Set initial directory of JavaFX FileChooser

I would like to allow users of my program to open files only from a certain directory in the project folder. On Stack Overflow, I often find the following solution: chooser.setInitialDirectory(new File(System.getProperty("user.home"));, but I am trying to reference the resources folder in project. I tried to use fileChooser.setInitialDirectory(new File("/resources/")); but I get java.lang.IllegalArgumentException: Folder parameter must be a valid folder. How can I fix this problem?