Enterprise Java Beans II

1
Enterprise Java Beans II

• CS-422
• Steflik

2
EJB Development

• The EJB Specification define six roles that are
  involved in the development and deployment of EJB
  applications
• Enterprise Bean Provider
• Application Assembler
• Deployer
• System Administrator
• EJB Server Provider
• EJB Container Provider

3
Enterprise Bean Provider

• A programmer type, who codes the EJB
• functions done by the Enterprise Bean Provider
• write a home interface for the bean
• write a component interface for the bean that
  declares various methods required by the
  application
• write an implementation class that implements the
  various business methods declared in the remote
  interface
• write a deployment descriptor describing the
  resources required by the bean and various other
  parameters
• Package the interfaces and implementation class
  along with the deployment descriptor into an EJB
  JAR file

4
Application Assembler

• A person with the domain knowledge and expertise
  to be able to gather together the beans written
  by several Bean Providers (including vendors) and
  by modifying the deployment descriptors assemble
  them into an applications that will represent a
  complete business solution.
• This assembly activity is usually done via GUI
  based tools provided by the application server
  OEM.
• The assembler should be able to understand the
  various interfaces declared by the Bean Providers
• Into pulling together the various Beans the
  assembler will allso collect together other
  components, such as JSP, HTML and graphics files.
  

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The Deployer

• The deployer takes an assembled application and
  deployes it to a specific environment
• the deployer need to have the detail knowledge
  required for the specific EJB server to be used
  and be familiar with the development procedures
  for that server
• the deployer must map the resources required for
  the application onto the current infrastructure
  (map data sources on the data bases)
• the deployer is also responsible for mapping
  security requirements onto the infrastructure
  (creating userids, password, user groups)

6
System Administrator

• The System Administrator is responsible for the
  overall operational well being of the
  installation
• Insure the availability of the application at all
  times
• Configure and administer the entire installation
• Support the networking infrastructure at the
  installation
• Create groups and users for the system to be used
  by the deployer while deploying the application
• Monitor the application performance using tools
  provided by the server provider
• Fine-tune the use of various resources required
  by the application

7
EJB Server Provider

• A system level expert with expertise in providing
  low-level support services for distributed object
  applications and distributed transaction
  management.
• Typically an OS vendor or middleware vendor
• can be assumed thast the same party plays the
  role of the EJB Container Provider

8
EJB Container Provider

• A system level expert that implements a secure,
  transaction enabled, and scaleable container that
  can be integrated with an EJB Server.
• The container provider is responsible for
• run-time environment for the deployed EJBs
• deployment Tool for deploying EJBs on the
  container

9
Developing an Enterprise Bean

• At it simplest an EJB consists of four elements
• a home interface
• a component interface
• a bean implementation class
• a deployment descripter
• well develop a simple bean that calculates our
  monthly net salarybased on annual salary,pension
  contributions and income tax.
• It will be a stateless session bean

10
Developing the Home Interface

• The Home Interface is responsible for managing
  the life-cycle operations upon a bean creating,
  removing and locating the bean. The Home
  interface is the first point of contact that a
  client has with a bean
• A client will obtain a reference to the the
  beans Home Interface via JNDI. You will see that
  each bean is registered in a JNDI server that can
  be used at run-time to get a reference to the
  beans Home Interface
• Once a client has a reference to the beans home
  interface it can perform operations on the bean
  through this interface these operations are
• create a new instance or find an existing
  instance (local and remote)
• access the EJBMetaData interface (remote only)
• get a serializable reference to a bean instance
  (remote only)
• remove the bean instance
• execute home business methods (remote entity
  beans only)

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Basic EJBHomeInterface
package javax.ejb import java.rmi.Remote
import java.rmi.RemoteExecption public
interface EJBHome extends Remote //
get a reference to the EJBMetaData object can
later be used to retrieve data about the bean
public abstract EJBMetaData
getEJBMetaData( ) throws RemoteExecption
// get a Handle to the home object basically a
persistent reference to the object
public abstract HomeHandle getHomeHandle( )
throws RemoteExecption // remove the
bean instance in the case of en entity bean
this is like deleting a row from the data store
public abstract void remove (Object
obj) throws RemoteExecption, RemoveExecption
public abstract void remove (Handle
handle) throws RemoteExecption, RemoveExecption

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Basic EJBLocalHome Interface
package javax.ejb public interface EJBLocalHome
public abstract void remove (Object
obj ) throws RemoveException, EJBException
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the SalaryHome Interface
package simpleBean public interface SalaryHome
extends javax.ejb.EJBHome Salary create()
throws java.rmi.RemoteException,
javax.ejb.CreateException
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the Component Interface
package javax.ejb import java.rmi.Remote import
java.rmi.RemoteException public interface
EJBObject extends Remote // get a
referenct to the home object public
abstract EJBHome getEJBHome( ) throws
RemoteException // get a Handle to the home
object public abstract Handle getHandle(
) throws RemoteException // for entity
beans get the beans Primary Key public
abstract Object getPrimaryKey( ) throws
RemoteException public abstract boolean
isIdentical (EJBObject ejbobject) throws
RemoteException public abstract void
remove( ) throws RemoteException,
RemoveException
15
the Salary Interface
package simpleBean public interface Salary
extends javax.ejb.EJBObject double
calculateSalary ( int annualSalary, int
pensionContrib, double bonus) throws
hava.rmi.RemoteException
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SalaryEJB Implementation
package simpleBean import javax.ejb. public
class SalaryEJB implements SessionBean
public void ejbCreate( ) public void
ejbRemove( ) public void ejbActivate(
) public void ejbPassivate( )
public void Ct( SessionContext ctx )
private static double taxRate 28 public
double calculateSalary (int annualSalary, int
pensionContrib, double bonus) double
monthly 0 monthly annualSalary/12
monthly - monthlu - (monthly
(pensionContrib/100)) monthly monthly
- (monthly (taxrate/100)) return
monthly
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Limitations to the EJB Model

• Bean must not use read/write static fields
• bean cant use threads or the Threading API
• bean cant use AWT for input or output
• bean cannot act as a network server, by
  listening,accepting or multicasting on a socket
• bean cannot use java.io package
• bean cant load a native driver
• bean cant use this as an argument or return
  value
• bean cant modify the class loader, stop the JVM,
  or change the input, output or error streams
• bean cant access or modify security settings
• bean must not attempt to define a class in a
  package
• bean must not use the subclass and object
  substitution features of the serialization
  protocol

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EJB Context

• In the SalaryBean implementation we had to invoke
  setSessionContext
• there are similar methods required for other bean
  types
• ex. setEntityContext for Entity Beans
• each of these methods accepts a subclass of an
  EJBContext to provide the bean instance with
  information about the container - the beans
  context
• The EJBContext interface

package javax.ejb import java.security.Identity
import java.security.Principle import
java.util.Properties import javax.transaction,Use
rTransaction public interface EJBContext
public abstract Identy getCallerIdentity( )
public abstract Principal getCallerPrincipal( )
public abstract EJBHome getEJBHome( )
public abstract Properties getEnvironment( )
public abstract boolean getRollbackOnly( ) throws
IllegalStateException public abstract
UserTransaction getUserTransaction( ) throws
IllegalStateException public abstract boolean
isCallInRole( String s) public abstract
boolean isCallerInRole (Identity identity)
public abstract void setRollbackOnly( ) throws
IllegalStateException
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EJBContext Interface

• Additionally SessionContext and EntityContext
  (but not MessageDrivenContext) define

public abstract EJBLocalObject getEJBLocalObject(
) throws IllegalStateException public abstract
EJBObject getEJBObject( ) throws
IllegalStateException
20
Deployment Descriptors
In the original EJB Specification the deployment
descriptor was written as a Java object, in the
EJB 1.1 Specification that was changed to be an
XML Document. DTD Element Optional Purpose ltejb-ja
rgt the root element of the deployment
descriptor, all other elements are children of
this ltdescriptiongt Yes textual description of the
parent element, many other elements can have
their own description elements ltdisplay-namegt Yes
a name that the deployment tool can use to
display the name ltsmall-icongt Yes relative path
to a small (16x16) jpeg or GIF to be used by
deployment tools ltlarge-icongt Yes relative
path to a large (32x32) jpeg or GIF to be used by
deployment tools ltenterprise-beansgt The
parent element that contains the declarations for
all beans within this application ltassembly-des
criptorgt Yes the parent element that contains
application assembly instructions for the EJB
application (includes transaction attributes,
method permissions, security roles and excluded
methods) ltejb-client-jargt Yes a JAR file that
contains the classes necessary for a client to
access the bean
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An EJB Deployment Descriptor
lt?xml version 1.0 ?gt lt!DOCTYPE ejb-jar PUBLIC
--//Sun Microsystems, Inc // DTD Enterprise
JavaBeans 1.1//EN httpjava.sun.com/dtd/ejb-jar
_2_0.dtdgt ltejb-jargt ltdescriptiongt
Single stateless bean to calculate Monthly
Salary lt/descriptiongt ltdisplay-namegtSimpl
e Beanlt/display-namegt ltenterprise-beansgt
ltsessiongt ltdescriptiongtSimple Salary
Beanlt/description ltdisplay-namegtSalary
Beanlt/display-namegt ltejb-namegtSalarylt/ejb-amegt
lthomegtsimpleBean.SalaryHomelt/homegt ltremotegt
simpleBean.Salarylt/remptegt ltejb-classgtsimpleBe
an.SalaryEJBlt/ejb-classgt ltsession-typegtStateles
slt/session-typegt lttransaction-typegtContainerlt/t
ransaction-typegt lt/enterprise-beansgt lt/ejb-jargt

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A Salary Client
import javax.ejb. import simpleBean. import
javax.naming.InitialContext class SalaryClient
public static void main (String args)
try
InitialContext ctx new InitialContext( )
Object objRef ctx.lookup(Salary)
SalaryHome home (SalaryHome)
javax.rmi.PortableRemoteObject.narrow(objRef,
SalaryHome.class)
Salary bean home.create( )
System.out.println ( Monthly net salary
bean.calculateSalary(28000, 2, 500))
catch (javax.namingException ne)
System.out.println( naming exception caught)
catch (javax.ejb.CreateException)
System.out.println( EJC Ceration Exception
caught) catch (java.rmi.RemoteExecp
tion) System.out.println(rmi RemoteExceprion
caught)
23
Entity Beans ( ver 1.1)

• Entity beans represent data in a datastore as a
  Java object, this usually means that the bean
  represents a row in a relational table.
• Since the bean and the database record are
  synonymous, any change in the bean must be
  synchronized with the database record this is
  called persistence
• there are two types of Entity beans, they are
  differentiated by how they handle persistence
• Container-Managed Persistence (CMP)
• the synchronization (persistence) is handled
  automatically by the container
• Bean-Managed Persistence (BMP)
• we manage the synchronization (persistence) in
  code in the bean and tell the container to keep
  its hands off

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CMP or BMP

• One of the services offered by the EJB container
  is to have the container manage the persistence,
  at deployment time the container will generate
  all of the code needed to synchronize the bean
  with the database.
• This lets the programmer focus on business logic
  and not have to be concerned over persistance
• by using CMP the bean becomes more independent of
  the database, this can make them easier to
  re-deploy using another database
• With BMP we must provide all of the SQL to manage
  the persistence as part of the bean, its more
  work but some EJB containers are not fully
  compliant with the EJB specification as relates
  to CMP so, the only option may be to use BMP.
• This may be only option when trying to use legacy
  databases (IBM/IMS) that are not SQL oriented
• to get finer graind control than what CMP
  provides

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Primary Keys

• The identity of an entity bean is its primary key
• primary key is represented by a primary key class
  that is defined by the developer, this class
  contains everthing necessary to find the entity
  in the datastore
• for BMP the primary key class must
• the primary key can be any legal value type in
  RMI/IIOP, must be serializable
• must provide suitable implementations of the
  hashCode( ) and equals( ) methods
• must have a unique value within the set of all
  beans of a particular type
• for CMP these additional rules apply
• key class must have a no-arguments public
  constructor
• must be able to map the beans state to the
  primary key and vice-versa