Enterprise Java Beans II

8/14/2019 Enterprise Java Beans II

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Enterprise Java Beans II

CS-422

Steflik


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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


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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


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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 developmentprocedures 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)


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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


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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


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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


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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


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Developing the Home Interface

The Home Interface is responsible for managing the life-cycleoperations 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 Keypublic abstract Object getPrimaryKey( ) throws RemoteException;

public abstract boolean isIdentical (EJBObject ejbobject) throws RemoteException;

public abstract void remove( ) throws RemoteException, RemoveException;

}


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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 Implementationpackage 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

EJB C t t


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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,UserTransaction;

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;


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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

the root element of the deployment descriptor, all other

elements are children of this

Yes textual description of the parent element, many other

elements can have their own description elements

Yes a name that the deployment tool can use to display the name

Yes relative path to a small (16x16) jpeg or GIF to be used by

deployment tools

Yes relative path to a large (32x32) jpeg or GIF to be used by

deployment tools

The parent element that contains the declarations for allbeans within this application

Yes the parent element that contains application assembly

instructions for the EJB application (includes; transaction

attributes, method permissions, security roles and excluded

methods)

Yes a JAR file that contains the classes necessary for a client to

access the bean

A l


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An EJB Deployment Descriptor

Single stateless bean to calculate Monthly Salary

Simple Bean

Simple Salary Bean


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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.RemoteExecption) { System.out.println(rmi RemoteExceprion caught); }

}

}


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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 calledpersistence

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, thiscan 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

Enterprise Java Beans II

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