Netty 心跳处理

在 Netty 中空闲检测需要引入 IdleStateHandler，然后实现自己的心跳处理 Handler，本文中服务端与客户端均向对方发送心跳包。

一、服务端

1.1 编解码及 Handler

...

.childHandler(new ChannelInitializer<SocketChannel>() {

    @Override
    protected void initChannel(SocketChannel channel) throws Exception {
        channel.pipeline().addLast("ping", new IdleStateHandler(10, 5, 10));
        channel.pipeline().addLast("encoder", new NettyMessageEncoder());
        channel.pipeline().addLast("decoder", new NettyMessageDecoder());
        channel.pipeline().addLast("message", new MessageHandler());
        channel.pipeline().addLast("heartbeat", new HeartbeatHandler());
    }
});

...

HeartbeatHandler 为 心跳处理 Handler

1.2 心跳处理 Handler

public class HeartbeatHandler extends ChannelInboundHandlerAdapter {
    private static final Logger LOGGER = LoggerFactory.getLogger(HeartbeatHandler.class);

    private final AttributeKey<Integer> counterAttr = AttributeKey.valueOf(ChannelSupervise.COUNTER_ATTR);;

    @Override
    public void userEventTriggered(ChannelHandlerContext ctx, Object evt) throws Exception {
        super.userEventTriggered(ctx, evt);

        if(evt instanceof IdleStateEvent) {
            IdleStateEvent idleStateEvent = (IdleStateEvent)evt;
            switch (idleStateEvent.state()) {
                case READER_IDLE:
                    NettyMessage<String> nettyMessage = new NettyMessage<>();
                    nettyMessage.setSessionId(0L);
                    nettyMessage.setType(NettyMessageTypeEnum.HEARTBEAT);

                    ctx.writeAndFlush(nettyMessage).addListener(future -> {
//                        if(future.isSuccess()) {
//                            ctx.channel().attr(counterAttr).set(0);
//                        }else {
                            Integer counter = ctx.channel().attr(counterAttr).get();
                            counter = counter + 1;
                            LOGGER.info(ctx.channel().id().asShortText() + "，发送心跳: " + counter);
                            if(counter >= 3) {
                                ctx.close();
                            } else {
                                ctx.channel().attr(counterAttr).set(counter);
                            }
//                        }
                    });
                    break;
                default:
                    break;
            }
        }
    }

    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        ctx.channel().attr(counterAttr).set(0);
        ChannelSupervise.addChannel(ctx.channel());
    }

    @Override
    public void channelInactive(ChannelHandlerContext ctx) throws Exception {
        ChannelSupervise.removeChannel(ctx.channel());
    }

    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {

        ctx.channel().attr(counterAttr).set(0);
        ctx.fireChannelRead(msg);
    }



    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        LOGGER.error("断开连接", cause);
        ctx.close();
    }
}

本例中，如果服务端连续发送三次心跳包，则认为客户端断开连接，使用 Netty 内置的 AttributeKey 计数 (本例中为方便测试注释掉部分代码，正常来说如果发送消息成功则证明客户端还在线，需要把计数重置为 0)。

二、客户端

2.1 编解码及 Handler

...

.handler(new ChannelInitializer<SocketChannel>() {

    @Override
    protected void initChannel(SocketChannel channel) throws Exception {
        channel.pipeline().addLast("ping", new IdleStateHandler(5, 5, 3));
        channel.pipeline().addLast("encoder", new NettyMessageEncoder());
        channel.pipeline().addLast("decoder", new NettyMessageDecoder());
        channel.pipeline().addLast("heartbeat", new HeartbeatHandler());
        channel.pipeline().addLast("logger", new LoggingHandler(LogLevel.INFO));
    }
});

...

HeartbeatHandler 为 心跳处理 Handler

2.2 心跳处理 Handler

public class HeartbeatHandler extends ChannelInboundHandlerAdapter {
    private static final Logger LOGGER = LoggerFactory.getLogger(HeartbeatHandler.class);

    @Override
    public void userEventTriggered(ChannelHandlerContext ctx, Object evt) throws Exception {

        if(evt instanceof IdleStateEvent) {
            IdleStateEvent idleStateEvent = (IdleStateEvent) evt;

            switch (idleStateEvent.state()){
                case WRITER_IDLE:
                    LOGGER.info("发送心跳包");
                    NettyMessage<String> nettyMessage = new NettyMessage<>();
                    nettyMessage.setSessionId(0L);
                    nettyMessage.setType(NettyMessageTypeEnum.HEARTBEAT);
                    ctx.writeAndFlush(nettyMessage).addListener(ChannelFutureListener.CLOSE_ON_FAILURE);
                    break;
                default:
                    break;
            }
        }

        super.userEventTriggered(ctx, evt);
    }

    ...
}

本例中，如果客户端发送心跳消息失败则断开连接。

1. Netty(一) SpringBoot 整合长连接心跳机制TCP-Heartbeat/)
2. 微言Netty：分布式服务框架

完整代码：GitHub

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