Week 6 lecture slides

Transcript Week 6 lecture slides

SOEN 6011
Software Engineering Processes
Section SS Fall 2007
Dr 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: 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.
Controller Illustration: Web-based
EA
Server
:Tut06ControllerServlet
Greeting.jsp
req:
HTTP Get
doGet(req,resp)
g:Greeting
setAttribute("Greeting",g)
forward(".../Greeting.jsp")
...
getAttribute(...)
g
getGreeting()
PATTERN: Controller
• What object in the domain (or application coordination
layer) receives requests for work from the UI layer?
Video Store
Presentation
Video ID
...
...
...
Clerk
...
Record Rental
...
Application
Logic
Now what happens?
rent(videoID)
???
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 represents
1.
2.
3.
4.
•
the overall system
A root object
A device that the software is running within, or
A major subsystem
A use case or session controller which represents a
use case scenario in which the system operation
occurs
Fig. 17.21
presses button
: Cashier
actionPerformed( actionEvent )
UI Layer
:SaleJFrame
system operation message
enterItem(itemID, qty)
Domain
Layer
: ???
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.
Data Source Domain Presentation
Fowler’s EA Patterns
Page Controller
Template View
Front Controller
Transform View
Transaction Script
Active Record
Domain Model
Table Module
Data Mapper
Row Data Gateway
Table Data Gateway
Front Controller
Fowler: 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 Controller
GoF design pattern: Command
Use a Command object to encapsulate the steps that
are executed by a command.
Command::doIt() executes command
Allows Command::unDoIt() etc
GoF design pattern: Decorator
Decorator::m() adds additional behaviour, but delegates
to real Object::m() for real behaviour
Eg, 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&…
Servlet
+ init ( )
+ destroy ( )
# processRequest ( )
# doGet ( )
# doPost ( )
+ getServletInfo ( )
+ forward ( )
+ forwardAbsolute ( )
+ getUrlBase ( )
Front Controller
0..1
FrontServlet
# processRequest ( )
- getCommand ( )
- getCommandClass ( )
# controller
FrontCommand
+ init ( )
+ processRequest ( )
AddStudent
Error
+ processRequest ( )
+ processRequest ( )
Front Controller
Front Controller: Sequence
Diagram
Front Controller:
ProcessRequest
Front Controller (cont’d)

Week 6 lecture slides

Transcript Week 6 lecture slides

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