Displaying a loading page betwen 2 pages

Hi,

here is my problem,

1/a user submit some data
2/data is send to an application server wich will store the result in a database
3/user is redirected to a waiting page
4/user is redirected to a page wich display the result once the data is ready

problem is, once I send my User to the waiting page, I'm stuck, since the servlet forwarded to it, it won't do anything anymore.

the servlet wich does not work (get stuck once the loading page is displayed)

package fr.efrei.pageDeChargement;

import java.io.IOException;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import com.google.appengine.api.datastore.DatastoreService;
import com.google.appengine.api.datastore.DatastoreServiceFactory;
import com.google.appengine.api.datastore.Entity;
import com.google.appengine.api.datastore.EntityNotFoundException;
import com.google.appengine.api.datastore.Key;
import com.google.appengine.api.datastore.KeyFactory;

public class AffichageChargementServlet  extends HttpServlet{
	
	public void doGet(HttpServletRequest req, HttpServletResponse resp) throws IOException {
		//getting entity key and information about wich page to laod
		String key = req.getParameter("key");
		String next = req.getParameter("next");
		
		System.out.println(next);
		
		if ("true".equals(next)){
			//is the entity available
			Key resultatKey = KeyFactory.createKey("Resultat", key);
			DatastoreService datastore = DatastoreServiceFactory.getDatastoreService();
			Entity result = null;
			while(true){
				try {
					result = datastore.get(resultatKey);
				} catch (EntityNotFoundException e) {
					System.out.println("Nope");
					//ne rien faire, la data n'est pas encore disponible
				}
				if(result != null){
					System.out.println("redirection to /affichageResults?key="+key);
					resp.sendRedirect("/affichageResults?key="+key);
				}
			}
		}
		//displaying loading page
		try {
			getServletContext().getRequestDispatcher("/loading.html?next=true&key="+key).forward(req, resp);
		} catch (ServletException e) {
			System.out.println("issue in AffichageChargementServlet when loading /loading.html");
			e.printStackTrace();
		}

}

Any ideas?
Thanks

Hi,

Have you Debug the application ? Are you able to reach inside the if condition..? You can print the logger or debug the application and see where you stuck? Any Exception in background.

Regards
Jatan

when entering the servlet the first timz next = false, so I'm not suposed to go inside the if.

when executing the line : getServletContext().getRequestDispatcher("/loading.html?next=true&key="+key).forward(req, resp);
Its just displaying loading.html, with the parameter from the servlet I was comming from (?next=false&key=xxx)

Basically it's not re-entering the servlet.

You have a redirect in a loop?

Once you redirect of forward, that's it. You can do nothing else.

Maybe you need to back up 10 steps or so and tell us what you are actually trying to accomplish.

Bear Bibeault wrote:You have a redirect in a loop?

the redirect is in a conditional block, so it's not really a problem

Once you redirect of forward, that's it. You can do nothing else.

yes, and i'm looking for a workaround or an other way of getting the same result.

Maybe you need to back up 10 steps or so and tell us what you are actually trying to accomplish.

this

1/a user submit some data
2/data is send to an application server wich will store the result in a database
3/user is redirected to a waiting page
4/user is redirected to a page wich display the result once the data is ready

How do you intend for the waiting page to know when the processing, which I assume is executing in a worker thread, is complete?

Or, perhaps I'm reading too much into this. From your list, it seems as if the "waiting page" may be completely superfluous. If the servlet stores the data in the database, what's the purpose of the "waiting page"? What's it "waiting" for?

it's waiting for the data to be stored in the database.

You cannot know how much tim the calculation will take before database storage, could be 2 seconds, could be 15 seconds.

If it were me, I likely wouldn't bother for such a short duration. But if you want to show a "waiting" notice while a request is processing, you're going about it the wrong way. You can't redirect or forward from the servlet until it's done, so the idea of showing a waiting page while the servlet is still processing isn't viable. You could go the thread route, but that's wildly overkill for this.

What I'd do is to submit the request as an Ajax call, display a waiting notice while it's processing, and simply remove the notice when the request completes.

Allright, impossible to do with only jsp/servlets.
I'll have to learn javascript/ajax then, thanks

thongvan alexis wrote:I'll have to learn javascript/ajax then, thanks

Javascript libraries like JQuery make this really easy. You can get it done within an hour of Googling, coding, and testing.