Netty 超时机制及心跳程序实现

出处:
http://waylau.com/netty-time-out-and-heartbeat/

本文介绍了 Netty 超时机制的原理,以及如何在连接闲置时发送一个心跳来维持连接。

Netty 超时机制的介绍

Netty 的超时类型 IdleState 主要分为:

  • ALL_IDLE : 一段时间内没有数据接收或者发送
  • READER_IDLE : 一段时间内没有数据接收
  • WRITER_IDLE : 一段时间内没有数据发送

在 Netty 的 timeout 包下,主要类有:

  • IdleStateEvent : 超时的事件
  • IdleStateHandler : 超时状态处理
  • ReadTimeoutHandler : 读超时状态处理
  • WriteTimeoutHandler : 写超时状态处理

其中 IdleStateHandler 包含了读\写超时状态处理,比如

private static final int READ_IDEL_TIME_OUT = 4; // 读超时
private static final int WRITE_IDEL_TIME_OUT = 5;// 写超时
private static final int ALL_IDEL_TIME_OUT = 7; // 所有超时

new IdleStateHandler(READ_IDEL_TIME_OUT,
            WRITE_IDEL_TIME_OUT, ALL_IDEL_TIME_OUT, TimeUnit.SECONDS));

上述例子,在 IdleStateHandler 中定义了读超时的时间是 4 秒, 写超时的时间是 5 秒,其他所有的超时时间是 7 秒。

应用 IdleStateHandler

既然 IdleStateHandler 包括了读\写超时状态处理,那么很多时候 ReadTimeoutHandler 、 WriteTimeoutHandler 都可以不用使用。定义另一个名为 HeartbeatHandlerInitializer 的 ChannelInitializer :

public class HeartbeatHandlerInitializer extends ChannelInitializer<Channel> {

    private static final int READ_IDEL_TIME_OUT = 4; // 读超时
    private static final int WRITE_IDEL_TIME_OUT = 5;// 写超时
    private static final int ALL_IDEL_TIME_OUT = 7; // 所有超时

    @Override
    protected void initChannel(Channel ch) throws Exception {
        ChannelPipeline pipeline = ch.pipeline();
        pipeline.addLast(new IdleStateHandler(READ_IDEL_TIME_OUT,
                WRITE_IDEL_TIME_OUT, ALL_IDEL_TIME_OUT, TimeUnit.SECONDS)); // 1
        pipeline.addLast(new HeartbeatServerHandler()); // 2
    }
}

使用了 IdleStateHandler ,分别设置了读、写超时的时间.

定义了一个 HeartbeatServerHandler 处理器,用来处理超时时,发送心跳

public class HeartbeatServerHandler extends ChannelInboundHandlerAdapter {

    // Return a unreleasable view on the given ByteBuf
    // which will just ignore release and retain calls.
    private static final ByteBuf HEARTBEAT_SEQUENCE = Unpooled
            .unreleasableBuffer(Unpooled.copiedBuffer("Heartbeat",
                    CharsetUtil.UTF_8));  // 1

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

        if (evt instanceof IdleStateEvent) {  // 2
            IdleStateEvent event = (IdleStateEvent) evt;  
            String type = "";
            if (event.state() == IdleState.READER_IDLE) {
                type = "read idle";
            } else if (event.state() == IdleState.WRITER_IDLE) {
                type = "write idle";
            } else if (event.state() == IdleState.ALL_IDLE) {
                type = "all idle";
            }

            ctx.writeAndFlush(HEARTBEAT_SEQUENCE.duplicate()).addListener(
                    ChannelFutureListener.CLOSE_ON_FAILURE);  // 3

            System.out.println( ctx.channel().remoteAddress()+"超时类型:" + type);
        } else {
            super.userEventTriggered(ctx, evt);
        }
    }
}

定义了心跳时,要发送的内容
判断是否是 IdleStateEvent 事件,是则处理
将心跳内容发送给客户端

服务器

public final class HeartbeatServer {

    static final int PORT = 8082;

    public static void main(String[] args) throws Exception {

        // Configure the server.
        EventLoopGroup bossGroup = new NioEventLoopGroup(1);
        EventLoopGroup workerGroup = new NioEventLoopGroup();
        try {
            ServerBootstrap b = new ServerBootstrap();
            b.group(bossGroup, workerGroup)
             .channel(NioServerSocketChannel.class)
             .option(ChannelOption.SO_BACKLOG, 100)
             .handler(new LoggingHandler(LogLevel.INFO))
             .childHandler(new HeartbeatHandlerInitializer());

            // Start the server.
            ChannelFuture f = b.bind(PORT).sync();

            // Wait until the server socket is closed.
            f.channel().closeFuture().sync();
        } finally {
            // Shut down all event loops to terminate all threads.
            bossGroup.shutdownGracefully();
            workerGroup.shutdownGracefully();
        }
    }
}

客户端测试

客户端用操作系统自带的 Telnet 程序即可:

telnet 127.0.0.1 8082

效果

Netty 超时机制及心跳程序实现_第1张图片

源码

见 https://github.com/waylau/netty-4-user-guide-demos 中 heartbeat包

参考

Netty 4.x 用户指南 https://github.com/waylau/netty-4-user-guide
Netty 实战(精髓) https://github.com/waylau/essential-netty-in-action

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