Cannot change version of project facet Dynamic Web Module to 2.5

在eclipse的工程上选择属性，再选择Project Facets里面中选择Dynamic Web Module ，将3.0修改为2.5，提示如下信息：

Cannot change version of project facet Dynamic Web Module to 2.5

修改办法：

Open the navigator view and find that there is a .settings folder under your project expand it and then open the file: org.eclipse.wst.common.project.facet.core.Delete
the content of this file and right click on the project and click on properties. Go to Project Facats in the popup window there you can click on runtime tabs and convert your project to the new facet you want.

或者直接修改

<installed facet="jst.web" version="2.5"/>

再次选择tomcat6就可以正常使用了。