How are you trying to read the file?
If a JAR is in the classpath, you should be able to open it with Class.getResource(String name) or Class.getResourceAsStream(String name)
You can also read a file from a JAR/EAR/WAR with a particular URL:
Where the first part is the path to the jar file, a '!', then the path within the JAR. See this example.