How to walk through Java class resources?

In general can't get a list of resources like this. Some classloaders may not even be able to support this - imagine a classloader which can fetch individual files from a web server, but the web server doesn't have to support listing the contents of a directory. For a jar file you can load the contents of the jar file explicitly, of course.

(This question is similar, btw.)

For resources in a JAR file, something like this works:

URL url = MyClass.class.getResource("MyClass.class");
String scheme = url.getProtocol();
if (!"jar".equals(scheme))
  throw new IllegalArgumentException("Unsupported scheme: " + scheme);
JarURLConnection con = (JarURLConnection) url.openConnection();
JarFile archive = con.getJarFile();
/* Search for the entries you care about. */
Enumeration<JarEntry> entries = archive.entries();
while (entries.hasMoreElements()) {
  JarEntry entry = entries.nextElement();
  if (entry.getName().startsWith("com/y/app/")) {
    ...
  }
}

You can do the same thing with resources "exploded" on the file system, or in many other repositories, but it's not quite as easy. You need specific code for each URL scheme you want to support.