我们用Eclipse创建Maven结构的web项目的时候选择了Artifact Id为maven-artchetype-webapp，由于这个catalog比较老，用的servlet还是2.3的，而一般现在至少都是2.5，在Project Facets里面修改Dynamic web module为2.5的时候就会出现Cannot change version of project facet Dynamic web module to 2.5，如图：
其实在右边可以看到改到2.5需要的条件以及有冲突的facets，解决这个问题的步骤如下：
1.把Servlet改成2.5，打开项目的web.xml，改之前：
1. <!DOCTYPE web-app PUBLIC
2. "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"
3. >
4.
5. <web-app>
6. <display-name>Archetype Created Web Application</display-name>
7. </web-app>
改后：
1. <?xml version="1.0" encoding="UTF-8"?>
2. <web-app version="2.5"
3. xmlns="http://java.sun.com/xml/ns/javaee"
4. xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
5. xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
6. >
7.
8. <display-name>Archetype Created Web Application</display-name>
9. </web-app>
2.修改项目的设置，在Navigator下打开项目.settings目录下的org.eclipse.jdt.core.prefs
1. eclipse.preferences.version=1
2. org.eclipse.jdt.core.compiler.codegen.inlineJsrBytecode=enabled
3. org.eclipse.jdt.core.compiler.codegen.targetPlatform=1.5
4. org.eclipse.jdt.core.compiler.compliance=1.5
5. org.eclipse.jdt.core.compiler.problem.assertIdentifier=error
6. org.eclipse.jdt.core.compiler.problem.enumIdentifier=error
7. org.eclipse.jdt.core.compiler.problem.forbiddenReference=warning
8. org.eclipse.jdt.core.compiler.source=1.5
把1.5改成1.6
?
1. eclipse.preferences.version=1
2. org.eclipse.jdt.core.compiler.codegen.inlineJsrBytecode=enabled
3. org.eclipse.jdt.core.compiler.codegen.targetPlatform=1.6
4. org.eclipse.jdt.core.compiler.compliance=1.6
5. org.eclipse.jdt.core.compiler.problem.assertIdentifier=error
6. org.eclipse.jdt.core.compiler.problem.enumIdentifier=error
7. org.eclipse.jdt.core.compiler.problem.forbiddenReference=warning
8. org.eclipse.jdt.core.compiler.source=1.6
打开org.eclipse.wst.common.component
1. <?xml version="1.0" encoding="UTF-8"?>
2. <project-modules id="moduleCoreId" project-version="1.5.0">
3. <wb-module deploy-name="test">
4. <wb-resource deploy-path="/" source-path="/target/m2e-wtp/web-resources"/>
5. <wb-resource deploy-path="/" source-path="/src/main/webapp" tag="defaultRootSource"/>
6. <wb-resource deploy-path="/WEB-INF/classes" source-path="/src/main/java"/>
7. <wb-resource deploy-path="/WEB-INF/classes" source-path="/src/main/resources"/>
8. <property name="context-root" value="test"/>
9. <property name="java-output-path" value="/test/target/classes"/>
10. </wb-module>
11. </project-modules>
把project-version="1.5.0"改成project-version="1.6.0"
1. <?xml version="1.0" encoding="UTF-8"?>
2. <project-modules id="moduleCoreId" project-version="1.6.0">
3. <wb-module deploy-name="test">
4. <wb-resource deploy-path="/" source-path="/target/m2e-wtp/web-resources"/>
5. <wb-resource deploy-path="/" source-path="/src/main/webapp" tag="defaultRootSource"/>
6. <wb-resource deploy-path="/WEB-INF/classes" source-path="/src/main/java"/>
7. <wb-resource deploy-path="/WEB-INF/classes" source-path="/src/main/resources"/>
8. <property name="context-root" value="test"/>
9. <property name="java-output-path" value="/test/target/classes"/>
10. </wb-module>
11. </project-modules>
打开org.eclipse.wst.common.project.facet.core.xml
1. <?xml version="1.0" encoding="UTF-8"?>
2. <faceted-project>
3. <fixed facet="wst.jsdt.web"/>
4. <installed facet="java" version="1.5"/>
5. <installed facet="jst.web" version="2.3"/>
6. <installed facet="wst.jsdt.web" version="1.0"/>
7. </faceted-project>
把<installed facet="java" version="1.5"/>改成<installed facet="java" version="1.6"/>，把 <installed facet="jst.web" version="2.3"/>改成 <installed facet="jst.web" version="2.5"/>
1. <?xml version="1.0" encoding="UTF-8"?>
2. <faceted-project>
3. <fixed facet="wst.jsdt.web"/>
4. <installed facet="java" version="1.6"/>
5. <installed facet="jst.web" version="2.5"/>
6. <installed facet="wst.jsdt.web" version="1.0"/>
7. </faceted-project>
都改好之后在打开看看，已经把Dynamic web module改成了2.5
最后把报错的工程delete掉 ,再重新import进来后,就可以了
