Java Web Programming [6/9] : MVC

Module 6: MVCThanisa Kruawaisayawan Thanachart Numnonda www.imcinstitute.com

Objectives Introduction of MVC pattern Evolution of Web Application design architecture  Model 1  Model 2  Application frameworks 2

MVC Pattern 3

Three Logical Layers in a Web Application: Model Model (Business process layer)  Models the data and behavior behind the business process  Responsible for actually doing  Performing DB queries  Calculating the business process  Processing orders  Encapsulate of data and behavior which are independent of presentation 4

Three Logical Layers in a Web Application: View View (Presentation layer)  Display information according to client types  Display result of business logic (Model)  Not concerned with how the information was obtained, or from where (since that is the responsibility of Model) 5

Three Logical Layers in a Web Application: Controller Controller (Control layer)  Serves as the logical connection between the users interaction and the business services on the back  Responsible for making decisions among multiple presentations  e.g. Users language, locale or access level dictates a different presentation.  A request enters the application through the control layer, it will decide how the request should be handled and what information should be returned 6

Web Applications It is often advantageous to treat each layer as an independent portion of your application Do not confuse logical separation of responsibilities with actual separation of components Some or of the layers can be combined into single components to reduce application complexity 7

Evolution of MVC Architecture1.No MVC2.MVC Model 1 (Page-centric)3.MVC Model 2 (Servlet-centric)4.Web application frameworks  Struts1.Standard-based Web application framework  JavaServer Faces (JSR-127) 8

Evolution of Web ApplicationDesign until Model 1 Architecture No MVC Model 1 architecture 9

Model 1 Architecture (Page-centric) 1 Request JSP 4 pages BROWSER Response 2 Java 3 Bean Servlet Enterprise Container Information Systems (EIS) 10

Page-centric Architecture Composed of a series of interrelated JSP pages – 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. <A HERF="find.jsp> – Through the action of submitting a form, e.g. <FORM ACTION="search.jsp"> 11

Page-centric Architecturememu.jsp catalog.jsp checkout.jsp dataBase page–centric catalog application 12

Page-centric Scenario View search.html Request 1 response list.jspClient Model response forward JavaBeans Request 2 Controller Request 3 find.jsp redirect delete.jsp 13

Model 2 Architecture (Servlet- centric) MVC Design Pattern 1 Request (Controller )BROWSER Servlet Redirect 3 In 2 st an tia te 5 (Model) (View) Java Bean Response JSP 4 Servlet Container (EIS) 14

Why Model 2 Architecture? What if you want to present different JSP pages depending on the data you receive?  JSP technology alone even with JavaBeans and custom tags (Model 1) cannot handle it well Solution  Use Servlet and JSP together (Model 2)  Servlet handles initial request, partially process the data, set up beans, then forward the results to one of a number of different JSP pages 15

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 decide upon the appropriate logic to handle the request – Performs redirecting 16

Servlet-centric Scenario View search.html Request 1 response list.jspClient Model response forward JavaBeans Request 2 Controller Request 3 servlet 17

Web Application Frameworks Based on MVC Model 2 architecture Web-tier applications share common set of functionality  Dispatching HTTP requests  Invoking model methods  Selecting and assembling views Provide classes and interfaces that can be used/extended by developers 18

Why Web Application Framework? De-coupling of presentation tier and business logic into separate 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 19

Why Web Application Framework? Frameworks have evolved with Java Server technology 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. 20

Web Application Frameworks Apache Struts JavaServer Faces (JSR-127)  A server side user interface component framework for JavaTM technology-based web applications Echo Tapestry 21

Acknowledgement Most contents are borrowed from thepresentation slides of Sang Shin, Java™Technology Evangelist, Sun Microsystems,Inc. 22

Thank you [email protected]/imcinstitute www.imcinstitute.com 23

Java Web Programming [6/9] : MVC

by IMC Institute on Jan 06, 2013

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