Entity Bean

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Entity Bean

• Chuyên d? L?p trình Java J2EEChuong 15
• Biên so?n Th.S Nguy?n van Lành

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Concepts

• An entity bean represents persistent data stored
  in one row of a database table .
• When an entity bean is created, the data is
  written to the appropriate database table row,
  and if the data in an entity bean is updated, the
  data in the appropriate database table row is
  also updated
• Entity beans differ from session beans in several
  ways.
• Entity beans are persistent entity bean's state
  exists beyond the lifetime of the application
• allow shared access may be shared by multiple
  clients
• have primary keys unique object identifier
• may participate in relationships with other
  entity beans

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When to Use Entity Beans

• The bean represents a business entity, not a
  procedure.
• For example, CreditCardEJB would be an entity
  bean
• CreditCardVerifierEJB would be a session bean.
• The bean's state must be persistent

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Types of persistent management

• Bean-Managed Persistence
• the bean developer takes responsibility for
  persistent storage in attributes
• Container-Managed Persistence 1.1
• persistent attributes are defined as attributes
  of the bean class and given in the deployment
  descriptor
• Container-Managed Persistence 2.0/2.1
• The bean developer works with an abstract bean
  class
• defines abstract access methods for reading and
  writing of attributes (During deployment the EJB
  container generates a derived class that
  implements all the abstract methods )

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Constitution of a entity bean

• Remote interface
• defines the business methods of the bean.
• Home interface
• defines the methods that allow a client to create
  and find an entity bean
• Enterprise Bean class
• provides the implementation for the business
  methods, finder methods, home methods
• Primary key class
• makes it possible to identify all entity bean
  identities uniquely
• Deployment Descriptor
• This configuration document defines the bean's
  runtime attributes, such as its transaction or
  security attributes
• Helper classes

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Remote Interface

• Each method in the remote interface must match a
  method in the enterprise bean class.
• The signatures of the methods in the remote
  interface must be identical to the signatures of
  the corresponding methods in the enterprise bean
  class.
• The arguments and return values must be valid RMI
  types.
• The throws clause must include java.rmi.RemoteExce
  ption

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Home Interface

• defines the methods that allow a client to create
  and find an entity bean
• create Method
• has the same number and types of arguments as its
  matching ejbCreate method in the enterprise bean
  class.
• returns the remote interface type of the
  enterprise bean.
• The throws clause includes the exceptions
  specified by the throws clause of the
  corresponding ejbCreate and ejbPostCreate
  methods.
• The throws clause includes the javax.ejb.CreateExc
  eption java.rmi.RemoteException

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Entity bean creation
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Home Interface

• finder Method
• Every finder method in the home interface
  corresponds to a finder method in the entity bean
  class.
• The name of a finder method in the home interface
  begins with find, whereas the corresponding name
  in the entity bean class begins with ejbFind
• The number and types of arguments must match
  those of the corresponding method in the entity
  bean class.
• The return type is the entity bean's remote
  interface type, or a collection of those types.
• The exceptions in the throws clause include those
  of the corresponding method in the entity bean
  class.
• The throws clause contains the javax.ejb.FinderExc
  eption java.rmi.RemoteException

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Home Interface

• finder Method in bean class
• All finder methods must begin with ejbFind.
• You must have at least one finder method, called
  ejbFindByPrimaryKey.
• You can have many different finder methods, each
  with different names and different parameters.
• A finder method must return either the primary
  key for the entity bean it finds or a collection
  of primary keys if it finds more than one.

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Home Interface

• home Method
• Each home method definition in the home interface
  corresponds to a method in the entity bean class.
  
• In the home interface, the method name is
  arbitrary, provided that it does not begin with
  create or find.
• In the bean class, the matching method name
  begins with ejbHome.
• For example, in the SavingsAccountBean class the
  name is ejbHomeChargeForLowBalance, but in the
  SavingsAccountHome interface the name is
  chargeForLowBalance
• The throws clause contains the java.rmi.RemoteExce
  ption

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BMP guidelines
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BMP guidelines
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BMP guidelines
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BMP guidelines
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Bean-DBMS synchronization
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CMP Entity Beans

• CMP Entity Beans Are Subclassed
• database-independent
• The container generates the JDBC code by
  subclassing your entity bean class.
• CMP Entity Beans Have No Declared Fields
• CMP Entity Beans Have a Query Language
• CMP Entity Beans Can Have ejbSelect() Methods

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Bean instance Pooling
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CMP Guidelines
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CMP Guidelines
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CMP Guidelines
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