問題描述
用Eclipse創建Maven結構的web項目的時候選擇了Artifact Id為maven-artchetype-webapp，由於這個catalog比較老，用的servlet還是2.3的，而一般現在都是用3.0，在Project Facets里面修改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，如圖：
解決這個問題的步驟如下：
1. 把Servlet改成3.0，打開項目的web.xml
<?
xml
version
=
"1.0"
encoding
=
"UTF-8"
?>
<
web-app
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"
id
=
"schedule-console"
version
=
"3.0"
>
2. 修改項目的設置，在Navigator下打開項目.settings目錄下的org.eclipse.jdt.core.prefs
把1.5改成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
3. 打開org.eclipse.wst.common.project.facet.core.xml
把java改為1.8， 把jst.web改為3.0；
<?
xml
version
=
"1.0"
encoding
=
"UTF-8"
?>
<
faceted-project
>
<
fixed
facet
=
"wst.jsdt.web"
/>
<
installed
facet
=
"jst.web"
version
=
"3.0"
/>
<
installed
facet
=
"wst.jsdt.web"
version
=
"1.0"
/>
<
installed
facet
=
"java"
version
=
"1.8"
/>
</
faceted-project
>
OK，搞定了。