Files not found after packing everything up to a Jar-File, though its working in Eclipse

Question

So my program is finally done in it's first version. I can run it in Eclipse IDE without any problems, but as soon as I pack it up into a Jar-File, it can't find the files that were in a folder within the project (declared as source folder). I already know, that while compiling, the folder structure changes and I tried working around that, but it doesn't work and I don't want to stick to such a work-around.
Project structure:

- src/main/java/
    + [my packages]
- resources/
     + configs/[some files]
     + languages/[some language files]
     + levelcards/[some images]

In my program im accessing ie the files inside "configs" with

new File("./resources/configs/[...]");

and it works absolutely fine, as the folder exists in the project. After compiling it doesn't though, so I tried it with

new File("./configs/[...]");

but it doesn't work either.
What I expect is it working regardless of me launching it in Eclipse or via the JRE directly, though I have no idea how to get it to that point. If you can help me out in any way, I would appreciate it!
Gregor

Answer 1

eg:

Assume have a Utility class which will read from file and return as String

class Utils{

public static String readFromFile(String filePath){
  InputStream inputStream=Utils.class.getResourceAsStream(filePath); //eg:- configs/temp_file.txt
/* Now once you get the InputStream there 
are lot of utility library to return as string */

String newLine = System.getProperty("line.separator");
 BufferedReader reader = new BufferedReader(
         new InputStreamReader(inputStream));
 StringBuilder result = new StringBuilder();
 for (String line; (line = reader.readLine()) != null; ) {
     if (result.length() > 0) {
         result.append(newLine);
     }
     result.append(line);
 }
 return result.toString();
}
}