1. Enterprise Java Beans

2. What Are EJB’s? Enterprise Java Beans
EJB: special kind of JavaBean for performing server-side business logic
More powerful version of the regular beans

3. Where they fit in a system

5. Developing EJP

6. Create enterprise application project

10. Create your EJP

14. Put business logic into your EJP

25. Create servlet which will call your business logic

30. Define dependency between Servlet and EJP

35. Put controller logic into your servlet

38. Create JSP File

42. Fill JSP file with user interface code

45. Deploy and Run

51. What Are EJB’s? Enterprise Java Beans
EJB: special kind of JavaBean for performing server-side business logic
More powerful version of the regular beans that we’ve used in class

52. Where they fit in a system

53. EJB’s in J2EE

54. EJB Container
Functions as a runtime environment for EJB components beans
Containers are transparent to the client in that there is no client API to manipulate the container
Container provides EJB instance life cycle management and EJB instance identification.
Manages the connections to the enterprise information systems (EISs)

55. EJB Container(cont’d)
Java Naming and Directory Interface, Enterprise Naming Context 

56. EJB Class A bean has a single Java class at its core
This class is written by a developer if it’s a session bean
This class is sometimes generated by a tool if it’s an entity bean
Implements application-specific business logic
Implements one of the following contracts:
javax.ejb.EntityBean
javax.ejb.SessionBean
These contracts provide for consistent behavior when activating beans, passivating beans, reading data, writing data
Every container can expect these methods in every bean

57. Three kinds of EJB’s Session
associate client information with a specific client
both stateless and stateful versions
Entity
groups associated information in an abstraction that provides transaction support
Message Bean - rarely used, hardly supported

58. What is a Session Bean?
Represents a single Client inside the J2EE server
one client at a time/ not persistent
when the client terminates, the session bean is disassociated from the client
There are two types: Stateful and Stateless...

59. Stateful
These represent a set of interactions between client and server.
Example: shopping cart
Saves information over several method invocations.
There is a lot of overhead associated with using stateful beans

60. Stateless Beans
A stateless bean does not save information between method calls.
Limited application
Little overhead
multiple clients can use the same bean instance without alteration
Example: fetch from a read-only database or send a confirmation for an order

61. Entity Beans Associates pieces of information in a group
Accessed by multiple clients at a time
Persistent and Serializable
The container loads and stores the entity beans in the database
These are more similar to regular beans

62. More on Entity Beans
Transactions: this is what makes an Entity Bean special.
Entity beans rely on the container to enforce robust transactions
example: Airline booking: if the flight booking action fails, then the credit card charge action fails, or vice versa.

63. Persistence in Entity Beans
Container managed persistence
the container controls when the bean is read from or written to the database
Bean managed persistence
the bean’s implementation performs all of the sql operations that loads, stores, and updates the bean’s data to or from the database.
Bean is responsible for connection allocation to the database

64. Connection Pooling
Setting up connections to the database is resource intensive
Connection pooling maintains a pool of database connections for the entity beans so that the connection is maintained when a bean finishes, and is available for other entity beans.
Specific to database and EJB container implementation

65. Message Beans
A message bean is an enterprise bean that allows J2EE applications to process messages asynchronously. It acts as a JMS message listener, which is similar to an event listener except that it receives messages instead of events.
Many systems do not yet support JMS, message bean use is currently not widespread

66. Using an Entity bean from a Session bean
An entity bean can be shared by multiple sessions.
This allows for data encapsulation; clients can interact with data via session beans within transaction boundaries.
Can do all database interaction from session bean as an alternative
encapsulation is weakened

67. Using EJB’s

68. An EJB Example... Online Banking Application
Demonstrates how all the component technologies--enterprise beans, J2EE application clients, and Web components fit together

69. Online Banking Application
Two clients:
a J2EE application client used by administrators to manage customers and accounts
Web client used by customers to access account histories and perform transactions. The clients access the customer, account, and transaction information maintained in a database through enterprise beans.

70. Online Bank Application Overview

71. Session beans used
The online bank application has three session beans: AccountControllerEJB, CustomerControllerEJB, and TxControllerEJB. These session beans provide a client's view of the application's business logic. Hidden from the clients are the server-side routines that implement the business logic, access databases, manage relationships, and perform error checking.

72. Entity Beans used
For each business entity represented in our simple bank, the bank application has a matching entity bean:
AccountEJB, CustomerEJB, TxEJB
The purpose of these beans is to provide an object view of these database tables: account, customer, and tx. For each column in a table, the corresponding entity bean has an instance variable. Because they use bean-managed persistence, the entity beans contain the SQL statements that access the tables. For example, the create method of the CustomerEJB entity bean calls the SQL INSERT command.

73. Database

74. JAR FILE Packaging EJB Components
An EJB application and its various components are deployed and distributed in the form of packages.
The process of packaging:
Enables you to handle and use multiple files related to one EJB component, simultaneously.
Saves disk space by compressing files.
The EJB components of an EJB application are packaged into Java Archive (JAR) files and the Web components are packaged into Web Archive (WAR) files.

75. The components of an enterprise bean are packaged as an ejb-jar file.
The various component files that are packaged into an ejb-jar file are:
Bean class file
Remote interface file
Local interface file
Local home interface file
Home interface file
Deployment descriptor file