Enterprise Java Bean

2110472 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 Beanpublic 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, http://developer.java.sun.com/developer/onlineTraining/.

EJB Tutorial, http://www.ejbtut.com/Overview.jsp. A. Hemrajani, The state of Java middleware, Part 2: Enterprise

JavaBeans, JavaWorld, April 1999, http://www.javaworld.com/javaworld/jw-04-1999/jw-04-middleware_p.html.