running maven jetty causes Duplicate fragment name error

Sometimes you get the following error from jetty when running demosite.

[artifact:mvn] java.lang.IllegalStateException: Duplicate fragment name: spring_web for jar:file 

[artifact:mvn]  at org.eclipse.jetty.webapp.MetaData.addFragment(MetaData.java:253)

Solution is to add to your pom.xml:                   

 <webAppConfig> 

<allowDuplicateFragmentNames>true</allowDuplicateFragmentNames>

 </webAppConfig> 

like so inside your jetty plugin configuration.

<plugin>
    <groupId>org.mortbay.jetty</groupId>
    <artifactId>jetty-maven-plugin</artifactId>
    <configuration>
      ...
      <webAppConfig>
        ...
        <allowDuplicateFragmentNames>true</allowDuplicateFragmentNames>
        ...
      </webAppConfig>
      ...
    </configuration>
  </plugin>