MVC Pattern (MVC Framework)

8/14/2019 MVC Pattern (MVC Framework)

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MVC PatternMVC Pattern

(MVC Framework)(MVC Framework)


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Agenda Introduction of MVC pattern

Evolution of Web Application designarchitecture Model 1

Model 2

Application frameworks


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Introduction toIntroduction to

MVC PatternMVC Pattern


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MVC Pattern


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Three Logical Layers in a Web

Application: Model

Model (Business process layer)

Models the data and behaviorbehind thebusiness process

Responsible for actually doing

Performing DB queries

Calculating the business process Processing orders

Encapsulate of data and behavior which areindependent of presentation


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Application: View

View (Presentation layer)

Display information according to client types Display result of business logic (Model)

Not concerned with how the information wasobtained, or from where (since that is the

responsibility of Model)


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Application: Controller Controller (Control layer)

Serves as the logical connection between the

user's interaction and the business services onthe back

Responsible for making decisions amongmultiple presentations

e.g. User's language, locale or access level dictates adifferent presentation.

A request enters the application through thecontrol layer, it will decide how the request

should be handled and what information shouldbe returned


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Web Applications

It is often advantageous to treat eachlayer as an independent portion of yourapplication

Do not confuse logical separation ofresponsibilities with actual separation ofcomponents

Some or of the layers can be combinedinto single components to reduceapplication complexity


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Evolution of WebEvolution of WebApplication DesignApplication Design

ArchitectureArchitecture


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Evolution of MVC Architecture

1.No MVC

2.MVC Model 1 (Page-centric)

3.MVC Model 2 (Servlet-centric)

4.Web application frameworks Struts

5.Standard-based Web application framework JavaServer Faces (JSR-127)


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Evolution of Web Application

Design until Model 1 Architecture

Model 1 architectureNo MVC


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Model 1Model 1

(Page-Centric(Page-CentricArchitecture)Architecture)


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Model 1 Architecture (Page-

centric)

Request

1

JSP

pages

JavaBean

Response

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2

3

BROWSER

Servlet

Container

Enterprise

InformationSystems (EIS)


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Page-centric Architecture

Composed of a series of interrelated JSPpages

JSP pages handle all aspects of the application -

presentation, control, and business process Business process logic and control decisions

are hard coded inside JSP pages in the form of JavaBeans, scriptlets, expression

Next page selection is determined by

A user clicking on a hyper link, e.g.


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Page-centric Architecture

memu.jsp catalog.jsp checkout.jsp

dataBase

pagecentric catalog application


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Page-centric Scenario

Client

View

search.html

list

.jspModel

JavaBeans

Controller

find.jsp

delete.jsp

redirect

forward

Request 1

Request 2

Request 3

response

response


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Model 2

(Servlet-CentricArchitecture)


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Model 2 Architecture (Servlet-

centric)

Request

1

(Controller)Servlet

(View)JSPResponse

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3

4

BROWSER

Servlet Container (EIS)

Redirect2

(Model)Java Bean

Insta

ntia

te

MVC Design Pattern


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Why Model 2 Architecture?

What if you want to present different JSPpages depending on the data you receive?

JSP technology alone even with JavaBeans andcustom tags (Model 1) cannot handle it well

Solution Use Servlet and JSP together (Model 2)

Servlet handles initial request, partially process thedata, set up beans, then forward the results to oneof a number of different JSP pages


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Servlet-centric Architecture

JSP pages are used only for presentation Control and application logic handled by a servlet

(or set of servlets)

Servlet serves as a gatekeeper Provides common services, such as authentication,

authorization, login, error handling, and etc

Servlet serves as a central controller Act as a state machine or an event dispatcher to decideupon the appropriate logic to handle the request

Performs redirecting


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Servlet-centric Scenario

Client

View

search.html

list.jsp

Model

JavaBeans

Controller

forward

Request 1

Request 2

Request 3

response

response

servlet


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Web ApplicationFrameworks


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Web Application Frameworks

Based on MVC Model 2 architecture

Web-tier applications share common set offunctionality Dispatching HTTP requests

Invoking model methods

Selecting and assembling views

Provide classes and interfaces that can beused/extended by developers


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Why Web Application Framework?

De-coupling of presentation tier and business logic intoseparate components

Provides a central point of control Provides rich set of features Facilitates unit-testing and maintenance Availability of compatible tools Provides stability Enjoys community-supports Simplifies internationalization Simplifies input validation


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Why Web Application Framework?

Frameworks have evolved with Java Servertechnology

JSP/Servlets are still hard to use Frameworks define re-usable components

to make this job easier. A good framework defines how components

work to create a usable application.


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Web Application Frameworks

Apache Struts

JavaServer Faces (JSR-127) A server side user interface component framework

for JavaTM technology-based web applications

Echo

Tapestry


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Passion!

Documents

MVC Pattern (MVC Framework)