Enterprise Java Bean 2110472 Computer Networks Natawut Nupairoj, Ph.D. Department of Computer...
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Transcript of Enterprise Java Bean 2110472 Computer Networks Natawut Nupairoj, Ph.D. Department of Computer...
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.