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From Eclipsepedia

Introduction

Jetty 9 Content Available on the Documentation Hub
Direct Link: http://www.eclipse.org/jetty/documentation/current/troubleshooting-locked-files-on-windows.html

Jetty buffers static content for webapps such as HTML files, CSS files, images, etc. If you are using NIO connectors, Jetty uses memory-mapped files to do this. The problem is that on Windows, memory mapping a file causes the file to lock, so that you cannot update or replace the file. Effectively this means that you have to stop Jetty to update a file.

Remedy

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 in the lib/jetty.jar at org/eclipse/jetty/webapp/webdefault.xml. Extract it to a convenient disk location and edit it to change useFileMappedBuffer to false.

<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.xml.

<Call name="addLifeCycle">
       <Arg>
         <New class="org.mortbay.jetty.deployer.WebAppDeployer">
           <Set name="contexts"><Ref id="Contexts"/></Set>
           <Set name="webAppDir"><SystemProperty name="jetty.home" default="."/>/webapps</Set>
           <Set name="parentLoaderPriority">false</Set>
           <Set name="extract">true</Set><
           <Set name="allowDuplicates">false</Set>
           <Set name="defaultsDescriptor">/home/fred/jetty/mywebdefaults.xml</Set> <!-- set to your customized defaults file -->
         </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.mortbay.jetty.webapp.WebAppContext">
   <Set name="contextPath">/</Set>
   <Set name="war">./webapps/fredapp</Set>
   <Set name="defaultsDescriptor">/home/fred/jetty/mywebdefaults.xml</Set>
   .
   .
  </New>

Alternate Remedy

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.mortbay.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.mortbay.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.

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