Bài giảng lập trình mạng stateful session bean GV nguyễn xuân vinh

 The bean class, the EJB object, the remote interface, the home interface, the home object, the deployment descriptors, and the jar files constitute the enterprise bean..  EJB contain

EJB: Stateful Session Bean

Presenter: Nguyễn Xuân VinhInformation Technology Faculty

 Define a Stateful Session Bean

 List the characteristics of a Stateful Session Bean

 Write Stateful session bean programs

 Differentiate between Stateless and Stateful Session beans

 The bean class, the EJB object, the remote interface, the home interface, the

home object, the deployment descriptors, and the jar files constitute the

enterprise bean.

 Bean class contains the implementation of the business logic methods

 EJB container performs important management functions when it intercepts

client requests such as:

* Transaction logic

* Security logic

* Bean instance logic

 The Remote interface duplicates the methods exposed by the bean class

 Responsibilities of the EJB home object:

* Creating EJB objects

* Searching for existing EJB Objects

* Removing EJB Objects

the classes, the home interface, and the remote interface that form the bean.

 The lifetime of a session bean may last till such time as that of

a client session It could be as long as a window is open or as long as an application is open Session beans do not, therefore, survive application server crashes or machine crashes.

 Home Interface

 Remote Interface

 Bean class

 The ejb-jar.xml file is a compressed file that contains

the declarations of the enterprise bean class, the remote interface and the home interface

 An EJB client can be:

the hard disk or other storage devices This process is called

passivation.

state is returned to the bean The bean is again ready to meet the

request This process is called activation

data from bit-blob

TRƯỜNG ĐẠI HỌC NÔNG LÂM TP.HCM KHOA CÔNG NGHỆ THÔNG TIN

Passivation of a Stateful Bean

Client

EJB Object Enterprise

bean

Other Enterprise beans

Storage

1 Invoke business methods

5 Store passivated bean state

The EJB Container/Server

2 Take the least recently used bean

3 Call ejbPassivate()

4 Serialize the bean state

EJB Object

Other Enterprise Beans

1 Invoke business methods

2 Retrieve the passivated state of bean

 The Bean Class

 The Home Interface

 The Client Code

 Deployment Descriptor

1 number(){

/ Implementation}

Remote Interface (Defines business methods of bean)

1 number()

Number extends EJBObject

Client

TRƯỜNG ĐẠI HỌC NÔNG LÂM TP.HCM KHOA CÔNG NGHỆ THÔNG TIN

The Bean Class

Stateful Session Bean Class

public class Numberbean implements SessionBean

private SessionContext ctx;

public int answer;

public void ejbCreate(int answer) throws CreateException public void ejbRemove()

public void ejbActivate() public void ejbPassivate() public void setSessionContext(SessionContext ctx)

TRƯỜNG ĐẠI HỌC NÔNG LÂM TP.HCM KHOA CÔNG NGHỆ THÔNG TIN

Goals of the Client Code

 It acquires a JNDI initial context and the naming context

 Home object is located using JNDI

 Client calls methods on the bean using the Home Object

 Conversations are created using home interface and used

from the client code

 Deployment descriptors limit the pool size

 Lastly, the EJB objects are removed

 The jar file is created using java appropriate statement

 Packages the remote interface, the bean class, the home interface and the XML files

 The jar file is copied into the deploy directory on the server and then deployed

 The creation and copying of the file in the deploy directory of the server marks the completion of the bean

TRƯỜNG ĐẠI HỌC NÔNG LÂM TP.HCMAdvantages and Disadvantages KHOA CÔNG NGHỆ THÔNG TIN

of Stateless Session bean

 Bandwidth could be reduced for other processes, as data has to

be passed each time

 Input/Output bottlenecks are more in stateless session beans

 Data is not pushed to the bean for every method invocation

 All resources are stored in a database when the bean is passive

TRƯỜNG ĐẠI HỌC NÔNG LÂM TP.HCM KHOA CÔNG NGHỆ THÔNG TIN

Practices used for writing Stateful Session Beans

conversations.

bean failures.

database or file is known as passivation.

with all its resources is known as activation.

ago is called the Least Recently Used method.

serialization.

is going to passivate the bean

conversational state is read back into the memory The container then re-constructs the memory-state using object serialization.

 A jar file is created in order to package the three files,

namely, the remote interface, the bean class, and the home interface

 To deploy the bean, the newly created jar file has to be

copied into the deploy directory on the server

 If the business process requires multiple invocations, a

stateful session bean has to be used However, if the

business process is only for a single method call, the

stateless session bean will suffice