J2EE Part 2: Enterprise JavaBeans

1. J2EE Part 2:Enterprise JavaBeans CSCI 4300 Images and code samples from jGuru EJB tutorial, http://java.sun.com/developer/onlineTraining/EJBIntro/EJBIntro.html

2. EJB container • Created by an application server program • We use SUN Application Server on zion.cs.uga.edu • Must write EJB to specified interfaces

3. EJB Interfaces • Client: a Java program (servlet, bean) • Home interface: local object • Remote interface: access the actual EJB, possibly across a network

4. EJB Interface example • CustomerHome home = // ... • // Use the home interface to create a new instance of the Customer bean. • Customer customer = home.create(customerID); • // using a business method on the Customer. • customer.setName(someName);

5. Entity beans represent data objects: import javax.ejb.EJBObject; import java.rmi.RemoteException; public interface Customer extends EJBObject { public Name getName() throws RemoteException; public void setName(Name name) throws RemoteException; public Address getAddress() throws RemoteException; public void setAddress(Address address) throws RemoteException; }

6. Session Beans represent business processes: public interface HotelClerk extends EJBObject { public void reserveRoom(Customer cust, RoomInfo ri, Date from, Date to) throws RemoteException; public RoomInfo availableRooms( Location loc, Date from, Date to) throws RemoteException; }

7. An Entity Bean class • The Bean class actually implements the EntityBean interface (business logic) • For example, maintains a database connection for customer info • Client reads and writes the bean, and does not need to do DB access

8. EJB lifecycle methods (home interface) public interface CustomerHome extends EJBHome { public Customer create(Integer customerNumber) throws RemoteException, CreateException; public Customer findByPrimaryKey( Integer customerNumber) throws RemoteException, FinderException; public Enumeration findByZipCode(int zipCode) throws RemoteException, FinderException; } -- these return instances of Customer, the remote interface

9. Stub and Skeleton Methods • Stub method on local system represents the remote object • Skeleton method on remote system represents the local client

10. Container-Managed Persistence • Persistence: arranging that data stored will be available in a later session • Container-Managed Persistence: EJB container automatically saves EntityBean contents to a database and restores on demand • Developer writes no DB code! • Easiest for developer, hardest for EJB container

11. EntityBean creation code

12. EntityBean business logic

13. EntityBean Callback methods

14. Customer Data Members

15. Serializable objects • Serializable: an object can be saved to a string and correctly restored from the string • A class whose data members are primitive values is automatically serializable • Classes that use trees, etc. can be made serializable:

16. Automatically generated SQL for this EntityBean:

17. Bean-Managed persistence The entity bean itself must contain the DB code to: • Store the bean data contents into the database • Restore the bean from its stored contents These methods invoked as callbacks from the EJB container

18. Stateless Session Beans • Represent business processes (transactions) • Contain no persistent data • Shared among multiple clients

19. Acme SessionBean creation • JNDI: Java Directory and Naming Interface (find objects in a networked environment) • InitialContext: provided by EJB container, gives JNDI access

20. Acme SessionBean operations • Normally, we would open an output stream and write the request to the server!

21. EJB Descriptor

22. Assembly descriptor

23. EJB Deployment The EJB jar file contains: • Home interface class • Remote interface class • Bean implementation class • META-INF/ejb-jar.xml Then, drop it into the JBOSS deploy directory!

24. WAR and EAR files Buildfile source: http://www.developer.com/java/data/article.php/10932_3405781_1