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The Answer Guy

By James T. Dennis, tag@lists.linuxgazette.net
Starshine Technical Services, http://www.starshine.org/

Java Telnet/Terminal:

From Spencer T. Kittelson on 28 Jul 1998

They're out there but not all there.

We have some old code that runs on terminals that we would like to drive with a Java based server. We are looking for the reverse equivalent of a terminal emulator, i.e. a Java toolkit that multiplexes serial/network character streams and provides support for character based devices. In particular we are looking for the Java equiv. of the C curses library.

Any ideas if and where such a thing exists?
Spencer

The canonical resource for finding Java applets and applications on the web is at "developer.com" (formerly known as Gamelan).

Here's URL that will provide you with a list of some telnet and terminal emulators writting in Java

http://www-c.developer.com/directories/find.cgi?search=Java+Telnet&num=50&sp=sp

(Be sure to cut and paste that without the linebreak, and the extraneous backslash that I use to indicate the line continuation).

There are a number of these listed there and I haven't tried any of them (well, I tried WebTerm awhile back and I did look at the online demo of JXterm, and Crosstie).

I've played with SCO's Tarantella --- which seems to be more of an X Windows in a Java frame --- and also provides support to access NT desktops through a Java frame. Alas, that seems to be a proprietary technology and it seems to require a SCO OpenServer to host part of it. (I suspect that means that it doesn't qualify as a "Pure Java" solution -- though the client side of it might be "pure Java").

WebTerm seems to be available for non-commercial use --- but doesn't define the term (do they mean you can't use it in your business environment or just that you can't sell copies of it). JXTerm and Crosstie seem to be commercial products.

One limitation of most of the Java implementations in existing web browsers is that the Java applets can normally only open connections to the same address from which they were fetched. This means that your host would have to run a web server with some HTML pages that contained the required applet markup. You could also distribute these to your systems along with an installation of the JRE (Java Runtime Environment) and a copy of 'appletviewer' --- that would allow you to run these without the common browser restrictions.

Another problem with these is that they are not trivial to install and run via the 'appletviewer' WebTerm 2.0 gave me grief about "missing resources" while the same copy of appletviewer was perfectly content to run the various other demos that I had laying around. I'm sure that it's some fussing with the CLASSPATH variable or some other thing that I don't have configured to it's liking. Frankly I haven't worried about it much.

I presume that your clients are PC's or NC's rather than Linux boxes. Otherwise I presume you'd just configure your browswers with 'telnet' configured as a helper app and just embed URL's of the form:

<a href="telnet://appserver.mydomain.org"> Telnet to our Application Server</a>

... and be done with it.

Naturally you can do that on your Windows boxes as well --- just install some sort of telnet utility and configure the browsers to use it. I personally like C-Kermit for telnet -- so you might consider using K'95 (the Win32 Kermit from Columbia University).

That would give you a consistent scripting, telnet and file transfer environment across your systems.

That approach (using helper apps) is likely to be much faster, more robust and probably and cheaper than trying to do this with Java applets. The usual telnet utilities have had years to mature and are written to the clients native API's --- so there's no fussing about that.

Copyright © 1998, James T. Dennis
Published in Linux Gazette Issue 32 September 1998

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