1. CS 355 – Software Engineering 1
Patterns – Big Picture
CS 355 – Software Engineering 1

2. Creational Design Patterns (so far)
Factory Method
Abstract Factory
Singleton
Builder
Prototype

3. Structural Design Patterns
Adapter
Bridge
Composite
Decorator
Façade
Proxy
Flyweight

4. Behavioral Design Patterns
Command
Observer
State
Strategy
Template Method
Visitor
Chain of Responsibility
Interpreter
Mediator
Memento

5. Other Basic Design Patterns

6. Builder Creational Description
Separate the construction of a complex object from its representation so that the same construction process can create different representations

7. Builder Example: Vacation planner
Vacations have days, days have activities
Every person has different set
How to create?
AbstractBuilder
Interface, methods to buildDay(), addHotel(), addEvent(), etc.
VacationBuilder
Concrete class with vacation variable, implementation of methods, method to retrieve the completed object
Client – high level activity with calls to interface methods as needed, call to method to get completed object

8. Prototype Creational Description:
Specify the kinds of objects to create using a prototypical instance, and create new objects by copying this prototype

9. Prototype Example: Monster creation in a game Interface: Monster
Concrete Classes: WellKnownMonster, DynamicPlayerGeneratedMonster
MonsterMaker – generates a monster by calling getMonster() on registry
Doesn’t know what type of monster it gets
MonsterRegistry – finds correct monster for situation, returns clone of concrete monster

10. Mediator Behavioral Description
Define an object that encapsulates how a set of objects interact. Mediator promotes loose coupling by keeping objects from referring to each other explicitly, and lets you vary their interaction independently

11. Mediator Example: Java-enabled house
Alarm, CoffeePot, Calendar, Sprinkler
Problem: interactions between each pair of objects, and possibly in both directions
Solution: Mediator object in the middle
Regular objects tell the mediator when their state changes
Mediator forwards requests for objects to respond to

12. Memento Behavioral Description
Without violating encapsulation, capture and externalize an object’s internal state so that the object can be restored to this state later

13. Memento Example – “Save current state” in game MasterGameObject (MGO)
Instance variable: gameState, referring to separate GameMemento object
Object getCurrentState() // return gs
restoreState(Object saved) // set gs
GameMemento
Has savedGameState
Client
Can now save current state to variable through MGO and restore it when desired

14. Flyweight Structural Description
Use when one instance of a class can, through an outside manager, provide many virtual instances, thus saving creation time

15. Flyweight Developing a landscape design software system
Tree class, has X/Y coordinates, an age, a display function which draws tree based on age
Problem: designs with large number of trees start slowing down
Solution: have one class (Flyweight) which holds all X/Y/Age information for each tree
To display all trees, use Flyweight class information as parameters to Tree display function
For each tree, display using Flyweight info.

16. Interpreter Behavioral
Given a language, define a representation for its grammar along with an interpreter that uses the representation to interpret sentences in the language

17. Interpreter Example – language for Duck simulation
right; while (daylight) fly; quack; …
Need to create a formal grammar
Pattern creates a class-based hierarchical representation of the grammar
Each class has an interpret() method

18. (much material from Core J2EE Patterns by Alur et. al.)
J2EE Design Patterns
(much material from Core J2EE Patterns by Alur et. al.)

19. J2EE Four/five tier system Client (applet or application)
HTML, Applet or Thick Client
Web container
JSP, Servlet
Business Tier
EJB
Resource Tier
Database Systems
Other components can exist in multiple tiers; often considered fifth (Integration) tier
E.g. JDBC, JMS, connectors, other middleware

20. J2EE General Issues Session Management Controlling Client Access
Session State on Client
Hidden fields, cookies
Security issues
Session State in Presentation Tier
Controlling Client Access
Guarding Views
Duplicate form submissions
Validation

21. Presentation Tier Patterns
Intercepting Filter
Front Controller
View Helper
Composite View
Service to Worker
Dispatcher View

22. Business Tier Patterns
Business Delegate
Value Object
Session Façade
Composite Entity
Value Object Assembler
Value List Handler
Service Locator

23. Integration Tier Patterns
Data Access Object
Service Activator

24. Intercepting Filter Presentation Tier
Problem: Request-handling mechanism receives many types of requests
Has client been authenticated?
Does client have valid session?
Is client’s IP address trusted?
Does request path violate any constraints?
What encoding is used?
Do we support the browser type?

25. Intercepting Filter (2)
Solution: Create pluggable filters to process requests in a standard manner
Structure:
Client
FilterManager, has
Filter Chain
Filter1, Filter2, …, FilterN
Target

26. Intercepting Filter (3)
Consequences:
Centralized control, loosely coupled handlers (+)
Improved reusability (+)
Flexible configuration (+)
Information sharing is inefficient (-)

27. Intercepting Filter (4)
What design patterns could be used in implementing the filters?

28. Front Controller Presentation Tier
Problem: If don’t use centralized mechanism, tend to get
Each view providing its own system services (duplicate code)
View navigation left to views (mix view content and view navigation)

29. Front Controller (2)
Solution: Use a controller as the initial point of contact for a request. Controller will manage the handling of the request, delegate business processing, choose the appropriate view, and manage selection of content creation strategies

30. Front Controller (3) Structure: Client FrontController Dispatcher View
Responsible for view management and navigation
View
Represent and dipslay information to client
Helper
Helps view or controller complete its processing (often a JavaBean or JSP)

31. Front Controller (4) Strategies: Servlet Front Strategy
Controller implemented as servlet
Preferred, as work is (mostly) not display
JSP Front Strategy
Controller implemented as JSP

33. Front Controller (5) Question:
What is the difference between Front Controller and MVC?

34. View Helper Presentation Tier
Problem: View changes often; how to keep display from intermixing with business and data access logic?
Solution:
View contains formatting code
Processing responsibilities are delegated to view helper classes, which also store intermediate data model
Helper can get data or properties

35. View Helper (2) Structure: Strategies: Client View
Helper(s) – 1 or more
Strategies:
JSP View Strategy
Preferred (why?)
Servlet View Strategy

36. Composite View Presentation Tier
Problem: Overall view often has many subviews
Example: main news page may have navigation, search, feature story, and headlines sections
Solution:
Use composite views that are composed of multiple atomic subviews

37. Composite View (2) Structure: Basic View has two subtypes
View (atomic)
CompositeView, consists of multiple BasicViews
Often also includes ViewManager between CompositeView and its BasicViews

38. Composite View (3) Consequences: Flexible (+) Runtime overhead (-)
Can be difficult to manage (-)

39. Service To Worker Presentation Tier Problem:
Combination of problems leading to Front Controller and View Helper
No centralized component for managing access control, content retrieval or view management
Duplicate control code gets generated in various views

40. Service To Worker (2) Solution: Structure
Combine a controller and dispatcher with views and helpers to handle client requests and prepare a dynamic presentation of the response.
Structure
Controllers delegate to helpers
Helpers populate intermediate model for view
Dispatcher responsible for view management and navigation

41. Dispatcher View Presentation Tier Problem: Solution
Combination of problems leading to Front Controller and View Helper
Same as Service to Worker
Solution
Similar to “Service To Worker”, except Dispatcher only works with Views, and Views use Helpers
Suitable if no outside resources necessary to choose the view

42. Business Tier Patterns
Mostly deal with EJBs
Not in our curriculum
Look up if doing EJB work
Patterns:
Business Delegate - example
Value Object
Session Façade
Composite Entity
Value Object Assembler
Value List Handler
Service Locator

43. Business Tier Patterns
Business Delegate
Use a business delegate to reduce coupling between presentation-tier clients and business services.
Business delegate hides implementation details of business service (e.g. lookup and access details of EJBs)
Business delegate uses Lookup Manager to find correct business service

44. Business Tier Patterns
Business Delegate (2)
Structure
Client
Business Delegate
Uses: Business Service
Has: Lookup Service
Lookup Service
Looks up / creates the appropriate Business Service

45. Data Access Object Integration Tier Problem:
Access to data varies by the source of the data
Can use JDBC, but still have issues
SQL statements vary by vendor
Access varies more if using non-relational data (OODB, flat files, etc.)

46. Data Access Object (2) Solution:
Use Data Access Object (DAO) to abstract and encapsulate all access to data source
DAO also manages connections

47. Data Access Object (3) Structure Business Object Uses DAO
Obtains/modifies: ValueObject
DAO
Creates/uses: ValueObject
Encapsulates: DataSource
ValueObject
Value object used as a data carrier
DataSource
Abstraction of physical data source
Often supports other features (e.g. connection pooling)

48. Data Access Object (4) Granularity Uses One per database
One per object
Uses
If one per object, can use DAO Factory
Abstract Factory
Factory Method

49. Patterns in Software Development

50. Patterns We’ve looked at: Design Patterns J2EE Patterns
Where does this fit in the software development process?
J2EE Patterns
What aspect(s) of the software development process do these patterns apply to?

51. Software Development Review
Requirements (Generation)
(Requirements) Analysis
Design
High-level
Low-level
Implementation
Testing
Maintenance

52. Another View of Software Development (Pressman, 2005)
Communication
Project initiation
Requirements Gathering
Planning
Estimating
Scheduling
Tracking
Modeling
Analysis
Design
Construction
Code
Test
Deployment
Delivery
Support
Feedback

53. Yet Another View of Software Development (Ambler 1998)
“Software Process is a collection of patterns that defines a set of activities, actions, work tasks, work products and/or related behaviors required to develop computer software”
Three types of patterns
Task patterns – software engineering action or work task
Example: Requirements Gathering
Stage patterns – define a framework activity for the process
Example: Communication
Incorporates task patterns such as Req. Gath.
Phase patterns – define the sequence of framework activities that occur within the process
Example: Spiral Model, or Prototyping

54. Domain Patterns Example: Security Patterns Single Point of Access
One place to access application initially
Avoid duplicate code that needs to be maintained
No back doors
Checkpoint
One point for authentication and authorization
Normally separate these two
Authentication is application-independent
Authorization is application-specific
Roles
Problem: combinatorial explosion of users and privileges
Solution: combine privileges into roles, assign users to roles

55. Resources for Patterns
Process Patterns
Architectural Patterns
Implementation Patterns
Book by Kent Beck, “Implementation Patterns”
Testing Patterns