Tomcat version 7.0 only supports J2EE 1.2, 1.3, 1.4, and Java EE 5 and 6 Web modules
1.在eclipse的workspace里面找到该项目.settings文件夹
2.编辑org.eclipse.wst.common.project.facet.core.xml文件
<?xml version="1.0" encoding="UTF-8"?><faceted-project>
<fixed facet="wst.jsdt.web"/>
<installed facet="wst.jsdt.web" version="1.0"/>
<installed facet="java" version="1.7"/>
<installed facet="jst.web" version="2.5"/>
</faceted-project>
3.重启eclipse
如果还是没有解决请参照链接中的解决办法：
http://caleb-520.iteye.com/blog/2262216