Enterprise Java Beans

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Enterprise Java Beans
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Model 1 J2EE - JSP/Servlets Only
Model/View/Controller
WebServer
JSP page
Servlet
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Model 2 Without EJBs
Model TwoArchitecture
View
WebServer

Control
Model
JSP page
Model ltltPOJOgtgt
ControlltltPOJOgtgt
Servlet
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Deploy Model 1 without EJBs
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Model 2 J2EE - EJBs
Model TwoArchitecture
View
WebServer

Control
Model
JSP page
EntityBean
Session Bean
Servlet
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Deploy Model 2 with EJBs
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Main idea behind EJBs
Encapsulate business logic and business data

• Application servers provide common underlying
  infrastructure (security, transaction management,
  persistence, communication, etc.)
• Provide means to create reusable components that
  can be shared across platforms
• Standard blueprint (architecture) for
  implementation Enterprise Java applications
• Decouple development, assembly and deployment

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EJB Benefits

• Flexibility, Scalability and Adaptability
• Design based on best practices (design patterns)
• Facilitates communication (common framework)
• Reusability
• More robust solutions and saves development time
• Security
• Transaction management
• Concurrency control
• Resource management
• Persistence
• Operating environment handling
• Error handling

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When should I Use J2EE Model 2?

• Multiple sources need to concurrently access and
  update data
• The application is transaction based
• You need fine grained security (i.e., restrict
  access to functionality at the class level)
• You need to scale your application to a large
  number of users
• High availability is required (little down time)
• To support multiple client types
• (e.g., PDA, browser, java application)

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Model 1 J2EE Web View
Model/View/Controller
WebServer
JSP page
Servlet
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Model 1 J2EE Other Views
Model/View/Controller
REWRITE!!!
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Model 2 J2EE Web View
Model TwoArchitecture
WebServer

View
Control
Model
Output
JSP page
EntityBean
Session Bean
Input
Servlet
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Model 2 J2EE Other Views
Model TwoArchitecture

Control
Model
View
EntityBean
Session Bean
REWRITE!!!
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Java Beans vs. Enterprise Java Beans
Java Beans
Enterprise Java Beans

• General purpose component

• Highly specialized business logic components

• Collection of classes based on patterns

• A single class

• Executed and used anywhere

• Executed only in an enterprise container

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Three types of EJBs

• Session beans control/business logic and
  transaction management (Control)
• Entity beans to access data objects (database,
  file system, etc.) (Model)
• Message beans to communicate with other
  applications

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EJB Model
EJB2
EJB2
EJB1
EJBContainer
EJB Pool
Server
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EJB Model
EJB1
EJB2
EJB2
EJBContainer
EJB3
EJB3
EJB Pool
EJB4
EJB4
EJB5
EJB5
Server
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EJB Model
EJB3
EJB2
EJB4