Session Bean

1
Session Bean

• Private object dedicated to the single client
  that initiated its birth -- "stateful"
• Short life span.
• Or, may be "stateless" to support multiple
  clients simultaneously
• Must be "thread safe"
• Can perform database manipulations.
• Typically, read only database operations
• Sessions Beans do not survive a crash.
• Anonymous, no primary key identifier
• Example Applications
• Catalog Bean, Employee ID Verification Bean

2
Thread Safe EJB

• Implement EJB methods as thread safe
• Use of local variables (temporary) are OK
• Use of session variables are OK
• Use of final class variables (constants) are OK
• Use of instance attributes -- Not OK
• Writing to a fixed data file -- Not OK
• Or, use synchronize feature of Java to control
  concurrent access
• Synchronize on a method to restrict access to the
  method to one caller at a time.
• Synchronize on (this) to restrict access to the
  EJB to one caller at a time.

3
Sample Stateless Session Bean

• package mypackage.impl
• import javax.ejb.SessionBean
• import javax.ejb.SessionContext
• import java.sql.
• import java.util.
• public class LocationsEJBBean implements
  SessionBean
• public void ejbCreate()
• public void ejbActivate()
• public void ejbPassivate()
• public void ejbRemove()

4
getLocations method

• public Object getLocations()
• String driver "oracle.jdbc.driver.OracleDrive
  r"
• String url "jdbcoraclethin_at_ouray.cudenver.
  edu1521oracle"
• String username "jgerlach"
• String password "xxxx"
• Connection connection
• Statement statement
• try
• Class.forName(driver)
• System.out.println("JDBC Driver loaded
  successfully")
• catch(ClassNotFoundException cnfe)
• cnfe.printStackTrace() return null
• try
• connection DriverManager.getConnection(url,
  username,password)
• connection.setAutoCommit(false)
• statement connection.createStatement()

5
Sample Client

• Hashtable env new Hashtable()
• env.put(Context.INITIAL_CONTEXT_FACTORY,
  "com.evermind.server.rmi.RMIInitialContextFactory"
  )
• env.put(Context.SECURITY_PRINCIPAL,
  "admin")
• env.put(Context.SECURITY_CREDENTIALS,
  "welcome")
• env.put(Context.PROVIDER_URL,
  "ormi//localhost23891/current-workspace-app")
• Context ctx new InitialContext(env)
• LocationsEJBHome locationsEJBHome
  (LocationsEJBHome)ctx.lookup("GerlachLocationsEJB"
  )
• LocationsEJB locationsEJB
• // Use a create() methods below to create a
  new instance
• locationsEJB locationsEJBHome.create()
• Object r locationsEJB.getLocations( )
• if (r null) System.out.println("Got
  nothing back") return
• Vector v (Vector) r
• for (int i 0 i lt v.size() i)
• System.out.println(v.get(i))

6
Session EJBs and Entity EJBs
ShoppingCart EJB
searchCatalog() getItem() addItemToOrder() deleteI
temFromOrder() placeOrder() setUpAccount()
Catalog EJB
Entity EJB Stateless Session EJB
Stateful Session EJB
7
Value Object

• A serializable object that is passed between
  client and server.
• Fine grain object, only getMethods
• Reduces strain on server and network by running
  the object on the client
• Examples account info, credit card info