whilst fooling around with SessionId and cookies...

I often use a little java program to (re)familiarize myself with header and session data. Whilst playing around I noticed that when I hit a page for the first time with

it retrieves and displays the session ID whereas the following methods return nulls the first time around

Only on refreshing or "hitting the page again" do they get "synchronized", of that's the right word.
(Q1) Are these the same thing: sessionId, JESSSIONID, cookies ? They display the same values.
(Q2) What is the method "request.getSession(true)" used for ? The arbitrarily assigned hex-value surely cannot identify the session uniquely ?
Here is the code, you need only modify the package, starting from your docbase.

/** Properties
 * Returns any parameters and lists server properties...
 */
package path.to.class_dir;
import javax.servlet.*;
import javax.servlet.http.*;
import java.io.IOException;
import java.io.PrintWriter;
public class properties extends HttpServlet {
  public final String COUNTER_KEY = "properties.count";
  public void doGet( HttpServletRequest req,  HttpServletResponse resp)
    throws ServletException, IOException
  {
    // Get an output stream that takes into account the proper character encoding ...
    PrintWriter out = resp.getWriter();
    resp.setContentType("text/html");
    // count the number of times the session is invoked
    HttpSession session = req.getSession(true);
    int count = 1;
    Integer ii = (Integer) session.getAttribute(COUNTER_KEY);
    if (ii != null) // ie if a previous session exists
    { count = ii.intValue() + 1;
    }
    session.setAttribute(COUNTER_KEY, new Integer(count));
    // Print the HTML header to the output stream ...
    out.println("<html>");
    out.println("<head>");
    out.println("<title>Needful Things About Server Properties and Request Headers</title>");
    out.println("</head>");
    out.println("<h2><center>");
    out.println("About This Server and Session</center></h2><br>");
    out.println("<center>All session data maintained at the servlet container level ie. by Tomcat.</center><br>");
    //
    out.println("<center>Your session ID is <b>"+ session.getId() +"</b>");
    out.println(" and you have hit this page <b>"+ count+ "</b> time(s) during this browser session.</center><br>" );
    out.println("<FORM ACTION=\"" +req.getRequestURI() +"\" METHOD=GET>");
        out.println("<CENTER>");
        out.println("<INPUT TYPE=submit VALUE=\"Hit page again\">");
        out.println("</CENTER></FONT>");
    out.println("</FORM>");
 
    // Create a table with info about the client ...
    out.println("<table border=1 width=90% align=center>" +
        "<TR BGCOLOR=\"#FFAD00\">\n"); 
    out.println("<tr><td>Method</td>");
    out.println("    <td>" + req.getMethod() + "</td></tr>");
    // next row ...
    out.println("<tr><td>User</td>");
    out.println("    <td>"+ req.getRemoteUser() +"</td></tr>");
    // next row ...
    out.println("<tr><td>Client</td>");
    out.println("    <td>"+ req.getRemoteHost() +"</td></tr>");
    // next row ...
    out.println("<tr><td>Context</td>");
    out.println("    <td>"+ req.getContextPath() +"</td></tr>");
    // next row...
    out.println("<tr><td>Request URI</td>");
    out.println("    <td>"+ req.getRequestURI() +"</td></tr>");
    // next row...
    out.println("<tr><td>Path Info</td>");
    out.println("    <td>"+ req.getPathInfo() +"</td><tr>");
    // next row...
    out.println("<tr><td>Protocol</td>");
    out.println("    <td>"+ req.getProtocol() +"</td></tr>");
    // next row...
    out.println("<tr><td>This Session</td>");
    out.println("    <td>"+ req.getSession(true) +"</td><tr>");
    // next row...
    out.println("<tr><td>SessionID</td>");
    out.println("    <td>"+ req.getRequestedSessionId() +"</td></tr>");
   
    // list of cookies
    out.println("<tr><td>Cookies</td>");
    Cookie[] cookieArray = req.getKookies();
    out.println("<TD><UL>");
    if (cookieArray!= null)
    { for (int i=cookieArray.length-1; i>=0; i--)
      { Cookie cookie = cookieArray[i];
        out.println("<LI>"+ cookie.getName()+ ": "+ cookie.getValue());
      }//end of for
    } else out.println("<LI> no cookies.");
    out.println("</UL></TD></TR>");
    // Get and dump all the request parameters in the URL
    // ...these comes after the ? in the URL e.g.
    // <a href="http://localhost:8080/examples/properties?a=hell&b=bloody" target="_blank" rel="nofollow">http://localhost:8080/examples/properties?a=hell&b=bloody</a>
    java.util.Enumeration enum = req.getParameterNames();
    while (enum.hasMoreElements()) {
      String name = (String) enum.nextElement();
      out.println("<tr>");
      out.println("<td>Parameter '"+ name + "'</td>");
      out.println("<td>" + req.getParameter(name) + "</td>");
      out.println("</tr>");
    }
    out.println("</table><br><hr>");
    //
    // Create a table with information about the server
    out.println("<h2><center>About Header Properties</center></h2><br>");
    out.println("<table border=1 width=90% align=center>" +
        "<TR BGCOLOR=\"#FDF5E6\">\n" +
        "<TH>Header Name<TH>Header Value");
    //java.util.Properties props = System.getProperties();
    java.util.Enumeration props = req.getHeaderNames();
    //
    while (props.hasMoreElements()) {
      String name2 = (String) props.nextElement();
      out.println("<tr><td>"+ name2 + "</td>");
      out.println("    <td>"+ req.getHeader(name2)+ "</td>");
      out.println("</tr>");
    }
    out.println("</table></BODY></center></html>"); 
    out.flush();
  }
  public void doPost(HttpServletRequest request,
                     HttpServletResponse response)
    throws ServletException, IOException
  { doGet(request, response);
  }//end of method doPost()
  public void init() throws ServletException {
    // initialie the servlet here. Use ServletConfig object to get
    //    initialization parameters...
    ServletConfig config = getServletConfig();
  }
  public void destroy() {
    // Clean up here
  }
}

One day, I too will be a java programmer, just not today!

I'm moving this to Servlets.