I am working with a registration form.  Currently when I press submit button and if any input is wrong , I am redirected to same page with all the previously filled fields blank. I want that my previously filled value persist. 

How to achieve this is Java?  I am using Java, .page file and xsl for rendering things. I can't use PHP for this.  Either I can do this on my xsl file or on Java script. 

If this is just a single jsp page form (i.e the form itself doesn't span multiple pages) you don't need to use the session. 

Maybe this MVC example will help? This is just a basic example. There are many different methods to do the same thing. 

(M) = Model 
(V) = View 
(C) = Controller 

First Part 
---------- 
1) User directs browser to RegistrationFormController (C) url 
2) LoginFormController is a servlet that creates an empty RegistrationForm bean and puts it on the request object, named "regDetails". The bean has methods such as setFirstName(String name) and getFirstName(). 
3) LoginFormController forwards (dispatches) the request to registrationForm.jsp (V) 
4) registrationForm.jsp uses JSTL to put values from bean (empty at the moment) in to the form values. 
e.g. 
<input type="text" value="<c:out value="${regDetails.firstName}"/> "/> 
<input type="text" value="<c:out value="${regDetails.firstName}"/> "/> 

Second Part 
-------------- 
1) User fills in form and clicks submit button. This posts the data to the RegistrationController (C) 
2) RegistrationController takes the submitted values from the request object and creates a RegistrationForm bean using these values. 
3) RegistrationController then validates the bean values to make sure they are of the correct data types, all mandatory fields have values etc. 
4) If no problems, calls some business logic (M) to do whatever you need to do with the data (save it to a database maybe?) - Note - this could also provide validation errors for example if the username already exists in the database etc. 
5) If problems, forward to success.jsp to display a success message. 
6) If problems, put bean back in response object. Add error message to response object. Forward to registrationForm.jsp again. 

That should at least get you started... 

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