Target runtime Apache Tomcat v5.5 is not defined.
工程出现红叉叉，报错的信息是Target runtime Apache Tomcat v5.5 is not defined.主要原因是org.eclipse.wst.common.project.facet.core.xml文件错误，我的server是websphere6.1因此把xml文件里面的配置稍微改下就Ok


<?xml version="1.0" encoding="UTF-8"?>
<faceted-project>
  <runtime name="Apache Tomcat v5.5"/>
  <fixed facet="jst.utility"/>
  <fixed facet="jst.java"/>
  <installed facet="jst.java" version="5.0"/>
  <installed facet="jst.utility" version="1.0"/>
</faceted-project>


改为


<?xml version="1.0" encoding="UTF-8"?>
<faceted-project>
  <runtime name="WebSphere Application Server v6.1"/>
  <fixed facet="jst.utility"/>
  <fixed facet="jst.java"/>
  <installed facet="jst.java" version="5.0"/>
  <installed facet="jst.utility" version="1.0"/>
</faceted-project>