Resource from src/main/resources not found after building with maven

Resources from src/main/resources will be put onto the root of the classpath, so you'll need to get the resource as:

new BufferedReader(new InputStreamReader(getClass().getResourceAsStream("/config.txt")));

You can verify by looking at the JAR/WAR file produced by maven as you'll find config.txt in the root of your archive.

FileReader reads from files on the file system.

Perhaps you intended to use something like this to load a file from the class path

// this will look in src/main/resources before building and myjar.jar! after building.
InputStream is = MyClass.class.getClassloader()
                     .getResourceAsStream("config.txt");

Or you could extract the file from the jar before reading it.