1. Error:

Using run – > in eclipse; When running on server, selecting tomcat7 will report an error: the server does not support version 3.1 of the J2EE Web module specification

2. Reasons:

Tomcat 6.0 supports servlet 2.5 at most, and now the project to be imported is version 3.0

3. Solutions:

There is a. Settings folder under the root directory of the project, and there is an org.eclipse.wst.common.project.facet.core.xml file under the folder. The contents are as follows:

<?xml version="1.0" encoding="UTF-8"?>
<faceted-project>
  <fixed facet="java"/>
  <fixed facet="jst.web"/>
  <fixed facet="wst.jsdt.web"/>
  <installed facet="java" version="1.6"/>
  <installed facet="jst.web" version="3.0"/>
  <installed facet="wst.jsdt.web" version="1.0"/>
</faceted-project>

Put

<installed facet="jst.web" version="3.0"/>

Change to

<installed facet="jst.web" version="2.5"/>

Done!