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JEE – Design Patterns
Front Controller
Intercepting Filter
Transfer Object
CS 446/646 ECE452
Jun 13th, 2011
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CHERITON SCHOOL OF
COMPUTER SCIENCE
Overview
JEE Core Design Patterns
Presentation
Tier
Business
Tier
Integration
Tier
Intercepting Filter
Business Delegate
Data Access Object
Front Controller
Service Locator
Service Activator
Context Object
Session Facade
Domain Store
App Controller
Application Service
Web Service Broker
View Helper
Business Object
Composite View
Composite Entity
Service to Worker
Transfer Object
Dispatcher View
TO Assembler
Value List Handler
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Front Controller
Intent
●
provide a single point for processing user requests
http://java.sun.com/blueprints/corej2eepatterns/Patterns/FrontController.html
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Front Controller
Motivation
●
single processing point for all
client requests
–
–
across views & session
can be used to inject cross-cutting concerns
●
●
–
–
logging
security
can we have multiple controllers?
we can map multiple requests to the same controller?
http://java.sun.com/blueprints/corej2eepatterns/Patterns/FrontController.html
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Front Controller
Motivation
●
separation of concerns
–
business code from presentation code
http://www.corej2eepatterns.com/Patterns2ndEd/FrontController.htm
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Front Controller
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http://www.corej2eepatterns.com/Patterns2ndEd/FrontController.htm
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Front Controller
Motivation
●
provides resource mapping
–
physical
●
–
http://server/resource.jsp
virtual/logical
●
●
●
http://server/servlet/resourceController
http://server/servlet/page1.help
logical partitioning of application views?
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Front Controller
Motivation
●
organic growth
–
controllers can be specialized (sub-classing)
●
●
GWTServlet
reusability
–
–
–
declarative vs. non-decalrative mapping
what is declarative mapping?
why do we care?
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Intercepting Filter
Intent
●
common mechanism for pre & post processing of user
requests
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Intercepting Filter
Filter chain
request
request
request
controller
filter1
filter2
response
response
response
how is this different from traditional pipes & filters?
how is this different from batch pipes & filters?
what type of data flows through the pipes?
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Intercepting Filter
Context
●
“presentation-tier request handling mechanism receives many
different types of requests, which require varied types of
processing”*
Common Examples*
●
has the client been authenticated?
●
does the client have a valid session?
●
is the client's IP address from a trusted network?
●
does the request path violate any constraints?
●
what encoding does the client use to send the data?
●
do we support the browser type of the client?
* http://java.sun.com/blueprints/corej2eepatterns/Patterns/InterceptingFilter.html
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Intercepting Filter
Easy Solution
●
if-then-else in the controller (why not?)
An Elegant Solution
●
common reusable processing
●
easy to add/modify/delete filtering functionality
–
even better if declarative
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Intercepting Filter
Sounds like Decorator (how?)
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http://en.wikipedia.org/wiki/Decorator_pattern
Intercepting Filter
Sounds like Decorator
http://msdn.microsoft.com/en-us/library/ff647251.aspx
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Intercepting Filter
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http://msdn.microsoft.com/en-us/library/ff647251.aspx
15
Intercepting Filter
What is the different between the two?
●
structure
–
FilterChain is no longer required
●
runtime behaviour
●
take another look at the diagram
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Intercepting Filter
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http://msdn.microsoft.com/en-us/library/ff647251.aspx
17
Intercepting Filter
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http://msdn.microsoft.com/en-us/library/ff647251.aspx
18
Intercepting Filter
Evolution
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Intercepting Filter
Evolution
What is the impact of this?
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Intercepting Filter
Evolution
What is the impact of this?
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Intercepting Filter
List some drawback of this design?
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Intercepting Filter
Motivation
●
functionality injection
●
improved reusability
–
●
filter chains can be defined in a number of ways
declarative configuration
Difficulties
●
information sharing
●
fault-tolerance
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Transfer Object
Intent
●
to transfer multiple data elements over a tier
getUserName()
getUserAge()
Client
getUserPrefs()
Business
Component
User
Looks harmless??
http://java.sun.com/blueprints/corej2eepatterns/Patterns/TransferObject.html
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Transfer Object
Solution
●
use a
Transfer Object
to encapsulate
the data
http://java.sun.com/blueprints/corej2eepatterns/Patterns/TransferObject.html
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Transfer Object
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CHERITON SCHOOL OF
http://java.sun.com/blueprints/corej2eepatterns/Patterns/TransferObject.html
COMPUTER SCIENCE
Transfer Objects
Scope & Complexity?
●
●
●
can we have multiple types of
transfer objects to represent data (a user)?
create the transfer
objects required
how complex?
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Transfer Object
Consequences
●
simplified remote interface
●
fewer remote calls
●
stale objects: very common problem for web apps
–
–
●
what are stale objects?
how would you deal with it?
serialization over the wire?
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