Webhooks was designed to run with Java version 1.8 or higher.
Check to see what version of Java is being used by Tomcat
Depending on your OS and Tomcat version, you can look up the Java version Tomcat is running with in the manager app, which is installed by default. Go to http://hostname:8080/manager/html
(replace hostname by hostname or localhost and your port number), scroll to the bottom, there you will find "JVM Version".
Another way would be to review tomcat logs. As in: