Transcript service locator pattern - Computer Science and Engineering

COMP9321 Web Application Engineering
Semester 2, 2015
Dr. Amin Beheshti
Service Oriented Computing Group, CSE, UNSW Australia
Week 8
http://webapps.cse.unsw.edu.au/webcms2/course/index.php?cid=2411
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Assignment 2
Deadline Extended:
The due date for assignment2 is (end of Mid Semester Break): Sunday,
October 4 2015, 23:59:59.
Demo: Week 10 (the week starting 5 October), during the lab times in
UNSW, CSE, Calendar:
http://www.cse.unsw.com/about-us/organisational-structure/student-services/calendar/
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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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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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Service Locator Pattern
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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.
• Locating a JNDI-managed service object is common to all clients that need to
access that service object.
• It is easy to see that many types of clients repeatedly use the JNDI service, and
the JNDI code appears multiple times across these clients. This results in an
unnecessary duplication of code in the clients that need to look up services.
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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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Service Locator Pattern
To build a service locator pattern, we need:
Service Locator
InitialContext
ServiceFactory
BusinessService
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Service Locator Pattern
To build a service locator pattern, we need:
Service Locator:
The Service Locator abstracts the API lookup services, vendor dependencies, lookup
complexities, and business object creation, and provides a simple interface to clients.
InitialContext
ServiceFactory
BusinessService
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Service Locator Pattern
To build a service locator pattern, we need:
Service Locator:
The Service Locator abstracts the API lookup services, vendor dependencies, lookup
complexities, and business object creation, and provides a simple interface to clients.
InitialContext:
The InitialContext object is the start point in the lookup and creation process.
ServiceFactory:
BusinessService:
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Service Locator Pattern
To build a service locator pattern, we need:
Service Locator:
The Service Locator abstracts the API lookup services, vendor dependencies, lookup
complexities, and business object creation, and provides a simple interface to clients.
InitialContext:
The InitialContext object is the start point in the lookup and creation process.
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.
BusinessService:
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Service Locator Pattern
To build a service locator pattern, we need:
Service Locator:
The Service Locator abstracts the API lookup services, vendor dependencies, lookup
complexities, and business object creation, and provides a simple interface to clients.
InitialContext:
The InitialContext object is the start point in the lookup and creation process.
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.
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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Service Locator Pattern
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Identifying Service Locator Pattern in the phonebook lab
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Identifying Service Locator Pattern in the phonebook lab
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Identifying Service Locator Pattern in the phonebook lab
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Dependency Injection
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Dependency
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SAX Books Parser Example
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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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Benefits of "dependency injection" …
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Data Access Object
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Data Access Object
Context
• 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.
http://www.oracle.com/technetwork/java/dataaccessobject-138824.html
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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.
http://www.oracle.com/technetwork/java/dataaccessobject-138824.html
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Data Access Object: Sequence Diagram
http://www.oracle.com/technetwork/java/dataaccessobject-138824.html
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Business Delegate
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Business Delegate
Context
• 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.
http://www.oracle.com/technetwork/java/businessdelegate-137562.html
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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.
• Using a Business Delegate reduces the coupling between presentation-tier clients
and the system's business services.
• 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.
http://www.oracle.com/technetwork/java/businessdelegate-137562.html
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Business Delegate
• Client: requests the BusinessDelegate to provide access to the
underlying business service.
• BusinessDelegate: uses a LookupService to locate the required
BusinessService component.
http://www.oracle.com/technetwork/java/businessdelegate-137562.html
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Business Delegate Sequence Diagrams
http://www.oracle.com/technetwork/java/businessdelegate-137562.html
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Business Delegate, 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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Business Delegate, 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.
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Business Delegate, 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.
http://www.programmableweb.com/
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API Engineering
Will be covered in COMP9322
API Engineering Seminar
Speaker:
Prof. Boualem Benatallah
Date: Thu 8/10/2015
Time: 15:00 - 17:00 (2 hours)
Room: K17_113
Reason: COMP9322 Open Lecture
Please Attend!
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More Patterns
Core J2EE Patterns Catalog:
http://www.oracle.com/technetwork/java/index-138725.html
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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A few more things to consider
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Guarding a View
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Guarding a View
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Guarding a View
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Guarding a View
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Guarding a View
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Duplicate Form Submissions
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Duplicate Form Submissions
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Duplicate Form Submissions
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Synchronizer Token
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Synchronizer Token
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Background Tasks
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Background Tasks
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Background Tasks
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References
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Core J2EE patterns, Deepak Alur, John Crupi and Dan Marlks, Prentice Hall
http://www.oracle.com/technetwork/java/index-138725.html
Patterns of Enterprise Application Architecture, Martin Fowler, Addison-Wesley
http://java.sun.com/blueprints/patterns/
http://www.oracle.com/technetwork/articles/javase/index-142890.html
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