As far as I know, RAS supports only Windows-based VMs.
I think that your best solution is to move the Java workload onto a windows server (Java should be cross-platform).
Otherwise, if these Java applications are available as applets, you can publish them as a URL via RAS.
As a last resort, or if you prefer to keep your Linux machines, you could use a double hop approach: setup RD on your linux machine (RDP/VNC/X11) then publish an RDP connection using Parallels client with auto-connection. However that would be inefficient (doubling of the network traffic) and not-user friendly (full Linux machine available to the user).
