基于Netty的WebSocket简单实现

引言：Netty是由JBOSS提供的一个java开源框架。Netty提供异步的、事件驱动的网络应用程序框架和工具，用以快速开发高性能、高可靠性的网络服务器和客户端程序。也就是说，Netty 是一个基于NIO的客户、服务器端编程框架，使用Netty 可以确保你快速和简单的开发出一个网络应用，例如实现了某种协议的客户，服务端应用。Netty相当简化和流线化了网络应用的编程开发过程，例如，TCP和UDP的socket服务开发。

下面我们就基于netty和tomcat实现一个websocket服务。(本示例基于maven构建，创建项目过程此处不再赘述)

项目依赖

        <dependency>
            <groupId>io.netty</groupId>
            <artifactId>netty-all</artifactId>
            <version>4.1.12.Final</version>
        </dependency>
        <dependency>
            <groupId>commons-logging</groupId>
            <artifactId>commons-logging</artifactId>
            <version>1.1.3</version>
        </dependency>
        <dependency>
            <groupId>log4j</groupId>
            <artifactId>log4j</artifactId>
            <version>1.2.17</version>
        </dependency>
        <!-- sevlet -->
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>javax.servlet-api</artifactId>
            <version>3.1.0</version>
            <scope>provided</scope>
        </dependency>

服务端程序

首先重写ChannelInitializer的初始化方法

package com.mxpio.nettywebsocket.server;

import io.netty.channel.ChannelInitializer;
import io.netty.channel.socket.SocketChannel;
import io.netty.handler.codec.http.HttpObjectAggregator;
import io.netty.handler.codec.http.HttpServerCodec;
import io.netty.handler.stream.ChunkedWriteHandler;

public class ChildChannelHandler extends ChannelInitializer<SocketChannel> {
    @Override
    protected void initChannel(SocketChannel e) throws Exception {

        e.pipeline().addLast("http-codec", new HttpServerCodec());
        e.pipeline().addLast("aggregator", new HttpObjectAggregator(65536));
        e.pipeline().addLast("http-chunked", new ChunkedWriteHandler());
        e.pipeline().addLast("handler", new MyWebSocketServerHandler());
    }
}

定义全局ChannelGroup

package com.mxpio.nettywebsocket.server;

import io.netty.channel.group.ChannelGroup;
import io.netty.channel.group.DefaultChannelGroup;
import io.netty.util.concurrent.GlobalEventExecutor;

public class Global {
    public static ChannelGroup group = new DefaultChannelGroup(GlobalEventExecutor.INSTANCE);

}

服务端核心类MyWebSocketServerHandler

package com.mxpio.nettywebsocket.server;

import java.util.Date;
import java.util.logging.Level;
import java.util.logging.Logger;
import com.mxpio.nettywebsocket.server.Global;
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.HttpResponseStatus;
import io.netty.handler.codec.http.HttpVersion;
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;

public class MyWebSocketServerHandler extends SimpleChannelInboundHandler<Object> {
    private static final Logger logger = Logger.getLogger(WebSocketServerHandshaker.class.getName());
    private WebSocketServerHandshaker handshaker;

    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        // 添加
        Global.group.add(ctx.channel());
        System.out.println("客户端与服务端连接开启");
    }

    @Override
    public void channelInactive(ChannelHandlerContext ctx) throws Exception {
        // 移除
        Global.group.remove(ctx.channel());
        System.out.println("客户端与服务端连接关闭");
    }

    @Override
    protected void channelRead0(ChannelHandlerContext ctx, Object msg) throws Exception {
        if (msg instanceof FullHttpRequest) {
            handleHttpRequest(ctx, ((FullHttpRequest) msg));
        } else if (msg instanceof WebSocketFrame) {
            handlerWebSocketFrame(ctx, (WebSocketFrame) msg);
        }
    }

    @Override
    public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {
        ctx.flush();
    }

    private void handlerWebSocketFrame(ChannelHandlerContext ctx, WebSocketFrame frame) {
        // 判断是否关闭链路的指令
        if (frame instanceof CloseWebSocketFrame) {
            handshaker.close(ctx.channel(), (CloseWebSocketFrame) frame.retain());
        }
        // 判断是否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)) {
            System.out.println("本例程仅支持文本消息，不支持二进制消息");
            throw new UnsupportedOperationException(
                    String.format("%s frame types not supported", frame.getClass().getName()));
        }
        // 返回应答消息
        String request = ((TextWebSocketFrame) frame).text();
        System.out.println("服务端收到：" + request);
        if (logger.isLoggable(Level.FINE)) {
            logger.fine(String.format("%s received %s", ctx.channel(), request));
        }
        TextWebSocketFrame tws = new TextWebSocketFrame(new Date().toString() + ctx.channel().id() + "：" + request);
        // 群发
        Global.group.writeAndFlush(tws);
        // 返回【谁发的发给谁】
        // ctx.channel().writeAndFlush(tws);
    }

    private void handleHttpRequest(ChannelHandlerContext ctx, FullHttpRequest req) {
        if (!req.decoderResult().isSuccess() || (!"websocket".equals(req.headers().get("Upgrade")))) {
            sendHttpResponse(ctx, req,
                    new DefaultFullHttpResponse(HttpVersion.HTTP_1_1, HttpResponseStatus.BAD_REQUEST));
            return;
        }
        WebSocketServerHandshakerFactory wsFactory = new WebSocketServerHandshakerFactory(
                "ws://localhost:7397/websocket", null, false);
        handshaker = wsFactory.newHandshaker(req);
        if (handshaker == null) {
            WebSocketServerHandshakerFactory.sendUnsupportedVersionResponse(ctx.channel());
        } else {
            handshaker.handshake(ctx.channel(), req);
        }
    }

    private static void sendHttpResponse(ChannelHandlerContext ctx, FullHttpRequest req, DefaultFullHttpResponse res) {
        // 返回应答给客户端
        if (res.status().code() != 200) {
            ByteBuf buf = Unpooled.copiedBuffer(res.status().toString(), CharsetUtil.UTF_8);
            res.content().writeBytes(buf);
            buf.release();
        }
        // 如果是非Keep-Alive，关闭连接
        ChannelFuture f = ctx.channel().writeAndFlush(res);
        if (!isKeepAlive(req) || res.status().code() != 200) {
            f.addListener(ChannelFutureListener.CLOSE);
        }
    }

    private static boolean isKeepAlive(FullHttpRequest req) {
        return false;
    }

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        cause.printStackTrace();
        ctx.close();
    }
}

启动器

1.java application方式启动

package com.mxpio.nettywebsocket.server;

import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.Channel;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.nio.NioServerSocketChannel;

public class NettyServer {
    public static void main(String[] args) {

        new NettyServer().run();
    }

    public void run() {

        EventLoopGroup bossGroup = new NioEventLoopGroup();
        EventLoopGroup workGroup = new NioEventLoopGroup();

        try {

            ServerBootstrap b = new ServerBootstrap();
            b.group(bossGroup, workGroup);
            b.channel(NioServerSocketChannel.class);
            b.childHandler(new ChildChannelHandler());

            System.out.println("服务端开启等待客户端连接 ... ...");

            Channel ch = b.bind(7397).sync().channel();

            ch.closeFuture().sync();

        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            bossGroup.shutdownGracefully();
            workGroup.shutdownGracefully();
        }
    }
}

2.在tomcat中基于listener启动

1.编写NettyListener继承ServletContextListener

package com.mxpio.nettywebsocket.listener;

import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;

import com.mxpio.nettywebsocket.server.ChildChannelHandler;

import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.Channel;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.nio.NioServerSocketChannel;

public class NettyListener implements ServletContextListener {
    @Override
    public void contextInitialized(ServletContextEvent sce) {
        System.err.println("nettyListener Startup!");
        new Thread() {
            @Override
            public void run() {
                EventLoopGroup bossGroup = new NioEventLoopGroup();
                EventLoopGroup workGroup = new NioEventLoopGroup();
                try {
                    ServerBootstrap b = new ServerBootstrap();
                    b.group(bossGroup, workGroup);
                    b.channel(NioServerSocketChannel.class);
                    b.childHandler(new ChildChannelHandler());

                    System.out.println("服务端开启等待客户端连接 ... ...");

                    Channel ch = b.bind(7397).sync().channel();

                    ch.closeFuture().sync();
                } catch (Exception e) {
                    e.printStackTrace();
                } finally {
                    bossGroup.shutdownGracefully();
                    workGroup.shutdownGracefully();
                }
            }
        }.start();

        System.err.println("nettyListener end!");
    }

    @Override
    public void contextDestroyed(ServletContextEvent sce) {

    }
}

2.web.xml配置：

<listener>
        <listener-class>com.mxpio.nettywebsocket.listener.NettyListener</listener-class>
    </listener>

测试客户端web页面

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>websocket演示</title>
</head>
</head>
<script type="text/javascript">
    var socket;
    if (!window.WebSocket) {
        window.WebSocket = window.MozWebSocket;
    }

    if (window.WebSocket) {
        socket = new WebSocket("ws://localhost:7397/websocket");
        socket.onmessage = function(event) {
            var ta = document.getElementById('responseText');
            ta.value += event.data + "\r\n";
        };

        socket.onopen = function(event) {
            var ta = document.getElementById('responseText');
            ta.value = "打开WebSoket 服务正常，浏览器支持WebSoket!" + "\r\n";

        };

        socket.onclose = function(event) {
            var ta = document.getElementById('responseText');
            ta.value = "";
            ta.value = "WebSocket 关闭" + "\r\n";
        };
    } else {
        alert("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>
<body>
    <form onSubmit="return false;">
        <input type="text" name="message" value="Netty The Sinper" /> <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: 1024px; height: 300px;"></textarea>
    </form>
</body>
</html>

至此，一个简单的webSocket示例就完成了。