WARNING: Unknown version string [3.1]. Default version will be used

Question

Whenever I run web aps in eclipse, I always got this warning:

WARNING: Unknown version string [3.1]. Default version will be used.

What is this? What should I do about this?

Answer 1

Or you could simply be using a web server that doesn't support Servlet 3.1. For example, Tomcat 7 only supports Servlet 3.0 and below. Whereas Tomcat 8 supports servlet 3.1.