SOEN 343 Software Design

SOEN 343Software Design

Section H Fall 2006

Dr Greg Butlerhttp://www.cs.concordia.ca/~gregb/home/soen343h-f06.html

Outline• Encapsulation, Information Hiding

• Servlets

• MVC– GRASP Controller principle (Larman 17.13)– Using servlets– In Fowler’s EAA

• Fowler’s data handling patterns

Encapsulation• A programming/design language

mechanism.

• A packaging / scoping mechanism for names– Names can refer to data, types, …– Especially, a means of packaging data.

Data

Access points at interface

Information Hiding

• Design principle by which a module is assigned a “secret”.

• A module’s secret is usually– A design decision.

• What type of design decisions might we want to hide from the clients of a module?

Information Hiding

• Often one hides, e.g.– Data representation.– Choice of algorithm.– Interface details / access mechanism of

external entity (e.g. database, hardware)– …

• Goal: particular design choice “invisible” to clients.

• Why would we want to do this?

Information Hiding

• Information Hiding may or may not be supported a the programming language level.

Servlets, The General Idea

• Applet as a client side Java application.• Servlet as a server side technology for

implementing part of the functionality of an application.

• HTTP (URL) requests cause a servlet to be:– Instantiated (if it did not exist).– Run.– The servlet builds a response which is then sent back

to the client (usually in the form of HTML).

Servlet: HelloWeb

public class HelloWebServlet extends HttpServlet

{protected void doGet(

HttpServletRequest request,HttpServletResponse response)throws ServletException, IOException

{ServletOutputStream out

= response.getOutputStream();out.println("Hello Web!");

}}

Java Server Page

• Servlet:– Embed HTML inside code.

• JSP– Embed code inside HTML.

HelloWeb.jsp

<%@ page contentType="text/html; charset=iso-8859-1" language="java" ... %>

<html><body>Hello Web!</body></html>

Hello.jsp

<%@ page contentType="text/html; charset=iso-8859-1" language="java" ... %>

<html><body>Hello <%= request.getParameter("name") %></body></html>

Java Server Page

• Implemented as a (special kind of) servlet.

Model-View-Controller (MVC)

Model

ViewController

Model-Views

GRASP: Controller

• Who handles a system event?– E.g. “List Movies”

• Main choices: assign to a design entity representing– Overall system,

or subsystem (façade controller).– A Use Case scenario

(often named, e.g. ListMovieHandler).

GRASP: Controller Illustration

actionPerformed( actionEvent )

:Register

: Cashier

:SaleJFrame

presses button

1: enterItem(itemID, qty)

:Sale1.1: makeLineItem(itemID, qty)

Interface Layer

Domain Layer

system event message

controller

GRASP: Controller Illustration

actionPerformed( actionEvent )

:Register

: Cashier

:SaleJFrame

presses button

1: enterItem(itemID, qty)

:Sale1.1: makeLineItem(itemID, qty)

Interface Layer

Domain Layer

system event message

controller

Presentation

Application

Controller Illustration: Web-based EA

Server :Tut06ControllerServlet

HTTP Get

doGet(req,resp)

g:Greeting

req:

setAttribute("Greeting",g)

forward(".../Greeting.jsp")

Greeting.jsp

getAttribute(...)

g

...

getGreeting()

Web-based Enterprise Applications

• The big picture …

Enterprise Applications: LayersDo

mai

nDa

ta S

ourc

ePr

esen

tatio

n

Dom

ain

Data

Sou

rce

Table Data Gateway

Transaction Script Domain Model

Data MapperRow Data Gateway

Front Controller

Template View

Transform View

Page Controller

Pres

enta

tion

Active Record

List of Main Patterns To Be Studied

Dom

ain

Data

Sou

rce

Table Data Gateway



Active Record

Front Controller

Template View

Transform View

Page Controller

Pres

enta

tion EA: MVC

Dom

ain

Data

Sou

rce

Domain Model

Template ViewPage Controller

Pres

enta

tion EA: MVC

Example: Greeting

Greeting

Template View(Greeting.jsp)

Page Controller(Greeting servlet)

Dom

ain

Data

Sou

rce

Table Data Gateway



Front Controller

Template View

Transform View

Page Controller

Pres

enta

tion

Active Record

Enterprise Application Patterns

Dom

ain

Data

Sou

rce

Table Data Gateway



Active Record

Front Controller

Template View

Transform View

Page Controller

Pres

enta

tion Data Source Patterns

Data Source Patterns

• Hide SQL.

• Provide an abstraction for – One data row.– A collection of data row(s).

Example: Person-Grade Table

Table attributes:

• name : String

• grade : intname grade

Table Data Gateway

PersGradeTDG

- PersGradeTDG()

+ find(name) : ResultSet

+ findInRange(fg,tg) : ResultSet

+ insert(name,grade) : void

+ update(name,grade) : void

+ delete(name) : void

Table Data Gateway: Find Code

Table Data Gateway: FindInRange

Active Record (Row Data Gateway)

PersGradeARname : String

grade : int

PersGradeAR(name, g)

find(name)

… // like RDG

// Can also have domain logic

getRank()

Documents

SOEN 343 Software Design