Today, I replaced the tomcat8 I used with tomcat7, and then I found that the project could not be deployed to tomcat, indicating that there were no deployable resources. After verification, I found that I was using a newer version of eclipse. The default configuration Dynamic web module version is 3.1, and tomcat7 does not support. So the org.eclipse.wst.common.project.facet.core.xml file in the project's .settings
<?xml version="1.0" encoding="UTF-8"?>
<faceted-project>
<fixed facet="jst.web"/>
<fixed facet="wst.jsdt.web"/>
<fixed facet="java"/>
<installed facet="java" version="1.8"/>
<installed facet="jst.web" version="3.1"/>
<installed facet="wst.jsdt.web" version="1.0"/>
</faceted-project>
Change <installed facet="jst.web" version="3.1"/>
to 2.5, and you can change it to a lower version.