According to Oracle documentation the schemagen tool is removed from the JDK as part of JEP 320 (http://openjdk.java.net/jeps/320). That JEP points to Maven artifacts that now s
The issue seems to be known with the jaxb-*:2.3.0
version - #jaxb-v2/issues/1168. Additionally, this would be resolved with a future release as marked in the known issues of jaxb running over java-9.
You can resolve this following the comment -
Please try 2.4.0-b180725.0644 - this is JPMS modularized RI working on JDKs with java.xml.bind module (9,10) and those without it (11-ea)
or try downloading the binary distribution from the same link.