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jsp question

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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matthew016
Asked:
matthew016
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4 Solutions
 
objectsCommented:
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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mukundha_expertCommented:
Load all the country names for the first request and store it as a session attribute,

so for further requests check the session attribute, if its not null and has values use them to print in the combo box. you no need to query everytime.

like,
  Object names ;
if ( session.getAttribute ("CountryName") == null )
{

  names = getNames();
 session.setAttribute ( "CountryName", names ) ;
}

else
 names = session.getAttribute ( "CountryName' ) ;


displayNames () ;
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enachemcCommented:
You can load your needed data once and cache it. You can cache your data in the session (per user) or in a static member of a class (per server).
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Tomas Helgi JohannssonCommented:
   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
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enachemcCommented:
I think an EJB Session Bean for this task is like using a rocket launcher to kill a fly.
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Tomas Helgi JohannssonCommented:
>I think an EJB Session Bean for this task is like using a rocket launcher to kill a fly.
Hmmm, yes you are right about that ;)

One other way to handle this is to create a HttpSessionListener and have it loaded in a static java-class/object as enachemc says.

Regards,
   Tomas Helgi  
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matthew016Author 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?
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objectsCommented:
> 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
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matthew016Author 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 ?

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objectsCommented:
As I said above, you can't avoid generating the select for each request, and it shouldn't create a performance concern to you anyway.
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matthew016Author Commented:
Thank u very much
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Tomas Helgi JohannssonCommented:
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
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Tomas Helgi JohannssonCommented:
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
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matthew016Author 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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