netty双向心跳的设计

• 心跳包：不带消息体
• 客户端定时20秒发送心跳包 -> 服务端回应
• 客户端检查60秒内未读到消息，则认为断线，关闭连接，启动断线重连
• 服务端检查60秒内未读到消息，则认为断线，关闭连接，移除连接映射关系

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/**
 * heart beat command
 * Created by lif on 2015/10/10.
 */
public class HeartBeatHandler extends ChannelInboundHandlerAdapter implements MsgHandler  {

    @Override
    public void userEventTriggered(ChannelHandlerContext ctx, Object evt) throws Exception {
        if (evt instanceof IdleStateEvent) {
            IdleStateEvent event = (IdleStateEvent) evt;
            if (event.state() == IdleState.READER_IDLE) {
                // Read timeout
                System.out.println("READER_IDLE: read timeout from " + ctx.channel().remoteAddress());

                String userId = CommonUtil.getLoginInfo(ctx.channel()).getUser_id();
                ConnectionManager.removeConn(userId);

                // close connection
                if (ctx.channel().isOpen()) {
                    ctx.channel().close();
                }

            }
        }
    }