I would try /usr/bin/java first.
After a power interrupt of my Raspberry Pi the traccar.service starts automatically.
I saved the original traccar.service file and modified traccar.service file both at another location.
AlfSolli and Richard: thanks a lot!!
And the traccar status is now also okay:
raoul@Raspberry:~$ systemctl is-active traccar active raoul@Raspberry:~$