Beyond Objects: Component Technology

1. Beyond Objects: Component Technology Bina Ramamurthy 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 and other associated issues??? B.Ramamurthy

3. Component Technology • We need an application architecture that works well in the new E-commerce 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. B.Ramamurthy

4. Presentation Logic Business Logic Database Server Two-tier applications B.Ramamurthy

5. Presentation Logic Business Logic Database Server Three-tier Applications B.Ramamurthy

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

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

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

9. 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. B.Ramamurthy

10. 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. B.Ramamurthy

11. Enterprise Application with many EJBs EJB4 EJB2 WebClient EJB1 EJB5 EJB3 EJB6 ApplClient Lets consider a shopping front application and figure out the possible components (EJBs) B.Ramamurthy

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

13. 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. B.Ramamurthy

14. 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. B.Ramamurthy

15. 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. B.Ramamurthy

16. EJB Types • There are two types of EJBs: Entity and Session • 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. • Among the the two types: There can be stateless and stateful beans. B.Ramamurthy

17. 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. Life Cycle Differences B.Ramamurthy

18. 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. B.Ramamurthy