我們用Eclipse建立Maven結構的web專案的時候選擇了Artifact Id為maven-artchetype-webapp，由於這個catalog比較老，用的servlet還是2.3的，而一般現在至少都是2.5，在Project Facets裡面修改Dynamic web module為3.0的時候就會出現Cannot change version of project facet Dynamic web module to 3.0

其實在右邊可以看到改到3.0需要的條件以及有衝突的facets，解決這個問題的步驟如下：
1.把Servlet改成3.0，開啟專案的web.xml，改之前：

<!DOCTYPE web-app PUBLIC
 "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"
 "http://java.sun.com/dtd/web-app_2_3.dtd" >

<web-app>
  <display-name>Archetype Created Web Application</display-name>
</web-app>

改後：

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="3.0"
 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xmlns="http://java.sun.com/xml/ns/javaee"
	xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd">
  <display-name>Archetype Created Web Application</display-name>
</web-app>
 

2.修改專案的設定，在Navigator下開啟專案.settings目錄下的org.eclipse.jdt.core.prefs

eclipse.preferences.version=1
org.eclipse.jdt.core.compiler.codegen.inlineJsrBytecode=enabled
org.eclipse.jdt.core.compiler.codegen.targetPlatform=1.5
org.eclipse.jdt.core.compiler.compliance=1.5
org.eclipse.jdt.core.compiler.problem.assertIdentifier=error
org.eclipse.jdt.core.compiler.problem.enumIdentifier=error
org.eclipse.jdt.core.compiler.problem.forbiddenReference=warning
org.eclipse.jdt.core.compiler.source=1.5
 

把1.5改成1.6以上（此處改為1.8）

eclipse.preferences.version=1
org.eclipse.jdt.core.compiler.codegen.inlineJsrBytecode=enabled
org.eclipse.jdt.core.compiler.codegen.targetPlatform=1.8
org.eclipse.jdt.core.compiler.compliance=1.8
org.eclipse.jdt.core.compiler.problem.assertIdentifier=error
org.eclipse.jdt.core.compiler.problem.enumIdentifier=error
org.eclipse.jdt.core.compiler.problem.forbiddenReference=warning
org.eclipse.jdt.core.compiler.source=1.8

開啟org.eclipse.wst.common.component

<?xml version="1.0" encoding="UTF-8"?>
<project-modules id="moduleCoreId" project-version="1.5.0">
    <wb-module deploy-name="test">
        <wb-resource deploy-path="/" source-path="/target/m2e-wtp/web-resources"/>
        <wb-resource deploy-path="/" source-path="/src/main/webapp" tag="defaultRootSource"/>
        <wb-resource deploy-path="/WEB-INF/classes" source-path="/src/main/java"/>
        <wb-resource deploy-path="/WEB-INF/classes" source-path="/src/main/resources"/>
        <property name="context-root" value="test"/>
        <property name="java-output-path" value="/test/target/classes"/>
    </wb-module>
</project-modules>

把project-version="1.5.0"改成project-version=“1.8.0”

<?xml version="1.0" encoding="UTF-8"?>
<project-modules id="moduleCoreId" project-version="1.8.0">
    <wb-module deploy-name="test">
        <wb-resource deploy-path="/" source-path="/target/m2e-wtp/web-resources"/>
        <wb-resource deploy-path="/" source-path="/src/main/webapp" tag="defaultRootSource"/>
        <wb-resource deploy-path="/WEB-INF/classes" source-path="/src/main/java"/>
        <wb-resource deploy-path="/WEB-INF/classes" source-path="/src/main/resources"/>
        <property name="context-root" value="test"/>
        <property name="java-output-path" value="/test/target/classes"/>
    </wb-module>
</project-modules>

開啟org.eclipse.wst.common.project.facet.core.xml

<?xml version="1.0" encoding="UTF-8"?>
<faceted-project>
  <fixed facet="wst.jsdt.web"/>
  <installed facet="java" version="1.5"/>
  <installed facet="jst.web" version="2.3"/>
  <installed facet="wst.jsdt.web" version="1.0"/>
</faceted-project>

把改成，把 改成

<?xml version="1.0" encoding="UTF-8"?>
<faceted-project>
  <fixed facet="wst.jsdt.web"/>
  <installed facet="java" version="1.8"/>
  <installed facet="jst.web" version="3.0"/>
  <installed facet="wst.jsdt.web" version="1.0"/>
</faceted-project>

都改好之後在開啟看看，已經把Dynamic web module改成了3.0