11.netty开发webSock协议

1.介绍

一般情况下网络都是请求/响应模式,在下一次点击发送请求之前什么都不会发生。后来出现的ajax是浏览器定期轮询捕捉用户在页面的操作并发送请求,这也是基于客户端浏览器实现的。

另一种情况,当服务器发现有新数据可用时通过推送的方式主动发送给客户端,而不是客户端主动发送请求。基于这种情况可以使用长轮询(客户端打开指定http连接,知道收到服务器的响应)

上面两种情况都有一个缺点：由于http协议的开销,导致他们都不能应用于低延迟的应用。所以h5定义的webSocket将socket引入server和client两端,通过socket建立持久的连接并且双方可以主动发送数据,而不是请求响应模式。

http协议弊端：半双工协议(同一时刻只能由一方发送向另一方,不能双方同时发送)、http消息冗长繁琐(消息头、消息体、换行符等等)、针对服务器推送的黑客攻击(长轮询)

webSocket特点：全双工、对代理和防火墙和路由器透明、无头部信息无cookie无身份验证、无安全开销、pingpong保持链路激活、双方可以主动发送请求

发起webSocket请求的过程：客户端必须先发送一个http请求,这个请求和普通的http请求不同,主要是请求头中附加了信息："Upgrade：WebSocke"表明是一个升级的http请求。server端生成应答信息发回给client这样就建立起一个WebSocket连接。之后双方可以互相发送数据

2.netty实现

handler：

接收到客户端请求后第一次通过http响应,响应成功双方建立起webSocket链路

client通过这个链路生成webSocket对象来发送请求

server将信息加上系统时间返回

package com.tyf.netty;import static io.netty.handler.codec.http.HttpHeaders.isKeepAlive;import static io.netty.handler.codec.http.HttpHeaders.setContentLength;import static io.netty.handler.codec.http.HttpResponseStatus.BAD_REQUEST;import static io.netty.handler.codec.http.HttpVersion.HTTP_1_1;import io.netty.buffer.ByteBuf;import io.netty.buffer.Unpooled;import io.netty.channel.ChannelFuture;import io.netty.channel.ChannelFutureListener;import io.netty.channel.ChannelHandlerContext;import io.netty.channel.SimpleChannelInboundHandler;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.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.util.CharsetUtil;import java.util.logging.Level;import java.util.logging.Logger;public class WebSocketServerHandler extends SimpleChannelInboundHandler<Object> {    private static final Logger logger = Logger.getLogger(WebSocketServerHandler.class.getName());    private WebSocketServerHandshaker handshaker;    @Override    public void messageReceived(ChannelHandlerContext ctx, Object msg)throws Exception {    // 第一次握手有http请求处理if (msg instanceof FullHttpRequest) {    handleHttpRequest(ctx, (FullHttpRequest) msg);}// WebSocket链路建立成功之后处理WebSocket请求else if (msg instanceof WebSocketFrame) {    handleWebSocketFrame(ctx, (WebSocketFrame) msg);}    }    @Override    public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {ctx.flush();    }    //http协议处理第一次握手    private void handleHttpRequest(ChannelHandlerContext ctx,FullHttpRequest req) throws Exception {// 如果HTTP解码失败，返回HHTP异常if (!req.getDecoderResult().isSuccess()|| (!"websocket".equals(req.headers().get("Upgrade")))) {    sendHttpResponse(ctx, req, new DefaultFullHttpResponse(HTTP_1_1,BAD_REQUEST));    return;}// 构造握手响应返回，本机测试。返回成功之后建立webSocket链路// 客户端通过ws://localhost:8080/websocket这个地址来生成websocket对象WebSocketServerHandshakerFactory wsFactory = new WebSocketServerHandshakerFactory("ws://localhost:8080/websocket", null, false);handshaker = wsFactory.newHandshaker(req);if (handshaker == null) {    WebSocketServerHandshakerFactory    .sendUnsupportedWebSocketVersionResponse(ctx.channel());} else {    handshaker.handshake(ctx.channel(), req);}    }    //处理双方的webSocket请求    private void handleWebSocketFrame(ChannelHandlerContext ctx,WebSocketFrame frame) {// 判断是否是关闭链路的指令if (frame instanceof CloseWebSocketFrame) {    handshaker.close(ctx.channel(),    (CloseWebSocketFrame) frame.retain());    return;}// 判断是否是Ping消息if (frame instanceof PingWebSocketFrame) {    ctx.channel().write(    new PongWebSocketFrame(frame.content().retain()));    return;}// 本例程仅支持文本消息，不支持二进制消息if (!(frame instanceof TextWebSocketFrame)) {    throw new UnsupportedOperationException(String.format(    "%s frame types not supported", frame.getClass().getName()));}// 返回应答消息String request = ((TextWebSocketFrame) frame).text();if (logger.isLoggable(Level.FINE)) {    logger.fine(String.format("%s received %s", ctx.channel(), request));}ctx.channel().write(new TextWebSocketFrame(request+ " , 欢迎使用Netty WebSocket服务，现在时刻："+ new java.util.Date().toString()));    }    private static void sendHttpResponse(ChannelHandlerContext ctx,    FullHttpRequest req, FullHttpResponse res) {// 返回应答给客户端if (res.getStatus().code() != 200) {    ByteBuf buf = Unpooled.copiedBuffer(res.getStatus().toString(),    CharsetUtil.UTF_8);    res.content().writeBytes(buf);    buf.release();    setContentLength(res, res.content().readableBytes());}// 如果是非Keep-Alive，关闭连接ChannelFuture f = ctx.channel().writeAndFlush(res);if (!isKeepAlive(req) || res.getStatus().code() != 200) {    f.addListener(ChannelFutureListener.CLOSE);}    }    @Override    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {cause.printStackTrace();ctx.close();    }}

server：

package com.tyf.netty;import io.netty.bootstrap.ServerBootstrap;import io.netty.channel.Channel;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.http.HttpObjectAggregator;import io.netty.handler.codec.http.HttpServerCodec;import io.netty.handler.stream.ChunkedWriteHandler;public class WebSocketServer {    public void run(int port) throws Exception {EventLoopGroup bossGroup = new NioEventLoopGroup();EventLoopGroup workerGroup = new NioEventLoopGroup();try {    ServerBootstrap b = new ServerBootstrap();    b.group(bossGroup, workerGroup)    .channel(NioServerSocketChannel.class)    .childHandler(new ChannelInitializer<SocketChannel>() {@Overrideprotected void initChannel(SocketChannel ch)throws Exception {    ChannelPipeline pipeline = ch.pipeline();    pipeline.addLast("http-codec",new HttpServerCodec());    pipeline.addLast("aggregator",new HttpObjectAggregator(65536));    ch.pipeline().addLast("http-chunked",new ChunkedWriteHandler());    pipeline.addLast("handler",new WebSocketServerHandler());}    });    //绑定本地8080端口    Channel ch = b.bind(port).sync().channel();    //future开启同步    ch.closeFuture().sync();} finally {    bossGroup.shutdownGracefully();    workerGroup.shutdownGracefully();}    }    public static void main(String[] args) throws Exception {int port = 8080;if (args.length > 0) {    try {port = Integer.parseInt(args[0]);    } catch (NumberFormatException e) {e.printStackTrace();    }}new WebSocketServer().run(port);    }}

client(客户端使用html和js来发送请求)：

<!DOCTYPE html><html><head><meta charset="UTF-8">Netty WebSocket 时间服务器</head><br><body><br><script type="text/javascript">var socket;if (!window.WebSocket) {window.WebSocket = window.MozWebSocket;}if (window.WebSocket) {socket = new WebSocket("ws://localhost:8080/websocket");socket.onmessage = function(event) {var ta = document.getElementById('responseText');ta.value="";ta.value = event.data};socket.onopen = function(event) {var ta = document.getElementById('responseText');ta.value = "打开WebSocket服务正常，浏览器支持WebSocket!";};socket.onclose = function(event) {var ta = document.getElementById('responseText');ta.value = "";ta.value = "WebSocket 关闭!"; };}else{alert("抱歉，您的浏览器不支持WebSocket协议!");}function send(message) {if (!window.WebSocket) { return; }if (socket.readyState == WebSocket.OPEN) {socket.send(message);}else{  alert("WebSocket连接没有建立成功!");}}</script><form onsubmit="return false;"><input type="text" name="message" value="Netty最佳实践"/><br><br><input type="button" value="发送WebSocket请求消息" onclick="send(this.form.message.value)"/><hr color="blue"/><h3>服务端返回的应答消息</h3><textarea id="responseText" style="width:500px;height:300px;"></textarea></form></body></html>

3.测试

直接运行server和client,使用客户端发送消息给server：