Netty 系列八（基于 WebSocket 的简单聊天室）.

<dependency>
     <groupId>io.netty</groupId>
     <artifactId>netty-all</artifactId>
     <version>5.0.0.Alpha2</version>
</dependency>

public class HttpRequestHandler extends SimpleChannelInboundHandler<FullHttpRequest> {

    private final String wsUri;
    private static File INDEX;

    static {
        URL location = HttpRequestHandler.class.getProtectionDomain().getCodeSource().getLocation();
        try {
            String path = location.toURI() + "index.html";
            path = !path.contains("file:") ? path : path.substring(5);
            INDEX = new File(path);
        } catch (URISyntaxException e) {
            e.printStackTrace();
        }
    }

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


    @Override
    protected void messageReceived(ChannelHandlerContext ctx, FullHttpRequest request) throws Exception {
        // 如果请求了Websocket，协议升级，增加引用计数(调用retain())，并将他传递给下一个 ChannelHandler
        // 之所以需要调用 retain() 方法，是因为调用 channelRead() 之后，资源会被 release() 方法释放掉，需要调用 retain() 保留资源
        if (wsUri.equalsIgnoreCase(request.uri())) {
            ctx.fireChannelRead(request.retain());
        } else {
            //处理 100 Continue 请求以符合 HTTP 1.1 规范
            if (HttpHeaderUtil.is100ContinueExpected(request)) {
                send100Continue(ctx);
            }
            // 读取 index.html
            RandomAccessFile randomAccessFile = new RandomAccessFile(INDEX, "r");
            HttpResponse response = new DefaultHttpResponse(request.protocolVersion(), HttpResponseStatus.OK);
            HttpHeaders headers = response.headers();
            //在该 HTTP 头信息被设置以后，HttpRequestHandler 将会写回一个 HttpResponse 给客户端
            headers.set(HttpHeaderNames.CONTENT_TYPE, "text/html; charset=UTF-8");
            boolean keepAlive = HttpHeaderUtil.isKeepAlive(request);
            if (keepAlive) {
                headers.setLong(HttpHeaderNames.CONTENT_LENGTH, randomAccessFile.length());
                headers.set(HttpHeaderNames.CONNECTION, HttpHeaderValues.KEEP_ALIVE);
            }
            ctx.write(response);
            //将 index.html 写给客户端
            if (ctx.pipeline().get(SslHandler.class) == null) {
                ctx.write(new DefaultFileRegion(randomAccessFile.getChannel(), 0, randomAccessFile.length()));
            } else {
                ctx.write(new ChunkedNioFile(randomAccessFile.getChannel()));
            }
            //写 LastHttpContent 并冲刷至客户端，标记响应的结束
            ChannelFuture channelFuture = ctx.writeAndFlush(LastHttpContent.EMPTY_LAST_CONTENT);
            if (!keepAlive) {
                channelFuture.addListener(ChannelFutureListener.CLOSE);
            }
        }

    }

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

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

/**
 * WebSocket 帧：WebSocket 以帧的方式传输数据，每一帧代表消息的一部分。一个完整的消息可能会包含许多帧
 */
public class TextWebSocketFrameHandler extends SimpleChannelInboundHandler<TextWebSocketFrame> {

    private final ChannelGroup group;

    public TextWebSocketFrameHandler(ChannelGroup group) {
        this.group = group;
    }

    @Override
    protected void messageReceived(ChannelHandlerContext ctx, TextWebSocketFrame msg) throws Exception {
        //增加消息的引用计数（保留消息），并将他写到 ChannelGroup 中所有已经连接的客户端
        Channel channel = ctx.channel();
        //自己发送的消息不返回给自己
        group.remove(channel);
        group.writeAndFlush(msg.retain());
        group.add(channel);
    }

    @Override
    public void userEventTriggered(ChannelHandlerContext ctx, Object evt) throws Exception {
        //是否握手成功，升级为 Websocket 协议
        if (evt == WebSocketServerProtocolHandler.ServerHandshakeStateEvent.HANDSHAKE_COMPLETE) {
            // 握手成功，移除 HttpRequestHandler，因此将不会接收到任何消息
            // 并把握手成功的 Channel 加入到 ChannelGroup 中
            ctx.pipeline().remove(HttpRequestHandler.class);
            group.writeAndFlush(new TextWebSocketFrame("Client " + ctx.channel() + " joined"));
            group.add(ctx.channel());
        } else if (evt instanceof IdleStateEvent) {
            IdleStateEvent stateEvent = (IdleStateEvent) evt;
            if (stateEvent.state() == IdleState.READER_IDLE) {
                group.remove(ctx.channel());
                ctx.writeAndFlush(new TextWebSocketFrame("由于您长时间不在线，系统已自动把你踢下线！")).addListener(ChannelFutureListener.CLOSE);
            }
        } else {
            super.userEventTriggered(ctx, evt);
        }
    }
}