[Request] Classpath Resources

[danthe1st]

A common source of confusion among (somewhat) new Java developers (especially when they are packaging their first application as a JAR) is resources on the classpath and how they are different from files.

I would request an article clarifying these things, specifically the following:

• What's the difference between resources and files?
• When I access a file in my source folder using java.io.File (or similar), why does it not work in a JAR deployed somewhere (in a different directory, on a different computer, ...)
  • Why should I not use files for accessing anything in the source folder?
• What does Class#getResource/Class#getResourceAsStream do?
• What's the difference between getClass.getResource("a.txt"), getClass().getResource("/a.txt") and getClass().getClassLoader().getResource("a.txt")?
  • Why does it not find my resource when I use the wrong one?
• Where should I put resources?
  • with Maven/Gradle but also in plain Eclipse/IntelliJ/VSC projects