Newbie question... I think

Question

hello fellow java developers!
I have a somewhat simple question, I think....
I have a web application that I built in 2 parts.
Part 1: Does some big task that takes lots of server time and acts as a resource
Part 2: Uses the resource created in (Part 1) to achieve a task.
Kind of like an indexer indexing a website, and a search box using the index - something similar to this...
My question is, how can I achieve (Part 1) so that it is something that remains accessible in memory in a jsp page? Is there something I can do on the server when it boots or something? I just don't know where to put it so that it will run once and be available until the server is turned off....
Thanks in advance!

Answer 1

Certainly this is quite possible.
If it is a shared resource accessible to all users, the best place to store it would be in ServletContext/application scope.
So write a servlet that as part of its init() method loads the resource, and stores it into memory:
public void init() throws ServletException{
  Object myInfo = executeBigTaskThatTakesLotsOfServerTime();
  ServletContext application = getServletConfig().getServletContext();
  application.setAttribute("resource", myInfo);
}That will execute the action, and store the into memory accessible by all users of your web application when this Servlet is loaded.
They can get it via <jsp:useBean scope="application"/>, <%= application.getAttribute("resource") %> or using EL ${applicationScope.resource} or even just ${resource}
Next question - how do you make this code run at startup?
In your web.xml - configure the servlet to <load-on-startup>
<servlet>
     <servlet-name>MyResourceLoader</servlet-name>
     <servlet-class>com.my.ResourceLoaderServlet</servlet-class>
     <load-on-startup>1</load-on-startup>
</servlet>You may want to start a seperate thread to do the resource loading, so you can let your server get on with starting up, but thats entirely up to you, and may result in the server being available for requests before your "indexing" service or whatever has finished. Up to you.
Cheers,
evnafets