I'm not sure exactly how much research you did into this, but it doesn't sound like you have the right solution for platform detection or the right idea for permission checking. You can find excellent Java API documentation
online. It is always best to use functions in the standard library rather than using Runtime.getRuntime().exec() to launch a native executable, which I suspect is what you are attempting for permissions checking.
Without actually seeing your code, I can say that your "solution" for patform detection sounds like an unreliable hack. Instead, you should probably be using System.getProperty("os.name") to check which OS your program was launched on. There is an excellent example of this technique available here
Similarly, you should probably be using the file class
built into the Java standard library for permissions checking. A descent example of something somewhat similar can be found here
I hope I have put you on the right path. If you have further questions, more specifics, such as the code you are struggling with, would be appreciated.