Okay I re-read the code and it is not exactly as I remembered it. Here are the rules:
- All modules listed in the jboss.protocol.handler.modules system property are loaded, one by one, to search for java.net.URLStreamHandlerFactory service implementations. Note that the module list is delimited by vertical bar characters ("|"); this was motivated by consistency with the java.protocol.handler.pkgs system property.
- The first such implementation that returns a URLStreamHandler for the given protocol name is used (and cached by the JVM).
- Otherwise null is returned and the search is retried next time.