Netty is just a simple understanding. Please correct any mistakes.

1. Why do you have a heartbeat

 If a connection is not used for a long time, it will be closed to reduce the connection pressure of the server.
 Because the server needs to keep the connection information of the client, the client is likely to have various conditions, such as forced shutdown, disconnection, etc., which leads to the failure of connection. In this case, waste of resources on the server

1. netty provides the heartbeat detection class IdleStateHandler

 new IdleStateHandler(10,0, 0, TimeUnit.SECONDS)
 The first parameter is read timeout
 The second parameter is write timeout
 The third parameter is read-write timeout
 Time 0 means no monitoring

1. When the heartbeat detection starts, the following methods will be triggered

 The timeout detection here only detects the current class for the current class channelRead0 Method
 
 //Only read timeout is detected here. The connection will be closed after 5 times of timeout
 
 public void userEventTriggered(ChannelHandlerContext ctx, Object evt) throws Exception {
 if (evt instanceof IdleStateEvent) {
			IdleStateEvent event = (IdleStateEvent) evt;
			System.out.println(ctx.channel().remoteAddress()+"Timeout times:"+count);
			String type = "";
			if (event.state() == IdleState.READER_IDLE) {
				type = "read idle";
				count++;
				if(count>5) {
					  System.out.println("Timeout reached maximum, disconnect");
		              ChannelManager.removeChannelByChannel(ctx.channel());
		              ctx.channel().close();
					}
			} else if (event.state() == IdleState.WRITER_IDLE) {
				type = "write idle";
				count=0;
			} else if (event.state() == IdleState.ALL_IDLE) {
				type = "all idle";
				count=0;
			}
			ctx.writeAndFlush(new TextWebSocketFrame("Heartbeat")).addListener(ChannelFutureListener.CLOSE_ON_FAILURE);
			System.out.println( ctx.channel().remoteAddress()+"Timeout type:" + type);
		}
		super.userEventTriggered(ctx, evt);
 
 }

1. Here is the data received by the front desk

Heartbeat is the heartbeat data pushed by the server

If the front desk receives the data and returns a piece of data, it will be OK. Otherwise, if it is more than 5, it will be disconnected

ws.send("Heartbeat");

If the foreground wants to realize disconnection and reconnection, it should be handled in the following methods

ws.onclose = function(evt){
  console.log("WebSocketClosed!");
};

ws.onerror = function(evt){
  console.log("WebSocketError!");
};

gitee sample code