CLIENT SET RESTRICTED

Usage: CLIENT <class> SET RESTRICTED [on|off]

When this option is set on it will only allow java clients to connect to the server.

Examples:
/as client WebMaster set restricted on
/as client WebMaster set restricted off

As stated under password, if you want to restrict most of your users to the java client, you can make a restricted client class as your z-default client class and add specific exceptions higher up. You can also have this before the z-default if you want java clients to have different settings than other users.