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Is there a way to override system name for Java app?

There is a Java Web Start application that I'm trying to run under Java on Linux. I'm using icedtea-netx on Ubuntu Linux. When I try to run the application, it starts up, shows the splash screen, then produces an error saying:
"Currently the application only supports the following system: Windows".
So I'm wondering, is there a way to set your system information in Java to pretend that it’s Windows? I understand that this program might really require some aspect of Windows, but I'd like to try anyways. Thanks.

Add program to mac osx and windows startup by code or installers?

I have a java system tray application that runs on both windows and mc osx.
I want to add my app to start up programs for both od those os-
which is best:
Check in code which os i'm on and then do a certain action accordingly?
Create a different installer for each os that will add the program to start up?
Also, is there any good example on the best Generic way adding program to windows(for all windows types??) by code or by install, and also a good example for creating a launch agent for the mac?
Thanks
Lior
Update
Initially i would go for #1, as it easier to manage other than managing installation packages for long. but on the other hand, it is not generic, and id like to keep my code generic as possible. And third, i'm on a very short schedule, if there is a 3rd party installers that can warp this up and create different os installer with start up, thats better, under the circumstance of course.

Since you are doing a multi platform Java application I advise you to follow it's 'Write once - run everywhere' rule and either create an self-executable jar file (both Mac and Windows are capable of running those, e.g. explained here) or you could try an out-of-the-box solution like IzPack

For #1: Check the system property os.name on a win 7 box you will get Windows 7. You can query system properties with
System.getProperty("os.name");

Fake X11 display?

I have a Java program using AWT which I would like to run on a headless system. The display for the program does nothing other than display stats. When the program finishes, it exits. There is no user interaction on the display. The program creates an output file which I use in my build system.
Is there a way to get the Java program to run without an X11 display configured? Can I force Java to run the program without trying to display anything? I do not have access to the source code (it is just .jar file), so I can't make modifications to the source.
Any thoughts on how I could get this to work?

The underlying question here is how to run Java applications without an X server; providing a "fake" X server is only one option. In Java 1.4 and up, you can do the following:
java -Djava.awt.headless=true
This allows applications which use AWT to run on headless systems even without an X server.

Xvfb can do what you ask for. I've not used it myself, but here is a link to wikipedia: http://en.wikipedia.org/wiki/Xvfb

You can use a vncserver.
vncserver :1001
export DISPLAY=localhost:1001
java..
The added advantages is that you can actually view the gui
using vncserver 'just in case'

Could also run Xvnc in a low resolution and color depth.

As mentioned by Charles Duffy the traditional method is to tell Java to go headless.
Note that you can always mount the jar in Eclipse and use jad+jadclipse to see what it actually does, and perhaps even override a class if you need to by putting another class-file in "front" of it in the classpath.
A facility that might be relevant if the program uses Java2D is that newer Java versions use optimizations in the X11 server to render faster. This alone might be a reason to devote an X11 server attached to a high performance graphics card to your graphics processing.

I've used with great success in the past the PJA libraries, they don't seem to be maintained anymore, but then again, just just want to run...

I was able to get headless mode in OpenJFX with the command line arguments
-Dglass.platform=Monocle -Dmonocle.platform=Headless -Dprism.order=sw

How to set or export display variable through java code?

We are required to add export DISPLAY=:0.0 in tomcat's startup file and batch server's startup file. This is to make java see the X11 Display libraries on Unix and run our applet. Without this export in the startup files, the applet throws a Headless Exception.
Though this explicit export makes the java applet run, it disrupts the other applications running on the server. Is there a way where I can make this export DISPLAY=:0.0 run from within java code instead of adding it to startup files? And if it is possible, would that be a good approach?
I have already tried setting the system property to -Djava.awt.headless=true , but it didn't work. As the link given above http://java.sun.com/developer/technicalArticles/J2SE/Desktop/headless/ also says that setting headless=true would work only for few components like Canvas, Panel but it will not work for the top level components.
So I feel the only option left for me is using export DISPLAY=:0.0. This is making my applet work when set in the startup files but causes problem for other applications running in the server. So if anybody could help me to make export DISPLAY=:0.0 work such that it doesn't interfere with other applications in the server. One way I thought was to export the display through code.
Any help would be highly appreciated.

I believe you can actually set the system property -Djava.awt.headless=true which will allow access to the graphic libraries without actually needing a display.
See http://java.sun.com/developer/technicalArticles/J2SE/Desktop/headless/ for more info.

From your question it seems that there is something seriously wrong with your configuration.
Tomcat should always be able to run server-side without a display.
Applets always run in browser and get the x11 environment from the browser. The applet's jar could be served by tomcat, or apache, or something else, but that's irrelevant.
If your applets communicate with the server, make sure that the server code is completely separate from your applet code (keep them in separate projects) and that it doesn't use any awt code. If it does (for image manipulation, etc.), then use -Djava.awt.headless as jdewald said.

How is this affecting other applications? How are you defining the environment variable in your start up scripts? If you're defining the variable correctly, it should only affect programs started by your start up script, i.e., Tomcat and the batch server.
Also, your original question doesn't really add up. Are you running both the server and client (Tomcat and the web browser) on the same machine?

java.awt.HeadlessException - Applet not displayed

I am using Tomcat 5.5.23, JDK 1.5 on HP Unix. We have an application which when invoked form tomcat starts an applet. It was working fine till JDK 1.4. But now we have moved to JDK 1.5 and the applet does not start. The exception thrown is -
java.awt.HeadlessException:
No X11 DISPLAY variable was set, but this program performed an operation which requires it.
I then added JAVA_OPTS="-Djava.awt.headless=true" to catalina.sh file. But still I get the same Headless exception, but this time without the X11 Display message.
Any help would be appreciated.

Odd.. you're trying to run an applet (I assume you are talking about a subclass of java.awt.Applet) inside tomcat? Generally this won't work because there's no display on which to display the applet.
Assuming you don't want the applet to display anywhere and you just want to execute some portion of it programmatically, you may be able to get by using a virtual X server such as Xvfb or Xvnc. Once you have Xvfb or Xvnc running on your host running tomcat, you might try to set the DISPLAY inside the tomcat startup scripts to use the display of the virtual X server.

-Djava.awt.headless=false
add above in your Tomcat startup script. it will work 100%

You are maybe using something in your Java code that can not work on a headless system, such as graphics components (Swing objects, images, etc.). Some of these components, instead of being directly handled by Java, are handled by underlying platform (Windows kernel itself or X-Window server on Unix). This way the overall performance of application is boosted.
So the question now is, ok if it was working on Java 1.4, why doesn't it work on 1.5? My bet, given the peformance boost since Java 1.2 that Swing has received over time, is that Sun has moved the management of some graphic objets to OS level to increase performance. So if you can not stick to 1.4, then you should revise your code.
This good article will help you understand how to modify your application to make it headless-friendly.

Applets are going to have a hard-time running server-side. They are designed to run inside of a container, such as a web browser. The exception is getting thrown most likely because the applet is trying to draw it's GUI -- and the server is providing no support for this. I'm surprised that it worked in JDK 1.4 -- I don't know what changed between the two revisions which would have affected this.

You may also have to install the x11 libraries, or at least explicitly export the path to them.
/usr/X11R6/lib

Open $CATALINA_HOME/bin/startup.sh file with your preferred text browser
Paste this line export CATALINA_OPTS="$CATALINA_OPTS -Djava.awt.headless=false" at the beginning of the file
Save and close the file
Restart Tomcat

In spring boot with database access, when you specify asterisks: **** as username and password, it will try to prompt the user for a username and password (you read that right), and it will throw this HeadlessException if it's not a gui application.