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From "Shapira, Yoav" <>
Subject RE: Issue getting Context inside a servlet
Date Wed, 13 Oct 2004 13:43:27 GMT

Why are you even going down this route?  Any solution you end up with
will be tied to Tomcat and not portable at all.  There's also no
guarantee we'll keep these internal APIs consistent or available to your
webapp in future Tomcat versions.

If you do want to keep going down this path, you probably need to mark
your context as privileged, like the manager webapp does (see its
context.xml file for an example).

The hack to get the DocBase getServletContext().getRealPath("/").  That
works for unpacked WARs but not packed WARs, where getRealPath(anything)
returns null.  If you need the "docBase" simply as a URL, you can always
do getServletContext().getResource("/") which will work in packed and
unpacked webapp deployments.

If you elaborate a bit on why you need the docbase, we might be able to
come up with better alternative approaches for you.

Don't make your solution container-specific unless you really have to.
Stick to the letter and the spirit of the Servlet Spec, and you'll end
up with a portable webapp.

Yoav Shapira

>-----Original Message-----
>From: Robin Curts []
>Sent: Wednesday, October 13, 2004 9:26 AM
>Subject: Issue getting Context inside a servlet
>What I am trying to accomplish:
>I'm trying to build a servlet that I can get the DocBase with, so I'm
>trying to locate org.apache.catalina.Context from the servlet.
>Tomcat Version: 5.0.28
>Java Version: 1.4.2_05
>What I'm doing:
>I am implementing ContainerServlet and this works great when I run the
>servlet through a web application defined in
>$catalina.home/servers/webapps/<my_webapp>.  Pretty much in the same
>place as the manager servlet.  However when I run it as an installed
>file I am getting a nasty null pointer exception (running from
>The issue:
>setWrapper() is never getting called when I have this inside the
>$catalina.home/webapps/ directory tree... only when I have it in
>$catalina.home/server/ directory tree.  Any thoughts on this?  When
>webapp goes live it will be installed as a WAR file and I won't be able
>to control what directory it is in.  Any thoughts?
>Here is my servlet, pretty basic, just trying to find the Context and
>import org.apache.catalina.*;
>import javax.servlet.http.*;
>import javax.servlet.*;
>import java.util.*;
>public class Ctx extends HttpServlet implements ContainerServlet {
>    Context context;
>    Deployer deployer;
>    Wrapper wrapper;
>    public Ctx() {
>        context = null;
>        deployer = null;
>        wrapper = null;
>    }
>    public Wrapper getWrapper() {
>        return wrapper;
>    }
>    public void setWrapper(Wrapper wrapper) {
>        this.wrapper = wrapper;
>        try {
>            context = (Context)wrapper.getParent();
>            deployer = (Deployer)context.getParent();
>        } catch (NullPointerException e) {
>            context = null;
>            deployer = null;
>        }
>    }
>    public void destroy() {
>        // do nothing
>    }
>    public void init() {
>        // do nothing
>    }
>    public void doPost(HttpServletRequest request, HttpServletResponse
>    throws IOException, ServletException {
>        doGet(request, response);
>    }
>    public void doGet(HttpServletRequest request, HttpServletResponse
>    throws IOException, ServletException {
>        PrintWriter out = response.getWriter();
>        response.setContentType("text/plain");
>        out.println("My Context Object: " + context);
>        out.println("Doc Base: " + context.getDocBase());
>        out.flush();
>        out.close();
>    }
>//-- SERVLET END --
> * Robin Curts
> *
> *
> * (813) 786-8634
> */
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