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jsp:forward ?

Posted on 2006-06-21
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Last Modified: 2010-04-01
Hi,
I'm new to JSP
I code a simple game in JSP,
where the user has to guess a number between 0 and 9

if he wins, he gets a congrats message, if he looses, another message is displayed.
If he wins OR loses, the statistics (number games played, ...) are displayed. So I have this code :

if user wins
   display "congrats" message
   display stats
else
   display "u lose" message
   display stats

I read in a book that I need , after displaying the messages, use
<jsp:forward page = stats.jsp"/>
to display the statistics because it is common code and better for refactoring.
(its just an educational example)
So I tried to use the forward:jsp action but I lose the messages 'congrats' and 'u lose'

<html>
  <head>
    <title>Jeu de devinette</title>
  </head>
  <body>
    <h3>Jeu de devinette</h3>
    <hr/>

<%// récupération de la partie en cours, au besoin création et rangement d'une nouvelle partie

  jeu.JeuDeDevinette jeu
              = (jeu.JeuDeDevinette)session.getAttribute("jeu");
  if (jeu == null) {
      jeu = new jeu.JeuDeDevinette();
      session.setAttribute("jeu", jeu);
  }

   String essai = request.getParameter("essai");
   out.print("ESSAIIII "+essai+"<br/>");
  // si l'utilisateur arrive pour la premiere fois sur la page, il n'a pas encore fourni de valeur
  if (essai != null) {
      jeu.setEssai(essai);
  }

  if (jeu.isGagne()) {
      out.println("Bravo, vous avez gagn&eacute;<br/>");
      out.println("<a href='jeu.jsp'>Rejouer</a>");
      // si l'utilisateur revient sur la page, il doit commencer automatiquement une nouvelle partie
      session.removeAttribute("jeu");
  %>
  <jsp:forward page="stat.jsp"/>
  <%
  }
  else if (jeu.getNombreDEssaisRestant() == 0) {
            out.println("D&eacute;sol&eacute;, vous avez perdu<br/>");
        out.print("Il fallait trouver ");
        out.println(jeu.getValeur());
        out.println("<br/><a href='jeu.jsp'>Rejouer</a>");
        // si l'utilisateur revient sur la page, il doit commencer automatiquement une nouvelle partie
        session.removeAttribute("jeu");
  }
  else {  // partie en cours, on n'a pas gagné ni perdu
      out.print("Il vous reste ");
      out.print(jeu.getNombreDEssaisRestant());
      out.println(" essai(s)<br/>");
      out.println("<form>");
      out.println("  essai : <input type='text' name='essai'/><br/>");
      out.println("  <input type='submit' value='Essayer'/>");
      out.println("</form>");

      // on triche en affichant la valeur à  trouver, pour faciliter les tests
      out.println(jeu.getValeur());
  }
%>

</body>
</html>

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Question by:matthew016
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10 Comments
 
LVL 23

Accepted Solution

by:
Siva Prasanna Kumar earned 1000 total points
ID: 16953210
if you want to show both Message as well as stats use <jsp:include page="stat.jsp"/> instead of
<jsp:forward page="stat.jsp"/>

Thank You.

0
 
LVL 3

Assisted Solution

by:runa_paathak
runa_paathak earned 600 total points
ID: 16957308
Else if you want to use <jsp:forward page = stats.jsp"/>, add the message string into request (request.setAttribute("msg"), msg) and then do <jsp:forward page = stats.jsp"/>. Display the message itself on stats.jsp by doing out.println(request.getAttribute("msg"))

Hope this helps.
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Author Comment

by:matthew016
ID: 16962381
Thank u,
What is the real use of jsp:forward then ?
Thx
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LVL 4

Assisted Solution

by:evnafets
evnafets earned 400 total points
ID: 16964216
You use a jsp:forward, when you want to cancel the current page and display a different one.
A jsp:include, includes the RESULT of invoking the url specified into the current page, at the current point.

0
 
LVL 23

Expert Comment

by:Siva Prasanna Kumar
ID: 16965750
Actuattly jsp:forward is very useful when you want to navigate from one JSP to another.
and when you say include it jsp:includes the secified JSP to the current JSP at runtime.

check out for better details

http://java.sun.com/products/jsp/tags/11/syntaxref11.fm9.html 
0
 
LVL 9

Author Comment

by:matthew016
ID: 16968614
isn't this already possible with html to navigate trough pages ?
why use jsp:forward and not an html request
0
 
LVL 23

Expert Comment

by:Siva Prasanna Kumar
ID: 16969579
what if you want to pass some active stuff between the pages??? and how will you maintain the sessions??? Lot many other reasons are there.
0
 
LVL 9

Author Comment

by:matthew016
ID: 16969645
Thank you :-)
0
 
LVL 4

Expert Comment

by:evnafets
ID: 16976994
A forward/include is different from HTML navigating the page, because it is all done in the same HTTP request.
To the client browser, all of the forwards/includes are invisible.
All it knows is it requested a url - eg stat.jsp

To build stat.jsp the server might use header.jsp, footer.jsp, statHeader.jsp and queryResults.jsp to make the final page - but the client knows nothing about it - all it knows is "stat.jsp" was requested, and it got back some HTML.

Forward lets you change your mind about which page to display, include lets you use a template multiple times in your site, without writing it every time.

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Author Comment

by:matthew016
ID: 16977045
Thanks for the additional info .
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