Solve the problem that the maven project in Eclipse cannot be added to tomcat

In the .setting folder under the project, find the org.eclipse.wst.common.project.facet.core.xml file and put

<?xml version="1.0" encoding="UTF-8"?>
<faceted-project>
  <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>

change into:

<?xml version="1.0" encoding="UTF-8"?>
<faceted-project>
  <fixed facet="wst.jsdt.web"/>
  <installed facet="java" version="1.6"/>
  <installed facet="jst.web" version="2.5"/>
  <installed facet="wst.jsdt.web" version="1.0"/>
</faceted-project>

That's it.