I would rely on the Java plug-in itself.

<sscce>
import java.io.File;

public class FileNameTest {

 public static void checkFileName(String name) {
   try {
     File file = new File(name);
     file.createNewFile();
     System.out.println( "File established: " + name );
   } catch (Exception e) {
     e.printStackTrace();
   }
 }

 public static void main(String[] args) {
   String name;

   name = "$haha";
   checkFileName(name);

   name = "?$haha";
   checkFileName(name);

   name = "/haha";
   checkFileName(name);
 }
}
</sscce>

HTH

This sounds easy to write using the java.util.regex package.
How should a file name look like ?

What's "it" in that sentence?  The code or the filename?  It's very easy to
make the code work in multiple OSs, of course.  It's very hard to make a
perfect validator to ensure that a filename would be valid in, say, the
Japanese release of Windows 95 when running under Solaris with an 8859-1
default encoding.

java.io.File forces some amount of well-formedness, and getCanonicalFile()
will normalize it using OS-specific code.  If you try to actually create or
read the file, you'll be certain that the path is valid.

You won't know if it would be valid on another OS, but you really can't
know that anyway - different paths, drive letter conventions, permissions,
conflicting files, etc, even on the same OS on another machine will break.
--
Mark Rafn    dagon@dagon.net    <http://www.dagon.net/>