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From "Andrew Hill" <andrew.david.h...@gridnode.com>
Subject RE: some best practices questions
Date Thu, 08 Jul 2004 07:36:34 GMT
People seem to treat using the session as though it were some kind of moral
sin.

There are technical pros and cons to using the session and these should be
considered when you do your coding, but the session scope is not harem. You
wont be cursed with eternal damnation because you shove a couple of dropdown
lists in the session for a while. It just has implications for
performance/scalabilty in certain situations that mean that avoiding its use
is often advantageous. (Such as the posibilty that "a while" could translate
to "until the session times out", and that if your in a clustered
environment the container may need to serialise the session around between
machines quite often)

Doing 'wierd stuff' (tm) in application scope or on the file system in an
effort to reproduce the effect of a session seems a bit dodgy to me (ie:
surely the container is far better at implementing sessions than you are!).
Now if its because you have thought it through carefully and logically and
that in this case it really is better to do it this way then thats a
different matter, but if its just due to some instinctive ideological
aversion to using the session api, well thats just nuts.

For this particular use case I would either just use the session, or
alternatively I would just look up the dropdowns from db each time and
accept the performance hit, but its (probably) not worth the development
time - including ongoing maintenance - to do anything overly tricky just for
a few dropdowns.

my 2c
-Andrew


-----Original Message-----
From: ravi.vedala@wipro.com [mailto:ravi.vedala@wipro.com]
Sent: Thursday, 8 July 2004 13:09
To: user@struts.apache.org
Subject: RE: some best practices questions


I think, performance wise File I/O is not the right idea.

What do you say ?

-----Original Message-----
From: Christina Siena [mailto:csiena@mountaincable.net]
Sent: Thursday, July 08, 2004 8:16 AM
To: Struts Users Mailing List
Subject: Re: some best practices questions

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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