Thanks for changing your display name, I appreciate it
There are a nmber of ways to do this, but you start to run into hard-coded locations or assumptions on the location of files. Depending on how you deploy your application, you may be able to use the ClassLoader to find the location of the JAR containing the source, then assume the properties file is in the same directory.
Hint: turn the class name into a file eg /com/mypackage/MyClass.class, use the ClassLoader to get the URL, use the URL to find the file, use the file to find the directory.
I'm not sure it's an elegant solution, maybe someone else has an opinion.