4.Netty的零拷贝

传统拷贝方式

1. 数据从磁盘读取到内核的read buffer
2. 数据从内核缓冲区拷贝到用户缓冲区
3. 数据从用户缓冲区拷贝到内核的socket buffer
4. 数据从内核的socket buffer拷贝到网卡接口（硬件）的缓冲区

零拷贝

1. 调用transferTo,数据从文件由DMA引擎拷贝到内核read buffer
2. 接着DMA从内核read buffer将数据拷贝到网卡接口buffer

Netty中的零拷贝体现在这三个方面：

1.bytebuffer

Netty发送和接收消息主要使用bytebuffer，bytebuffer使用对外内存（DirectMemory）直接进行Socket读写。

2.Composite Buffers

传统的ByteBuffer，如果需要将两个ByteBuffer中的数据组合到一起，我们需要首先创建一个size=size1+size2大小的新的数组，然后将两个数组中的数据拷贝到新的数组中。但是使用Netty提供的组合ByteBuf，就可以避免这样的操作，因为CompositeByteBuf并没有真正将多个Buffer组合起来，而是保存了它们的引用，从而避免了数据的拷贝，实现了零拷贝。

3.对于FileChannel.transferTo的使用

Netty中使用了FileChannel的transferTo方法，该方法依赖于操作系统实现零拷贝。

二、Netty组件

1. Channel – 对应NIO中的channel
2. EventLoop --对应NIO中的while循环
3. ChannelHandler和ChannelPipline --对应NIO客户逻辑实现handleRead和handleWrite
4. ByteBuf --对应Nio中的ByteBuffer
5. BootStrap和BootServerStrap --对应NIO中的Selecter、ServerSocketChannel等的创建、配置、启动

Reactor线程模型

Rector线程模型有三种形式：

1.单线程模型：

2.多线程模型：

3.mutiple模型

Netty对这三种模式都有支持

三、简单的例子

1.引入pom包

 <dependency>
            <groupId>io.netty</groupId>
            <artifactId>netty-all</artifactId>
            <version>4.1.42.Final</version>
        </dependency>

2.服务器端

public class TimeServer {

    public void bind(int port) throws InterruptedException {
        EventLoopGroup boosGroup=new NioEventLoopGroup();
        EventLoopGroup workerGroup=new NioEventLoopGroup();

        try{
            ServerBootstrap b=new ServerBootstrap();
            b.group(boosGroup,workerGroup)
                    .channel(NIOServerSocketChannel.class)
                    .option(ChannelOption.SO_BACKLOG,1024)
                    .childHandler(new ChildChannelHandler());

            //绑定端口，同步等待成功
            ChannelFuture future = b.bind(port).sync();
            //等待服务端监听关闭
            future.channel().closeFuture().sync();
        }finally {
            //优雅退出，释放线程池资源
            boosGroup.shutdownGracefully();
            workerGroup.shutdownGracefully();
        }
    }

    public static void main(String[] args) throws InterruptedException {
        new TimeServer().bind(8888);
    }


    private class ChildChannelHandler extends ChannelInitializer<SocketChannel> {

        @Override
        protected void initChannel(SocketChannel socketChannel) throws Exception {
            socketChannel.pipeline().addLast(new TimeServerHandler());
        }
    }
}

public class TimeServerHandler extends ChannelInboundHandlerAdapter {


    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        ByteBuf buf=(ByteBuf)msg;
        byte[] req=new byte[buf.readableBytes()];
        buf.readBytes(req);
        String body=new String(req,"UTF-8");
        System.out.println(body);
        SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        String currentTime=simpleDateFormat.format(new Date());
        ByteBuf resp = Unpooled.copiedBuffer(currentTime.getBytes());
        ctx.write(resp);
    }

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

实战弹幕系统

java：

public class WebSocketDanmuServer {

    private int port;

    public WebSocketDanmuServer(int port) {
        this.port = port;
    }

    public void run(){
        EventLoopGroup bossGroup=new NioEventLoopGroup(1);
        EventLoopGroup workGroup=new NioEventLoopGroup(8);
        try {
        ServerBootstrap b=new ServerBootstrap();
        b.group(bossGroup,workGroup)
                .channel(NioServerSocketChannel.class)
                .childHandler(new WebsocketDanmuServerInitializer())
                .option(ChannelOption.SO_BACKLOG,128)
                .childOption(ChannelOption.SO_KEEPALIVE,true);

        System.out.println("弹幕系统启动了 "+port);


            ChannelFuture future = b.bind(port).sync();

            future.channel().closeFuture().sync();

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

    public static void main(String[] args) {
        new WebSocketDanmuServer(8080).run();
    }
}

public class WebsocketDanmuServerInitializer extends ChannelInitializer<SocketChannel> {


    @Override
    protected void initChannel(SocketChannel socketChannel) throws Exception {
        ChannelPipeline pipeline = socketChannel.pipeline();
        pipeline.addLast("http-decodec",new HttpRequestDecoder());
        pipeline.addLast("http-aggregator",new HttpObjectAggregator(65536));
        pipeline.addLast("http-encodec",new HttpResponseEncoder());
        pipeline.addLast("http-chunked",new ChunkedWriteHandler());
       /*
			pipeline.addLast(new HttpServerCodec());
			pipeline.addLast(new HttpObjectAggregator(64*1024));
			pipeline.addLast(new ChunkedWriteHandler());
		*/
        pipeline.addLast("http-request",new HttpRequestHandler("/ws"));
        pipeline.addLast("WebSocket-protocol",new WebSocketServerProtocolHandler("/ws"));
        pipeline.addLast("WebSocket-request",new TextWebSocketFrameHandler());
    }
}

public class HttpRequestHandler extends SimpleChannelInboundHandler<FullHttpRequest> {

    private final String wsUri;
    private static final File INDEX;


    static {
        URL location=HttpRequestHandler.class.getProtectionDomain().getCodeSource().getLocation();
        try {
            String path = location.toURI() + "WebsocketDanMu.html";
            path = !path.contains("file:") ? path : path.substring(5);
            INDEX = new File(path);
        } catch (URISyntaxException e) {
            throw new IllegalStateException("Unable to locate WebsocketChatClient.html", e);
        }
    }

    public HttpRequestHandler(String wsUri) {
        this.wsUri = wsUri;
    }

    private static void send100Continue(ChannelHandlerContext ctx) {
        FullHttpResponse response = new DefaultFullHttpResponse(HttpVersion.HTTP_1_1, HttpResponseStatus.CONTINUE);
        ctx.writeAndFlush(response);
    }


    @Override
    protected void channelRead0(ChannelHandlerContext ctx, FullHttpRequest request) throws Exception {
        if(wsUri.equalsIgnoreCase(request.getUri())){
            ctx.fireChannelRead(request.retain());
        }else {
            if(HttpHeaders.is100ContinueExpected(request)){
                send100Continue(ctx);
            }
            RandomaccessFile file = new RandomAccessFile(INDEX, "r");//4

            HttpResponse response = new DefaultHttpResponse(request.getProtocolVersion(), HttpResponseStatus.OK);
            response.headers().set(HttpHeaders.Names.CONTENT_TYPE, "text/html; charset=UTF-8");

            boolean keepAlive = HttpHeaders.isKeepAlive(request);

            if (keepAlive) {                                        //5
                response.headers().set(HttpHeaders.Names.CONTENT_LENGTH, file.length());
                response.headers().set(HttpHeaders.Names.CONNECTION, HttpHeaders.Values.KEEP_ALIVE);
            }
            ctx.write(response);                    //6

            if (ctx.pipeline().get(SslHandler.class) == null) {     //7
                ctx.write(new DefaultFileRegion(file.getChannel(), 0, file.length()));
            } else {
                ctx.write(new ChunkedNioFile(file.getChannel()));
            }
            ChannelFuture future = ctx.writeAndFlush(LastHttpContent.EMPTY_LAST_CONTENT);           //8
            if (!keepAlive) {
                future.addListener(ChannelFutureListener.CLOSE);        //9
            }

            file.close();
        }
        }


}

public class TextWebSocketFrameHandler extends SimpleChannelInboundHandler<TextWebSocketFrame> {


    public static ChannelGroup channels = new DefaultChannelGroup(GlobalEventExecutor.INSTANCE);

    @Override
    protected void channelRead0(ChannelHandlerContext ctx, TextWebSocketFrame msg) throws Exception {
        Channel incoming=ctx.channel();
        for (Channel channel:channels){
            if(channel!=incoming){
                channel.writeAndFlush(new TextWebSocketFrame(msg.text()));
            }else {
                channel.writeAndFlush(new TextWebSocketFrame("我发送的 "+msg.text()));
            }
        }
    }


    @Override
    public void handlerAdded(ChannelHandlerContext ctx) throws Exception {  // (2)
        Channel incoming = ctx.channel();

        // Broadcast a message to multiple Channels
        channels.writeAndFlush(new TextWebSocketFrame("[SERVER] - " + incoming.remoteAddress() + " 加入"));

        channels.add(incoming);
        System.out.println("Client:"+incoming.remoteAddress() +"加入");
    }

    @Override
    public void handlerRemoved(ChannelHandlerContext ctx) throws Exception {  // (3)
        Channel incoming = ctx.channel();

        // Broadcast a message to multiple Channels
        channels.writeAndFlush(new TextWebSocketFrame("[SERVER] - " + incoming.remoteAddress() + " 离开"));

        System.err.println("Client:"+incoming.remoteAddress() +"离开");

        // A closed Channel is automatically removed from ChannelGroup,
        // so there is no need to do "channels.remove(ctx.channel());"
    }

    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception { // (5)
        Channel incoming = ctx.channel();
        System.out.println("Client:"+incoming.remoteAddress()+"在线");
    }

    @Override
    public void channelInactive(ChannelHandlerContext ctx) throws Exception { // (6)
        Channel incoming = ctx.channel();
        System.err.println("Client:"+incoming.remoteAddress()+"掉线");
    }

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause)	// (7)
            throws Exception {
        Channel incoming = ctx.channel();
        System.err.println("Client:"+incoming.remoteAddress()+"异常");
        // 当出现异常就关闭连接
        cause.printStackTrace();
        ctx.close();
    }


}

html:

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
    <meta name="Keywords" content="danmu">
    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
    <title>弹幕网站</title>
    <style type="text/css">
        body {
            background: url(http://ot0ak6eri.bkt.clouddn.com/01.jpg); no-repeat:top center;
            font-size: 12px;
            font-family: "微软雅黑";
        }


        * {
            margin: 0;
            padding: 0;
        }
        /* screen start*/
        .screen {
            width: 300px;
            height: 100px;
            background: #669900;
        }


        .dm {
            width: 100%;
            height: 100%;
            position: absolute;
            top: 0;
            left: 0;
            display: none;
        }


        .dm .d_screen .d_del {
            width: 38px;
            height: 38px;
            background: #600;
            display: block;
            text-align: center;
            line-height: 38px;
            text-decoration: none;
            font-size: 20px;
            color: #fff;
            border-radius: 19px;
            border: 1px solid #fff;
            z-index: 2;
            position: absolute;
            right: 20px;
            top: 20px;
            outline: none;
        }


        .dm .d_screen .d_del:hover {
            background: #F00;
        }


        .dm .d_screen .d_mask {
            width: 100%;
            height: 100%;
            background: #000;
            position: absolute;
            top: 0;
            left: 0;
            opacity: 0.6;
            filter: alpha(opacity = 60);
            z-index: 1;
        }


        .dm .d_screen .d_show {
            position: relative;
            z-index: 2;
        }


        .dm .d_screen .d_show div {
            font-size: 26px;
            line-height: 36px;
            font-weight: 500;
            position: absolute;
            top: 76px;
            left: 10;
            color: #fff;
        }
        /*end screen*/


        /*send start*/
        .send {
            width: 100%;
            height: 76px;
            position: absolute;
            bottom: 0;
            left: 0;
            border: 1px solid red;
        }


        .send .s_filter {
            width: 100%;
            height: 76px;
            background: #000;
            position: absolute;
            bottom: 0;
            left: 0;
            opacity: 0.6;
            filter: alpha(opacity = 60);
        }


        .send  .s_con {
            width: 100%;
            height: 76px;
            position: absolute;
            top: 0;
            left: 0;
            z-index: 2;
            text-align: center;
            line-height: 76px;
        }


        .send .s_con .s_text {
            width: 800px;
            height: 36px;
            border: 0;
            border-radius: 6px 0 0 6px;
            outline: none;
        }


        .send .s_con .s_submit {
            width: 100px;
            height: 36px;
            border-radius: 0 6px 6px 0;
            outline: none;
            font-size: 14px;
            color: #fff;
            background: #65c33d;
            font-family: "微软雅黑";
            cursor: pointer;
            border: 1px solid #5bba32;
        }


        .send .s_con .s_submit:hover {
            background: #3eaf0e;
        }
        /*end send*/
    </style>


</head>
<body>
<a href="#" id="startDm">开启弹幕</a>
<!-- dm start -->
<div class="dm">
    <!-- d_screen start -->
    <div class="d_screen">
        <a href="#" class="d_del">X</a>
        <div class="d_mask"></div>
        <div class="d_show">
        </div>
    </div>
    <!-- end d_screen -->


    <!-- send start -->
    <div class="send">
        <div class="s_filter"></div>
        <div class="s_con">
            <input type="text" class="s_text" /> <input type="button"
                                                        value="发表评论" class="s_submit" id="btn"/>
        </div>
    </div>
    <!-- end send -->
</div>
<!-- end dm-->
<script type="text/JavaScript"
        src="http://ajax.aspnetcdn.com/ajax/jQuery/jquery-1.8.0.js"></script>

<script type="text/javascript" >

    String.prototype.endWith=function(str){
        if(str==null||str==""||this.length==0||str.length>this.length)
            return false;
        if(this.substring(this.length-str.length)==str)
            return true;
        else
            return false;
        return true;
    }

    String.prototype.startWith=function(str){
        if(str==null||str==""||this.length==0||str.length>this.length)
            return false;
        if(this.substr(0,str.length)==str)
            return true;
        else
            return false;
        return true;
    }
</script>
<!--<script type="text/javascript" src="websocket.js"></script>-->
<script type="text/javascript">
    $(function() {

        $("#startDm,.d_del").click(function() {
            $("#startDm,.dm").toggle(1000);
//init_screen();
        });
        $("#btn").click(function(){
            send();
        });
        $(".s_text").keydown(function() {
            var code = window.event.keyCode;





            if (code == 13)//回车键按下时，输出到弹幕


            {
                send();
            }
        });


    });


    function launch()
    {

        var _height = $(window).height();
        var _left = $(window).width() - $("#"+index).width();
        var time=10000;
        if(index%2==0)
            time=20000;
        _top+=80;
        if(_top>_height-100)
            _top=80;
        $("#"+index).css({
            left:_left,
            top:_top,
            color:getRandomColor()

        });
        $("#"+index).animate({
                left:"-"+_left+"px"},
            time,
            function(){});
        index++;
    }



    /* //初始化弹幕
     function init_screen() {
     var _top = 0;
     var _height = $(window).height();
     $(".d_show").find("div").show().each(function() {
     var _left = $(window).width() - $(this).width();
     var time=10000;
     if($(this).index()%2==0)
     time=20000;
     _top+=80;
     if(_top>_height-100)
     _top=80;
     $(this).css({
     left:_left,
     top:_top,
     color:getRandomColor()

     });
     $(this).animate({
     left:"-"+_left+"px"},
     time,
     function(){});


     });
     } */

    //随机获取颜色值
    function getRandomColor() {
        return '#' + (function(h) {
            return new Array(7 - h.length).join("0") + h
        })((Math.random() * 0x1000000 << 0).toString(16))
    }
</script>

<script type="text/javascript">

    var websocket=null;
    var _top=80;
    var index=0;

    var host=window.location.host;
    //判断当前浏览器是否支持WebSocket
    if('WebSocket' in window){
        websocket=new WebSocket("ws://"+host+"/ws");
    }
    else{
        alert("Not Support WebSocket!");
    }


    //连接发生错误的回调方法
    websocket.onerror = function(){
        setMessageInnerHTML("error");
    };

    //连接成功建立的回调方法
    websocket.onopen = function(event){
        setMessageInnerHTML("open");
    }

    //接收到消息的回调方法
    // 收到服务器发送的消息
    websocket.onmessage = function(){
        setMessageInnerHTML(event.data);
    }

    //连接关闭的回调方法
    websocket.onclose = function(){
        setMessageInnerHTML("close");
    }


    //监听窗口关闭事件，当窗口关闭时，主动去关闭websocket连接，防止连接还没断开就关闭窗口，server端会抛异常。
    window.onbeforeunload = function(){
        websocket.close();
    }


    //将消息显示在网页上
    function setMessageInnerHTML(innerHTML){
        //修改背景图
        var imgurl;
        if (innerHTML.startWith("~background,")) {
            var cmd = innerHTML;
            imgurl = cmd.split(",")[1];
            document.body.style.background = "url("+imgurl+")";
        }else{
            $(".d_show").Append("<div id='"+index+"'>"+ innerHTML + "</div>");
        }

        launch();
    }


    //发送消息
    function send(){
        //var message = document.getElementById('text').value;
        var message = $(".s_text").val();
        $(".s_text").val("");
        websocket.send(message);
    }
</script>

</body>
</html>