Tài liệu Entity Bean - Chuyên đề Lập trình Java & J2EE (Chương 15) pdf

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Entity Bean
Chuyên đề Lập trình Java & J2EE
Chương 15
Biên soạn: Th.S Nguyễn văn Lành
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Concepts
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An entity bean represents persistent data stored in one
row of a database table .
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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
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Entity beans differ from session beans in several ways.

Entity beans are persistent: entity bean's state exists
beyond the lifetime of the application
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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

CreditCardVerierEJB 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
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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
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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.RemoteException
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Home Interface

denes the methods that allow a client
to create and nd 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.CreateException &
java.rmi.RemoteException
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Entity bean creation
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Home Interface

nder 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
nd, 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.FinderException &

java.rmi.RemoteException
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Home Interface

nder 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
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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 nd.

In the bean class, the matching method name
begins with ejbHome.


For example, in the SavingsAccountBean class the name is
ejb HomeChargeForLowBalance, but in the
SavingsAccountHome interface the name is
chargeForLowBalance

The throws clause contains the
java.rmi.RemoteException
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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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