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matthew016
matthew016 asked
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Last Modified: 2013-11-23
Hi,
Im devlopping a website.

I have all the countries stored in my DB,
When a user wants to subscribe to the website, ha has to select his country.

I loaded the countries from my DB in memory in a "load-on-start" servlet.
I'm making a JSP file that gets the countries and display them in a combobox.

My question :

For every request,
the jsp file needs to get the countries and display them from a java class.
But I want the countries to be loaded in this combobox just once (not for every new request).

Thank you for any help.
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Mick BarryJava Developer
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Commented:
not sure I follwo, every request is going to need to generate a response page so will need to generate the <select>.
Perhaps build the select in an include
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Tomas Helgi JohannssonDatabase Administrator / Software Engineer
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Commented:
   Hi!

Store the country-names in an EJB Session Bean and let the server handle the load and cache of the data.
In that way country-names are stored in memory at startup and can be accessed quickly.

Regards,
  Tomas Helgi

Commented:
I think an EJB Session Bean for this task is like using a rocket launcher to kill a fly.
Tomas Helgi JohannssonDatabase Administrator / Software Engineer
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Author

Commented:
If I store them in a session, the countries need to be loaded for each user no?
I want to load them just for once.

So actually I could load them in a static class and then access this class with a loop in the select.
Well actually I already did that and I tought it was a problem for performance and that
I could find a better solution.

>Perhaps build the select in an include
why?
Mick BarryJava Developer
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Top Expert 2010

Commented:
> I want to load them just for once.

thought u said you'd already loaded them?

> So actually I could load them in a static class and then access this class with a loop in the select.

should load them into a static class.
you should load them once and store them in the application context

>>Perhaps build the select in an include
>why?

In case you want to add the select to >1 pages

Author

Commented:
> I want to load them just for once.
>thought u said you'd already loaded them?

Actually I meant load them once from the application into my jsp page ...
I don't know if this affects performance because
at every request a big loop in the select is executed, and laod them from the class.
Then I have a loop to select language, and other loop.
U know what I mean ?

Java Developer
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Author

Commented:
Thank u very much
Tomas Helgi JohannssonDatabase Administrator / Software Engineer
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Commented:
As I said before.
Create a HttpSessionListener class and put a static java-class/object in that class which then can be accessed from all JSP pages. Doing this you load the data ONCE when the web-app is first loaded and destroyed when no users are browsing the web by counting active users.
Do it something like this :

import javax.servlet.http.HttpSessionListener;
import javax.servlet.http.HttpSessionEvent;

public class SessionCounter implements HttpSessionListener {

      private static int activeSessions = 0;
                private static myCountry countries;  // this class holds the countries ;)
                private static boolean countries_loaded = false

      public void sessionCreated(HttpSessionEvent se) {
            activeSessions++;
                                if(activeSessions > 0 and !countries_loaded){
                                      countries_loaded = true;
                                      countries = new myCountry();
                                      ......
                                }
      }

      public void sessionDestroyed(HttpSessionEvent se) {
            if(activeSessions > 0)
                  activeSessions--;
      }

      public static int getActiveSessions() {
            return activeSessions;
      }
}

Regards,
    Tomas Helgi
Tomas Helgi JohannssonDatabase Administrator / Software Engineer
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Commented:
Hmmm forgot one thing. ;)

import javax.servlet.http.HttpSessionListener;
import javax.servlet.http.HttpSessionEvent;

public class SessionCounter implements HttpSessionListener {

     private static int activeSessions = 0;
                private static myCountry countries;  // this class holds the countries ;)
                private static boolean countries_loaded = false

     public void sessionCreated(HttpSessionEvent se) {
          activeSessions++;
                                if(activeSessions > 0 and !countries_loaded){
                                      countries_loaded = true;
                                      countries = new myCountry();
                                      ......
                                }
     }

     public void sessionDestroyed(HttpSessionEvent se) {
          if(activeSessions > 0)
               activeSessions--;
     }

     public static int getActiveSessions() {
          return activeSessions;
     }

     public static myCountry getCountryClass(){
          return countries;
     }
}

Regards,
  Tomas Helgi

Author

Commented:
Thank u Tomas but I can't see why I should destroy the data when no sessions are active,
also I can't see any code that "destroys" the data like u say.

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