[Springframework-developer] Some questions about Spring Portlet MVC

[Joerg H. <joe...@gm...>]

Hello,

in my habit to use libs/frameworks as best as possible I often drive them to
their extremes and come across some issues in them or at least questions others
might not have had and can't answer me. That's the case at the moment with
Spring Portlet MVC. I have posted them in the forum [1, 2, 3], but nobody could
really give answers to them. And since Spring developers were rarely seen in the
forum I decided to ask those questions here again. :-)

All the questions are related and result from a feature I implemented in the
last two weeks: a generic table view. That means you have a search form, this
fills a criteria and the result is shown as table. Since this is very common
functionality I built an abstraction of it. There is a TableViewConfig
configuring the final result table (columns to view, order of columns, order of
rows). There is an object the form is bound to and with which the result is
retrieved using criteria by example. The last part is done by a CriteriaProvider
(creating Hibernate's DetachedCriteria for example) and a DAO.

The Portlet MVC part consists of two controllers: TableViewController for
displaying the search form and the result. And TableViewConfigController for
displaying a form for configuring the TableViewConfig, i.e. where you can change
the order of the columns or switch on or off the one or the other column. The
default view (actually view mode) is the TableViewController, you put your
criteria into the search form and get the result. If you want to change the
TableViewConfig you can switch to the edit mode and the
TableViewConfigController comes into play. On saving the TableViewConfig I want
to switch back to the view mode and show the new result according to the new
TableViewConfig.

=====

Issue 1 [1] I have (which is also not much related to my particular use case) is
the usage of two different controllers for action and render phase. This is made
easy by Spring since the HandlerMapping is executed for each phase.
Unfortunately it seems not well-supported since you are more or less forced to
use the same command object for both controllers. In the use case on saving the
TableViewConfig (action request and form submit) I want to switch to
TableViewController and render the result as it were a form submit in the same
controller (isFormSubmission() returning true). But that's not possible since I
need a different form backing object for this controller. In the case of
isFormSubmission() returning true Spring Portlet MVC expects the form backing
object to be found in the PortletSession (getRenderCommand(RenderRequest)). Only
when isFormSubmission() does not return true a new form backing object is
created. So with

response_.setRenderParameter(getFormSubmitParameterName(), "false");

in the TableViewConfigController I force the TableViewController to create its
own form backing object, but can't display the search result immediately since
I'm no longer in form submission rendering.

=====

The second issue is about missing value change listeners [2] or something like
this. On changing the order of the columns (TableViewConfigController) I want to
redisplay the form, i.e. go into form change processing. But it seems impossible
to determine changes to the form backing object in Spring MVC. I worked around
it by setting a parameter on such form submits on the client with Javascript and
trigger on this one in isFormChangeRequest(). A better solution is welcome.

=====

The third issue consists of multiple parts. It comes with using selects in the
search from and not only plain text inputs. My TableViewConfig actually has a
list of TableViewColumns, of which each has for example a property "path",
"name", "type" ("input", "select"). For selects there is additionally
"optionsPath", "itemValue" and "itemLabel" matching the attribute names of
Spring's form taglib. Normally it would look like

<form:select path="company">
  <form:options items="${companies}" itemValue="id" itemLabel="name"/>
</form:select>

With my abstraction it would be

<!-- context set to tableView.columns[i] via spring:nestedPath -->
<form:select path="${path}">
  <form:options items="${${optionsPath}}" itemValue="${itemValue}"
itemLabel="${itemLabel}"/>
</form:select>

First problem with it is ${${, so nested property evaluation, which is not
supported by JSTL. Lucky me, Spring's OptionsTag allows to pass an expression,
so that I only need to prevent JSTL from interpreting the nested expression. I
do it with something like (don't have access to the code at the moment)

<c:set var="optionsPathExpr" value="${'${'}${optionsPath}${'}'}"/>
<form:options items="${optionsPathExpr}" itemValue="${itemValue}"
itemLabel="${itemLabel}"/>

This works due to Spring's resolving of the "optionsPathExpr". But it's awkward
and nicer solutions are welcome. I'll also come back to it later since it gets
an issue again ...

Now there is the requirement to style the item labels and I'm at [3] or [4].
<form:select> and <form:options> only allow to set plain itemLabel and
itemValue. It can again be an expression, but the result of it is interpreted as
property of the bean. I can not construct complex labels, while a kind of a
template would be nice as shown in [4] and [5].

Workaround up to now, e.g. for i18n, is to use <c:forEach> and <form:option> as
shown in [3] since <form:option> can be any JSP stuff. I COULD use it, it would
stay as generic as the other solution, it's only a bit longer. BUT (coming back
to the nested expression evaluation) I lose Spring's resolving of the
"optionsPathExpr". I don't see a way to rewrite

<form:select path="${path}">
  <c:forEach items="${${optionsPath}}">
    <form:option value="${item}"><!--complex label--></form:option>
  </c:forEach>
</form:select>

Nested expressions don't work and using the "workaround" from above <c:forEach>
would try to iterate on the string "${optionsPathExpr}". That problem is not
related to Spring directly, but if anybody knows a solution I'll be happy.

While [4] for others is just a shorter way of writing for me it's the only
option I see at the moment.

=====

Thank you for still reading this lengthy post. I appreciate any input and help
on my problems.

Regards
Joerg

[1] http://forum.springframework.org/showthread.php?t=38451
[2] http://forum.springframework.org/showthread.php?t=38499
[3] http://forum.springframework.org/showthread.php?t=38795
[4] http://opensource.atlassian.com/projects/spring/browse/SPR-3484
[5] http://opensource.atlassian.com/projects/spring/browse/SPR-2659