Chapter 23: Entity Beans

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Chapter 23 Entity Beans
Reference Building J2EE Apps with WebSphere
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Objectives

• Discuss transactional properties of EJBs
• Discuss EJB-QL
• Discuss Business Tier J2EE Patterns
• Value Objects
• Session Façade
• Advanced EJB Topics
• Not covered in this course

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EJB Transactional Characteristics

• Reference Pages 552 - 556
• The EJB specification gives you options for
  defining transactions
• Container managed transactions (CMT)
• For reusability, set Required for all session
  beans and entity beans
• Bean managed transactions (BMT)
• Less flexible
• Client demarked transaction

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EJB Transactional Levels
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EJB Transactional Levels (Cont.)
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EJB Transactional Levels (Cont.)
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EJB Query Language

• Enterprise JavaBean Query Language (EJB QL) was
  introduced in the EJB 2.0 specification to
  support the abstract persistence model
• EJB QL language for expressing the equivalent of
  SQL SELECT statements for CMP beans
• Useful for generating code for custom Find method
• E.g. findAll() method (pages 556 558)
• SELECT object(itm) FROM Item AS itm ORDER BY
  itm.name

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Comparing EJB QL and SQL Statements
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Value Object Pattern

• Reference Pages 559 - 560
• To avoid multiple getter and setter method calls
  between client and EJBs.
• Value Object pattern makes use of JavaBeans
• Implements java.io.Serializable
• Has getter and setter methods
• Without Value Objects
• Use multiple method arguments in Session beans
  business methods
• E.g., setItemDetails(int, String) instead of
  setItemDetails(ItemVO)

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Session Façade Pattern

• Reference Pages 561 - 567
• Encapsulates the complexity of interactions
  between business objects participating in the
  application workflow.
• Benefits
• Reduce tight coupling between client and business
  objects (EJBs)
• Reduce number of business method invocations
  between client and server
• Protect misuse of business objects by imposing a
  uniform access strategy for clients

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Web Clients

• Reference Pages 569 - 578
• Front Controller Pattern
• Only one servlet services multiple commands
• Command Pattern
• Delegates a request to the command handler
• Matches a command to a specific JSP view.
• Note This is an advanced topic
• Not covered in this course

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Advanced EJB Topics

• Reference Pages 586 - 588
• Message-Driven Beans
• initiates processing in response to an external
  event resembles stateless session beans
• Access Beans
• IBM-specific JavaBean wrappers may not be
  portable to other J2EE servers
• EJB Security
• EJB developers are not responsible for user
  authentication or authorization (mapping the
  user to a role)