Jetty provides a configuration switch in the webdefault.xml file for the DefaultServlet that enables or disables the use of memory-mapped files. If you are running on Windows and are having file-locking problems, you should set this switch to disable memory-mapped file buffers.

The default webdefault.xml file is found in the jetty distribution under the etc/ directory or in the jetty-webapp-9.0.2-SNAPSHOT.jar artifact at org/eclipse/jetty/webapp/webdefault.xml. Edit the file in the distribution or extract it to a convenient disk location and edit it to change useFileMappedBuffer to false. The easiest option is to simply edit the default file contained in the jetty distribution itself.

<init-param>
   <param-name>useFileMappedBuffer</param-name>
   <param-value>true</param-value> <!-- change to false -->
 </init-param>
 
    

Make sure to apply your custom webdefault.xml file to all of your webapps. You can do that by changing the configuration of the Deployment Manager in etc/jetty-deploy.xml.

<Call id="webappprovider" name="addAppProvider">
  <Arg>
    <New class="org.eclipse.jetty.deploy.providers.WebAppProvider">
      .
      .
      <!-- this should be the new custom webdefault.xml or change should be made in this file -->
      <Set name="defaultsDescriptor"><Property name="jetty.home" default="." />/etc/webdefault.xml</Set>
      <Set name="scanInterval">1</Set>
      <Set name="extractWars">true</Set>
      .
      .
    </New>
  </Arg>
</Call>

    

Alternatively, if you have individually configured your webapps with context xml files, you need to call the WebAppContext.setDefaultsDescriptor(String path) method:

<New id="myWebAppContext"  class="org.eclipse.jetty.webapp.WebAppContext">
  <Set name="contextPath">/</Set>
  <Set name="war">./webapps/fredapp</Set>
  <Set name="defaultsDescriptor">/home/fred/jetty/mywebdefaults.xml</Set>
  .
  .
</New>

    

You can force a WebAppContext to always copy a web app directory on deployment to avoid the file locking issue. Configure this in a context deployment file as follows:

<New id="myWebAppContext"  class="org.eclipse.jetty.webapp.WebAppContext">
  <Set name="contextPath">/</Set>
  <Set name="war">./webapps/fredapp</Set>
  <Set name="copyWebDir">true</Set>
  .
  .
</New>

    

You can also configure the default Jetty Servlet directly in the web.xml. For example:

<web-app ...>
 ...
 <servlet>
     <servlet-name>Default</servlet-name>
     <servlet-class>org.eclipse.jetty.servlet.DefaultServlet</servlet-class>
     <init-param>
       <param-name>useFileMappedBuffer</param-name>
       <param-value>false</param-value>
     </init-param>
     <load-on-startup>0</load-on-startup>
   </servlet>
 ...
 </web-app>
 
    

This might completely redefine the default servlet configuration (not sure about that, if anyone can confirm). You could still simply extract the webdefault file as explained above, and copy-paste the complete default servlet definition in your web.xml, changing that useFileMappedBuffer parameter to false.