What technologies to use when building an android client-server application?

Question

Android

Now I'm running a Java application on the server.
Androyd works with it using socket technology (Through stream reader / writer)
Maybe there are some other technologies for interacting with the server?
I know that there is no RMI on android, but there is apacheHttp, can I tie it to tomcat and work like with a servlet?
About the problem:
www.youtube.com/watch?v=D5yT-I9efjg I
really liked it. I also want to try with the domestic OWEN PLC150.
If we consider the exchange protocol, then there is TCP Modbus: 1 master (bucketphone) - many clients.
Of course I'll try directly from the phone, but it will be safer through the server (the server will act as the network master).
I'm thinking of working through a PostgreSQL database. The server polls the controller cyclically and writes to the PLC output status database. Relevance 0.2 seconds. Androyd writes the states of the entries to the database with a timestamp of the entry. The server sends the status to the PLC.
This way I can connect many androids.
How do you like the idea? Or is there a better method?