Re: JSP still relevant
On Sat, 27 Jun 2009, Arved Sandstrom wrote:
Tom Anderson wrote:
On Fri, 26 Jun 2009, Lew wrote:
Tom Anderson wrote:
The problem is not java in JSPs, it's logic in JSPs. If you factored the
above code out into a custom tag, or a bean or something, where it could
be written in java and then cleanly integrated with JSP, i think that
would be ideal. But as long as the advice is "don't use scriptlets",
rather than "don't put logic in JSPs", that's not what people are going
to do.
Arved Sandstrom wrote:
Nicely put - I agree 100%.
Although I deal with JSF and Facelets those pages are susceptible to the
same problems. I keep my <c:if>...</c:if> logic confined to deciding what
sections of XHTML to show, based on role, that kind of thing.
Actually, I do see that advice phrased as "don't put business logic in
JSPs, only view logic" from a lot of sources. That is, of course, the
intent behind the less rigorously-phrased form.
But even that is wrong (IMNERHO) - in the example i give, and the nightmare
system i work with, the logic in question is all view logic. Unless the
promulgators of this advice think that the choice of which message to
display in that example is business logic? The writing of view logic in JSP
is something that i don't see warnings against - indeed, i see a whole
industry and community that's built around the idea that programming with
tags is a legitimate thing to do.
Identifying something as presentation logic rather than business logic is
sometimes hard to do. Let me elaborate on my above example - let's say that
my application page navigation is assisted by the provision of a row of
category tabs, each displaying a row of links underneath the tab row when the
specific category tab is clicked. Let's also say that each page (I usually
use Facelets in JSF for my J2EE apps) can have divs for top-level structure
when rendered.
It's not uncommon to want to display specific tabs, and specific links for
each tab, in this example, when the logged-in user has specific roles. It's
also not uncommon to want to display certain divs making up an XHTML page not
only based on logged-in role, but also on other factors. Finally, perhaps
you'd like to enable the input form elements when the page is in a "Edit"
mode, but disable them when the page is in a "View" mode.
Provided that the logic for doing all of this resides in the web tier
(specifically in XHTML and JSF managed beans) I don't really have a problem
if much of it is done using JSTL tags or Facelets function tags. To me all of
this is presentation logic.
I agree entirely that it's presentation logic, but it's exactly this kind
of stuff that i don't want to see done with tags. Those pages are going to
be full of great big unreadable verbose gobs of JSP code mixed in the the
page HTML, when it could all be cleanly separated into java code.
The alternative would be to have more pages and Java logic in managed
beans deciding what page to show at a finer granularity...with Facelets
this would not be too onerous but ultimately I see the tags as cleanly
accomplishing the same thing.
I don't see why you'd have to have more pages - but then i know nothing
about JSF.
I can see the point of your example. In the applications I've recently worked
on, this kind of information (overall page number, or the contextual
information accompanying a paginated data table) is computed in, and resides
in, a JSF backing bean, and all the Facelets page does is use JSF UI elements
to pull that data in.
That sounds like the kind of thing i envisage.
As another example, what would be your viewpoint on JSF EL?
I've never used JSF. How does it compare to JSP EL?
A typical example of how I might use it is if I had values in one column
of a table, which must be colour-coded black, red or green according to
the value of yet another column. The appropriate CSS style attribute
must be determined somewhere, and to me the best place to do that is
right on the page. This is a readable compression of view logic akin to
using tags, IMO.
I like the backing bean approach. You'd write something like:
<c:forEach items="maintable.rows" var="row">
<td class="<c:out value=""${row.HTMLClass}>"></td>
</c:forEach>
There, i'm using JSTL and EL purely as the glue to get values from the
objects backing the page.
tom
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