Target runtime Apache Tomcat v6.0 is not defined.

选择natigator 然后选择 “org.eclipse.wst.common.project.facet.core.xml”

<?xml version="1.0" encoding="UTF-8"?>
<faceted-project>
? <runtime name="Apache Tomcat v6.0"/>
? <fixed facet="wst.jsdt.web"/>
? <fixed facet="java"/>
? <fixed facet="jst.web"/>
? <installed facet="java" version="1.6"/>
? <installed facet="jst.web" version="2.5"/>
? <installed facet="wst.jsdt.web" version="1.0"/>

</faceted-project>

去掉
? <runtime name="Apache Tomcat v6.0"/>

?

改成
<?xml version="1.0" encoding="UTF-8"?>
<faceted-project>
? <runtime name="Apache Tomcat v6.0"/>
? <fixed facet="wst.jsdt.web"/>
? <fixed facet="java"/>
? <fixed facet="jst.web"/>
? <installed facet="java" version="1.6"/>
? <installed facet="jst.web" version="2.5"/>
? <installed facet="wst.jsdt.web" version="1.0"/>
</faceted-project>