Does your device really "log in" to the server using telnet, or does
it simply use a Socket to connect to a specific port on the server?

If the former, then write a script like this:

 #!/bin/sh
 cat >> barcode_file

... and change the client's login shell to this script.

If the latter, configure inetd to do "cat >> barcode_file" for
connections arriving on the specified port. Or perhaps even better,
have your application listen to that port and read the values itself,
instead of using the file system as a communications mechanism.

Regardless of which method you choose, there are synchronization
issues that need to be addressed if more than one client will be
logging in at a time.

What does any of this have to do with J2EE, or Java?

/gordon

As you were asking about using telnet client classes to allow your Java
application to talk to a telnet server, I was assuming you'd want to use
something like the following to login, send one barcode to the telnet
server and logout again:

    Telnet tnc = new Telnet();

    tnc.login(hostname, username);
    tnc.password(password);
    tnc.sendCommand("store_barcode " + barcode);
    if (tnc.responseOK())
        tnc.logout();
    else
        /* report errors and clean up */

... that is, assuming that there is a telnet client class with methods
corresponding roughly to the actions you'd take if you were manually
running a telnet session.

You can get a script to execute automatically with one of the following:
- if you have root access to the server you could use a captive login
  in place of the shell
- you can change the bash .profile file in the user to do much the same.

HOWEVER, once you've done that you can't login to that user normally,
because doing so will always run your script and then logout. That means
you'll need a second (normal) login user with full access rights over
the first user so you can get in for maintenance, e.g. to install a
modified version of your script, run unit tests or to clean up after a
failure. But why bother? The method I outlined is easy to do and still
allows normal logins to the user via a normal telnet session.