GoF J2EE Design Patterns
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This document provides an overview of design patterns including the Gang of Four (GoF) patterns. It discusses creation patterns like abstract factory and singleton that deal with object creation. Structural patterns like adapter, decorator, and composite that deal with class and object structure. Behavioral patterns like strategy and state that deal with object interaction and behavior. Examples of each pattern type are provided.
GoF J2EE Design Patterns
- 1. @Diego Thanh Nguyen -‐ http://free.smartbiz.vn J2EE DESIGN PATTERN 10/8/12 www.smartbiz.vn 1
- 2. Table Of Content q I. GoF Design Pattern v I.1. Creation Patterns v I.2. Structural Patterns v I.3. Behavioral Patterns q II. J2EE Presentation: q III. J2EE Business: q IV. J2EE Integration 10/8/12 www.smartbiz.vn 2
- 3. I. How Design Patterns Arise ? Pattern 1. Context Problem a design situation giving rise to a design problem Problem a set of forces occuring in that context Solution 2. Context a form or rule that can be applied to resolve these forces Forces IF you Nind yourself in CONTEXT 3. for example EXAMPLES, Solution with PROBLEM, entailing FORCES THEN for some REASONS, apply DESIGN FORM AND/OR RULE BeneFits Consequences to construct SOLUTION Related Patterns leading to NEW CONTEXT & OTHER PATTERNS 10/8/12 www.smartbiz.vn 3
- 4. I. Design-‐Pattern Catalog ! ! Purpose! Creational! Structural! Behavioral! Class! • Factory!Method! • Adapter! • Interperter! • Singleton! • Façade! • Observer! • Factory! • Decorator! • Command! • Abstract!Factory! • Composite! • Iterator! Scope! • Builder! • Adapter! • Chain!of!Responsibility! Object! • Prototype! • Bridge! • Mediator! • Object!Pool! • Flyweight! • Momento! • Proxy! • State! • Strategy! • Visitor! ! ! Defer object creation to Describe algorithms and another object Nlow control Describe ways to assemble objects 10/8/12 www.smartbiz.vn 4
- 5. I.1. Creation Patterns q Creational Patterns prescribe the way that objects are created. These patterns are used when a decision must be made at the time a class is instantiated. q Singleton: ensure a class has one Instance, and provide a global point of access to it. q Abstract Factory: provide an interface for creating families of related or dependent objects without specifying their concrete classes. 10/8/12 www.smartbiz.vn 5
- 6. I.1.1 Abstract Factory q Intent: create families of related objects without specifying subclass names q Applicability: when clients cannot anticipate groups of classes to instantiate q Concrete factories create groups of strategies 10/8/12 www.smartbiz.vn 6
- 7. I.2. Structural Patterns q Structural Patterns prescribe the organization of classes and objects. q Adapter v Convert the interface of a class into another interface that clients expect v Adapter lets classes work together that couldn’t otherwise because of incompatible interfaces q Decorator v Extend the functionality of the original class in a way that is transparent to the client class 10/8/12 www.smartbiz.vn 7
- 8. I.2.1. Composite q Intent v treat individual objects & multiple, recursively-‐ composed objects uniformly q Applicability v Objects must be composed recursively, v and no distinction between individual & composed elements, v and objects in structure can be treated uniformly 10/8/12 www.smartbiz.vn 8
- 9. I.2.1. Composite q CORBA Naming Service example using CosNaming::BindingIterator (which is an example of the “Batch Iterator” pattern compound from POSA5) Composite Node Leaf Node 10/8/12 www.smartbiz.vn 9
- 10. I.3. Behavioral Patterns q Behavioral Patterns prescribe the way objects interact with each other. They help make complex behavior manageable by specifying the responsibilities of objects and the ways they communicate with each other. q State: allow an object to alter its behavior when its internal state changes 10/8/12 www.smartbiz.vn 10
- 11. I.3.1. Strategy q Intent v deNine a family of algorithms, encapsulate each one, & make them v interchangeable to let clients & algorithms vary independently q Applicability v When object is conNigurable with one of many algorithms, v and all algorithms can be encapsulated, v and one interface covers all encapsulations 10/8/12 www.smartbiz.vn 11
- 12. I.3.1. Strategy q Strategy applied in distributed (middleware) Hook for marshaling Hook for strategy the request demuxing Hook for the event strategy demuxing strategy Hook for the Hook for the connection concurrency management strategy strategy Hook for the underlying transport strategy 10/8/12 www.smartbiz.vn 12
- 13. I.3.1. Oracle Fusion Component OracleFusion Groupware API: A unified interface for all connectors that access the groupware servers via WebDAV, applying Singleton, Façade and Factory design patterns All connectors utilize the Jakarta EnterConnect Groupware API Jackrabbit (client-side) API to send requests to and receive Exchange OpenGroupware Lotus Domino responses from a variety of Connector Connector Connector WebDAV-enabled groupware servers MS Exchange 2003 Email Jakarta Slide API WebDAV Server XML HTTP request Calendar Jakarta Commons HTTP Client JDOM (JSR 102) Contact XML HTTP response Jakarta Commons Logging Java Transaction API Task Uploaded Document Jakarta Jackrabbit re-uses some of open source libraries such as the Jakarta Commons library (HTTP Client &Logging), JDOM (JSR 102), JTA, JMX, … 13
- 14. I.3.2. OF Design Pattern q Singleton: the Connector class must only have one instance because it’s wasteful & useless to keep several instances on memory. Keeping so many connectors will difNicult to manage lifecycle & impact the performance of application. q Factory Method: because of we assume our API can be used against multiple servers so that there must be a Connector for each server (i.e. ECExchangeConnector, ECLotusDominoConnector, ECOpenGroupwareConnector). Each connector is responsible for manufacturing its own managers (MailManager, CalendarManager, TasksManager) and delegate the jobs to them. The connector will only be determined by the client depending on the conNiguration. v For example, if a client (portlet) need to send a mail by Exchange server then it will call the ECExchangeConnector; this connector then will use its localized manager ExchangeMailManager to make life easier. q Abstract Factory: ECGroupwareFactory is the abstract factory class for all connectors because it will expose a uniFied interface for connectors to client. q Facade: the uniFied interface will be deFined in the Façade pattern. As stated before, a speciNic Connector will delegate the appropriate jobs to its subsystems (managers). The façade pattern also decouples the managers from the client and other managers, thereby promoting independence and portability. 10/8/12 www.smartbiz.vn 14
- 15. I.3.1. OF Design Pattern <<Factory Method>> «interface» TasksManager <<Abstract Factory>> ECGroupwareFactory <<Façade>> ExchangeTasksManager <<Singleton>> ECLotusDominoConnector ECOpenGroupwareConnector ECExchangeConnector ExchangeCalendarManager ExchangMailManager «interface» «interface» MailManager CalendarManager Apache Slide Class 15 10/8/12 www.smartbiz.vn
- 16. I.4.1. Observer Pattern q Easier to keep a consistent and maintainable view of the data v Half as many connections between actions, views v Views are independent and unaware of each other Data Action Action Action Action Action Action Action Action View à View & Action à Data notiNies observers via events View Messages about the data when the state of the data changes 10/8/12 www.smartbiz.vn 16
- 17. I.4.2. Implementing an Observer 1. Assign the subject to the observers (MainForm_Load) IssueSubject 10/8/12 www.smartbiz.vn 17
- 18. I.4.3. Implementing an Observer 1. Assign the subject to the observers (MainForm_Load) m_subject = new IssueSubject() paneA.Subject = m_subject b paneB.Subject = m_subject ... c d a IssueSubject 10/8/12 www.smartbiz.vn 18
- 19. I.4.4. Implementing an Observer 1. Assign the subject to the observers (MainForm_Load) m_subject = new IssueSubject() paneA.Subject = m_subject b paneB.Subject = m_subject ... c d 2. Observers bind and save changes to Subject.DataSet a IssueSubject 10/8/12 www.smartbiz.vn 19
- 20. I.4.5. Implementing an Observer 1. Assign the subject to the observers (MainForm_Load) m_subject = new IssueSubject() paneA.Subject = m_subject paneB.Subject = m_subject ... b c d 2. Observers bind and save changes to Subject.DataSet a 3. When data changes, subject raises DataChanged event IssueSubject 10/8/12 www.smartbiz.vn 20
- 21. I.4.6. Implementing an Observer 1. Assign the subject to the observers (MainForm_Load) m_subject = new IssueSubject() paneA.Subject = m_subject b paneB.Subject = m_subject ... c d 2. Observers bind and save changes to Subject.DataSet a 3. When data changes, subject raises DataChanged event 4. Observers handle subject events to rebind data, if IssueSubject they care m_subject.DataChanged += … ‘ rebind 10/8/12 www.smartbiz.vn 21
- 22. I.5.1. Coordinate Command State q Related menu and toolbar widgets are not automatically handled together q Command Pattern v Command objects unify the state and action for related UI widgets q Example: v “Save” action Ø Menu item Ø Toolbar button Ø Context menu 10/8/12 www.smartbiz.vn 22
- 23. I.5.2. Implementing a Command 1. Create a Command for each action in MainForm_Load() action = new Command.Action(this.WorkOfNline_Action) ofNlineCommand = new Command(action) 2. Wire menu items and toolbar buttons to the Command using Commander objects MenuItemCommander.Connect(menuWorkOfNline, ofFlineCommand ) ToolBarButtonCommander.Connect(tlbOfNline, ofFlineCommand ) 3. Control button and menu item state through the Command ' Disable all UI widgets connected to this command ofNlineCommand.IsEnabled = false 10/8/12 www.smartbiz.vn 23
- 24. I.6.1. Accelerated J2EE Development q Architect Service-‐Oriented Components v Design for Flexible, Agile Applications and Iterative Development q Apply/Extend Pre-‐Built COTS Components v Infrastructure and Common Business Components q Generate/Extend Custom Components v Rapidly Specify and Provision New Components q Leverage Industry Development Standards v Frameworks (STRUTS, Spring / Weld, Hibernate) v Patterns (MVC) v XML, Best Practices 10/8/12 www.smartbiz.vn 24
- 25. II. J2EE Application Design Patterns Business Logic & Data Integration Presentation Messaging Fabric & Persistence EJB Container EJB Container Response 8. Execute Business Resources Biz Method 13. Request Service 14. CRUD Facade 10b. Data Data Query 9. Get/Set Access Database <<de-‐serialize>> Web Server & 18. Response Assemble Remove Object Serialized RMI JMS Servlet Engine Value Data Directory Object 16. Forward JSF, JSP JMS (Taglibs) <<creates>> Value 12. 1. Request Object Get/Set 17. State? Assembler <<uses>> Action Remove Data Servlet 10a. Access <<uses>> Invoke Proxy 4. Dispatch 2. Fill State Data XML 11. Entity Connection 3. Validate CRUD Connection Action to Bean Pool (Stateless) Data Factory Form & Value Session Forward <<uses>> Object Bean Mappings Action Form 5. Get Delegate Action Object 15. Fill State <<uses>> Key Other Infrastructure 6. Execute <<supplies>> RMI Business Business <<uses>> EJB Container Value Model Delegate Delegate M JMS Object Pattern Factory Adapter 7a. Event Security Messaging Event Execute View Interceptor Management Command NotiFication Biz Method Business V Pattern Framework Framework Factory Framework Service Proxy <<uses>> Controller C Pattern <<uses>> 7b. CRUD Data Data Message Q Filter Service Access & Channel Other Interceptors Activation Proxy To DAO P Pattern Locator 10/8/12 www.smartbiz.vn 25
- 26. II. Model-‐View-‐Controller – Passive :Controller :Model :View handleEvent service update getData 10/8/12 www.smartbiz.vn 26
- 27. II. Model-‐View-‐Controller – Active Controller <<interface>> Observer Model +update() View :Model :View handleEvent notify update getData data 10/8/12 www.smartbiz.vn 27
- 28. II.1. Presentation Tier Patterns q Intercepting Filter q Front Controller: Use of a Controller to handle all web requests q Dispatcher View: The controller works with a Dispatcher that handles navigation q Composite View q View Helper q Service to Worker 10/8/12 www.smartbiz.vn 28
- 29. II.2. Intercepting Filter q Problems: v Verify authentication v Check type of client v Is the session valid? q Solution: implement one or more Intercepting Nilters. q Sample: Filter-‐servlet -‐ can transparently pre and post process all requests in an unlimited length Nilter chain. 10/8/12 www.smartbiz.vn 29
- 30. II.3. Front Controller & Dispatcher q Front Controller -‐ Problems: v Multiple views. v Navigation logic embedded in views. v DifNicult to maintain view logic as application grows. v Want to reuse view navigation within multiple clients. 10/8/12 www.smartbiz.vn 30
- 31. II.3. Front Controller -‐ Dispatcher Client FrontController Dispatcher Vi ew Helper 1: Send Request 1.1: Delegate Request 1.1.1: Forward Request 2: Send Request 2.1: Forward Request 3: Send Request 3.1: Process Request 10/8/12 www.smartbiz.vn 31
- 32. III.4. View Helper q Problem: v Many common operations in each view. v Often view output is dependant on business data. v Create more cohesive look and feel. v Like to hand off UI to web design group q Solution: v Basically anything that helps you display your model data in a reusable fashion. v Implemented as JavaBeans, Tags or XML/XSLT q See the JSTL, JSF and Struts. 10/8/12 www.smartbiz.vn 32
- 33. II.5. Composite View q Problem: v Many common & recurring components in a view. v Fragments may display differently given user type (i.e. faculty, student). v Look and feel in Nlux needs to be easily updateable. q Differs from View Helper as the Composite View decides which sub-‐views to include while View Helper generally decides how to display a given sub-‐view. 10/8/12 www.smartbiz.vn 33
- 34. III. Business Tier Patterns q Business Delegate: use of a Business Delegate to hide Implementation Detail. q Session Façade q Service Locator q Value Object q Composite Entity q Value Object Assembler q Value List Handler 10/8/12 www.smartbiz.vn 34
- 35. III.1. Business Delegate Cl ient BusinessService 1: Creat e wi th ID BusinessDelegate 1.1: Convert ID to Handle Handle 1.1.1: Create 2: Invoke 2.1: Get Business Service 2.1. 1: Connect 2.1. 2: Return Business Service 2.2: Invoke 10/8/12 www.smartbiz.vn 35
- 36. III.2. Session Façade Pattern q Problem: v Need very loose coupling between client and ever changing business tier. v Data tier changing; need to improve reuse. q Session Bean EJB Tier provides uniNied approach q Façade hides Entity Bean Details Session Client Entity Bean Bean 10/8/12 www.smartbiz.vn 36
- 37. IV. Integration q Data Access Object q Service Activator q User WorkNlow Integrator 10/8/12 www.smartbiz.vn 37
- 38. IV.1. Data Access Object Business DataAcces accesses Object sObject inherits inherits inherits Oracle Sybase DB2DAO DAO DAO adapts adapts adapts Oracle DB2 Sybase Database Database Database 10/8/12 www.smartbiz.vn 38
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