Is this possible??? servlet to servlet?

Question

Is it possible for one servlet to make some sort of call to another servlet and recieve information back without losing "control"? For example, you start Servlet A and you send it a username and password. Servlet A then calls Servlet B, and sends Servlet B the same username and password. Servlet A should then receive some information back from Servlet B and then Servlet A continues processing. (please don't get stuck as to why I don't send servlet B the username and password and do everything in one servlet.)
Is this situation possible? If it is can someone point me in a direction on how to do this? Preferably with some example code if it's available.
I'd really appreciate some help on this.
Thanks,
James

Answer 1

I actually had to solve this problem. There are other servlets running within the same container/process as my own who's code I didn't have access to. My first attempt was to call the other servlet(s) via the URLConnection class, however, this option presents some complications when https is employed. It does so especially when using an unsigned certificate for testing. Below is the code I used to call a servlet within the same container process and a servlet to serve as an example of how to use it.
***** ServletCaller.java ***********
import java.lang.reflect.Method;
import javax.servlet.http.*;
import javax.servlet.*;
public class ServletCaller
     public static void callServlet( String servletName,                     ServletConfig config, HttpServletRequest req,                     HttpServletResponse resp ) throws Exception
          Class [] doGetArgTypes =                                    {HttpServletRequest.class,
               HttpServletResponse.class};
          Class [] initArgType = {ServletConfig.class};
          Object [] doGetArgs = {req,resp};
          Object [] initArg = {config};
          Class clz = Class.forName(servletName);
          Object servlet = clz.newInstance();
          Method initMethod = clz.getMethod("init",initArgType);
          Method doGetMethod = clz.getMethod                              ("doGet",doGetArgTypes);
          initMethod.invoke(servlet,initArg);
          doGetMethod.invoke(servlet,doGetArgs);
******* TestServlet.java ***********
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import CustomRequest; // Extends HttpServletRequest
import CustomResponse; // Extends HttpServletResponse
import ServletCaller;
public class TestServlet extends HttpServlet
     protected void doGet(HttpServletRequest req,                          HttpServletResponse resp)
          throws ServletException, IOException
     {try{
          CustomRequest r = new CustomRequest(req);
          CustomResponse rp = new CustomResponse();
          r.setQueryString("ARG1=VALUE1&ARG2=VALUE2&"
               +"ARG3=&ARG4=VALUE4");
          ServletCaller.callServlet("SnoopServlet",
               this.getServletConfig(),r,rp);
          // Get response from CustomResponse object
          String s = rp.getOutput();
          resp.setContentType("text/html");
          resp.getOutputStream().println(s);
     }catch(Exception e){throw new IOException(e.getMessage());}
The CustomRequest and CustomResponse class definitions are HUGE, but were relatively easy to build. If you're having trouble building them I can post them too.
Hope this helps.
--Kurt