IMPORTANT NOTICE TO STUDENTS These slides are NOT to be used as a replacement for student notes. These slides are sometimes vague and incomplete on purpose to spark class discussions

JEE – Design Patterns Front Controller Intercepting Filter Transfer Object

CS 446/646 ECE452 Jun 13th, 2011

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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 WATERLOO CHERITON SCHOOL OF COMPUTER SCIENCE

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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 WATERLOO CHERITON SCHOOL OF COMPUTER SCIENCE

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Front Controller Motivation ●

separation of concerns –

business code from presentation code

http://www.corej2eepatterns.com/Patterns2ndEd/FrontController.htm WATERLOO CHERITON SCHOOL OF COMPUTER SCIENCE

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Front Controller

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http://www.corej2eepatterns.com/Patterns2ndEd/FrontController.htm CHERITON SCHOOL OF COMPUTER SCIENCE

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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? WATERLOO CHERITON SCHOOL OF COMPUTER SCIENCE

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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 WATERLOO

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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 WATERLOO CHERITON SCHOOL OF COMPUTER SCIENCE

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Intercepting Filter

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http://msdn.microsoft.com/en-us/library/ff647251.aspx

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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

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Intercepting Filter

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http://msdn.microsoft.com/en-us/library/ff647251.aspx

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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 WATERLOO CHERITON SCHOOL OF COMPUTER SCIENCE

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Transfer Object Solution ●

use a Transfer Object to encapsulate the data

http://java.sun.com/blueprints/corej2eepatterns/Patterns/TransferObject.html WATERLOO CHERITON SCHOOL OF COMPUTER SCIENCE

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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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