views:

1332

answers:

6

I'm trying to build a Servlet that calls a JSP page similar to the following:

public void doGet(HttpServletRequest req, HttpServletResponse resp)
  throws IOException, ServletException {
 req.getRequestDispatcher("/WEB-INF/main.jsp").forward(req, resp);
}

I need this Servlet to respond to the domain's root (eg: http://example.com/) so I'm using the following mapping in the web.xml:

<servlet-mapping>
 <servlet-name>MainServlet</servlet-name>
 <url-pattern>/*</url-pattern>
</servlet-mapping>

The problem I'm having is that this matches EVERYTHING, so when the dispatcher forwards to "/WEB-INF/main.jsp" this matches the url-pattern so the Servlet gets run again. This results in a loop that runs until it dies with a java.lang.StackOverflowError.

How can I match the root without preventing other scripts from being runnable?

+2  A: 

You can create a welcome file named index.jsp in the root with the following code using JSTL or otherwise.

<c:redirect url="/main"/>

So in the web.xml file you will have this:

<welcome-file-list>
    <welcome-file>index.jsp</welcome-file>        
</welcome-file-list>

So anyone requesting the root will be redirected to /main. Now your servlet can be mapped to main.

<servlet-mapping>
    <servlet-name>MainServlet</servlet-name>
    <url-pattern>/main</url-pattern>
</servlet-mapping>
Vincent Ramdhanie
Ok, I get that this would work, but it fells like such a hack. Is it really not possible to have a servlet handle the root on its own?
fiXedd
A: 

You can't redirect to WEB-INF. A servlet container will never serve requests for documents in that folder.

If you want your application (not just a servlet, but the entire application) to be available under the root context ("/" of "http://www.domainname.com/"), then you need to set up a context entry for it - not a servlet mapping.

With Tomcat, you add a new <Context> mapping (in one of about 3 different possible places).

matt b
I'm not doing a redirect, I'm doing a forward. That's internal, so it souldn't matter if they're publicaly visible, right? Either way, moving them out of the WEB-INF didn't help.I'm not using Tomcat, but I'll look in to context mapping, thanks.
fiXedd
The container will serve resources under WEB-INFs when the request is being forwarded. It's a valid, and useful site structure paradigm.
atc
@fiXedd you are correct, I misunderstood
matt b
A: 

Have you tried the below? (Note the missing *, which is a wild card and is the reason that your configuration catches everything.)

<servlet-mapping>
        <servlet-name>MainServlet</servlet-name>
        <url-pattern>/index.jsp</url-pattern>
</servlet-mapping>

(Edited as per comments from just /.)

Stu Thompson
I did... it had the exact same result. I should have mentioned I'm doing this on App Engine. I'm starting to think they're mapping is, uh, wonky.
fiXedd
OK, try index.jsp then?
Stu Thompson
+1  A: 

Try just to remove '*' from the pattern, i.e.

<url-pattern>/</url-pattern>
Gennady Shumakher
@fiXedd has apparently tried that and it doesn't work. (See my answer's edit history.) Maybe something to do with running on App Engine...
Stu Thompson
A: 

A solution is mentioned in another thread http://stackoverflow.com/questions/491773/url-pattern-for-servlet-mapping-in-web-xml using URLrewrite -> http://tuckey.org/urlrewrite/

Taveren
+1  A: 

The original question doesn't mention that they're trying to map a root servlet on App Engine - it's easy on Tomcat (and other servlet containers as far as I know) but App Engine isn't a normal servlet container.

My normal way of building a web application with servlets is to extend HttpServlet, add a "page" object with title, content, errors, messages etc. and for output forward to a JSP template. This has been an absolute nightmare getting working in App Engine.

  • JSP files can't be "named" without a "/" at the beginning.
  • JSP files can't be in a subdirectory
  • Servlets can't be mapped to the root of your application with a "/" url-pattern

Here's my web.xml (edited for brevity) which finally worked.

<web-app>
  <servlet>
    <!-- this servlet needs to redirect to a NamedDispatcher
         called "template" -->
    <servlet-name>Home</servlet-name>
    <servlet-class>my.domain.HomeSv</servlet-class>
  </servlet>
  <servlet>
    <!-- jsp file must apparently be in root directory and have "/" at
         start of path -->
    <servlet-name>template</servlet-name>
    <jsp-file>/template.jsp</jsp-file>
  </servlet>
  <servlet-mapping>
    <!-- map your home servlet to somewhere other than "/" -->
    <servlet-name>Home</servlet-name>
    <url-pattern>/home</url-pattern>
  </servlet-mapping>
  <welcome-file-list>
    <!-- make your Home servlet the welcome file -->
    <welcome-file>home</welcome-file>
  </welcome-file-list>
</web-app>

I haven't been particularly scientific about validating all this - but it seems to work for me now and I'm pretty happy about that.

Sam Lowry