服务器和客户端需要进行维护，netty提供了心跳检测机制

特殊代码标注

new LoggingHandler(LogLevel.INFO) // 日志级别添加，添加后netty会打印日志

readerIdleTime 读空闲事件 writerIdleTime写空闲时间 allIdleTime既没有读也没有写的时间
IdleStateHandler 处理空闲状态的时间检测，通过这个可以触发一个IdelStateEvent事件 ，当没有执行读写或者读写事件的时候就会触发。
IdleStateHandler 触发后 通过调用userEventTiggered 来进行业务处理
new IdleStateHandler(3,5,7, TimeUnit.SECONDS)

区分 IdleStateHandler handlerRemoved

IdleStateHandler 能够实时触发，可以在保持连接的时候，来检测到连接的一个状态。
handlerRemoved 只能检测服务关闭的过程。

最终通过自定义的handler 来触发心跳的事件 ，通过下一个pipline来处理

import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelPipeline;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioServerSocketChannel;
import io.netty.handler.logging.LogLevel;
import io.netty.handler.logging.LoggingHandler;
import io.netty.handler.timeout.IdleStateHandler;

import java.util.concurrent.TimeUnit;

public class HeartBeatServer {

private final  int prot = 9999;

public  void run () throws Exception{
    ServerBootstrap serverBootstrap = new ServerBootstrap();
    EventLoopGroup bossGroup = new NioEventLoopGroup();
    EventLoopGroup workGroup = new NioEventLoopGroup();
    try{
        serverBootstrap.group(bossGroup,workGroup)
                .channel(NioServerSocketChannel.class)
                .handler(new LoggingHandler(LogLevel.INFO))
                .childHandler(new ChannelInitializer<SocketChannel>() {
                    @Override
                    protected void initChannel(SocketChannel socketChannel) throws Exception {
                        ChannelPipeline pipeline = socketChannel.pipeline();
                        // 定义包
                        pipeline.addLast(new IdleStateHandler(3,5,7, TimeUnit.SECONDS));
                        //自定义pipline
                        pipeline.addLast( new MyselfHeartBeatHandler());
                    }
                });
        ChannelFuture channelFuture = serverBootstrap.bind(prot).sync();
        channelFuture.channel().closeFuture().sync();
    }finally {
        bossGroup.shutdownGracefully();
        workGroup.shutdownGracefully();

    }
}

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

    new HeartBeatServer().run();



}

}

import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;
import io.netty.handler.timeout.IdleStateEvent;
import io.netty.handler.timeout.IdleStateHandler;

public class MyselfHeartBeatHandler extends ChannelInboundHandlerAdapter {

@Override
public void userEventTriggered(ChannelHandlerContext ctx, Object evt) throws Exception {
    // 判断是否是 IdeState类型
    if(evt instanceof IdleStateEvent){
        IdleStateEvent event = (IdleStateEvent) evt;
        String eventState =null;
        switch (event.state()){
            case ALL_IDLE:
                eventState="读写空闲";
                break;
            case READER_IDLE:
                eventState="读空闲";
                break;
            case WRITER_IDLE:
                 eventState="写空闲";
                 break;
        }
        System.out.println(ctx.channel().remoteAddress()+"发生"+eventState);
    }



}

}

原文地址：https://www.cnblogs.com/chianw877466657/p/13087938.html