1. COMP9321 Web Application Engineering Semester 1, 2017
Dr. Amin Beheshti
Service Oriented Computing Group, CSE, UNSW Australia
Week 8
2457
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2. Assignment 1 Marks on GradeBook Assignment 2 is due end of Week 9: Sunday, 7 May 2017, 23:59:59
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3. J2EE Design Patterns Last Week, Design Pattern Part I:
Model View Controller:
MVC is the J2EE BluePrints recommended architectural design pattern for interactive applications.
Front Controller (Command):
For providing a central dispatch point to handle all incoming requests.
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4. J2EE Design Patterns This Week, Design Pattern Part II:
Service Locator:
Typically used in business layer for locating resources (such as database connection)
Data Access Object:
A typical pattern for data access layer (linking the data storage layer with the application)
Business Delegate:
A pattern to reduce coupling between presentation-tier clients and business services.
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5. First.. What is Cohesion & Coupling?
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6. Cohesion Seven levels of Cohesion: 7. Functional 6. Informational
Cohesion is defined as the ‘degree of interaction within a module’.
Seven levels of Cohesion:
7. Functional
6. Informational
5. Communicational
4. Procedural
3. Temporal
2. Logical
1. Coincidental
Best
Worst
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7. Cohesion Seven levels of Cohesion: 7. Functional 6. Informational
Cohesion is defined as the ‘degree of interaction within a module’.
Seven levels of Cohesion:
7. Functional
6. Informational
5. Communicational
4. Procedural
3. Temporal
2. Logical
1. Coincidental
Best
Worst
Coincidental: module performs multiple, completely unrelated actions
(degrades maintainability & modules are not reusable)
COMP9321, 17s1, Week 8

8. Cohesion Seven levels of Cohesion: 7. Functional 6. Informational
Cohesion is defined as the ‘degree of interaction within a module’.
Seven levels of Cohesion:
7. Functional
6. Informational
5. Communicational
4. Procedural
3. Temporal
2. Logical
1. Coincidental
Best
Worst
Logical: module performs series of related actions, one of which is selected by calling module.
(interface difficult to understand & module difficult to reuse)
COMP9321, 17s1, Week 8

9. Cohesion Seven levels of Cohesion: 7. Functional 6. Informational
Cohesion is defined as the ‘degree of interaction within a module’.
Seven levels of Cohesion:
7. Functional
6. Informational
5. Communicational
4. Procedural
3. Temporal
2. Logical
1. Coincidental
Best
Worst
Temporal : module performs series of actions related in time.
(code spread out -> not maintainable or reusable)
COMP9321, 17s1, Week 8

10. Cohesion Seven levels of Cohesion: 7. Functional 6. Informational
Cohesion is defined as the ‘degree of interaction within a module’.
Seven levels of Cohesion:
7. Functional
6. Informational
5. Communicational
4. Procedural
3. Temporal
2. Logical
1. Coincidental
Best
Worst
Procedural : module performs series of actions related by procedure to be followed by product.
(not reusable)
COMP9321, 17s1, Week 8

11. Cohesion Seven levels of Cohesion: 7. Functional 6. Informational
Cohesion is defined as the ‘degree of interaction within a module’.
Seven levels of Cohesion:
7. Functional
6. Informational
5. Communicational
4. Procedural
3. Temporal
2. Logical
1. Coincidental
Best
Worst
Communicational :
A communicationally cohesive module is one which performs several functions on the same input or output data. For example, obtain author, title, or price of book from bibliographic record, based on a passed flag (not reusable)
COMP9321, 17s1, Week 8

12. Cohesion Seven levels of Cohesion: 7. Functional 6. Informational
Cohesion is defined as the ‘degree of interaction within a module’.
Seven levels of Cohesion:
7. Functional
6. Informational
5. Communicational
4. Procedural
3. Temporal
2. Logical
1. Coincidental
Best
Worst
Informational : module performs a number of actions, each with its own entry point, with independent code for each action, all performed on the same data structure
(This is an ADT!)
COMP9321, 17s1, Week 8

13. Cohesion Seven levels of Cohesion: 7. Functional 6. Informational
Cohesion is defined as the ‘degree of interaction within a module’.
Seven levels of Cohesion:
7. Functional
6. Informational
5. Communicational
4. Procedural
3. Temporal
2. Logical
1. Coincidental
Best
Worst
Functional : module performs exactly one action
(more reusable, corrective maintenance easier, easier to extend product‎)
Microservices
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14. Coupling Seven levels of Coupling: 5. Data 4. Stamp 3. Control
Coupling is defined as the ‘degree of interaction between two modules’.
Seven levels of Coupling:
5. Data
4. Stamp
3. Control
2. Common
1. Content
Best
Worst
COMP9321, 17s1, Week 8

15. Coupling Seven levels of Coupling: 5. Data 4. Stamp 3. Control
Coupling is defined as the ‘degree of interaction between two modules’.
Seven levels of Coupling:
5. Data
4. Stamp
3. Control
2. Common
1. Content
Best
Worst
Content : one module directly references contents of the other module. e.g., accessing local data of another module.
(almost any change to M1 requires changes to M2‎)
COMP9321, 17s1, Week 8

16. Coupling Seven levels of Coupling: 5. Data 4. Stamp 3. Control
Coupling is defined as the ‘degree of interaction between two modules’.
Seven levels of Coupling:
5. Data
4. Stamp
3. Control
2. Common
1. Content
Best
Worst
Common : two modules have write access to the same global data.
(difficult to reuse + module exposed to more data than necessary ‎)
COMP9321, 17s1, Week 8

17. Coupling Seven levels of Coupling: 5. Data 4. Stamp 3. Control
Coupling is defined as the ‘degree of interaction between two modules’.
Seven levels of Coupling:
5. Data
4. Stamp
3. Control
2. Common
1. Content
Best
Worst
Control : one module passes an element of control to the other.
(modules are not independent)
COMP9321, 17s1, Week 8

18. Coupling Seven levels of Coupling: 5. Data 4. Stamp 3. Control
Coupling is defined as the ‘degree of interaction between two modules’.
Seven levels of Coupling:
5. Data
4. Stamp
3. Control
2. Common
1. Content
Best
Worst
Stamp : data structure is passed as parameter, but called module operates on only some of individual components.
(affects understanding + unlikely to be reusable + passes more data than necessary)
COMP9321, 17s1, Week 8

19. Coupling Seven levels of Coupling: 5. Data 4. Stamp 3. Control
Coupling is defined as the ‘degree of interaction between two modules’.
Seven levels of Coupling:
5. Data
4. Stamp
3. Control
2. Common
1. Content
Best
Worst
Data : every argument is either a simple argument or a data structure in which all elements are used by the called module.
 Each datum is an elementary piece, and these are the only data shared; e.g., passing an integer to a function that computes a square root.
(maintenance is easier) <good design has high cohesion & weak coupling>
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20. Service Locator Pattern
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21. Service Locator Pattern
Context
Service lookup and creation involves complex interfaces and network operations.
Problem
The service locator pattern is a design pattern used in software development to encapsulate the processes involved in obtaining a service with a strong abstraction layer.
When J2EE clients interact with the server side components (EJB: Enterprise Java Beans) or DataSources, clients must locate the service component, which referred to as a lookup operation in JNDI:  Java Naming and Directory Interface.
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22. Service Locator Pattern
Solution
Using a central registry known as the "service locator", which on request returns the information necessary to perform a certain task.
Service Locator object will abstract all JNDI usage to hide the complexities of initial context creation and lookup operations
Multiple clients can reuse the Service Locator object to reduce code complexity, provide a single point of control
msdn.microsoft.com
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23. Service Locator Pattern
The Service Locator abstracts the API lookup services, vendor dependencies, lookup complexities, and business object creation, and provides a simple interface to clients.
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24. Service Locator Pattern
InitialContext:
The InitialContext object is the start point in the lookup and creation process.
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25. Service Locator Pattern
ServiceFactory:
The ServiceFactory object represents an object that provides life cycle management for the BusinessService objects. eg., The ServiceFactory object for enterprise beans is an EJBHome object.
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26. Service Locator Pattern
BusinessService: is a role that is fulled by the service that the client is seeking to access. The BusinessService object :
is created or looked up or removed by the ServiceFactory.
in the context of an EJB application is an enterprise bean.
the context of JDBC is a DataSource.
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27. Service Locator Pattern
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28. Service Locator Pattern
To build a service locator pattern, we need:
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29. Dependency Injection
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30. Dependency
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31. SAX Books Parser Example
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32. What is "dependency injection" ?
In software engineering, dependency injection is a software design pattern that implements inversion of control for resolving dependencies.
Dependency injection means giving an object its instance variables.
Dependency injection provides the ability to pass by reference (or "inject"), service objects into a client (a class or a delegate) at deployment time.
This is a top-down approach, in contrast to a bottom-up one wherein the clients discover or create service objects on their own.  
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33. Benefits of "dependency injection" …
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34.  Data Access Object
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35. Data Access Object Context Problem
Access to data varies depending on the source of the data. Access to persistent storage, such as to a database, varies greatly depending on the type of storage (relational databases, object-oriented databases, flat files, and so forth) and the vendor implementation.
Problem
For many applications, persistent storage is implemented with different mechanisms, and there are marked differences in the APIs used to access these different persistent storage mechanisms. Other applications may need to access data that resides on separate systems.
An example is where data is provided by services through external systems such as business-to-business (B2B) integration systems, credit card bureau service, and so forth.
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36. Data Access Object Solution
Use a Data Access Object (DAO) to abstract and encapsulate all access to the data source. The DAO manages the connection with the data source to obtain and store data.
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37. Data Access Object: Sequence Diagram
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38. Business Delegate
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39. Business Delegate Context Problem
A multi-tiered, distributed system requires remote method invocations to send and receive data across tiers. Clients are exposed to the complexity of dealing with distributed components.
Problem
Presentation-tier components interact directly with business services. This direct interaction exposes the underlying implementation details of the business service application program interface (API) to the presentation tier.
As a result, the presentation-tier components are vulnerable to changes in the implementation of the business services: When the implementation of the business services change, the exposed implementation code in the presentation tier must change too.
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40. Business Delegate Solution
Use a Business Delegate to reduce coupling between presentation-tier clients and business services.
The Business Delegate hides the underlying implementation details of the business service, such as lookup and access details of the EJB architecture.
Another benefit is that the delegate may cache results and references to remote business services. Caching can significantly improve performance, because it limits unnecessary and potentially costly round trips over the network.
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41. Business Delegate
Client: requests the BusinessDelegate to provide access to the underlying business service.
BusinessDelegate: uses a LookupService to locate the required BusinessService component.
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42. Business Delegate Sequence Diagrams
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43. API and API Engineering
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44. API and API Engineering
What is API?
Application programming interface (API) is a set of routines, protocols, and tools for building software applications.
An API expresses a software component in terms of its operations, inputs, outputs, and underlying types.
An API defines functionalities that are independent of their respective implementations.
A good API makes it easier to develop a program by providing all the building blocks. A programmer then puts the blocks together.
What is API Engineering?
API engineering is an application of engineering to the design, development, and maintenance of APIs.
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45. API and API Engineering
Web APIs?
Web APIs are the defined interfaces through which interactions happen between an enterprise and applications that use its assets.
When used in the context of web development, an API is typically defined as a set of HTTP request messages, along with a definition of the structure of response messages, which is usually in an XML or JSON (JavaScript Object Notation) format.
Microservice
e.g. Microservices in IBM Bluemix
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46. API and API Engineering
Web APIs?
While "web API" historically has been virtually synonymous for web service, the recent trend (so-called Web 2.0) has been moving away from Simple Object Access Protocol (SOAP) based web services and service-oriented architecture (SOA) towards more direct representational state transfer (REST) style web resources and resource-oriented architecture (ROA).
Part of this trend is related to the Semantic Web movement toward Resource Description Framework (RDF).
Web APIs allow the combination of multiple APIs into new applications known as mashups.
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47. authored by architects from the Sun Java Center.
More Patterns
Core J2EE Patterns Catalog:
On this site, you will find the entire Java 2 Platform, Enterprise Edition (J2EE) Pattern catalog from the book Core J2EE Patterns: Best Practices and Design Strategies 
authored by architects from the Sun Java Center.
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48. A few more things to consider
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49. Guarding a View
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50. Guarding a View
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51. Guarding a View
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52. Guarding a View
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53. Guarding a View
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54. Duplicate Form Submissions
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55. Duplicate Form Submissions
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56. Duplicate Form Submissions
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57. Synchronizer Token
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58. Synchronizer Token
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59. Background Tasks
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60. Background Tasks
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61. References
Core J2EE patterns, Deepak Alur, John Crupi and Dan Marlks, Prentice Hall
Patterns of Enterprise Application Architecture, Martin Fowler, Addison-Wesley
From Modules to Objects, Professor James Landay, Software Engineering Lecture
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62. COMP9321, 17s1, Week 8