Can I do CGI with Jetty?

Yes!

The Jetty distribution includes a CGI servlet org.mortbay.servlet.CGI. You configure it in your xml configuration file along these lines:

  <Call name="addContext">
    <Arg>/cgi-bin/*</Arg>
    <Set name="ResourceBase">/home/jules/www/cgi-bin</Set>
    <Set name="ServingDynamicServlets">TRUE</Set>
    <Call name="addServlet">
      <Arg>Common Gateway Interface</Arg>
      <Arg>/</Arg>
      <Arg>com.mortbay.Servlet.CGI</Arg>
     <Put name="Path">/usr/local/bin:/usr/ucb:/bin:/usr/bin</Put>
    </Call>
  </Call>

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