Jeff:
I'll try to give you some pointers, based on *my* implementation of model 2
architecture....
<snip>
>Craig gave some pseudocode for an action class that had the perform method:
>
> public interface Action {
> public void perform(HttpServlet servlet, HttpServletRequest
>request, HttpServletResponse response)
> throws IOException, ServletException;
> } // ends interface Action
>
>(thanks Craig)
</snip>
Here's my action interface:
/* Action.java */
import java.io.IOException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.ServletException;
public interface Action {
public void perform(HttpServlet servlet,
HttpServletRequest request,
HttpServletResponse response,
String targetPage)
throws IOException, ServletException;
} // ends interface Action
In my controller servlet configuration file, I specify the "default target
page" which is supposed to represent the happy days scenario. Naturally,
each individual class that implements the Action interface is free to
override/ignore the default target page if necessary.
>Now my questions are, what is the advantage is passing an HttpServlet
>object? I understand HttpServletRequest and HttpServletResponse, but why
>HttpServlet? Also, assuming you answer this, HOW do you pass this inside
>the servlet (sounds trivial but I have never tried any such thing)?
"I did it 'cause Craig did it this way!" Seriously, I don't recall the
specific reasons, but in a nutshell, it facilitates accessing HttpServlet
methods (and you could always cast this to your controller's class name to
do something special).
>There was mention of 2 HashTables (or HashMaps) used in the controller
>Servlet. If I am understanding correctly, the first maps the requestURI to
>the appropriate action class, and the second is used to store an instance of
>the appropriate action class? So, in theory, you would grab the requestURI
>and look it up in the first HashTable. Once the appropriate class is
>determined, you look for an instance of that class in the second HashTable?
>You would then call the perform method on that class (if it exists) or
>instantiate the class and call the perform method? I have not worked a lot
>with dynamic class loading so a little help here would be greatly
>appreciated. Maybe a little pseudocode to get me over the hump?
Within my controller servlet I have the following:
/**
* declare inner classes.
*/
class ActionObjectWrapper {
String theRequestUri;
String theClassname;
String theTargetPage;
Action theObject = null;
} // ends inner class ActionObjectWrapper
/**
* declare member (instance) variables.
*/
HashSet m_objectCache = null;
So, the object cache is loaded up at initialization time from the
configuration file. When a request comes in I search thru the HashSet using
the request URI as the key. If theObject is null, then you need to
instantiate it before calling perform().
>I had some concern about something craig mentioned in the brevity of his
>action classes (being 50 - 100 line mostly performing setXXX()). In my
>servlet, I am doing all my setXXX() error checking where it seems you are
>performing this in the bean (or maybe I am just not writing as concise
>code?). If this is the case, how do you know when the data is inappropriate
>for the field (ie, characters were found in a social security number?). In
>my case, I do this checking in the servlet. If an error has occured, I set
>the bean to an appropriate value (sometimes to null, and sometimes to the
>input value so that it can be easily modified by the user). Otherwise I
>just set the bean property. Could you go into a little more detail on this
>please? As I mentioned earlier, it is hard to learn alternative design
>strategies when there are little to no examples to learn from =).
>
>One more thing (as if this email isnt long enough). . . I read mention of
>using yet a public HashTable (or was it a method)? to determine which page
>the action class should forward to instead of hardcoding the value within
>the action class. Is this really all that advantageous? I like the idea of
>having logic names mapped to a specific file name, but otherwise, this seems
>to be overhead in projects that dont span hundreds of pages (or dont have
>the possibility of spanning that large). I assume, in this strategy, the
>action class would lookup the logical name prior to forwarding to the .jsp
>refered to in the controller servlet?
>
>I hope this all makes sense.
>
>Thanks to everyone for helping me in understanding some of these basic
>issues I am having. I look forward to your replies :).
>
>Thanks
>
>Jeff
Hope I've answered *some* of your questions - don't have time for more
right now....
Mike
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