Essentially, this is what ASP.NET does by default. The original values for the
controls that you want to persist are encoded and serialized and written to the form
as a single hidden variable. Then on the server side, it unmarshalls the hidden
variable and restores the controls to their original state. Any request parameters are
then applied so update the controls to their new values.
IMHO, it would be very useful to have a tag that serialized the ActionForm so that you
would have a copy of its prior state. Ideally, the request processor would first
repopulate the ActionForm from the serialized copy, and then look to the request
parameters (a la .NET).
Or course, there is no free lunch. You save on the server, but you pay on the client,
since all this serialized data has to be rendered by your browser. But, it would avoid
over-using session scope.
-Ted.
On Wed, 07 Jul 2004 22:46:04 -0400, Christina Siena wrote:
> I have an idea how to persist the data that I currently place in
> session scope but I need to run it by someone.
>
>
> Recall when I said that placing data in session scope is frowned
> upon by some members of my team? Well no one said anything about
> not using Java serialization. Why couldn't I serialize the
> same data that I currently keep in session scope? I've already
> implemented a solution for streaming images so creating a temp file
> should not be a problem. Here is what I think I will need:
>
>
> In the action where the data is first retrieved:
>
>
> try {
> final String prefix = "myVehicleLineMap";
> final String suffix = null;
> File file = File.createTempFile(prefix, suffix); FileOutputStream
> fileOutputStream = new FileOutputStream(file); ObjectOutputStream
> objectOutputStream = new ObjectOutputStream(fileOutputStream);
> objectOutputStream.writeObject(myMap); objectOutputStream.flush();
> myForm.setTempFileName(file.getAbsolutePath()); } catch (Exception
> e) {
> System.out.println(this.getClass().getName() + "==>> " +
> e.toString()); }
>
> In the action where the data needs to be re-accessed to prepare the
> page for re-display:
>
>
> try {
>
>
> FileInputStream fileInputStream = new
> FileInputStream(myForm.getTempFileName()); ObjectInputStream
> objectInputStream = new ObjectInputStream(fileInputStream);
> SortedMap myMap = (SortedMap) objectInputStream.readObject(); //
> use myMap as before (when in session scope) } catch (Exception e) {
> System.out.println(this.getClass().getName() + "==>> " +
> e.toString()); }
>
> This is just an idea at this point, so I would welcome any
> feedback. I'm not sure if this will work or if its feasible, but at
> least it may generate some more ideas.
>
>
> ----- Original Message -----
> From: Michael McGrady
> To: Struts Users Mailing List
> Sent: Tuesday, July 06, 2004 11:59 PM
> Subject: Re: some best practices questions
>
>
> Ever thought about creating a new scope managed by your own manager
> from application scope? That is an approach I have been thinking
> of more and more as of late.
>
> At 08:35 PM 7/6/2004, you wrote:
>> I used hidden select lists to restore user selections since I
>> wasn't "allowed" to place the whole form in session scope. The
>> management/maintenance of user selections was indeed ugly (but
>> its done and works fine). My question has to do with the data
>> retrieved from the db (from which the user makes selections). For
>> example, when the form is initially displayed, I populate a list
>> of vehicle lines (i.e. Focus, Mustang, Freestar, and so on). The
>> user can copy a vehicle line from the source list to the target
>> list. The target list consists of user selections. When the page
>> needs to be re-displayed as a result of some other query, I
>> needed to re-populate the list of vehicle lines (the source
>> list). I felt that re-retrieving the same vehicle lines from the
>> db again was silly (since I got it once I simply put a map in
>> session and use it when needed). When posting the form, the list
>> of label value beans is no longer available in the action, so my
>> options were: (1) either store in hidden lists (concatenating the
>> key with the description) or (2) re-retrieve the vehicle lines
>> from the db or (3) place them in session the first they are
>> retrieved and get them from session scope. I chose the third and
>> wondered about some best practices others have used in similar
>> situations. ----- Original Message ----- From: Rick Reumann To:
>> Struts Users Mailing List Sent: Tuesday, July 06, 2004 10:58 PM
>> Subject: Re: some best practices questions
>>
>>
>> Christina Siena wrote:
>>
>>
>>> I recently developed an application with a complex UI. One of
>>> the pages required querying the database based on user
>>> selection and re-displaying the page with the retrieved data
>>> and any previous existing user selections. Four different
>>> fields can trigger a db query resulting in page re-display and
>>> validations can also result in page re-display. Each time the
>>> page is re-displayed, the "state" of the page must be
>>> "remembered" from the last time it was displayed. (still with
>>> me so far?) Most of the data retrieved is list data displayed
>>> in single- or multi-select lists and populated using
>>> html:options collection and LabelValueBean. (for those of you
>>> reading this post who have developed similar code, you will
>>> know what I'm referring to).
>>>
>>> In the action, the retrieved data is placed in session scope to
>>> minimize db hits. I thought this was a good idea at the time.
>>> For some reason, placing data in session scope is frowned upon
>>> by some members of my team (even if improves performance).
>>> Anyways, what I need are some ideas of the best practices that
>>> fellow Struts users follow when a page requires querying the db
>>> and re-displaying the page with the retrieved data and previous
>>> selections if placing the data in session scope is not an
>>> option. How can I recall the previously retrieved data without
>>> requerying the db? Would it make sense to hide the data in the
>>> page? (i.e. either using hidden fields or hidden select lists
>>> or to generate a JavaScript array). What are the risks, if any,
>>> of hiding the data in the page? (i.e. performance).
>>>
>>> If anyone has developed similar pages, can you tell me if you
>>> decided for or against placing data in session scope and why?
>>>
>>
>> Here's is my 2cents. Personally I'm not as anti-session as most
>> people, and I think to use it or not use has to be taken on a
>> case per case basis. If your queries to generate the lists are
>> not going be cached in anyway by the backend and/or they are
>> expensive queries to run, the Session can be a better place to
>> temporarilly store this information as the user progresses
>> through the 'flow' as you've described above. Sure the data each
>> time might not be perfectly fresh, so if that is a requirement
>> than you will need to query after each new selection is chosen.
>> I'd opt for testing out performance making a new query each time
>> to generate your lists for the drop downs and see how it behaves.
>> (If your data in the database will never be altered by an
>> external process you can really leverage something like iBATIS
>> that will cache queries for you so everything is golden).
>>
>> You are asking a two part question, though, and one thing I think
>> that you 'might' be confusing is the use of the lists in Session
>> versus the ActionForm in Session (retaining user's selections).
>> From what you are describing I would DEFIINITELY keep your form
>> bean in Session scope for this. This way any chosen parameters
>> will be remembered as you are brought back to the page. This is a
>> perfectly legit use of the Session and don't let anyone convince
>> you in to using a bunch of hidden variables and storing your form
>> bean in request scope each time. (To me that is so stupid, how
>> much memory is a Form bean going to take up in Session scope
>> weighed out agains the ugliness and maintenance of dealing with a
>> bunch of hidden variables and making sure they are always set
>> etc. USE the Session in this case for you form bean). You are
>> basically describing in a sense a "wizard" where the user might
>> be brought along to different pages to collect data in a form,
>> only you are simply reusing the same form with different lists.
>>
>> --
>> Rick
>>
>>
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