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

 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 th

 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

When to Use Entity

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 )

Constitution of a 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

Remote Interface

a method in the enterprise bean class

interface must be identical to the signatures of the corresponding methods in the enterprise bean

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.CreateException

& java.rmi.RemoteException

Entity bean creation

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.FinderException & java.rmi.RemoteException

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

 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.RemoteException

BMP guidelines

BMP guidelines

BMP guidelines

BMP guidelines

Bean-DBMS synchronization

CMP Entity Beans

 CMP Entity Beans Are Subclassed

 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

Bean instance Pooling

CMP Guidelines

CMP Guidelines

CMP Guidelines