D J wrote:
> I have a small servlet-base application that searches a back-end
> database. I want to port this application from a monolithic servlet
> (with embedded HTML) into the "Model 2" approach described in the JSP
> spec (using JSDK2.1 and JSP.92). Being very new to JSP, I have some
> questions.
>
Good choice ... unmixing the presentation and the processing is a better idea
IMHO.
>
> Imagine this user error situation. The user is presented with a HTML
> form that allows them to enter a name to search for. Currently in my
> servlet app, once the form is submitted, the servlet checks for
> invalid input. If the input is invalid (ie. the search for field is
> blank), I return the original search form with a descriptive error
> message. This way, I don't want waste the user's time redirecting
> their browser to another error page (and thus force them to click
> return to the search form).
>
> How can such an user interface be implemented in the Model 2 approach?
>
> Could this work?
> Make the original search form a JSP file that submits the form to a
> search servlet. Upon discovering invalid input, the servlet would
> create a "UserError" bean, set the "message" property and then send
> it back to the search JSP. The JSP would contain some Java scripting
> to detect the UserError bean and display the error.
>
> DJ
>
I deal with this kind of thing in a very similar manner, using the following
approach:
* Define a bean whose properties are all of the entry fields on a form.
* In a servlet, create this bean with default values and stuff it in the
session
* Forward control to the JSP page, which is programmed to use the current
values in the bean as the data in the input fields (using the <DISPLAY> tag
to grab them).
* User fills out the form and submits to a servlet, which does the validation.
* In addition to validation, the servlet updates the bean properties to reflect
the last values entered by the user.
* If the servlet discovers a problem, create an error message bean with some
sort of message describing the problem, and stash it in the request (so you
don't have to worry about cleaning it up later).
* Then, forward control back to the JSP page with the original input form.
* Include some conditional logic (in my case it's at the top of the page) to
extract and display the error text. Something like:
<excludeif property="errorbean:message" match="null">
<display property="errorbean:message">
</excludeif>
* When the JSP page displays the form again, it will grab the original bean's
values, which now contain whatever he/she entered last time.
Craig McClanahan
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