Thank you, @FlorianBome, for this information. This solution sounds interesting. So, the A&H protocol seems to be raw MIDI data which is encapsulated in a TCP/IP stream. (I found further information at MIDI Control - Allen & Heath).
So, my PC with the Java program could act as an A&H desk. Probably, I have to configure the PC’s firewall, so that it will accept incoming TCP/IP connections.
The Bome Network MIDI protocol is somewhat complex, so we haven’t disclosed how it works. We also think that it’s better to go with standards…
Yes, I think standards are really helpful. If you use standard specifications (like RFC or MIDI), you do not have to write them. 
You ‘only’ have to comply with them. The MIDI 1.0 protocol is one of my favorite: easy design, but also open to extensions. - There are so many vendors and devices which support it.
I think, first I have to collect some experience with Java and IP support. Right now, this is only a spare time project, so I am not in a hurry.