blocks|key|262458|text|在我的例子中，web.xml由dtd引用。在我将其更改为xsd+reference之后，就像悉尼发布的那个一样，它起作用了。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|262459|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

In my case the web.xml was referenced by a dtd. After I changed this to xsd reference like the one posted by Sydney it worked.

blocks|key|45972|text|我遇到了同样的问题，我甚至试图删除项目并重新添加它。诀窍是删除了.settings目录。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|45973|entityMap^0|W|9|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|K|8|@]|D|@]|E|$]]]|G|$]]

I had the same issue and I even tried to remove the project and add it again. What did the trick was to remove the <code>.settings</code> directory.

blocks|key|262533|text|我想我和你有同样的问题。我的web.xml是2.5版，而项目是(右击项目->属性->项目方面->)+Dynamic+Web+Module+2.3。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|262534|尽管我试图将版本从2.3改为2.5，但ECLIPSE不允许这样做。解决方案:我删除了动态Web模块标题下的复选标记，保存并更新了项目。自动重新唤醒是进入具有正确版本的框。我使用的是Eclipse+Kepler。|262535|附言:看看下面的comments+of+Jonathan，非常有用。|offset|length|262536|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/questions/18122336/cannot-change-version-of-project-facet-dynamic-web-module-to-3-0#comment35597136_21547854^0|0|0|8|K|0|0^^$0|@$1|2|3|4|5|6|7|P|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|Q|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|R|8|@]|9|@$F|S|G|T|1|U]]|A|$]]|$1|H|3|-4|5|6|7|V|8|@]|9|@]|A|$]]]|I|$J|$5|K|L|M|A|$N|O]]]]

I think I had the same problem as you. My web.xml had version 2.5 while the project had the (right-click on Project-> Properties-> Project Facets->) Dynamic Web Module 2.3.

Although I tried to change the version from 2.3 to 2.5 ECLIPSE did not permit it. 
Solution: I removed the check mark under the heading Dynamic Web Module, I saved and I had Update Project. Automatically re-awakening is entering the box with the correct version. I use Eclipse Kepler. 

p.s.: look at the <a href="https://stackoverflow.com/questions/18122336/cannot-change-version-of-project-facet-dynamic-web-module-to-3-0#comment35597136_21547854">comments of Jonathan</a> just below, very useful.

blocks|key|262613|text|web.xml技巧之所以有效，是因为您现在显式地告诉WTP您正在使用特定的servlet版本，而不管容器支持什么。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|262614|在我的例子中，我在Maven项目中使用注释配置，并且我没有web.xml文件。事实证明，在没有web.xml的情况下，WTP会查看您的Maven依赖项，以确定要使用的Servlet版本。在我的例子中，我定义了以下内容：|262615|<dependency>
++<groupId>javax</groupId>
++<artifactId>javaee-api</artifactId>
++<version>7.0</version>
++<scope>provided</scope>
</dependency>|code-block|syntax|javascript|262616|将其改为6.0解决了这个问题，现在使用Servlet3.0而不是JavaEE+7的默认版本3.1。因为我必须从Tomcat8升级到Tomcat7，Tomcat7只支持JavaEE+6Web+profile。现在，一切都运行得很好。|262617|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|N|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|O|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|P|8|@]|9|@]|A|$]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

The web.xml trick works because you're now explicitly telling WTP that you are using that specific servlet version, regardless of what the container supports. 

In my case, I am using the annotation config within a Maven project and I do not have a web.xml file. It turns out that in the absence of a web.xml, WTP looks at your Maven dependencies to determine what Servlet version to use. In my case, I had defined the following:

<pre><code>&lt;dependency&gt;
 &lt;groupId&gt;javax&lt;/groupId&gt;
 &lt;artifactId&gt;javaee-api&lt;/artifactId&gt;
 &lt;version&gt;7.0&lt;/version&gt;
 &lt;scope&gt;provided&lt;/scope&gt;
&lt;/dependency&gt;
</code></pre>

Changing it to 6.0 fixed the problem and it's now using Servlet 3.0 instead of 3.1, which is the default for JavaEE 7. Since I had to go from Tomcat 8 to Tomcat 7, Tomcat 7 only supports the JavaEE 6 Web profile. Now things work wonderfully.

blocks|key|262640|text|执行maven更新或重新导入项目没有任何帮助。@悉尼的答案是正确的；此外，我必须在JavaServer+Faces+2.2+requires+Dynamic+Web+Module+2.5+or+newer中所说的不同工作空间中重新创建项目|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|262641|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/questions/22361005/javaserver-faces-2-2-can-not-be-installed/22362617?noredirect=1#22362617^0|15|1P|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@$A|M|B|N|1|O]]|C|$]]|$1|D|3|-4|5|6|7|P|8|@]|9|@]|C|$]]]|E|$F|$5|G|H|I|C|$J|K]]]]

Doing maven update or reimporting the project did not help. @Sydney's answer is right; in addition I have to recreate the project in different workspace as said in <a href="https://stackoverflow.com/questions/22361005/javaserver-faces-2-2-can-not-be-installed/22362617?noredirect=1#22362617">JavaServer Faces 2.2 requires Dynamic Web Module 2.5 or newer</a>

blocks|key|46121|text|删除|type|unstyled|depth|inlineStyleRanges|entityRanges|data|46122|.settings+
.classpatch+
.projejct+
target|code-block|syntax|javascript|46123|并再次导入maven项目。|46124|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

Delete 

<pre><code>.settings 
.classpatch 
.projejct 
target
</code></pre>

and import again the maven project.

blocks|key|46199|text|我也遇到了同样的问题，仅在.settings文件夹中编辑web.xml和更改文件都无济于事。我的解决方案是通过编辑pom.xml直接指向maven编译器插件以使用所需的java版本：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|46200|++<build>
++++...
++++<plugins>
++++++<plugin>
++++++++<artifactId>maven-compiler-plugin</artifactId>
++++++++<version>3.1</version>
++++++++<configuration>
++++++++++<source>1.7</source>
++++++++++<target>1.7</target>
++++++++</configuration>
++++++</plugin>
++++</plugins>++++
++</build>+|code-block|syntax|javascript|46201|现在运行Maven->Update+project，然后您可以在属性->project+facets->Dynamic+Web+module+version中更改servlets版本，或者像前面编写的那样，通过手动编辑项目的.settings文件夹中的org.eclipse.wst.common.project.facet.core.xml。|46202|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

I had the same issue, editing web.xml as well as changing file in .settings folder alone didn't help. My solution was to directly point maven compiler plugin to use the desired java version by editing pom.xml:

<pre><code> &lt;build&gt;
 ...
 &lt;plugins&gt;
 &lt;plugin&gt;
 &lt;artifactId&gt;maven-compiler-plugin&lt;/artifactId&gt;
 &lt;version&gt;3.1&lt;/version&gt;
 &lt;configuration&gt;
 &lt;source&gt;1.7&lt;/source&gt;
 &lt;target&gt;1.7&lt;/target&gt;
 &lt;/configuration&gt;
 &lt;/plugin&gt;
 &lt;/plugins&gt; 
 &lt;/build&gt; 
</code></pre>

Now run Maven->Update project and after that you can change servlets version in properties->project facets->Dynamic Web module version or, as written earlier, by manually editing org.eclipse.wst.common.project.facet.core.xml in .settings folder of your project.

blocks|key|46237|text|打开org.eclipse.wst.common.project.facet.core.xml文件并将jst.web版本更改为3.0。还要将web.xml更新到3.0版。保存并更新项目。希望这能有所帮助。我正在使用Eclipse+Juno|type|unstyled|depth|inlineStyleRanges|entityRanges|data|46238|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

Open the org.eclipse.wst.common.project.facet.core.xml file and change the jst.web version to 3.0. Also update the web.xml to version 3.0. Save and update the project. Hope this helps. I am using Eclipse Juno

blocks|key|262827|text|这是pagurix答案的一个变体，但使用的是Eclipse+Mars。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|262828|将web.xml文件更改为web.bak|262829|忽略错误，我们下一步将重新生成它。|262830|进入项目属性->项目方面，并将Dynamic+Web+Module版本设置为您需要的版本。Eclipse现在允许您保存。|262831|现在右键单击该项目。选择Java工具->生成部署描述符存根。|262832|这将创建一个具有所需版本的新web.xml。|262833|打开新的web.xml并将XML头和完整的web应用程序开始标记复制到原始的web.bak中，删除新的web.xml并将web.bak重命名为web.xml。|262834|好了。|262835|entityMap^0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|R|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|S|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|T|8|@]|9|@]|A|$]]|$1|F|3|G|5|6|7|U|8|@]|9|@]|A|$]]|$1|H|3|I|5|6|7|V|8|@]|9|@]|A|$]]|$1|J|3|K|5|6|7|W|8|@]|9|@]|A|$]]|$1|L|3|M|5|6|7|X|8|@]|9|@]|A|$]]|$1|N|3|O|5|6|7|Y|8|@]|9|@]|A|$]]|$1|P|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]]|Q|$]]

This is a variation on pagurix's answer, but using Eclipse Mars. 

Change your web.xml file to web.bak 

Ignore the errors, we'll regenerate it next. 

Go into project properties -> project facets and set the Dynamic Web Module version to what you need. Eclipse now allows you to save. 

Now right-click on the project. Choose Java EE Tools -> Generate Deployment Descriptor Stub. 

This creates a new web.xml with the required version. 

Open the new web.xml and copy across the XML header and the complete web-app opening tag to your original web.bak, delete the new web.xml and rename web.bak back to web.xml.

Done.

blocks|key|262857|text|此版本问题右键单击项目->属性->项目方面->右键单击动态Web模块->取消锁定->取消选中->选择2.5版本->应用->更新maven|type|unstyled|depth|inlineStyleRanges|entityRanges|data|262858|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

This Problem With version right click on the project->properties->Project Facets->right click on Dynamic Web Module->unlock it-> uncheck->select 2.5 version->Apply->Update the maven

blocks|key|262915|text|我使用的是web.xml中的Web+Module+3.0，但在properties>Dynamic+Web+Module中使用的是3.1|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|262916|我将web.xml更改为：|262917|<?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"+xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"+xsi:schemaLocation="http://java.sun.com/xml/ns/javaee+http://java.sun.com/xml/ns/javaee/web-app_3_1.xsd"+id="WebApp_ID"+version="3.1">|code-block|syntax|javascript|262918|完成此更改后，执行以下操作：right+click+on+project>Maven>Update+Project...|262919|entityMap^0|5|7|E|E|V|T|1T|3|0|2|7|0|0|E|1A|0^^$0|@$1|2|3|4|5|6|7|Q|8|@$9|R|A|S|B|C]|$9|T|A|U|B|C]|$9|V|A|W|B|C]|$9|X|A|Y|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|Z|8|@$9|10|A|11|B|C]]|D|@]|E|$]]|$1|H|3|I|5|J|7|12|8|@]|D|@]|E|$K|L]]|$1|M|3|N|5|6|7|13|8|@$9|14|A|15|B|C]]|D|@]|E|$]]|$1|O|3|-4|5|6|7|16|8|@]|D|@]|E|$]]]|P|$]]

Mine was <code>Web Module 3.0</code> in <code>web.xml</code>, but in <code>properties&gt;Dynamic Web Module</code> It was on <code>3.1</code>

I changed the <code>web.xml</code> to this:

<pre><code>&lt;?xml version="1.0" encoding="UTF-8"?&gt;
&lt;web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_1.xsd" id="WebApp_ID" version="3.1"&gt;
</code></pre>

after this change, do: <code>right click on project&gt;Maven&gt;Update Project...</code>

blocks|key|46408|text|如果雪梨的回答仍然不起作用，那就试试下面的吧。按照雪梨的回答，转到Properties+>+Projects+Facets，取消选择Dynamic+Web+Module，然后更改版本以匹配您的web.config，然后再次选择。应用>保存，然后Maven更新。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|46409|web.xml|46410|<web-app+xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns="http://xmlns.jcp.org/xml/ns/javaee"
xmlns:web="http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"
xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee
http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"
id="Web_App_1"+version="3.1">

<display-name>JavaServerFaces</display-name>


<context-param>
++++<param-name>javax.faces.PROJECT_STAGE</param-name>
++++<param-value>Development</param-value>
</context-param>


<welcome-file-list>
++++<welcome-file>jsfs/hello.xhtml</welcome-file>
</welcome-file-list>


<servlet>
++++<servlet-name>Faces+Servlet</servlet-name>
++++<servlet-class>javax.faces.webapp.FacesServlet</servlet-class>
++++<load-on-startup>1</load-on-startup>
</servlet>


<servlet-mapping>
++++<servlet-name>Faces+Servlet</servlet-name>
++++<url-pattern>jsfs/*</url-pattern>
</servlet-mapping>
<servlet-mapping>
++++<servlet-name>Faces+Servlet</servlet-name>
++++<url-pattern>*.jsf</url-pattern>
</servlet-mapping>
<servlet-mapping>
++++<servlet-name>Faces+Servlet</servlet-name>
++++<url-pattern>*.faces</url-pattern>
</servlet-mapping>
<servlet-mapping>
++++<servlet-name>Faces+Servlet</servlet-name>
++++<url-pattern>*.xhtml</url-pattern>
</servlet-mapping>|code-block|syntax|javascript|46411|​|46412|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|N|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|O|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|P|8|@]|9|@]|A|$]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

If answer by Sydney still doesn't help then try below.
After following Sydney's answer, goto Properties > Projects Facets deselect Dynamic Web Module and then change the version to match your web.config and then select again. Apply > Save
Then Maven Update.

web.xml

<pre><code>&lt;web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns="http://xmlns.jcp.org/xml/ns/javaee"
xmlns:web="http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"
xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee
http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"
id="Web_App_1" version="3.1"&gt;

&lt;display-name&gt;JavaServerFaces&lt;/display-name&gt;

&lt;!-- Change to "Production" when you are ready to deploy --&gt;
&lt;context-param&gt;
 &lt;param-name&gt;javax.faces.PROJECT_STAGE&lt;/param-name&gt;
 &lt;param-value&gt;Development&lt;/param-value&gt;
&lt;/context-param&gt;

&lt;!-- Welcome page --&gt;
&lt;welcome-file-list&gt;
 &lt;welcome-file&gt;jsfs/hello.xhtml&lt;/welcome-file&gt;
&lt;/welcome-file-list&gt;

&lt;!-- JSF mapping --&gt;
&lt;servlet&gt;
 &lt;servlet-name&gt;Faces Servlet&lt;/servlet-name&gt;
 &lt;servlet-class&gt;javax.faces.webapp.FacesServlet&lt;/servlet-class&gt;
 &lt;load-on-startup&gt;1&lt;/load-on-startup&gt;
&lt;/servlet&gt;

&lt;!-- Map these files with JSF --&gt;
&lt;servlet-mapping&gt;
 &lt;servlet-name&gt;Faces Servlet&lt;/servlet-name&gt;
 &lt;url-pattern&gt;jsfs/*&lt;/url-pattern&gt;
&lt;/servlet-mapping&gt;
&lt;servlet-mapping&gt;
 &lt;servlet-name&gt;Faces Servlet&lt;/servlet-name&gt;
 &lt;url-pattern&gt;*.jsf&lt;/url-pattern&gt;
&lt;/servlet-mapping&gt;
&lt;servlet-mapping&gt;
 &lt;servlet-name&gt;Faces Servlet&lt;/servlet-name&gt;
 &lt;url-pattern&gt;*.faces&lt;/url-pattern&gt;
&lt;/servlet-mapping&gt;
&lt;servlet-mapping&gt;
 &lt;servlet-name&gt;Faces Servlet&lt;/servlet-name&gt;
 &lt;url-pattern&gt;*.xhtml&lt;/url-pattern&gt;
&lt;/servlet-mapping&gt;
</code></pre>

blocks|key|46454|text|我也遇到了同样的问题，删除.settings文件夹解决了这个问题|type|unstyled|depth|inlineStyleRanges|entityRanges|data|46455|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

I had the same issue ,deleting the .settings folder resolved the issue

blocks|key|263033|text|对于maven+eclipse+web项目，更改动态web模块版本需要检查三个地方。如果使用eclipse，并且在您检查了以下各项之后:+1)+web.xml|type|unstyled|depth|inlineStyleRanges|entityRanges|data|263034|<web-app+xmlns="http://java.sun.com/xml/ns/javaee"
+++++++++xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+++++++++xsi:schemaLocation="http://java.sun.com/xml/ns/javaee+
++++++++++http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
++++version="3.0">|code-block|syntax|javascript|263035|2)+maven：|263036|<dependency>
++++++<groupId>javax.servlet</groupId>
++++++<artifactId>javax.servlet-api</artifactId>
++++++<version>3.0.1</version>
++++++<scope>provided</scope>+++##+ensure+you+have+tomcat+7+not+other+version
</dependency>

<plugin>
++++++<groupId>org.apache.maven.plugins</groupId>
++++++<artifactId>maven-compiler-plugin</artifactId>
++++++<version>3.0</version>
++++++<configuration>
++++++++++++<source>1.7</source>+##+at+least+6
++++++++++++<target>1.7</target>
++++++</configuration>
</plugin>|263037|3)+eclipse构建路径，编译器版本为1.7|263038|在maven中，你仍然有一个错误标记：|263039|cannot+change+version+of+project+facet+dynamic+web+module+to+3.0+one+or+more+constrants+have+not+been+satisfied|263040|然后，您可以:取消选中动态web模块，然后重新选中它。我想是因为eclipse文件的.settings被破坏了。关于第二个技巧，tomcat+which+version是一个很好的说明。|offset|length|263041|entityMap|0|LINK|mutability|MUTABLE|url|http://tomcat.apache.org/whichversion.html^0|0|0|0|0|0|0|0|1S|K|0|0^^$0|@$1|2|3|4|5|6|7|12|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|13|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|14|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|15|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|16|8|@]|9|@]|A|$]]|$1|M|3|N|5|6|7|17|8|@]|9|@]|A|$]]|$1|O|3|P|5|D|7|18|8|@]|9|@]|A|$E|F]]|$1|Q|3|R|5|6|7|19|8|@]|9|@$S|1A|T|1B|1|1C]]|A|$]]|$1|U|3|-4|5|6|7|1D|8|@]|9|@]|A|$]]]|V|$W|$5|X|Y|Z|A|$10|11]]]]

For a maven eclipse web project, changing dynamic web module version needs to check three places. If one uses eclipse, and after you have checked the following:
1) web.xml 

<pre><code>&lt;web-app xmlns="http://java.sun.com/xml/ns/javaee"
 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 xsi:schemaLocation="http://java.sun.com/xml/ns/javaee 
 http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
 version="3.0"&gt;
</code></pre>

2) maven: 

<pre><code>&lt;dependency&gt;
 &lt;groupId&gt;javax.servlet&lt;/groupId&gt;
 &lt;artifactId&gt;javax.servlet-api&lt;/artifactId&gt;
 &lt;version&gt;3.0.1&lt;/version&gt;
 &lt;scope&gt;provided&lt;/scope&gt; ## ensure you have tomcat 7 not other version
&lt;/dependency&gt;

&lt;plugin&gt;
 &lt;groupId&gt;org.apache.maven.plugins&lt;/groupId&gt;
 &lt;artifactId&gt;maven-compiler-plugin&lt;/artifactId&gt;
 &lt;version&gt;3.0&lt;/version&gt;
 &lt;configuration&gt;
 &lt;source&gt;1.7&lt;/source&gt; ## at least 6
 &lt;target&gt;1.7&lt;/target&gt;
 &lt;/configuration&gt;
&lt;/plugin&gt;
</code></pre>

3) eclipse build path and compiler version is 1.7

you still have an error marker at maven:

<pre><code>cannot change version of project facet dynamic web module to 3.0 one or more constrants have not been satisfied
</code></pre>

Then you can:
uncheck the dynamic web module, and recheck it.
I think it is because .settings of eclipse file is corrupted somehow. About the second tip <a href="http://tomcat.apache.org/whichversion.html" rel="nofollow">tomcat which version</a> is a good note.

blocks|key|46609|text|我也遇到了同样的问题--我只是从我的工作区中删除了这个项目，然后清理了"eclipse文件/文件夹，例如：.project、.settings等)，然后再次导入了maven项目，它工作了。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|46610|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

I had the same problem - I just removed the project from my workspace, then cleaned up the "eclipse files/folders, for example: .project, .settings, etc) then imported the maven project again, it worked.

I am using maven to create a dynamic webapp in Eclipse. I added some folders like <code>src/test/java</code> and <code>src/test/resources</code>. Also I changed the library in Java Build Path to obtain the JavaSE-1.7. It's all OK up to here.

When I tried to change the Projects Facet Dynamic Web Module something went wrong. I had change the Java to 1.7 in the same place. And it still told me, cannot change version of project facet Dynamic Web Module to 3.0.

I have changed everything that would effect the changing I think.

Cannot change version of project facet Dynamic Web Module to 3.0?

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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