[MVC-Programmers] Re: question (related to now I know why I was initializing Map inconstructor)...

[Vic Cekvenich]

Rick Reumann wrote:

On Fri, Jun 06,'03 (09:28 PM GMT-0400), Rick wrote: 
 
  

- I say 'should' because of course I haven't tested it yet. Hope it
works:)
    

Well of course I spoke too soon. I should have realized the plan I had
of course wouldn't work. I'm really stumped by the best way to handle
this Vic, and I'm sure it will come up in the future....

The problem is when you have a FormBean tied to an Action, 

(of course in my head I think of html form tag and then... the formBean is tied to the form/page, and not the action, but...)

the first
thing Struts does is look for that FormBean in scope and if not in scope
it creates the FormBean and then tries to populate the bean from any
request parameters. 

OK, but most of the time .... there are none "parametars" / propeties since we in esence do a redirect.

Of course this all happens with the default stuff
(RequestProcessor etc).  So the problem is if you call an Action and
pass in any properties BEFORE this FormBean is ever created at least one
time and put into session scope, you will end up with null pointer
exceptions since _current Map will be null. 

This happens on a submit back to the action, not other wise, methinks.

This is sort of a big
problem since you aren't always going to create a blank form with the
"New" dispatch before you do anything. 
  

I think of it as .... in the action, a developer has a chance to pre-populate. (on a submit, Struts populates form (page) values before the action, but otherwise we redirect)

None of the solutions I can think of I like that much. Currently I'm
doing this (which I really don't like)...

First added these methods to BaseBean...

public Map getCurrentMap() {
        return _current;
    }

This has to be in there already, don't tell me I don't have this and use propery? Please let know.

    public void initializeCurrentMap() {
        _rlist.add(new HashMap());
        _size = _rlist.size();
        _current = (HashMap)_rlist.get(size() - 1);
    }


Then in one of my Display disptach actions...


  

By the time you code anything, Struts did it's thing.

//make sure you have a ProjectDetailBean in session scope 
//intialized with a new _current Map

if ( ae.getSessionBean("projectDetailBean") == null ) {
	ProjectDetailBean projectDetailBean = new
	ProjectDetailBean();           
	projectDetailBean.initializeCurrentMap();            		
	ae.setSesBean("projectDetailBean", projectDetailBean );          }
else {
	ProjectDetailBean projectDetailBean =
	(ProjectDetailBean)ae.getReq().getSession().getAttribute(
			"projectDetail Bean");            
	if (projectDetailBean.getCurrentMap()== null ) {               
		projectDetailBean.initializeCurrentMap();               
 	}
}
  

?? I do not do any of this in bP and it does all the CRUD, etc. ??
But it's not to bad the code.

I really don't like the above very much since it now makes this Action
to have to be TOTALLY aware of where it's going to.

You are thining good, OO and modular, actions should NOT know what is going on in bean.

Some other ideas I thought of....

1) Go ahead and just initialize a FormBeans with a new _current Map when
the user logs in and put them all in Session scope. 

For all the possible beans and put in scope, nope.

2) The best solution is probably to subclass the RequestProcessor and
modify the processActionForm class. Have it check to see if the FormBean
is of type BaseBean and if so make sure that _current is not null, and
if it is make sure the _rlist is initialized with a new _current
HashMap.
  

Only if the RequestPorcessor has some data we care about, which would for a submit not for a redirect.

This number 2 solution might be the best option. Another good reason
for option 2 above is it will allow you to then use beans with Request
scope. Currently the way bP is set up the user really will have to
almost always be using Session scope for all beans. If they don't
Session scope you can quickly run into problems since _current could be
null.


Either way something needs to be done since it is common to go directly
to an action from a forward link with passed in parameters.

I do this here similar in MRCmsAdmin.jsp
    <c:url value="contentAdminPg" var ="url">
            <c:param name="ID" value="${row.id}"/>
            <c:param name="Dispatch" value="Edit"/>
    </c:url>
    <a href ='' >
         <c:out value="${row.id}"/>
     </a>

And in userList.jsp
  <display:column property="handle"      width="40%"        title="Handle"    styleClass="text"
          href=""                 paramId="ID" paramProperty="id" />

Also most my List Action forward to the "zoom" action, within the list action mappings (chaining?)

And found no issues here or other project I did. I guess I still don't get where you are stuck this time. I must say I admire your presistance, you will go far in Sofware.

 If there is
a bean associated with the Action (which there almost always would be)

A bean should ONLY be maped to a action mapping if it is for R/W, updates, inserts.
If the page is display only, than there should NOT be a bean in action maping, and most of the pages just display data. So I say most of the time there is no form bean assiociated with the action.
If it's display only, then in action you say bean = new bean and put it in request scope (not session for read only. For R/W it should be ins ession becuase validation errors, etc.)

and this bean wasn't set up some time along the way in Session scope,
then _current will be null. 

See above.

-- 
Vic Cekvenich,
Struts Instructor,
1-800-917-JAVA

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