How to specify the file path in java which has variable in it's path?

I have two projects. One at location a and other at b.

Project a needs to load the conf file from project b's directory.
I can't hardcode the path for file which is located in b's directory because If I run this on different machine everymachine's username will be different and path can be different as well.

So I want to do is, everyone sets their conf file path as environment varibale in .bashrc. That way I want to use exported variable path in my java code. Now the question is how do I do that?

Following is something similar to what I want to do:

I have one varibale stored in my system at .bashrc as follows:

export variableName1=~/path_to_file

Now I want to use this variable in java while loading the config file as follows:

        Config config = ConfigFactory.parseFile(new File("${variableName1}/path_to_file"));

How do I do that?

I tried getting the value of variableName1 as follows:

        String value =  System.getProperty("variableName1");
                          OR
        String value =  System.getenv("variableName1");

But this returns null value only.

That's an environment variable so is accessed with

String myDirectory = System.getenv("variableName1");

Step 1:
You need to export the variable name in .bashrc file for accessing from all terminal.

export variableName1="~/path_to_file"

Then restart the computer.

Step 2:

In Java code you can get the value by:

 String value =  System.getenv("variableName1");