Re: The "Presentation" Layer

[john e <jacobus1968@xxxxxxxxxxx>]

Joe,

Again, model 1 or 2, the servlet is a server program. It's not that you can simply start a servlet which then displays a page. The output of a servlet is always in response to an HTTP request.

In model 2 simply more of the application code (like what page to display next) resides on the server. But it's still client/server.

You said "the SUBMIT button on the JSP page returns to the calling servlet.". It does not return. A SUBMIT is a request. It is the beginning of a request-reponse cycle, not the end. The framework simply assures that the SUBMIT request is delegated to the same servlet that produced the page containing the SUBMIT.



> Date: Fri, 18 Jul 2008 09:27:32 -0500
> From: joepluta@xxxxxxxxxxxxxxxxx
> To: web400@xxxxxxxxxxxx
> Subject: Re: [WEB400] The "Presentation" Layer
>
> john e wrote:
> > Joe wrote:
> > > he entire page-at-a-time browser interface all the way up to JSP Model 
> > > 2 has been server/client
> > >     
> >
> > I don't understand. Whether page-at-a-time or ajax, it's always client/server and not server/client because the browser always initiates the request. The browser is under control. The server responds to requests, whether this is with a complete page or simply some data.
> >   
> That's typically JSP Model 1.  In JSP Model 2, the servlet on the host 
> puts data into the session, and then initiates the display of a specific 
> JSP page.  That page is displayed to the user, who then hits a button to 
> submit the page back to the same servlet.
>
> In JSP Model 1, each button on the screen initiates a request to a 
> different page.  Frameworks like Struts attempted to externalize that 
> application flow to some degree, but it still wasn't quite the same.  
> With JSP Model 2, the control is moved entirely to the servlet.  The 
> user simple enters data and hits a button; the application determines 
> the next page to display.
>
> > Having all application code on the server and "nothing" (i.e. only HTML) on the client doesn't make it server/client.  It's just that you're entire application is structured as functions that are executed as a result of the browser (client) making requests.
> >   
> Again, it's how you write the servlet.  The primary characteristics of 
> JSP Model 2 are: the servlet identifies the page to display, and the 
> SUBMIT button on the JSP page returns to the calling servlet.  These two 
> design components turn it from a rough client/server to server/client.
>
>
> > If the server outputs a complete page to the browser then this is a response to a request of the client. When done the server simply waits for the next request. This is different from server/client where the client program on the host is under control. It outputs a screen to the terminal whenever it wants to, not after receiving a request from the terminal. 
> >   
> Again, in JSP Model 2, the servlet is the controller.  It determines the 
> next page to display.
>
> Joe
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