息体、换行符等。
3. 为了实现消息推送，需要采用轮训方式由浏览器向客户端发送请求，来获取服务器信息，效率很低。

（二）websocket

由于http的一些缺点，引入了websocket，来解决浏览器和服务器交互的一些问题，websocket具有以下特点：

1. 单一的tcp连接，采用全双工通讯模式；
2. 对代理、防火墙和路由器透明；
3. 无头部信息、Cookie和身份验证；
4. 无安全开销；
5. 通过"ping / pong " 帧保持链路激活；
6. 服务器可以主动传送消息给客户端，不用再通过轮训来获取服务端信息；

二、Netty开发websocket

这里使用netty开发一个web群聊功能，来展示Netty对websocket协议的支持。

（一）服务端

package com.firewolf.java.io.http.websocket;import static io.netty.handler.codec.http.HttpHeaderNames.CONTENT_TYPE;
import static io.netty.handler.codec.http.HttpResponseStatus.OK;import com.firewolf.java.io.http.utils.NettyHttpUtils;
import io.netty.bootstrap.ServerBootstrap;
import io.netty.buffer.Unpooled;
import io.netty.channel.Channel;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelOption;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.SimpleChannelInboundHandler;
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.DefaultFullHttpResponse;
import io.netty.handler.codec.http.FullHttpRequest;
import io.netty.handler.codec.http.FullHttpResponse;
import io.netty.handler.codec.http.HttpObjectAggregator;
import io.netty.handler.codec.http.HttpRequest;
import io.netty.handler.codec.http.HttpServerCodec;
import io.netty.handler.codec.http.HttpUtil;
import io.netty.handler.codec.http.websocketx.CloseWebSocketFrame;
import io.netty.handler.codec.http.websocketx.PingWebSocketFrame;
import io.netty.handler.codec.http.websocketx.PongWebSocketFrame;
import io.netty.handler.codec.http.websocketx.TextWebSocketFrame;
import io.netty.handler.codec.http.websocketx.WebSocketFrame;
import io.netty.handler.codec.http.websocketx.WebSocketServerHandshaker;
import io.netty.handler.codec.http.websocketx.WebSocketServerHandshakerFactory;
import io.netty.handler.stream.ChunkedWriteHandler;
import java.io.BufferedReader;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.util.HashMap;
import java.util.Map;/*** 作者：刘兴 时间:2019-05-30**/
public final class NettyWebChatServer {private String chatHtml = System.getProperty("user.dir")+ "/netty-04-http/src/main/java/com/firewolf/java/io/http/websocket/chat.html";//创建websocket连接的工厂private WebSocketServerHandshakerFactory factory = null;//保存所有的连接private Map<Channel, WebSocketServerHandshaker> webConnections = new HashMap<>();private int port;public NettyWebChatServer(int port) {this.port = port;}public void startUp() {EventLoopGroup bossGroup = new NioEventLoopGroup(1);EventLoopGroup workerGroup = new NioEventLoopGroup();try {ServerBootstrap b = new ServerBootstrap();b.option(ChannelOption.SO_BACKLOG, 1024);b.group(bossGroup, workerGroup).channel(NioServerSocketChannel.class).childHandler(new ChannelInitializer<SocketChannel>() {@Overrideprotected void initChannel(SocketChannel socketChannel) throws Exception {socketChannel.pipeline().addLast(new HttpServerCodec()) //请求解码器和响应编码器，等价于下面两行.addLast(new HttpObjectAggregator(65535)).addLast(new ChunkedWriteHandler()).addLast(new NettyWebChatServerHandler());}});Channel ch = b.bind(port).sync().channel();System.out.println(String.format("聊天服务已经启动，端口号为：%s", port));ch.closeFuture().sync();} catch (Exception e) {e.printStackTrace();} finally {//关闭服务bossGroup.shutdownGracefully();workerGroup.shutdownGracefully();}}class NettyWebChatServerHandler extends SimpleChannelInboundHandler<Object> {@Overridepublic void channelRead0(ChannelHandlerContext ctx, Object msg) {//传统的Http介入,if (msg instanceof FullHttpRequest) {handleHttpRequest(ctx, (FullHttpRequest) msg);} else if (msg instanceof WebSocketFrame) {//WebSocket信息接入handleWebMessage(ctx, (WebSocketFrame) msg);}}@Overridepublic void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {cause.printStackTrace();ctx.close();}/*** 处理http请求*/private void handleHttpRequest(ChannelHandlerContext ctx, FullHttpRequest request) {if ("/".equals(request.uri())) {//如果请求的是主页：localhost:8888/，那么就返回聊天页面，responseChatPage(ctx, request);} else {//其他情况认为是前端发起了websocket连接handWebConnect(ctx, request);}}private void responseChatPage(ChannelHandlerContext ctx, HttpRequest req) {try {boolean keepAlive = HttpUtil.isKeepAlive(req);BufferedReader br = new BufferedReader(new FileReader(new File(chatHtml)));StringBuffer result = new StringBuffer();String line = null;while ((line = br.readLine()) != null) {result.append(line);}//构造响应数据FullHttpResponse response = new DefaultFullHttpResponse(req.protocolVersion(), OK,Unpooled.wrappedBuffer(result.toString().getBytes()));response.headers().set(CONTENT_TYPE, "text/html;charset=UTF-8"); //设置响应类型//给客户端响应信息NettyHttpUtils.sendResponse(ctx, req, keepAlive, response);} catch (Exception e) {e.printStackTrace();}}/*** 处理web连接*/private void handWebConnect(ChannelHandlerContext ctx, FullHttpRequest request) {if (!"websocket".equals(request.headers().get("Upgrade"))) { //不是websock握手请求，不建立连接return;}if (factory == null) {factory = new WebSocketServerHandshakerFactory("ws://localhost:8888/websocket",null, false);}//建立websocket连接WebSocketServerHandshaker handlerShaker = factory.newHandshaker(request);if (handlerShaker == null) {WebSocketServerHandshakerFactory.sendUnsupportedVersionResponse(ctx.channel());} else {handlerShaker.handshake(ctx.channel(), request);webConnections.put(ctx.channel(), handlerShaker);}}/*** 处理webSocket信息*/private void handleWebMessage(ChannelHandlerContext ctx, WebSocketFrame frame) {if (frame instanceof CloseWebSocketFrame) { //关闭连接webConnections.get(ctx.channel()).close(ctx.channel(), ((CloseWebSocketFrame) frame).retain());webConnections.remove(ctx.channel());} else if (frame instanceof PingWebSocketFrame) { //Ping信息，返回Pongctx.channel().writeAndFlush(new PongWebSocketFrame());} else if (frame instanceof TextWebSocketFrame) { //文本信息，进行转发TextWebSocketFrame textFrame = (TextWebSocketFrame) frame;webConnections.keySet().forEach(x -> {String prefix = "有人说： ";if (x.id().asShortText().equals(ctx.channel().id().asShortText())) {prefix = "我说： ";}x.writeAndFlush(new TextWebSocketFrame(prefix + textFrame.text()));});} else { //其他的类型，不进行支持System.out.println("信息暂时不支持");ctx.channel().writeAndFlush(new TextWebSocketFrame("您的消息内容暂时不支持!!!"));}}}public static void main(String[] args) throws Exception {new NettyWebChatServer(8888).startUp();}
}

（二）页面

<html>
<head><meta http-equiv="Content-Type" content="text/html; charset = utf-8"/><title>WebSocket客户端</title><script type="text/javascript">var socket;if (!window.WebSocket) {window.WebSocket = window.MozWebSocket;}if (window.WebSocket) {socket = new WebSocket("ws://127.0.0.1:8888/websocket");socket.onmessage = function (event) {var ta = document.getElementById('responseContent');ta.value += event.data + "\r\n";};socket.onopen = function (event) {var ta = document.getElementById('responseContent');ta.value = "你当前的浏览器支持WebSocket,请进行后续操作\r\n";};socket.onclose = function (event) {var ta = document.getElementById('responseContent');ta.value = "";ta.value = "WebSocket连接已经关闭\r\n";};} else {alert("您的浏览器不支持WebSocket");}function send(message) {if (!window.WebSocket) {return;}if (socket.readyState == WebSocket.OPEN) {socket.send(message);document.getElementById("inputMessage").value = "";} else {alert("WebSocket连接没有建立成功！！");}}</script>
</head>
<body style="padding-left: 300px;padding-top: 80px;">
<form onSubmit="return false;"><h2 style="color: red;">Web群聊聊天大厅!!!</h2><br><textarea id="responseContent" style="width:500px; height:300px" readonly></textarea><br/><br/><input type="text" id="inputMessage" name="message" value="" style="width: 390px; height: 30px;"/><button style="width: 100px; height: 30px;margin-left: 10px;" onClick="send(this.form.message.value)"> 发送消息</button>
</form>
</body>
</html>

（三）测试

启动项目后浏览器输入：http://localhost:8888，会展示出聊天页面：

我们打开两个聊天窗口，就可以进行聊天了：

这里面为了简单，页面直接写到了前台，实际上我们可以配合springboot，或者是nginx来专门单独的管理chat.html。