1. “Controlling your application” (the business logic)
EJB Session Beans
“Controlling your application”
(the business logic)

2. Model 2 with J2EE EJB’s Model Two Architecture Control Model
Web Container
EJB Container
View
Control
Model
Web Server
HTTP Request
Servlet (request handler)
Entity EJB
Entity EJB
Session EJB
Session EJB
Session Bean
Java Bean
Java Bean
Java Bean
<<creates>>
<<forward>>
HTTP Response
The Model 2 architecture breaks up the Model-View-Controller pattern such that each part of the model can run in a different container on a different server. What is the purpose of breaking the pattern in this way?
Adaptability
Flexibility
Scalability
Thus far we have implemented the View and the Control. To implement the Model we will need to develop a seaparate tier of code to handle all of the dataaccess.
One way to do this is to create your own custom code (A Data Access Object)
Create your own custom code to access the database
Access the database or flat file
Manage persistence of data
System dependent
Database/file dependent
JSP
(view builder)

3. Advantages Automatic Transaction management Resource management
Security
Modularity
Simple programming interface
Advantages
Remember that one of the advantages of Session Beans is that the Application Server stores the EJB in memory in the “bean pool”. This allows the bean to remain in memory and shared over large number of clients. Entity Java Beans work the same way but for data objects.
Much simpler programming interface for client to access that data
Greater portability, maintainability, reliability, code re-use
Automatically handles transaction processing for you

4. Clients View of Session EJB
Remote Interface
Client Program
Bean (Implementation)
Local Interface
Structure of Entity Java Beans
Similar to Session Beans. There is a Client view and a Server View
The client view – represents the client programmers interface view to the bean. These are the methods that you as a programmer have access to. This is the public interface to the bean. It acts as a façade to hide the complexity of the bean implementation from the developer.
The bean class – represents the detailed implementation of the bean. All of the methods in the interface and the all other required methods by the container are implemented in this class
Client Interface
Implementation

5. Session EJB Developers View
<<EJB Session Bean>> OrderControl
<<Realization>> CustomerOrderEJB
+startOrder() +addItem() +deleteItem() +checkout() +cancelOrder() +checkOrder()
<<Remote Interface>> CustomerOrderRemote
+startOrder() +addItem() +deleteItem() +checkout() +cancelOrder() +checkOrder()
The actual implementation of the Home and Remote interface methods is done by creating the EJB Entity class. This class is some times called the “implementation” or “bean” class. The implementation class contains class variables that refer the Context object that EJB is running in and the different data elements represented in the Entity bean. It contains default constructor method and methods that implement the required methods of the home interface and the remote interface. There are also other methods that are used to manage the Entity bean such as ejbPostCreate(), ejbActivate(), ejbPassivate(), ejbLoad(), ejbStore(), setEntityContext(), and getEntityContext().
Client Interface
Implementation

6. Remote vs. Local Entity Beans
Please Use Whenever Possible!!!
Remote Session EJB
Anywhere on the network
Pass by value
Local EJB are faster but not as flexible, scalable and adaptable
On same server as Session Beans
No network traffic
Pass by reference

7. Stateful vs. Stateless Transactions
Please Use Whenever Possible!!!
A stateless transactions is
One call to server
Does not the save transaction state data
No memory is allocated in the pool for each session with a client
EJB is never passivated or activated
Stateful transaction
Used for multi-step transactions
Saves state data for each client session
Memory is allocated in pool for each client session
EJB is passivated and activated

8. Stateless Session Bean LifeCycle
Does not exist
Class.newInstance(),
@PostConstruct
Ready in pool
Business method

9. Stateful EJB Session Bean Lifecycle
System exception
Does not exist
@PrePassivate()
Ready in pool
Passive
business methods
@PostActivate ()

10. Guidelines for use Coarse-Grained better than Finely-Grained
Use stateless whenever possible
Use the remote interface for flexibility
Guidelines for use
Coarse-Grained Business Objects vs. Finely-Grained Business Objects
There is some extra overhead associated with using entity beans (locating the object and accessing it) and there over use can effect performance.
Entity beans should seldom be used to represent individual table is a database but a broader end users logical view of the data.
For example, A Customer Order and all the information contained in the customer order (order information, and line items purchased on order and totals).
You would not create an entity bean for each database table involved in the order.
Probably not best for doing simple data access like performing simple queries. Entity Java Beans are more complex to create than the data access code to perform a query.
Recommendation – Use for logical data objects that are involved in transactions (update, delete or inserting). Do not use for fine grained simple data access, unless, there is some overriding design requirement that would deem only the use of EJBs. For example, the code must be designed to support multiple types of databases such that the databases are interchangeable.

11. Locating an EJB
Must use a directory service and DNS to locate network objects
JNDI (Java Naming Directory Interface)
Programming interface to the directory services to locate any object in a network (files, EJBs, web services, etc.)
EJB’s can be remote anywhere on the network
Must use a directory service and DNS to locate network objects
JNDI (Java Naming Directory Interface) - java programming interface to DNS It makes easy to access and use the directory services to locate any object in a network
files, EJBs, web services, etc.)

12. Directory Service names
Most use X.500 naming standard
c (country name)
o (organizationName)
ou (organizationUnitName)
l (localityName)
cn (commonName)
dc (domainComponent)
uid (userid)
Each type of directory service has it’s own naming syntax
LDAP example
cn=Martin Bond, ou=Authors, o=SAMS, c=us
Microsoft Active Directory Service
cn=Martin Bond/ou=Authors/o=SAMS/c=us

13. JNDI names JNDI names are not specific to directory services
JNDI maps universal name to specific directory service syntax
Typical JNDI name
“SAMS/authors/Martin Bond”

14. Outline for using remote EJBs
Get initial JNDI naming context
Use JNDI to lookup and find EJB
Call business function

15. Defining the JNDI name
The JNDI name is best defined in the Session EJB “Bean” class as a constant value.
The JNDI name must follow a specific format for the EJB 3.0 architectures. The format is “BeanClassName/remote” where BeanClassName is the name of the class.

16. Calling business methods
try {
InitialContext initialContext = new InitialContext(); // get jndi context
String jndiName = BusinessRulesBean.RemoteJNDIName; ; // get jndi name
// lookup and get remote interface for session bean
BusinessRulesRemote businessRulesRemote =
(BusinessRulesRemote) initialContext.lookup(jndiName );
// call any business methods defined in the interface
Person person = businessRulesRemote.login(username, password); … }
catch (NamingException ne) {
throw new MyAppException( “Session EJB not found, jndiname=” + jndiName));
catch (Exception e) {
throw new MyAppException(ee.getMessage());

17. Calling business methods
try {
InitialContext initialContext = new InitialContext(); // get jndi context
String jndiName = BusinessRulesBean.RemoteJNDIName; ; // get jndi name
// lookup and get remote interface for session bean
BusinessRulesRemote businessRulesRemote =
(BusinessRulesRemote) initialContext.lookup(jndiName );
// call any business methods defined in the interface
Person person = businessRulesRemote.login(username, password); … }
catch (NamingException ne) {
throw new MyAppException( “Session EJB not found, jndiname=” + jndiName));
catch (Exception e) {
throw new MyAppException(ee.getMessage());

18. Calling business methods
try {
InitialContext initialContext = new InitialContext(); // get jndi context
String jndiName = BusinessRulesBean.RemoteJNDIName; ; // get jndi name
// lookup and get remote interface for session bean
BusinessRulesRemote businessRulesRemote =
(BusinessRulesRemote) initialContext.lookup(jndiName );
// call any business methods defined in the interface
Person person = businessRulesRemote.login(username, password); … }
catch (NamingException ne) {
throw new MyAppException( “Session EJB not found, jndiname=” + jndiName));
catch (Exception e) {
throw new MyAppException(ee.getMessage());

19. Calling business methods
try {
InitialContext initialContext = new InitialContext(); // get jndi context
String jndiName = BusinessRulesBean.RemoteJNDIName; ; // get jndi name
// lookup and get remote interface for session bean
BusinessRulesRemote businessRulesRemote =
(BusinessRulesRemote) initialContext.lookup(jndiName );
// call any business methods defined in the interface
Person person = businessRulesRemote.login(username, password); … }
catch (NamingException ne) {
throw new MyAppException( “Session EJB not found, jndiname=” + jndiName));
catch (Exception e) {
throw new MyAppException(ee.getMessage());

20. Calling business methods
try {
InitialContext initialContext = new InitialContext(); // get jndi context
String jndiName = BusinessRulesBean.RemoteJNDIName; ; // get jndi name
// lookup and get remote interface for session bean
BusinessRulesRemote businessRulesRemote =
(BusinessRulesRemote) initialContext.lookup(jndiName );
// call any business methods defined in the interface
Person person = businessRulesRemote.login(username, password); … }
catch (NamingException ne) {
throw new MyAppException( “Session EJB not found, jndiname=” + jndiName));
catch (Exception e) {
throw new MyAppException(e.getMessage());

21. Insert object into Datastore
public void addBranch() {
// create a branch java bean
Branch branch = new Branch();
branch.setName(“Bank of Nauvoo”);
branch.setPhone(“ ”);
// inserts a branch into the database
entityManager.persist(branch); }

22. Update Object in Datastore
public void renameBranch(String branchid, String newName) {
// get branch by its Primary Key from datastore
Branch branch = (Branch) entityManager.find(Branch.class, branchid);
// update the branch
branch.setBranchname(newName);
entityManager.merge(branch); }

23. Delete Object from Datastore
public void deleteBranch(String branchid) {
// get branch by its Primary Key from datastore
Branch branch = (Branch) entityManager.find(Branch.class, branchid);
// Delete the branch
entityManager.remove(branch); }

24. Query Object/s from Datastore
public Collection<Branch> getBranches(String name){
// Define query prepared statement
String ejbql = "SELECT b FROM Branch b WHERE b.branchname LIKE :branchname”;
// Create query object
Query query = entityManager.createQuery(ejbql);
// Substitute value to search for in prepared statement
query.setParameter("branchname", searchValue);
// Execute query to get list of branches
List<Branch>branches = query.getResultList();
return branches; }

25. Entity Bean query language (ejb-ql)
select_clause from_clause [where_clause]
SELECT j FROM Job AS j
WHERE j.jobType = ‘web development’
From Examples:
SELECT j.* FROM Job AS j
WHERE j.jobType = ‘web development’;
SQL equivalent:

26. Entity Bean query language (ejb-ql)
select_clause from_clause [where_clause]
SELECT s FROM Job AS j, INNER JOIN j.Skills AS s
From Examples:
SELECT s.* FROM Job AS j INNER JOIN JobSkill AS s ON j.FK_skillID = s.skillID
SQL equivalent:

27. Entity Bean query language (ejb-ql)
Inner Joins of Entities
Where Examples:
SELECT OBJECT o
FROM Customer AS c, INNER JOIN c.orders AS o, INNER JOIN o.items AS I
WHERE c.lastName = ‘FLINTSTONE”
SELECT C.*, O.*, I.*  
FROM Customer C INNER JOIN Orders O INNER JOIN Items I
ON C.customerId = O.FK_CustomerId
ON O.FK_ItemId = I.ItemId
WHERE C.lastName = ‘FLINSTONE’;
SQL equivalent: