tomcat7 was built with Java8 for Ubuntu 16.04 and it should be compatible with Java7

[Pablo Pazos]

Running Tomcat7 on Ubuntu 16.04 with Java7 gives an exception when deploying apps.

Error: SEVERE: Context initialization failed
java.lang.NoSuchMethodError: java.util.concurrent.ConcurrentHashMap.keySet()Ljava/util/concurrent/ConcurrentHashMap$KeySetView;
    at org.apache.catalina.core.ApplicationContext.getInitParameterNames(ApplicationContext.java:368)

Bug report: https://bz.apache.org/bugzilla/show_bug.cgi?id=55554

Description and possible solution: http://stackoverflow.com/questions/38583495/getting-error-while-running-webservices-on-tomcat7-server-ubuntu-16-04-lts

It seems on the Apache builds this is not happening and it is an issue with the Ubuntu packages for 16.04

The docs say that Tomcat7 should work on Java7, and event with Java6: http://tomcat.apache.org/whichversion.html

The current build for Ubuntu 16.04 doesn't comply with that. The error happened to tens of people already, and maybe more (by looking at the google results).