This is not really a Perl question but a Java security question (I’m assuming you mean Java applets!).

I'd say it depends on the version of Java that is used to run the applet. In early versions applets, by design, had many restrictions. They run in the applet sandbox. Therefor it is impossible to read/write files or start programs on the host executing the applet (there are many more restrictions). So it used to be impossible.

In the course of time the Java security model was seen as too restrictive and things started to change. Right now, I am not convinced it is impossible but I would strongly recommend against it. The best advice I can give is to rethink the problem!

If you insist of running something from an applet I suggest you investigate javasecurity/applets.

HTH
dHarry