From JRubyWiki
<!DOCTYPE web-app PUBLIC "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"
"http://java.sun.com/dtd/web-app_2_3.dtd">
<web-app>
<context-param>
<param-name>jruby.standalone</param-name>
<param-value>true</param-value>
</context-param>
<context-param>
<param-name>rails.root</param-name>
<param-value>/WEB-INF/rails/</param-value>
</context-param>
<context-param>
<param-name>files.prefix</param-name>
<param-value>/WEB-INF/rails/public</param-value>
</context-param>
<context-param>
<param-name>rails.env</param-name>
<param-value>development</param-value>
</context-param>
<context-param>
<param-name>files.default</param-name>
<param-value>rails</param-value>
<description>The files servlet should forward to the rails servlet if no file could be found</description>
</context-param>
<listener>
<listener-class>org.jruby.webapp.RailsContextListener</listener-class>
</listener>
<servlet>
<servlet-name>rails</servlet-name>
<servlet-class>org.jruby.webapp.RailsServlet</servlet-class>
</servlet>
<servlet>
<servlet-name>files</servlet-name>
<servlet-class>org.jruby.webapp.FileServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>files</servlet-name>
<url-pattern>/</url-pattern>
</servlet-mapping>
</web-app>