I know this is age, but I have not found the answer anywhere on the Internet, and it seems that it has become easier. Hope this helps someone:
webdefault.xml jetty-version.jar, : C:\Documents and
\JB.m2\\org\mortbay\jetty\jetty\6.1.22\jetty-6.1.22.jar org/mortbay/jetty/webapp/webdefault.xml
webdefault.xml
webdefault.xml :
<servlet id="jsp">
....
<init-param>
<param-name>keepgenerated</param-name>
<param-value>true</param-value>
</init-param>
maven pom.xml:
<plugin>
<groupId>org.mortbay.jetty</groupId>
<artifactId>maven-jetty-plugin</artifactId>
<configuration>
<webDefaultXml>webdefault.xml</webDefaultXml>
</configuration>
</plugin>
mvn jetty:run maven, jsp target\work\jsp\org\apache\jsp\WEB_002dINF\jsp