SOEN 6011 Software Engineering Processes

SOEN 6011Software Engineering Processes

Section SS Fall 2007Dr Greg Butler

http://www.cs.concordia.ca/~gregb/home/soen6011-f2007.html

Week 6• Servlets and JSP• Larman Controller Principle• Fowler Front Controller

– GoF Command pattern– Java reflection to instantiate Command

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: HelloWebpublic 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.

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()

PATTERN: Controller

• What object in the domain (or application coordination layer) receives requests for work from the UI layer?

???

Presentation

ApplicationLogic

Video Store

Record Rental

Video ID

...

...

...

... ...

Clerk

rent(videoID)

Now what happens?

PATTERN: Controller (Larman 17.13)

Problem: What object in the domain (or application coordination layer) receives requests for work from the UI layer?

System operations (see SSD): major input events to the system

The controller is the first object beyond the UI layer that is responsible for receiving or handling a system operations message.

Note that UI objects delegate system operation request to a controller.

PATTERN: Controller (Larman 17.13)

Solution: Assign the responsibility to a class representing one of the following choices:

• A façade controller, which represents1. the overall system2. A root object3. A device that the software is running within, or4. A major subsystem

• A use case or session controller which represents a use case scenario in which the system operation occurs

Fig. 17.21

Which class of object should be responsible for receiving this system event message?

It is sometimes called the controller or coordinator. It does not normally do the work, but delegates it to other objects.

The controller is a kind of "facade" onto the domain layer from the interface layer.

actionPerformed( actionEvent )

: ???

: Cashier

:SaleJFrame

presses button

enterItem(itemID, qty)

UI Layer

Domain Layer

system operation message

Dom

ain

Data

Sou

rce

Transaction Script Domain Model

Data Mapper

Row Data Gateway

Front Controller

Template View

Transform View

Page Controller

Pres

enta

tion

Active Record

Fowler’s EA Patterns

Table Module

Table Data Gateway

Front ControllerFowler: A controller that handles all requests

for a web site.

The Front Controller consolidates all request handling by channeling requests through a single handler object. This object can carry out common behaviour which can be modified at runtime with decorators. This handler then dispatches to command objects for behaviour particular to a request.

Front ControllerGoF design pattern: Command

Use a Command object to encapsulate the steps that are executed by a command.

Command::doIt() executes commandAllows Command::unDoIt() etc

GoF design pattern: DecoratorDecorator::m() adds additional behaviour, but delegates

to real Object::m() for real behaviourEg, logging command execution before/after executing

command

Page vs Front Controller – Differences in URL Page Controllers for A1 • http:/stu.cs/343A1/ViewTaskList• http:/stu.cs/343A1/AddTask• http:/stu.cs/343A1/RemoveAllTasks• …

Front Controller for A1• Base URL: http:/stu.cs/343A1/frontController• …/frontController

?command=ViewTaskList• …/frontController

?command=AddTaskGrade&title=abc&…

Front Controller

FrontServlet

# processRequest ( )- getCommand ( )- getCommandClass ( )

FrontCommand

+ init ( )+ processRequest ( )

AddStudent

+ processRequest ( )

Servlet

+ init ( )+ destroy ( )# processRequest ( )# doGet ( )# doPost ( )+ getServletInfo ( )+ forward ( )+ forwardAbsolute ( )+ getUrlBase ( )

# controller

0..1

Error

+ processRequest ( )

Front Controller

Front Controller: Sequence Diagram

Front Controller: ProcessRequest

Front Controller (cont’d)

Documents

SOEN 6011 Software Engineering Processes