Download Enterprise Java Bean

Enterprise Java Bean
2110472 Computer Networks
Natawut Nupairoj, Ph.D.
Department of Computer Engineering
Chulalongkorn University
Outline
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Overview.
EJB Architecture.
EJB Interfaces.
Example.
Overview
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What is EJB ?
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Component-based Server-side (similar to Servlet).
Same as Servlet ?
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Transaction
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Atomic execution of multiple operations.
Ex: Transfer money between two accounts
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Withdraw from the source account.
Deposit to the destined account.
Must execute all-or-nothing.
Overview
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Distributed
 Invoke EJB over the network
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Interface vs. implementation.
Overview
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The caller feels like invoke local class instance
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Location independence
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Use method as you call Java class.
Can be on any server.
Advance techniques: load balancing, fault tolerance, …
Security
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Who can use what ?
Access control.
Data as an Object
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Typical JSP:
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Built-in SQL statement in JSP page.
Problems ?
For the user of EJB
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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
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Entity Bean
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Data object with actual storage
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Room, customer, etc.
Permanent / persistence.
Container-managed vs. bean-managed.
Session Bean
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Business processes / methods
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Reserve_room, availableRoom, etc.
Stateless (one action) vs. stateful (sequence of
actions).
EJB Container
EJB Conceptual View
EJB Home Interface
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Allow client to manage the bean (factory)
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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
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Interface to the actual data
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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
customerID = id.intValue();
return null;
}
public void ejbPostCreate(Integer
public Customer ejbCreate(Integer
myName = name;
return ejbCreate(id);
}
public void ejbPostCreate(Integer
id) {
id) { }
id, Name name) {
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
public void
public void
public void
public void
public void
public void
public void
}
METHODS
setEntityContext(EntityContext cntx) { }
unsetEntityContext() { }
ejbLoad() { }
ejbStore() { }
ejbActivate() { }
ejbPassivate() { }
ejbRemove() { }
References
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jGuru, Enterprise JavaBeans Technology Fundamentals,
http://developer.java.sun.com/developer/onlineTraining/.
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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-04middleware_p.html.