EJB.ppthckhkhohjpfuysfzhxjvkgur6eydgdcjjggjj
- 1. 01/17/2025 1 Enterprise Java Beans Dr M.Rani Reddy
- 2. 01/17/2025 2 J2EE Technology Architecture Server platform JTS JMAPI JNDI JMS JDBC JAXP JAAS … Enterprise Java Beans Components Java Server pages Servlets Application clients Web clients IIOP, others html
- 3. 01/17/2025 3 Enterprise Java Bean(EJB) An enterprise bean is a server-side component that contains the business logic of an application. At runtime, the application clients execute the business logic by invoking the enterprise bean's methods. Main goal of Enterprise Java Bean (EJB) architecture is to free the application developer from having to deal with the system level aspects of an application. This allows the bean developer to focus solely on the logic of the application.
- 4. 01/17/2025 4 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.
- 5. 01/17/2025 5 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.
- 6. 01/17/2025 6 Enterprise Application with many EJBs WebClient ApplClient EJB1 EJB2 EJB3 EJB4 EJB5 EJB6 Lets consider a shopping front application and figure out the possible components (EJBs)
- 7. 01/17/2025 7 Deployment with Multiple EJB Clients Web Container1 Deploys: WebApp1 EJB Container1 Deploys : EJB1,EJB2,EJB3 Client Container1 Deploys : Client1 EJB Container2 Deploys : EJB4 Client Container3 Deploys : EJB5,EJB6
- 8. 01/17/2025 8 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.
- 9. 01/17/2025 9 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.
- 10. 01/17/2025 10 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.
- 11. 01/17/2025 11 EJB Types There are three types of EJBs: Entity, session and message-driven 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.
- 12. 01/17/2025 12 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.
- 13. 01/17/2025 13 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.
- 14. 01/17/2025 14 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
- 15. 01/17/2025 15 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 management, clustering..
- 16. 01/17/2025 16 Enterprise Bean Parts <<Home Interface>> AccountHome create() find() remove() <<Remote Interface>> Account debit() credit() getBalance() <<Enterrpise Bean class> AccountBean ejbCreate() ejbFind() ejbRemove() debit() credit() getBalance() Deployment Descriptor name = AccountEJB class = AccountBean home = AccountHome remote = Account type = Entity transaction = required …..
- 17. 01/17/2025 17 AccountHome Interface port java.rmi.RemoteException; port javax.ejb.CreateException; port javax.ejb.FinderException; port java.util.Collection; blic interface AccountHome extends javax.ejb.EJBHome { eate methods ount create (String lastName, String firstName) throws RemoteException, CreateException, BadNameException; ount create (String lastName) throws RemoteException, CreateException; nd methods ount findByPrimaryKey (AccountKey primaryKey) throws RemoteException, FinderException; ection findInActive(Date sinceWhen) throws RemoteException, FinderException, BadDateException;
- 18. 01/17/2025 18 Account Interface import java.rmi.RemoteException; public interface Account extends javax.ejb.EJBObject { BigDecimal getBalance() throws RemoteException; void credit(BiGDecimal amount) throws RemoteException; Void debit(BigDecimal amount) throws RemoteException, InSufficientFundsException; }
- 19. 01/17/2025 19 B.Ramamurthy AccountBean class ublic class AccountBean implements javax.ejb.EntityBean { / life cycle methods from home interface ublic AccountKey ejbCreate (String latName, String firstName) throws … {…} ublic AccountKey ejbCreate(String lastName) throws …{…} ublic AccountKey ejbFindByPrimaryKey(AccountKey primarykey)… {…} ublic Collection ejbFindInactive( Data sinecWhen).. {…} / business methods from remote interface ublic BigDecimal getBalance() {….} ublic void credit(BigDecimal amt) {…} ublic void debit(BigDecimal amt) throws InsufficientFundException {….} / container callbacks from EntityBean container ublic ejbRemove( ) throws RemoveException{ …} ublic void setEntityContext(EntityContext ec) {…} ublic unsetEntityContext(EntityContext ec) {…} ublic void ejbActivate() {…} ublic void ejbLoad() {….} ublic void ejbStore() {….}