Application jar path??

Question

Hi all:
I have the following situation:
We're writting an application where all the class files are jar'ed together.
We're supplying html help with the application.
The file structure will look like this after installation:
appDirectory
- app.jar
- helpDirectory
--- aBunchOfHelpFiles.html
The problem I have is this. I want to be able to get the path of the helpDirectory from within the application so that I can display them in some html enabled frame. getting the user's current directory is easy, getting the user's home directory is easy, but how do you get the directory where the jar is located? I've been trying to use this approach:
        URL urlAppDir = ClassLoader.getSystemResource("package/App.class");
        File fileAppDir = new File(urlAppDir.getFile());
        while(!fileAppDir.isDirectory()){
            fileAppDir = fileAppDir.getParentFile();
            System.out.print("fileAppDir = " + fileAppDir);
            System.out.println(" :  " + fileAppDir.isDirectory());
        }but it produces this output...
fileAppDir = file:\C:\A\B\C\app.jar!\package : false
fileAppDir = file:\C:\A\B\C\app.jar! : false
fileAppDir = file:\C:\A\B\C : false
fileAppDir = file:\C:\A\B : false
fileAppDir = file:\C:\A : false
fileAppDir = file:\C: : false
fileAppDir = file: : false
fileAppDir = null
<null pointer exception because fileAppDir became null and tried to execute isDirectory() method>
Why doesn't this walk up work? And is there a better approach for getting the directory in which an application's jar file exists?
Thanks in advance,
Jeremy

Answer 1

I found the solution to the walk up problem I was having, but I'm not exactly sure why the solution works. I needed to get the AbsoluteFile of the ParentFile. If anyone could explain this, or offer a simpler/better way of attaining an application's jar file's directory, I'd appreciate it.
        URL urlAppDir = ClassLoader.getSystemResource("package/App.class");
        File fileAppDir = new File(urlAppDir.getFile());
        while(!fileAppDir.isDirectory()){
            //  Get the AbsoluteFile of the parent file... 
            //  I'm not entirely clear what the difference is, but it works.
            fileAppDir = fileAppDir.getParentFile().getAbsoluteFile();
            System.out.print("fileAppDir = " + fileAppDir);
            System.out.println(" :  " + fileAppDir.isDirectory());
        }Thanks,
Jeremy