In a web application there is no "current directory" so you cannot load files from a "relative path". If you really want to load something from a File, you need to specify the full path (on Windows that might be C:\software\projects\wibble\src\config\stuff.properties or whatever.)
This is obviously dangerous - this is probably not where the properties file will be located on the live server.
A better way to read such information is using
Java's "resource" mechanism. Place the file in WEB-INF/classes and load it as a "resource" using something like:
Does that help?