J2EE Applications Programming

1
J2EE Applications Programming

• Java
• JDBC
• Enterprise JavaBean
• Remote Method Invocation
• Application
• Applet
• Java Bean
• Servlet/Java Server Page

2
J2EE Platform
3
EJB Architecture

• Enterprise Beans
• Session Bean
• Entity Bean
• Data Access Object
• Value Object

4
Entity Bean

• Shared across multiple clients
• Unique primary key
• Object wrapper to RDB
• Lifespan that goes past a single client's session
• Recoverable, automatically restored to state of
  last committed transaction or database operation.

5
Dept Table

• Dept Table
• DeptNo -- Two digit integer
• DeptName -- String e.g. Accounting
• DeptLocation -- String e.g. New York
• OLD, Homespun Dept Class Methods
• connect() -- create network connection to
  database
• createTable() -- create dept table schema
• insertRow(int id, String name, String location)
  -- create a new row in the dept table
• commit() -- commits database changes
• close() -- closes the network connection to
  database
• displayAllRows() -- display the contents of the
  dept table

6
Entity Beans

• Entity beans are container managed. The
  container handles data persistence by providing
  calls to
• ejbCreate Container calls this method when the
  client calls the create method. It inserts the
  bean's data into the database.
• ejbFindByPrimaryKey Container calls this method
  when a client calls the findByPrimaryKey method.
  It returns the primary key value so the container
  can call ejbLoad method to initialize entity
  bean.
• The ejbLoad and ejbStore methods are called by
  the container to synchronize the bean's state
  with the underlying database. A "store and load"
  sequence is produced whenever a client invokes a
  set/get method. When the client invokes a finder
  method, load is called to initialize the bean.
• The ejbPassivate and ejbActivate methods are
  called by the container before the container
  swaps the bean in and out of storage. These
  methods release objects (resources).
• setEntityContext The entity context is
  dynamically updated by the container, maintaining
  current data for each client.

7
CMP vs. BMP

• Container Managed Persistence
• The container is responsible for transferring the
  attributes of the EJB to the relational
  database.
• Gain Programmer Productivity, Application
  Reliability
• Loss Machine Efficiency
• Bean Managed Persistence
• The programmer is responsible developing the code
  for transferring the attributes of the EJB to
  the relational database.
• Gain Machine Efficiency
• Loss Programmer Productivity, Application
  Reliability

8
DeptBean's Attributes

• package GerlachPackage.impl
• import javax.ejb.EntityBean
• import javax.ejb.EntityContext
• import GerlachPackage.DeptPK
• public class DeptBean implements EntityBean
• public EntityContext entityContext
• public long deptno
• public String dname
• public String loc

9
DeptBean's Accessor Methods

public long getDeptno() return deptno
public void setDeptno(long newDeptno) deptno
newDeptno public String getDname() return
dname public void setDname(String newDname)
dname newDname public String getLoc()
return loc public void setLoc(String
newLoc) loc newLoc
10
DeptBean's EJB Methods -- CMP

• public DeptPK ejbCreate()
• return null
• public void ejbPostCreate()
• public DeptPK ejbCreate(long deptno)
• this.deptno deptno
• return new DeptPK(deptno)
• public void ejbPostCreate(long deptno)
• public void ejbActivate()
• public void ejbLoad()
• public void ejbPassivate()
• public void ejbRemove()
• public void ejbStore()
• public void setEntityContext(EntityContext ctx)
• this.entityContext ctx

11
Primary Key Class

• package GerlachPackage
• import java.io.Serializable
• public class DeptPK implements Serializable
• public long deptno
• public DeptPK()
• public DeptPK(long deptno)
• this.deptno deptno
• public boolean equals(Object other)
• // Add custom equals() impl here
• return super.equals(other)
• public int hashCode()

12
Sample BMP

• public String ejbFindByPrimaryKey(String
  primaryKey)
• throws RemoteException, FinderException,
  SQLException
• //This method locates the row in the table using
  the social security number, and the ejbLoad
  method loads the data into a Bean
• String keynull
• try
• ic new InitialContext()
• DataSource ds (DataSource)
  ic.lookup(dbName)
• con ds.getConnection()
• ps con.prepareStatement("SELECT socsec
  FROM BONUS WHERE socsec ? ")
• ps.setString(1, primaryKey)
• ResultSet rs ps.executeQuery()
• if(rs.next())
• key primaryKey
• else
• System.out.println("Find Error")
• catch (javax.naming.NamingException ex)
  ex.printStackTrace()
• try

13
Sample BMP

• public void ejbLoad()
• //Load data from database
• try
• ic new InitialContext()
• DataSource ds (DataSource)
  ic.lookup(dbName)
• con ds.getConnection()
• ps con.prepareStatement("SELECT FROM
  BONUS WHERE SOCSEC ?")
• ps.setString(1, this.socsec)
• ResultSet rs ps.executeQuery()
• if(rs.next())
• this.bonus rs.getDouble(2)
• else
• System.out.println("Load Error")
• catch (java.sql.SQLException ex)
  ex.printStackTrace()
• catch (javax.naming.NamingException ex)
  ex.printStackTrace()
• try
• ps.close()
• con.close()

14
Sample BMP

• public void ejbStore()
• //Store data to database after Bean created
• try
• DataSource ds (DataSource)ic.lookup(dbName
  )
• con ds.getConnection()
• ps con.prepareStatement("UPDATE BONUS SET
  BONUS ? WHERE SOCSEC ?")
• ps.setDouble(1, bonus)
• ps.setString(2, socsec)
• int rowCount ps.executeUpdate()
• catch (javax.naming.NamingException ex)
  ex.printStackTrace()
• catch (java.sql.SQLException ex)
  ex.printStackTrace()
• try
• ps.close()
• con.close()
• catch (java.sql.SQLException ex)
  ex.printStackTrace()

15
Sample BMP

• public void ejbRemove() throws RemoteException
• try
• DataSource ds (DataSource)ic.lookup(dbName
  )
• con ds.getConnection()
• ps con.prepareStatement("DELETE FROM
  BONUS WHERE SOCSEC ?")
• ps.setString(1, socsec)
• ps.executeUpdate()
• catch (java.sql.SQLException ex)
  ex.printStackTrace()
• catch (Exception ex) ex.printStackTrace()
  
• try
• ps.close()
• con.close()
• catch (java.sql.SQLException ex)
  ex.printStackTrace()

16
Sample BMP

• public void ejbActivate()
• //When a bean is activated, the container calls
  its ejbLoad method.
• socsec (String)context.getPrimaryKey()
• public void ejbPassivate()
• //When a bean is passivated, the container calls
  its ejbStore method.
• socsec null

17
Sample BMP

• public void setEntityContext(javax.ejb.EntityCont
  ext ctx)
• this.context context
• public void unsetEntityContext()
• context null

18
EJB Implementation Issues

• Concurrency Control
• Connection Pooling
• Database Synchronization

19
Bean-Managed Persistence

• ejbLoad is called by the container prior to all
  calls to getMethods and setMethods.
• ejbStore is called by the container after all
  calls to getMethods and setMethods.
• To improve efficiency
• No caching
• getMethods and setMethods access database
  directly using SQL
• ejbStore and ejbLoad are no-ops
• Caching
• Define transactional boundaries begin/commit
• Or, use a "modified flag" to control load and
  store methods

20
CMP Life Cycle

• Client talks to the EJB through its container.
  The client looks up the EJB based on its given
  name. Sample chain of events of running an
  application.
• Client creates EJB
• setEntityContext method
• Create method
• Post create method
• Client finds the EJB
• setEntityContext method
• Find by primary key
• Load method
• Client invokes getMethod
• Load method
• Store method
• Client invokes setMethod
• Load method
• Store method

21
Entity Bean Guidelines

• Bean requires persistent storage
• Represents a course-grained business object
• Shared across multiple clients
• Stateful conversational mode
• Represent a single logical row of database (table
  or view)
• Get/Set methods should manipulate attributes of
  the bean
• Each method secures and releases a database
  connection
• Examples Purchase order, Customer

22
Assemble and Deploy EJB

• Compile the Entity Bean
• Assemble the J2EE Application
• JNDI name for the enterprise bean ("Dept")
• Creates a separate .JAR file to hold each EJB
• Creates a deployment description for the
  application e.g. jgerlach.deploy
• The EJB .JAR files are packaged into an .EAR file
  with the deployment descriptor
• Deploy the JEEE Application
• Transfer (.EAR file) to J2EE installation
  directories and Root Context of the application
  server

23
Settings for EJB Deployment

• Oracle 9iAS Application Server Connection
• User id admin
• Password corbaisfun
• URL ormi//javacr.cudenver.edu23791
• EJB Deployment Profile
• Application name ltfirst letter of first namegt
  ltlast namegt
• E.g., jgerlach.ear
• EJB Name ltfirst letter of first namegt ltlast
  namegt ltejb namegt
• E.g., jgerlachDept