一起学netty（17）netty实现websocket协议

Websocket协议和http协议的关系

websocket是基于TCP的一个应用协议，与HTTP协议的关联之处在于websocket的握手数据被HTTP服务器当作HTTP包来处理，主要通过Update request HTTP包建立起连接，之后的通信全部使用websocket自己的协议，就和http没啥关系了。有兴趣的同学可以多了解一下websocket协议报文的详细信息。

Netty实现websocket协议

import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.*;
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.TextWebSocketFrame;
import io.netty.handler.codec.http.websocketx.WebSocketServerProtocolHandler;
import io.netty.handler.stream.ChunkedWriteHandler;

public class NettyServerWebsocker {
    public static void main(String[] args) throws InterruptedException {
        NioEventLoopGroup boot = new NioEventLoopGroup(1);
        NioEventLoopGroup work = new NioEventLoopGroup(8);
        ServerBootstrap bootstrap = new ServerBootstrap();
        bootstrap.group(boot,work)
                .channel(NioServerSocketChannel.class)
                .childHandler(new ChannelInitializer<SocketChannel>() {
                    @Override
                    protected void initChannel(SocketChannel socketChannel) throws Exception {
                        ChannelPipeline pipeline = socketChannel.pipeline();
                        // 建立连接时需要http协议的支持
                        pipeline.addLast(new HttpServerCodec());
                        // 以块的方式来写的处理器
                        pipeline.addLast(new ChunkedWriteHandler());
                        //netty是基于分段请求的，HttpObjectAggregator的作用是将请求分段再聚合,参数是聚合字节的最大长度
                        pipeline.addLast(new HttpObjectAggregator(1024*64));
                        //这个是websocket的handler，是netty提供的，也可以自定义，建议就用默认的
                        pipeline.addLast(new WebSocketServerProtocolHandler("/ws"));

                        // 消息处理器
                        pipeline.addLast(new SimpleChannelInboundHandler<TextWebSocketFrame>() {
                            @Override
                            protected void channelRead0(ChannelHandlerContext channelHandlerContext, TextWebSocketFrame text) throws Exception {
                                System.out.println(text.text());
                                channelHandlerContext.writeAndFlush(new TextWebSocketFrame("我收到你的消息了"+text.text()));
                                channelHandlerContext.fireChannelActive();
                            }
                        });
                    }
                });
        // 绑定端口
        ChannelFuture bind = bootstrap.bind(8678).sync();
        bind.channel().closeFuture().sync();
    }
}

websocket数据包的类型有四种，TextWebSocketFrame（文本消息）、BinaryWebSocketFrame（二进制消息）、PongWebSocketFrame（PING存活检测消息）、CloseWebSocketFrame（关闭指令消息）。

上述代码只能接收TextWebSocketFrame文本类型的消息，如果需要接收其他类型的消息可以继承ChannelInboundHandlerAdapter类在channelRead方法中判断。

客户端（js代码）

<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>websocket</title>
</head>
<body>
<!--  网页控件元素，类似按钮/图片/文章什么的都写在这里  -->
<input type = "text" id ="v">
<input type = "button" id = "b" onclick="send()" value="send">
<div id ="text">
</div>
</body>
<script>

	let ws = new WebSocket("ws://localhost:8678/ws");
	 ws.onopen = function (event) {
		 console.log("Send Text WS was opened.");
		 ws.send("hello");
	 };
	 ws.onmessage = function (event) {
		 console.log("response text msg: " + event.data);
		 document.getElementById("text").innerHTML=event.data;
	 };
	 ws.onerror = function (event) {
		 console.log("Send Text fired an error");
	 };
	 ws.onclose = function (event) {
		 console.log("WebSocket instance closed.");
	 };
	 function send(){
		 var v = document.getElementById("v").value;
		 ws.send(v);
	 }
</script>
</html>