Getting location of file as string in resource fol

I have completed a program in eclipse and now I would like to export it as a single runnable jar file. The program contains a resource folder with images and text files in it. This is located beneath the source folder.

The res file is not added to the build path however when I run the program in Eclipse it still works. The thing that is confusing me is that the res file is being saved into the runnable jar file when I export it as I can open the Jar file with WinRar and I see the folder is there with all the objects in it. But when I run the problem it stops at the point that the resource folder is referenced. To add to my confusion when I manually copy and paste the res folder next to where the runnable jar file is saved and run the program it works exactly as it should do.

Now I know this is something to do with how I reference the files in my code. At the moment I have it like this

reader = new LineNumberReader(new FileReader("res/usernames.txt"));

This works exactly how I want and accesses the res folder without any exceptions - in Eclipse and when I move the resource folder next to the Jar file.

I would like it to work normally but without having a folder outside of the Jar file I would like it all encapsulated in one Jar file.

I did a lot of research and what seems to be a common fix - may I add I don't really know how it works but everyone seems to mention it - is to somewhere use:

myClass().getResource()

When I create a new FileReader it needs a String input however when I use myClass().getResource() it returns a resource and not a string. I also don't have a clue how it is meant to reference the resource folder. Should I move the resource folder into the source folder?

Does anyone know how I can reference the resource folder from within the runnable jar file?

Sorry for rambling question I know what I want for my final product but I'm getting confused by the build paths and referencing from within classes and I have searched online for a long time trying to figure it out.

Resources, when you deploy your software, are not deployed as files in a folder. They are packaged as part of the jar of your application. And you access them by retrieving them from inside the jar. The class loader knows how to retrieve stuff from the jar, and therefore you use your class's class loader to get the information.

This means you cannot use things like FileReader on them, or anything else that expects a file. The resources are not files anymore. They are bundles of bytes sitting inside the jar which only the class loader knows how to retrieve.

If the resources are things like images etc., that can be used by java classes that know how to access resource URLs (that is, get the data from the jar when they are given its location in the jar), you can use the ClassLoader.getResource(String) method to get the URL and pass it to the class that handles them.

If you have anything you want to do directly with the data in the resource, which you would usually do by reading it from a file, you can instead use the method ClassLoader.getResourceAsStream(String).

This method returns an InputStream, which you can use like any other InputStream - apply a Reader to it or something like that.

So you can change your code to something like:

InputStream is = myClass().getResourceAsStream("res/usernames.txt");
reader = new LineNumberReader( new InputStreamReader(is) );

Note that I used the getResourceAsStream() method from Class rather than ClassLoader. There is a little difference in the way the two versions look for the resource inside the jar. Please read the relevant documentation for Class and ClassLoader.