Hi Cristian, Model-View-Controller is a design idiom originally deve- loped at the Xerox labs in the early 80's., primarily with GUIs in mind back then. IIRC it has first been implemen- ted in SmallTalk, but influenced other frameworks of the 90's in a major way, including the Document-View-Archi- tecture of Microsoft's MFC (in fact, they bought this framework to some degree. It has also influenced the Java Foundation Classes framework, the entire Swing UI makes intensive use of this design paradigm. The basic idea behind MVC is to strictly separate the tasks | roles associated to each component in the Presentation layer. Basically, the View component (screen) is what the user gets to see, the Controller part (keyboard, mouse) coordinates the input the user provides and controls the information flow to the Model, which otherwise is known as the (abstract) Business Logic which is completely shielded from its actual representation this way. The general concept is to shield different applica- tion layers from each other, there's an abundance of additional layers below the Business Logic level | facade, with each layer providing a clearly defined interface, abstracting and hiding the inter- nal implementation. As long as the interface is guaranteed, you are free to change the internal behavior as you like later on. Look upon this all as object orientation ported to system architec- ture, some way.
When web technology became prominent, it was soon decovered that the MVC concept fits quite well there, too. In a typical, commercial-grade web application, MVC usually is implemented in the following way: the View component is made of JSPs. A Servlet is assigned the Controller task, retrieving the input the user provides (via HTML forms), collecting the requested information by talking to the Model (which may be a database, an Enterprise Java Bean or even just another (service) layer and delivering the result back to the View part, usually by forwarding it to JSPs that perform the actual representation. In a more advanced design, implemented in Struts for example, the Controller uses a Delegate pattern otherwise known as the 'action' approach. In Struts, the Controller servlet handles the entire web-specific communication, delegating requests to specialized 'action' classes. These are basically just normal Java classes, having access to all the capabili- ties the platform provides, which retrieve or modify 'data' (in fact, by calling subse- quent application layers) and point the Controller to where to look for the results, afterwards. Struts heavily makes use of so-called 'ActionForms' in this context, which in fact are simple Java Beans or Value Objects in EJB slang, providing an additional layer of abstration this way, and uses a declarative mechanism for telling 'what will happen next' to the application known as 'ActionMapping'. The Struts design is truly powerful. In fact, it is flexible enough to replace the entire View part, which is made of JSP and custom taglibs currently to one using an XML/XSLT approach. This was originally described by two French Java architects from orbeon.com in an article on Java World. There is a more advanced design around known as StrutsCX, pub- lished and explained in a German Java magazine some time ago. You may get the details from http://it.cappuccinonet.com/strutscx/ it's also available from SourceForge now. The Struts implementation of things follows something to be recognized as 'MVC2'. If I'm correct, there is no fixed definition of MVC anyway, but in a case of doubt, I'd refer to the Struts documen- tation first which explains the foundations it has been developed on, too. You can get it from here: http://jakarta.apache.org/struts/userGuide/introduction.html#mvc Finally, the official Sun J2EE 'blueprint' explanation of MVC/MVC2 is to be found here: http://java.sun.com/blueprints/guidelines/designing_enterprise_applicati ons_2e/web-tier/web-tier5.html HTH, -- Chris (SCPJ2) > -----Original Message----- > From: A mailing list about Java Server Pages specification > and reference [mailto:[EMAIL PROTECTED]] On Behalf Of > Cristian G. Amayo > Sent: Monday, December 02, 2002 7:33 PM > To: [EMAIL PROTECTED] > Subject: Info about Model-View-Controller > > > Hello, > > Does somebody remember the "Model-View-Controller" Sun > definition (1999-2000)? > I was trying to find the pages related at the > http://java.sun.com site but nothing. > > Can somebody send me > some links or info about? > > Thank you, regards. > > Cristian G. Amayo > http://cgamayo.tripod.com =========================================================================== To unsubscribe: mailto [EMAIL PROTECTED] with body: "signoff JSP-INTEREST". For digest: mailto [EMAIL PROTECTED] with body: "set JSP-INTEREST DIGEST". Some relevant FAQs on JSP/Servlets can be found at: http://archives.java.sun.com/jsp-interest.html http://java.sun.com/products/jsp/faq.html http://www.esperanto.org.nz/jsp/jspfaq.jsp http://www.jguru.com/faq/index.jsp http://www.jspinsider.com
