1. Entity Bean Chuyên đề Lập trình Java & J2EE Chương 15
Biên soạn: Th.S Nguyễn văn Lành

2. 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

3. 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

4. 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 )

5. 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

6. 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

7. 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

8. Entity bean creation

9. 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

10. 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.

11. 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.RemoteException

12. BMP guidelines

13. BMP guidelines

14. BMP guidelines

15. BMP guidelines

17. Bean-DBMS synchronization

18. 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

19. Bean instance Pooling

20. CMP Guidelines

21. CMP Guidelines

22. CMP Guidelines