Use Servlet to instantiate a Class that keeps in memory

Question

Hi,
I have a specific question on how to handle the following situation:
- a page calls a servlet, this servlet generates some HTML
- when the servlet is called via a HTML action like <FORM METHOD=POST action=<servlet> I want to instantiate (from the servlet code) a class that stays in memory even after the servlet is out of scope. This class should reside on the client side.
I am using Tomcat 5.5.9 and Java 1.5.0_2.
Is this possible, any suggestions, tips etc ?
Regards,
Coen

Answer 1

Hi RahulSharna,
I want to avoid using javascript or Applets, I just
need some sort of shadow class that keeps track of
changes and validations in the form.
So I post a form into a client side class instead of
a servlet on the server side.
Thanks,
Coenthe only way this can be done is with dynamic content on the client end(in other words the webbrowser). and that would be with javascript, applets or flash.
I see two problems with your approach:
first, html-forms send its data to other webbrowsers. either by a http-GET or a http-POST request. now unless you have a webserver on the client end, you cant receive form-posts.
secondary, Servlets/JSP are ment as HTTP-services. They don't require a jvm on the client side. they are merely a replacement for cgi's, php, perl and other server-side-scripting languages. hence, you just can't send a class, instanciated on the server, to the client.
(if you use other Java EE technology, like JINI and EJB, you can send copies of class instances to the client end. but in those cases, the client end is not a webbrwoser, but rather a java application communicating with a webservice.)
In your case, id recomend, that you validate it with javascript in realtime(i think thats commonly referred as "AJAX" nowadays) and ensure a validation on the server side as well.
on the servlet side, i would recomend a Controller(servlet)-View(jsp) based implementation: the servlet receives the form-input, validates it, and then forwards the request to the various jsp-views. on fail, it could send the caller back to the one containing the form, and thus already fill the previously entered fields again(this is a matter of the jsp tho).