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I am a newbie to writing JSPs.

In my JSP I have dynamically created a form with select boxes (i.e. these fields are not in html)

In one of the selectboxes, I implemented a onchange method which passes the value as a parameter and re-displays the form. When the form is redisplayed the parameter I've passed, sets the value of another select box according to the parameter's value, using an external XML file.

One Problem is that after the onchange method as the current page is resent and reloaded, selected values of the other fields (around 10 fields) are lost.

Currently I use the following approach using the Session to address this problem in my JSP; in the onchange method, I use javascript to load selected values and pass them as parameters to a servlet in a GET request. In the servlet, I receive the parameters and set attributes in the session.

In the JSP, I use getAttributes in the session and change the selected values during the dynamic creation of the form.

I wonder if there is a simpler way to do this as I have to create a lots of fields for this to work. Also I didnt make use of a databean in this case.

Since dynamic creation of fields is using java logic, Is it true that ajax can't be used?

Could you please advise me on the quality of my design? Am I staying true to the MVC design pattern?

VMAtm
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vincentlcy
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1 Answers1

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If I am not wrong, your whole question basically boils (understatement) down to the following:

I have a form with a bunch of dropdowns. I am submitting a form during onchange of a dropdown. How do I retain the selected value of all other dropdows after submit?

Yes?

OK, just set the selected attribute whenever the dropdown option's value matches the submitted request parameter value. The below example assumes that you've a Map<String, String> as ${fooOptions}:

<select name="foo">
  <c:forEach items="${fooOptions}" var="fooOption">
    <option value="${fooOption.key}" ${fooOption.key == param.foo ? 'selected' : ''}>${fooOption.value}</option>
  </c:forEach>
</select>

Do you see? When the form get submitted, the currently selected option of the dropdown with the name "foo" get sent as a request parameter and is in the server side available as request parameter ${param.foo}. While dynamically generating the options, you just check if the option's value equals to the request parameter value and if so, then just set the selected attribute.

Please note that this has nothing to do with sessions and such. They serve a different purpose, generally with regard to the current visitor in person, such as its login, preferences, shopping cart, etc. Do not use it to store form values. It'll only conflict whenever you've multiple browser windows/tabs open in the same session.

JavaScript is only helpful if you would like to do the ajax magic. But I guess that it's only another steep learning curve for you. Perhaps for later. In any way, you can find some kickoff examples in this answer: How to use Servlets and Ajax?

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BalusC
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  • Thanks very much for your answer! I think you provide great insight to me. One thing i am wondering is that as I am currently using javascript for the onchange method which use code like document.location = servlet?parameter1=parameter1, so is that I am not submitting a form but instead, recreating the form? or they are the same? If I am not submitting the form during onchange, does this method work in retaining the selected values? – vincentlcy Sep 19 '11 at 17:52
  • Yes, it will work equally well if you include the selected value as request parameter of the redirected URL. – BalusC Sep 19 '11 at 18:01