Netty與WebSocket：輕松搞定消息推送

作者：一安 2024-08-02 09:00:17

學過 Netty 的都知道，Netty 對 NIO 進行了很好的封裝，簡單的 API，龐大的開源社區。深受廣大程序員喜愛。基于此本文分享一下基礎的 netty 使用。實戰制作一個 Netty + websocket 的消息推送小栗子。

netty服務器

@Component
public class NettyServer {

    static final Logger log = LoggerFactory.getLogger(NettyServer.class);

    /**
     * 端口號
     */
    @Value("${webSocket.netty.port:8888}")
    int port;

    EventLoopGroup bossGroup;
    EventLoopGroup workGroup;

    @Autowired
    ProjectInitializer nettyInitializer;

    @PostConstruct
    public void start() throws InterruptedException {
        new Thread(() -> {
            bossGroup = new NioEventLoopGroup();
            workGroup = new NioEventLoopGroup();
            ServerBootstrap bootstrap = new ServerBootstrap();
            // bossGroup輔助客戶端的tcp連接請求, workGroup負責與客戶端之前的讀寫操作
            bootstrap.group(bossGroup, workGroup);
            // 設置NIO類型的channel
            bootstrap.channel(NioServerSocketChannel.class);
            // 設置監聽端口
            bootstrap.localAddress(new InetSocketAddress(port));
            // 設置管道
            bootstrap.childHandler(nettyInitializer);

            // 配置完成，開始綁定server，通過調用sync同步方法阻塞直到綁定成功
            ChannelFuture channelFuture = null;
            try {
                channelFuture = bootstrap.bind().sync();
                log.info("Server started and listen on:{}", channelFuture.channel().localAddress());
                // 對關閉通道進行監聽
                channelFuture.channel().closeFuture().sync();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }).start();
    }

    /**
     * 釋放資源
     */
    @PreDestroy
    public void destroy() throws InterruptedException {
        if (bossGroup != null) {
            bossGroup.shutdownGracefully().sync();
        }
        if (workGroup != null) {
            workGroup.shutdownGracefully().sync();
        }
    }
}

Netty配置

管理全局Channel以及用戶對應的channel（推送消息）

public class NettyConfig {

    /**
     * 定義全局單利channel組 管理所有channel
     */
    private static volatile ChannelGroup channelGroup = null;

    /**
     * 存放請求ID與channel的對應關系
     */
    private static volatile ConcurrentHashMap<String, Channel> channelMap = null;

    /**
     * 定義兩把鎖
     */
    private static final Object lock1 = new Object();
    private static final Object lock2 = new Object();


    public static ChannelGroup getChannelGroup() {
        if (null == channelGroup) {
            synchronized (lock1) {
                if (null == channelGroup) {
                    channelGroup = new DefaultChannelGroup(GlobalEventExecutor.INSTANCE);
                }
            }
        }
        return channelGroup;
    }

    public static ConcurrentHashMap<String, Channel> getChannelMap() {
        if (null == channelMap) {
            synchronized (lock2) {
                if (null == channelMap) {
                    channelMap = new ConcurrentHashMap<>();
                }
            }
        }
        return channelMap;
    }

    public static Channel getChannel(String userId) {
        if (null == channelMap) {
            return getChannelMap().get(userId);
        }
        return channelMap.get(userId);
    }
}

管道配置

@Component
public class ProjectInitializer extends ChannelInitializer<SocketChannel> {

    /**
     * webSocket協議名
     */
    static final String WEBSOCKET_PROTOCOL = "WebSocket";

    /**
     * webSocket路徑
     */
    @Value("${webSocket.netty.path:/webSocket}")
    String webSocketPath;
    @Autowired
    WebSocketHandler webSocketHandler;

    @Override
    protected void initChannel(SocketChannel socketChannel) throws Exception {
        // 設置管道
        ChannelPipeline pipeline = socketChannel.pipeline();
        // 流水線管理通道中的處理程序（Handler），用來處理業務
        // webSocket協議本身是基于http協議的，所以這邊也要使用http編解碼器
        pipeline.addLast(new HttpServerCodec());
        pipeline.addLast(new ObjectEncoder());
        // 以塊的方式來寫的處理器
        pipeline.addLast(new ChunkedWriteHandler());
        pipeline.addLast(new HttpObjectAggregator(8192));
        pipeline.addLast(new WebSocketServerProtocolHandler(webSocketPath, WEBSOCKET_PROTOCOL, true, 65536 * 10));
        // 自定義的handler，處理業務邏輯
        pipeline.addLast(webSocketHandler);
    }
}

自定義handler

@Component
@ChannelHandler.Sharable
public class WebSocketHandler extends SimpleChannelInboundHandler<TextWebSocketFrame> {
    private static final Logger log = LoggerFactory.getLogger(NettyServer.class);

    /**
     * 一旦連接，第一個被執行
     */
    @Override
    public void handlerAdded(ChannelHandlerContext ctx) throws Exception {
        log.info("有新的客戶端鏈接：[{}]", ctx.channel().id().asLongText());
        // 添加到channelGroup 通道組
        NettyConfig.getChannelGroup().add(ctx.channel());
    }

    /**
     * 讀取數據
     */
    @Override
    protected void channelRead0(ChannelHandlerContext ctx, TextWebSocketFrame msg) throws Exception {
        log.info("服務器收到消息：{}", msg.text());

        // 獲取用戶ID,關聯channel
        JSONObject jsonObject = JSONUtil.parseObj(msg.text());
        String uid = jsonObject.getStr("uid");
        NettyConfig.getChannelMap().put(uid, ctx.channel());

        // 將用戶ID作為自定義屬性加入到channel中，方便隨時channel中獲取用戶ID
        AttributeKey<String> key = AttributeKey.valueOf("userId");
        ctx.channel().attr(key).setIfAbsent(uid);

        // 回復消息
        ctx.channel().writeAndFlush(new TextWebSocketFrame("服務器收到消息啦"));
    }

    @Override
    public void handlerRemoved(ChannelHandlerContext ctx) throws Exception {
        log.info("用戶下線了:{}", ctx.channel().id().asLongText());
        // 刪除通道
        NettyConfig.getChannelGroup().remove(ctx.channel());
        removeUserId(ctx);
    }

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        log.info("異常：{}", cause.getMessage());
        // 刪除通道
        NettyConfig.getChannelGroup().remove(ctx.channel());
        removeUserId(ctx);
        ctx.close();
    }

    /**
     * 刪除用戶與channel的對應關系
     */
    private void removeUserId(ChannelHandlerContext ctx) {
        AttributeKey<String> key = AttributeKey.valueOf("userId");
        String userId = ctx.channel().attr(key).get();
        NettyConfig.getChannelMap().remove(userId);
    }
}

推送消息接口及實現類

public interface PushMsgService {

    /**
     * 推送給指定用戶
     */
    void pushMsgToOne(String userId, String msg);

    /**
     * 推送給所有用戶
     */
    void pushMsgToAll(String msg);

}
@Service
public class PushMsgServiceImpl implements PushMsgService {

    @Override
    public void pushMsgToOne(String userId, String msg) {
        Channel channel = NettyConfig.getChannel(userId);
        if (Objects.isNull(channel)) {
            throw new RuntimeException("未連接socket服務器");
        }

        channel.writeAndFlush(new TextWebSocketFrame(msg));
    }

    @Override
    public void pushMsgToAll(String msg) {
        NettyConfig.getChannelGroup().writeAndFlush(new TextWebSocketFrame(msg));
    }
}