Installation on Ubuntu 16.04.4 does not find java

I can't install traccar server on Ubuntu 16.04.4 because the installer thinks there is no java installed:

root@rsfs4:~# ./traccar.run 
Creating directory out
Verifying archive integrity...  100%   All good.
Uncompressing traccar  100%  
/usr/bin/java
Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 1
    at Test.main(Test.java:3)
Java 7 or higher is required

which is not true, I've installed and the system knows about it:

root@rsfs4:~# java -version
openjdk version "9-internal"
OpenJDK Runtime Environment (build 9-internal+0-2016-04-14-195246.buildd.src)
OpenJDK 64-Bit Server VM (build 9-internal+0-2016-04-14-195246.buildd.src, mixed mode)
root@rsfs4:~# 

and the path to java is correct too:

root@rsfs4:~# which java
/usr/bin/java
root@rsfs4:~# 

Don't use Java 9. Install Java 8.

thanks, that worked