	CS 635 Advanced Object-Oriented Design & Programming Spring Semester, 2004 Model-View-Controller part 2
	Previous Lecture Notes Index Next © 2004, All Rights Reserved, SDSU & Roger Whitney San Diego State University -- This page last updated 20-Apr-04

References

Patterns of Enterprise Application Architecture, Folwer, 2003, pp 330-386

Core J2EE Patterns: Best Practices and Design Strategies, 2nd, Alur, Crupi, Malks, 2003


Doc 17, Model-View-Controller part 2 Slide # 2

Transform View

A view that processes domain data elements by element and transforms them into HTML

Given a domain object, MusicAlbum, how to generate a web page for the object?

Use Template View
Convert object into html


Doc 17, Model-View-Controller part 2 Slide # 3

Converting object into html
One could add toHtml to the object

MusicAlbum ragas = new MusicAlbum.find(“Passages”);
String html = ragas.toHtml();

Domain object is coupled to view language
Provides only one way to display object

Better use XML and XSLT

Convert domain object to XML

Use XSLT to convert XML into HTML

Now we can produce many different views of the object without changing the object


Doc 17, Model-View-Controller part 2 Slide # 4

Transform View Verses Template View
Template View
More tools support

No language to learn

Transform View
Easier to avoid domain logic in view

Testing can be done without Web server

Easier to make global changes to Web site


Doc 17, Model-View-Controller part 2 Slide # 5

Context Object

Problem
Avoid using protocol-specific system information outside its relevant context

Forces

You have components and services that need access to system information

Decouple application components & services from protocol specifics

You want to expose only relevant APIs within a context

Example

public class AlbumController extends ActionServlet {
   public void doGet(HttpServletRequest request, 
         HttpServletResponse response)
         throws IOException, ServletException {

HttpServletRequest & HttpServletReponse contain protocol specific information and API


Doc 17, Model-View-Controller part 2 Slide # 6

Solution
Use Context Object to encapsulate state in a protocol-independent way to be shared throughout the application


Doc 17, Model-View-Controller part 2 Slide # 7

Application Controller

Action management – map a request to an action that handles request

View management – locate and use the correct view

Problem
Centralize & modularize action and view management

Forces

Want to reuse action & view management
Improve request-handling extensibility
Improve code modularity & maintainability

Solution
Use an Application Controller to centralize retrieval and invocation of commands and views

A centralized point for handling screen navigation and the flow of the applications


Doc 17, Model-View-Controller part 2 Slide # 8

Structure

When to use it
When web pages should be visited in particular order

Different views are used depending on the state of objects


Doc 17, Model-View-Controller part 2 Slide # 9

Continuation-Based Web Servers

Cocoon Flow (Java +Javascript+XSLT)

http://wiki.cocoondev.org/

Seaside (Smalltalk)

http://www.beta4.com/seaside2/

PLT Scheme

http://www.plt-scheme.org/

Sisc (Scheme in Java)

http://sisc.sourceforge.net/


Doc 17, Model-View-Controller part 2 Slide # 10

Seaside
http://beta4.com/seaside2/

Free with source

Squeak Smalltalk
VisualWorks Smalltalk
Ruby (called Borges)

http://segment7.net/projects/ruby/borges/index.html

Runs on:

Unix
MacOS
Linux
Windows

Runs standalone or behind:

Apache
Microsoft IIS
Netscape Server
Others (CGI, FastCGI)


Doc 17, Model-View-Controller part 2 Slide # 11

Example
ContinuationExample Subclass of WAComponent

renderContentOn: html 
   html title: 'Continuation Example'.
   html heading: 'The First Page'.
   html anchorWithAction: [self tryMe] text: 'Start'

tryMe
   | name count message |
   name := self request: 'Your name'.
   count := 1.
   message := name , ' ready to stop yet? '.
   [self confirm: message , count printString] 
      whileFalse: [count := count + 1].
   self inform: 'Good bye'


Doc 17, Model-View-Controller part 2 Slide # 12

Java Psuedocode

renderContentOn(WAHtmlRenderer html) {
    html.title(”Continuation Example”);
    html.heading(”The First Page”);
    html.anchorWithAction( tryMe, “Start”);
}
   
tryMe() {
    String name = request(”Your name”);
    int count = 1;
    String message = name + “ ready to stop yet”;
    while ( !confirm( message + count) ) {
        count = count + 1;
    }
    inform( “Good bye”);
}


Doc 17, Model-View-Controller part 2 Slide # 13

Wafer Project

Simple web blog implementation
Used to compare Java Web frameworks
http://www.waferproject.org
Implemented in Seaside by Todd Blanchard

Wafer Web Blog Implementation

Metric	Java Struts	Seaside
Development Time	1-2 weeks	~6 hours
Size	4 MB	26 KB
Files	155	1
Source Size	159 KB	26 KB
Classes	36	12

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