1. Component-based Applications
Bina Ramamurthy
2/24/2019
B.Ramamurthy

2. Introduction
Issues: Basic object-technology could not fulfill the promises such as reusability and interoperability fully in the context internet and enterprise level applications. Deployment was still a major problem and as a result portability and mobility are impaired.
Does component technology address these issues?
2/24/2019
B.Ramamurthy

3. Component Technology
We need an application architecture that works well in the new E-commerce, e-science age.
Programmer productivity, cost-effective deployment, rapid time to market, seamless integration, application portability, scalability, security are some of the challenges that component technology tries to address head on.
Enterprise Java Beans is Sun’s server component model that provides portability across application servers, and supports complex systems features such as transactions, security, etc. on behalf of the application components.
EJB is a specification provided by Sun and many third party vendors have products compliant with this specification: BEA systems, IONA, IBM, Oracle, Sybase, Gemstone.
2/24/2019
B.Ramamurthy

4. J2EE Application Programming Model for Web-based applications
Web Service
Business Logic
Web
Application
Database
Server
Enterprise
Java Beans
EJB container
Web Container
Web
client
2/24/2019
B.Ramamurthy

5. J2EE Application Programming Model for Three-tier Applications
Presentation
Components
Database
Server
Enterprise
Java Beans
EJB container
Application
Container
Business Logic
2/24/2019
B.Ramamurthy

6. J2EE Application Programming Model for Web-based Applets
Web Service
Business Logic
Web
Application
Container
Enterprise
Java Beans
EJB container
Browser
Database
Server
Applet
internet
2/24/2019
B.Ramamurthy

7. Roles in EJB Development
Bean developer: Develops bean component.
Application assembler: composes EJBs to form applications
Deployer: deploys EJB applications within an operation environment.
System administrator: Configures and administers the EJB computing and networking infrastructure.
EJB Container Provider and EJB server provider: Vendors specializing in low level services such as transactions and application mgt.
2/24/2019
B.Ramamurthy

8. Enterprise Java Bean (EJB)
Deployable unit of code.
At run-time, an enterprise bean resides in an EJB container.
An EJB container provides the deployment environment and runtime environment for enterprise beans including services such as security, transaction, deployment, concurrency etc.
Process of installing an EJB in a container is called EJB deployment.
2/24/2019
B.Ramamurthy

9. Enterprise Application with many EJBs
WebClient
EJB1
EJB5
EJB3
EJB6
ApplClient
Lets consider a shopping front application and figure out the
possible components (EJBs)
2/24/2019
B.Ramamurthy

10. Deployment with Multiple EJB Clients
Container2
Deploys :
EJB4
Web
Container1
Deploys:
WebApp1
EJB
Container1
Deploys :
EJB1,EJB2,EJB3
Client
Container1
Deploys :
Client1
Client
Container3
Deploys :
EJB5,EJB6
2/24/2019
B.Ramamurthy

11. Business Entities, Processes and Rules
EJB Applications organize business rules into components.
Components typically represent a business entity or business process.
Entity: is an object representing some information maintained in the enterprise. Has a “state” which may be persistent.
Example: Customer, Order, Employee,
Relationships are defined among the entities: dependencies.
2/24/2019
B.Ramamurthy

12. Process
Is an object that typically encapsulates an interaction of a user with business entities.
A process typically updated and changes the state of the entities.
A business process may have its own state which may exist only for the duration of the process; at the completion of the process the state ceases to exist.
Process state may be transient or persistent.
States ate transient for conversational processes and persistent for collaborative processes.
2/24/2019
B.Ramamurthy

13. Rules
Rules that apply to the state of an entity should be implemented in the component that represents the entity.
Rules that apply to the processes should be implemented in the component that represents the processes.
2/24/2019
B.Ramamurthy

14. EJB Types There are two types of EJBs:
Entity, session and message
We will discuss messaging bean in a separate discussion.
The syntax of the session bean and entity bean client-view API is almost identical.
But they have different life cycle, different persistence management, etc.
EJBs can be stateless and stateful beans.
2/24/2019
B.Ramamurthy

15. Life Cycle Differences
Session Bean
Object state:
Maintained by container
Object Sharing:
No sharing: per client
State Externalization:
State is inaccessible to other programs
Transactions:
Not recoverable
Failure Recovery:
Not guaranteed to survive failures
Entity Bean
Maintained by DB
Shared by multiple client
Accessible to other programs
State changed transactionally and is recoverable.
Survives failures and restored when the container restarts.
2/24/2019
B.Ramamurthy

16. Choosing Entity or Session Bean
Entity (business entity) is typically implemented as entity bean or a dependent object of an entity bean.
Conversational (business) process as a session bean.
Collaborative bean as an entity bean.
Any process that requires persistence is implemented as an entity bean.
When exposure to other applications are not needed for an entity or process (local/private process) then they are implemented as bean dependent objects.
2/24/2019
B.Ramamurthy

17. Parts of EJB
EJB class that implements the business methods and life cycle methods; uses other helper classes and libraries to implement.
Client-view API: consists of EJB home interface and remote interface.
Home interface: controls life cycle : create, remove, find methods
Remote interface: to invoke the EJB object methods
2/24/2019
B.Ramamurthy

18. Parts of EJB (contd.)
Deployment Descriptor: XML document for bean assembler and deployer;
A declaration about EJB environment needed for customizing the bean to the operating environment.
Container Runtime services include: transactions, security,distribution,load balancing, multithreading, persistence, failure recovery, resource pooling, state amnagement, clustering..
2/24/2019
B.Ramamurthy