Enterprise Java Bean Computer Networks Natawut Nupairoj, Ph.D. Department of Computer Engineering Chulalongkorn University

Outline Overview. EJB Architecture. EJB Interfaces. Example.

Overview What is EJB ? Component-based Server-side (similar to Servlet). Same as Servlet ? Transaction Atomic execution of multiple operations. Ex: Transfer money between two accounts  Withdraw from the source account.  Deposit to the destined account.  Must execute all-or-nothing.

Overview Distributed Invoke EJB over the network  Interface vs. implementation.

Overview The caller feels like invoke local class instance  Use method as you call Java class. Location independence  Can be on any server.  Advance techniques: load balancing, fault tolerance, … Security Who can use what ? Access control.

Data as an Object Typical JSP: Built-in SQL statement in JSP page. Problems ? For the user of EJB Data are objects. Each field is a data member of a Java class. No direct contact to database (let EJB handle it).

Example: Using EJB Integer id = new Integer(351); Customer cust = custHome.findByPrimaryKey(id); System.out.println(cust.getName()); Customer customer = custHome.create(new Integer(804)); Name name = new Name("Richard", "Wayne", "Monson-Haefel"); customer.setName(name);

EJB Basic Architecture

EJB Type Entity Bean Data object with actual storage Room, customer, etc. Permanent / persistence. Container-managed vs. bean-managed. Session Bean Business processes / methods Reserve_room, availableRoom, etc. Stateless (one action) vs. stateful (sequence of actions).

EJB Container

EJB Conceptual View

EJB Home Interface Allow client to manage the bean (factory) Create a new bean or find the existing bean. Developer must define the primary key (type). No need to write “Implementation”. 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; }

EJB Remote Interface Interface to the actual data Define how the data looks like. Access (get/set) data in each field. 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; }

Ex: Using EJB Interfaces Integer id = new Integer(351); Customer cust = custHome.findByPrimaryKey(id); System.out.println(cust.getName()); Customer customer = custHome.create(new Integer(804)); Name name = new Name("Richard", "Wayne", "Monson-Haefel"); customer.setName(name);

Container-Managed Bean public class CustomerBean implements EntityBean { int customerID; Address myAddress; Name myName; CreditCard myCreditCard; // CREATION METHODS public Customer ejbCreate(Integer id) { customerID = id.intValue(); return null; } public void ejbPostCreate(Integer id) { } public Customer ejbCreate(Integer id, Name name) { myName = name; return ejbCreate(id); } public void ejbPostCreate(Integer id, Name name) { }

Container-Managed Bean // BUSINESS METHODS public Name getName() { return myName; } public void setName(Name name) { myName = name; } public Address getAddress() { return myAddress; } public void setAddress(Address address) { myAddress = address; } public CreditCard getCreditCard() { return myCreditCard; } public void setCreditCard(CreditCard card) { myCreditCard = card; }

Container-Managed Bean // CALLBACK METHODS public void setEntityContext(EntityContext cntx) { } public void unsetEntityContext() { } public void ejbLoad() { } public void ejbStore() { } public void ejbActivate() { } public void ejbPassivate() { } public void ejbRemove() { } }

References jGuru, Enterprise JavaBeans Technology Fundamentals, EJB Tutorial, A. Hemrajani, The state of Java middleware, Part 2: Enterprise JavaBeans, JavaWorld, April 1999, middleware_p.html. middleware_p.html