Here's some minor modifications:

1. Since it listens on a network socket, make it a dependency of `network.target`.
2. `nohup` is not needed since `systemd` will daemonize the executable for you.
3. I think a separate shell script would be an overkill, so just merge it into the service file.

So the service file looks like this:
 
 [Unit]
 Description=Some job
 After=network.target

 [Service]
 WorkingDirectory=/home/user/tmp/testout
 ExecStart=java -jar /home/user/programming/tests/java/core/SocketTest/SocketTest.jar < /dev/null >/dev/null
 User=dlt
 Type=simple

 [Install]
 WantedBy=multi-user.target

As far as I know, there is no special caveat of running Java application with Systemd.