Telnet won't connect to localhost after I create a simple server in Java

Question

Right now, I made a simple server in java as so:

import Java.net.*;
import Java.io.*;
import Java.util.*;

class Server{
public static void main(String[] args){
         int PORT = 13;
             try(ServerSocket server = new ServerSocket(PORT)){
                while(true){
                    try(Socket connection = server.accept()){
                         Writer out = new OutputStreamWriter(connection.getOutputStream());
                         Date now = new Date();
                         out.write(now.toString());
                         out.flush();
                         connection.close();
                     } catch(IOException ex){}
                 }
             }
             catch(IOException ex){
                System.err.println(ex);
             }
         }
    }

I compile and run this from the command line. Being on Port 13, I try to run this on telnet as so: telnet localhost 13 but all it gives me is "Connection to host lost". Mind you, I did this after enabling telnet on Windows 10 and installing it. Is there a simple step I'm missing?

None of your code appears to be in a method; Your `import` statements aren't correct either. Post **real** code. Also, don't silently swallow `Exception`s. — Elliott Frisch, May 16 '18 at 22:15
@ElliottFrisch Ooops, I meant to put that in the main. I left that out as I copied and pasted my code. — Brock Lesnar, May 16 '18 at 22:19
Remember that port numbers below 1024 are *reserved*, and you need special privileges to bind sockets to those ports. — Some programmer dude, May 16 '18 at 22:20
@Someprogrammerdude I've tried using Port 8050, but it still gives me the same response — Brock Lesnar, May 16 '18 at 22:21

user207421 · Accepted Answer · 2018-05-17T09:04:04.937

0

Telnet won't connect to localhost ...

Yes it did. That's why it said 'connection to host lost' instead of 'connection refused'.

And here's what happened. You coded:

connection.close();

You got:

connection to host lost

You closed the connection; Telnet told you so.

That's what's supposed to happen.

There is no problem here to solve.

Or else you got an I/O exception in the server accept loop.

But as you are ignoring them it is impossible to say which.

edited May 17 '18 at 09:04

answered May 17 '18 at 00:11

user207421

305,947
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307
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Thanks, I just copied the example from my textbook.Maybe they used a previous version of Telnet...? – Brock Lesnar May 17 '18 at 05:01
No, they just didn't tell you what should happen correctly. Everything here is working as designed. Possibly you should have sent a line terminator with the date. Windows Telnet has a nasty habit of clearing the window when disconnection happens. – user207421 May 17 '18 at 05:46

Prathamesh Jagtap · Answer 2 · 2018-05-16T22:44:15.097

-1

In your program, following events occurs:

Server starts at 13
telnet localhost 13 : connects to that server
As soon as connection is established, server sends date
You will see date on your client
out.flush() says the client I am done writing
telnet client don't understand server command (Date)
telnet closes the connection

Telnet - Connection to host lost - on port 1099 in local machine

edited May 16 '18 at 22:44

answered May 16 '18 at 22:38

Prathamesh Jagtap

393
1
5

Telnet doesn't have to understand anything except IAC commands. Anything else it just displays. And 'connection to host lost' does not mean that Telnet has closed the connection: it means the *peer* has closed the connection. And `out.flush()` doesn't 'say' anything to the client. It just flushes buffered data at the server. A Telnet or even TCP peer *never* knows when its remote peer is done writing. – user207421 May 17 '18 at 00:29
And the link in your answer is irrelevant. That is a case where the *server* didn't understand the Telnet *client*, and where the server closed the connection (as in fact it did here). You are alleging, incorrectly, that the Telnet client didn't understand the server, and that the client closed the connection. – user207421 May 17 '18 at 02:51

Telnet won't connect to localhost after I create a simple server in Java

2 Answers2