原文連結：https://www.dubby.cn/detail.html?id=9104

獲取程式碼 https://github.com/dubby1994/netty-study/tree/master

1.依賴

 <dependency>
     <groupId>io.netty</groupId>
     <artifactId>netty-all</artifactId>
     <version>4.1.28.Final</version>
 </dependency>
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2.實現

WebSocketServer.java:

public final class WebSocketServer {
    static final int PORT = 8080;
    public static void main(String[] args) throws Exception {
        EventLoopGroup bossGroup = new NioEventLoopGroup(1);
        EventLoopGroup workerGroup = new NioEventLoopGroup();
        try {
            ServerBootstrap b = new ServerBootstrap();
            b.group(bossGroup, workerGroup)
             .channel(NioServerSocketChannel.class)
             .childHandler(new WebSocketServerInitializer());
            Channel ch = b.bind(PORT).sync().channel();
            ch.closeFuture().sync();
        } finally {
            bossGroup.shutdownGracefully();
            workerGroup.shutdownGracefully();
        }
    }
}
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WebSocketServerInitializer.java:

public class WebSocketServerInitializer extends ChannelInitializer<SocketChannel> {
    @Override
    public void initChannel(SocketChannel ch) throws Exception {
        ChannelPipeline pipeline = ch.pipeline();
        pipeline.addLast(new HttpServerCodec());
        pipeline.addLast(new HttpObjectAggregator(65536));
        pipeline.addLast(new WebSocketServerHandler());
    }
}
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WebSocketServerHandler.java:

public class WebSocketServerHandler extends SimpleChannelInboundHandler<Object> {
    private static final ChannelGroup channels = new DefaultChannelGroup(GlobalEventExecutor.INSTANCE);
    private static final String WEBSOCKET_PATH = "/websocket";
    private WebSocketServerHandshaker handshaker;
    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        super.channelActive(ctx);
        channels.add(ctx.channel());
    }
    @Override
    public void channelInactive(ChannelHandlerContext ctx) throws Exception {
        super.channelInactive(ctx);
        channels.remove(ctx.channel());
    }
    @Override
    public void channelRead0(ChannelHandlerContext ctx, Object msg) {
        if (msg instanceof FullHttpRequest) {
            handleHttpRequest(ctx, (FullHttpRequest) msg);
        } else if (msg instanceof WebSocketFrame) {
            handleWebSocketFrame(ctx, (WebSocketFrame) msg);
        }
    }
    @Override
    public void channelReadComplete(ChannelHandlerContext ctx) {
        ctx.flush();
    }
    private void handleHttpRequest(ChannelHandlerContext ctx, FullHttpRequest req) {
        // Handle a bad request.
        if (!req.decoderResult().isSuccess()) {
            sendHttpResponse(ctx, req, new DefaultFullHttpResponse(HTTP_1_1, BAD_REQUEST));
            return;
        }
        // Allow only GET methods.
        if (req.method() != GET) {
            sendHttpResponse(ctx, req, new DefaultFullHttpResponse(HTTP_1_1, FORBIDDEN));
            return;
        }
        // Handshake
        WebSocketServerHandshakerFactory wsFactory = new WebSocketServerHandshakerFactory(getWebSocketLocation(req), null, true, 5 * 1024 * 1024);
        handshaker = wsFactory.newHandshaker(req);
        if (handshaker == null) {
            WebSocketServerHandshakerFactory.sendUnsupportedVersionResponse(ctx.channel());
        } else {
            handshaker.handshake(ctx.channel(), req);
        }
    }
    private void handleWebSocketFrame(ChannelHandlerContext ctx, WebSocketFrame frame) {
        if (frame instanceof CloseWebSocketFrame) {
            handshaker.close(ctx.channel(), (CloseWebSocketFrame) frame.retain());
            return;
        }
        if (frame instanceof PingWebSocketFrame) {
            ctx.write(new PongWebSocketFrame(frame.content().retain()));
            return;
        }
        if (frame instanceof TextWebSocketFrame) {
            System.out.println(ctx.name() + "\t" + ((TextWebSocketFrame) frame).text());

            //廣播給所有客戶端
            channels.writeAndFlush(new TextWebSocketFrame(((TextWebSocketFrame) frame).text()));
            return;
        }
        if (frame instanceof BinaryWebSocketFrame) {
            ctx.write(frame.retain());
        }
    }
    private static void sendHttpResponse(ChannelHandlerContext ctx, FullHttpRequest req, FullHttpResponse res) {
        if (res.status().code() != HttpResponseStatus.OK.code()) {
            ByteBuf buf = Unpooled.copiedBuffer(res.status().toString(), CharsetUtil.UTF_8);
            res.content().writeBytes(buf);
            buf.release();
            HttpUtil.setContentLength(res, res.content().readableBytes());
        }
        ChannelFuture f = ctx.channel().writeAndFlush(res);
        if (!HttpUtil.isKeepAlive(req) || res.status().code() != HttpResponseStatus.OK.code()) {
            f.addListener(ChannelFutureListener.CLOSE);
        }
    }
    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {
        cause.printStackTrace();
        ctx.close();
    }
    private static String getWebSocketLocation(FullHttpRequest req) {
        String location = req.headers().get(HttpHeaderNames.HOST) + WEBSOCKET_PATH;
        return "ws://" + location;
    }
}
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這裡你也可以自己搞個集合來維護channel，然後自己搞個執行緒池來執行，不過Netty已經幫我想到了，所以提供了ChannelGroup來維護channel。

3.示例