j2ee and ejb

8/2/2019 J2EE and Ejb

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J2EE and Enterprise Java Beans

Ajay Bajaj

Kunal Mehta

Arun MarioliDhairya Shah


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Distributed Multi-tiered Applications

The J2EE platform uses a multi-tiered distributedapplication model for both enterprise applications

Application logic is divided into components

according to function, and the various applicationcomponents that make up a J2EE application areinstalled on different machines depending on the tierin the multi-tiered J2EE environment to which theapplication component belongs


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J2EE Architecture

J2EE multi-tieredapplications are generallyconsidered to be three-tiered

applications because theyare distributed over threedifferent locations

client machines

the J2EE server machine

the database or legacymachines at the back end


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J2EE Architecture

Three-tiered applicationsthat run in this way extendthe standard two-tiered client

and server model by placinga multithreaded applicationserver between the clientapplication and back-endstorage


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J2EE Containers

The application server maintains control andprovides services through an interface or

framework known as a container There are five defined container types in the

J2EE specification


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Server J2EE Containers

Three of these are server-side containers: The server itself, which provides the J2EE runtime

environment and the other two containers

An EJB container to manage EJB components A Web container to manage servlets and JSP pages


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Client J2EE Containers

The other two container types are client-side: An application container for stand-alone GUIs, console

An applet container, meaning a browser, usually with

the Java Plug-in


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J2EE Components

As said earlier, J2EE applications are madeup of components

A J2EE componentis a self-containedfunctional software unit that is assembled intoa J2EE application with its related classesand files and that communicates with other

components


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Components

Client components run on the client machine,which correlate to the client containers

Web components -servlets and JSP pages EJB Components


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Packaging Applications andComponents

Under J2EE, applications and componentsreside in Java Archive (JAR) files

These JARs are named with differentextensions to denote their purpose, and theterminology is important


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Various File types

Enterprise Archive (EAR) files represent theapplication, and contain all other server-sidecomponent archives that comprise theapplication

Client interface files and EJB componentsreside in JAR files

Web components reside in Web Archive(WAR) files


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Deployment Descriptors

Deployment descriptors are included in the JARs, alongwith component-related resources

Deployment descriptors are XML documents that describeconfiguration and other deployment settings (remember

that the J2EE application server controls many functionalaspects of the services it provides)

The statements in the deployment descriptor aredeclarative instructions to the J2EE container; for example,transactional settings are defined in the deployment

descriptor and implemented by the J2EE container


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Deployment Descriptors

Most J2EE Web Services vendors provide a GUI toolfor generating deployment descriptors andperforming deployment because creating manual

entries is tedious and error prone

The deployment descriptor for an EJB componentmust be named ejb-jar.xml, and it resides in theMETA-INF directory inside the EJB JAR file


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EJB Components

EJB components are server-side, modular, andreusable, comprising specific units of functionality

They are similar to the Java classes we create every

day, but are subject to special restrictions and mustprovide specific interfaces for container and clientuse and access

We should consider using EJB components forapplications that require scalability, transactionalprocessing, or availability to multiple client types


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EJB Components- Major Types

Session beans These may be either statefulor statelessand are primarily

used to encapsulate business logic, carry out tasks on behalfof a client, and act as controllers or managers for other beans

Entity beans Entity beans represent persistent objects or business

concepts that exist beyond a specific application's lifetime;they are typically stored in a relational database


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The homeand componentinterface

A bean's home interface specifies methods that allow theclient to create, remove, and find objects of the same type

The home interface provides bean management and lifecycle methods

EJB functionality is obtained through the bean'scomponent interface, which defines the business methodsvisible to, and callable by, the client

The developer writes the component interface, and the

container creates the implementation for client interaction


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Overview

Enterprise JavaBeans is a specification for creatingserver-side secure, scalable, transactional, multi-usersecure enterprise-level applications.

These server-side components, called enterprisebeans, are distributed objects that are hosted inEnterprise Java Bean containers and provide remoteservices for clients distributed throughout the

network.


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Java Beans vs. EJB

Can be either visible non-visible.

Local Invocation Synchronous Invocation

Decidedly non-visible remoteobjects

Remote and Local Invocation Synchronous and

Asynchronous Invocation Object Pooling Transparent Persistence Supports Transactions Support Relationships

between entity EJBs J2EE Security Features


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Advantages of EJB

Simplifies the development of middlewarecomponents that are secure, transactional,scalable & portable.

Simplifies the process to focus mainly onbusiness logic rather than applicationdevelopment.

Overall increase in developer productivity

Reduces the time to market for mission criticalapplications


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Purpose of EJBs

SESSION Beans (verbs of the system):

Model task or workflow

Faade for Entity beans

Maintain conversational state with clients

ENTITY Beans (nouns of the system):

Object/Relational (O/R) mapping

Transparent and implicit persistence with transaction support

Message Driven Beans:

Asynchronous communication with MOM

Conduit for non-J2EE resources to access Session and EntityBeans via JCA Resource adapters.


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EJB serveraka Enterprise Java Server (EJS)

EJS are analogous to the CORBA ORB. Part of an application server that hosts EJB containers EJBs do not interact directly with the EJB server EJB specification outlines eight services that must be provided by an

EJB server: Naming Transaction Security Persistence Concurrency

Life cycle Messaging Timer


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Three Tier Architecture UsingEJBs

MessageBroker

EJB Container

EntityEJBwCMP

SessionEJB

WEB Container

ServletLocal

Interface

Remote

Interface

EIS RDBMS

MsgDrvEJB

JDBC

JCAResouceAdapter

JMS

EIS other

Presentation Business Data

Queue/TopicJMS

EntityEJBwBMP

EntityEJBwCMP = Entity Bean with Container Managed PersistenceEntityEJBwBMP = Entity Bean with Bean Managed PersistenceMsgDrvEJB = Message Driven EJB

EIS other


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EJB Container

Functions as a runtime environment for EJBcomponents beans

Containers are transparent to the client in that thereis no client API to manipulate the container

Container provides EJB instance life cyclemanagement and EJB instance identification.

Manages the connections to the enterpriseinformation systems (EISs)


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EJB Container(contd)


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EJB Client

Finds EJB container via JNDI.

Invokes methods on EJB beans.


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EJB components


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EJB Interfaces -Local and Remote

Local Interface Used for invoking EJBs within the same JVM (process) @Local annotation marks an interface local Parameters passed by reference

Remote Interface Used for invoking EJBs across JVMs (processes) @Remote annotation marks an interface remote Parameters passed by value (serialization/de- serialization)

Note: An EJB can be implement both interfaces if needed.


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Business Interface

Defines business methods

Session beans and message-driven beansrequire a business interface, optional forentity beans.

Business interface do not extend local orremote component interface unlike EJB2.x

Business Interfaces are POJIs (Plain OldJava Interfaces)

B i I f l


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Business Interface - examples

Shopping cart that maintains state

public interface ShoppingStatefulCart {

void startShopping(String customerId);

void addProduct(String productId);

float getTotal();

} Shopping cart that does not maintain state

public interface ShoppingStatelessCart {

String startShopping(String customerId); //return cartId

void addProduct(String cartId, String productId);float getTotal(String cartId);

}

S l S i EJB (SLSB)


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Stateless Session EJB (SLSB)

Does not maintain any conversational state with client Instances are pooled to service multiple clients @Stateless annotation marks a been stateless.

Lifecycle event callbacks supported for stateless sessionbeans (optional) @PostConstructoccurs before the first business method

invocation on the bean @PreDestroyoccurs at the time the bean instance is

destroyed


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Stateless Session EJBexample (1/2)

The business interface:public interface HelloSessionEJB3Interface{

public String sayHello();

}


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Stateless Session EJBexample (2/2)

The stateless bean with local interface:import javax.ejb.*;import javax.annotation.*;@Local({HelloSessionEJB3Interface.class})@Statelesspublic class HelloSessionEJB3 implements

HelloSessionEJB3Interface{public String sayHello(){

return "Hello from Stateless bean;}@PreDestroyvoid restInPeace() {

System.out.println(I am about to die now);

}}

St t f l S i EJB (SFSB)


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Stateful Session EJB (SFSB)

Maintains conversational state with client

Each instance is bound to specific client session

Support callbacks for the lifecycle events listed

on the next slide


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SFSB Lifecycle Events

@PostConstructsame as SLSB, once for each session @PreDestroysame as SLSB, once for each session @PostActivatecontainer picks a instance from pool and

assigns to a specific client session

@PrePassivatecontainer returns the instance to pool afterthe session is terminated

@Initdesignates the initialization method of a statefulsession bean

@Removecauses the container to remove the stateful session

bean, first invoking the beans PreDestroy method if any

Stateful Session EJB example


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Stateful Session EJB example(1/2)

Define remote business interface (remote can bemarked in bean class also) :

@Remotepublic interface ShoppingCart {

public void addItem(String item);public void addItem(String item);

public Collection getItems();

}

St t f l S i EJB l


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Stateful Session EJB example(2/2)

@Statefulpublic class CartBean implementsShoppingCart {private ArrayList items;@PostConstructpublic void initArray() {

items = new ArrayList();}

public void addItem(String item) {items.add(item);

}public void removeItem(String item) {

items.remove(item);}public Collection getItems() {

return items;}@Removevoid logoff() {items=null;}

}


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Entity EJB (1)

It is permanent. Standard Java objects come intoexistence when they are created in a program. When theprogram terminates, the object is lost. But an entity beanstays around until it is deleted. In practice, entity beans

need to be backed up by some kind of permanent storage,typically a database. A program can create an entity bean,then the program can be stopped and restarted. The entitybean will continue to exist. After being restarted, theprogram can again find the entity bean it was working with,

and continue using the same entity bean.


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Entity EJB (2)

It is identified by a primary key. Entity Beans musthave a primary key. The primary key is unique --each entity bean is uniquely identified by its primary

key. For example, an "employee" entity bean mayhave Social Security numbers as primary keys. Youcan only use entity beans when your objects have aunique identifier field, or when you can add such a

field. Note: Session beans do not have a primary key.


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Entity Bean Class

@Entity annotation marks a class as Enity EJB

Persistent state of an entity bean is represented bynon-public instance variables

For single-valued persistent properties, these methodsignatures are: getProperty()

void setProperty( t)

Must be a non-final concrete class

Must have public or protected no-argumentconstructor


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Entity Bean Class (cont.)

No methods of the entity bean class may be final If entity bean must be passed by value (through a

remote interface) it must implementSerializableinterface.


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Entity EJB

CMP (Container Managed Persistence) Container maintains persistence transparently using

JDBC calls

BMP (Bean Managed Persistence) Programmer provides persistence logic

Used to connect to non-JDBC data sources like LDAP,mainframe etc.

Useful for executing stored procedures that returnresult sets


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Entity EJB example (1)

@Entity // mark as Entity Beanpublic class Customer implements Serializable {

private Long id;private String name;private Collection orders = new

HashSet();@Id(generate=SEQUENCE) // primary keypublic Long getId() {return id;}public void setId(Long id) {

this.id = id;}


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Entity EJB example (2)

@OneToMany // relationship between Customerand Orders

public Collection getOrders() {return orders;}

public void setOrders(Collectionorders) {

this.orders = orders;}

}


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EntityManager

EntityManager API is used to:

create and remove persistent entity instances

to find entities by their primary key identity, and to

query over entities

EntityManager supports EJBQL and (non-portable)native SQL


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Entity Bean Life CycleEntity bean instance has four possible states: New entity bean instance has no persistent identity, and is not

yet associated with a persistence context. Managed entity bean instance is an instance with a persistent

identity that is currently associated with a persistence context. Detachedentity bean instance is an instance with a persistentidentity that is not (or no longer) associated with a persistencecontext.

Removed entity bean instance is an instance with a persistent

identity, associated with a persistence context, scheduled forremoval from the database.

Example of Use of


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Example of Use ofEntityManager API

@Stateless public class OrderEntry {

@Inject EntityManager em;

public void enterOrder(int custID, OrdernewOrder) {

Customer cust =(Customer)em.find("Customer",

custID);

cust.getOrders().add(newOrder);

newOrder.setCustomer(cust);

}

}


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Message Driven EJB example


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Message Driven EJB example

import javax.jms.Message;import javax.jms.MessageListener;import javax.ejb.MessageDriven;@MessageDrivenpublic class MessageDrivenEJBBean implements

MessageListener {

public voidonMessage(Message message) {if(message instanceof MyMessageType1)

doSomething(); // business method 1if(message instanceof MyMessageType2)

doSomethingElse(); // business method 2

}}

EJB Query Language (EJBQL)


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EJB Query Language (EJBQL)

EJBQL : RDBMS vendor independent querysyntax

Query API supports both static queries (i.e.,named queries) and dynamic queries.

Since EJB3.0, supports HAVING, GROUPBY, LEFT/RIGHT JOIN etc.


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EJBQL - examples Define named query:@NamedQuery(

name="findAllCustomersWithName",queryString="SELECT c FROM Customer c WHERE c.nameLIKE :custName"

) Use named query:@Inject public EntityManager em;//..List customers =

em.createNamedQuery("findAllCustomersWithName")

.setParameter("custName", "Smith")

.getResultList();


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EJB Security Architecture

Client Security: The Enterprise JavaBean (EJB) server automatically

performs the steps necessary to ensure that deployed

enterprise bean applications are only available toauthorized users.

One of these steps is authenticating clients thatrequest access to EJB homes, beans, and individualmethods on the beans.


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Understanding EJB Security

Two security measures that client must pass when you addsecurity to EJB systemAuthenticationand Authorization.

Authentication must be performed before any EJB method iscalled.

Authorization occurs at the beginning of each EJB methodcall.


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Authentication in EJB

Two ways to perform authentication in EJB: We can call authentication logic through Java Authentication

and Authorization Service(JAAS), a separate J2EE API.

JAAS is a portable interface that enables you to authenticateand authorize users in Java. It allows to login to the systemwithout knowing about the underlying security system beingused.


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Authorization in EJB

Two ways to perform authorization in EJB: With programmatic authorization, we can hard code security

checks into our bean code.

With declarative authorization, the container performs allauthorization checks for us.


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Deploying EJBs

EJB 3.0 annotations will replace EJB 2.0deployment descriptors in almost all cases

Values can be specified using annotations inthe bean class itself

Deployment descriptor may be usedtooverride the values from annotations


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Some EJB Servers

Company Product

IBM WebSphere BEA Systems BEA WebLogic

Sun Microsystems Sun Application Server Oracle Oracle Application Server JBoss JBoss


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References (1) SUN EJB Specifications

http://java.sun.com/products/ejb/docs.html IBM RedBooks

http://www.redbooks.ibm.com/redbooks.nsf/redbooks/

IBM WebSphere Developer Technical Journalhttp://www.ibm.com/developerworks/websphere/

Oracle Technology Networkhttp://www.oracle.com/technology/tech/java/index.html
http://java.sun.com/products/ejb/docs.htmlhttp://www.redbooks.ibm.com/redbooks.nsf/redbooks/http://www.ibm.com/developerworks/websphere/http://www.oracle.com/technology/tech/java/index.htmlhttp://www.oracle.com/technology/tech/java/index.htmlhttp://www.ibm.com/developerworks/websphere/http://www.redbooks.ibm.com/redbooks.nsf/redbooks/http://java.sun.com/products/ejb/docs.html


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References (2)

Java.net http://www.java.net/

JavaWorldwww.javaworld.com/channel_content/jw-ejbs-index.shtml

TheServerSidehttp://www.theserverside.com/

Richard Monson-Haefel, Enterprise JAVABEANS

Tate, Clark, Lee, Lisnkey, BITTER EJB

Feghhi, Jalal, Web developer's guide to JavaBeans
http://www.java.net/http://www.javaworld.com/channel_content/jw-ejbs-index.shtmlhttp://www.javaworld.com/channel_content/jw-ejbs-index.shtmlhttp://www.theserverside.com/http://www.theserverside.com/http://www.javaworld.com/channel_content/jw-ejbs-index.shtmlhttp://www.javaworld.com/channel_content/jw-ejbs-index.shtmlhttp://www.javaworld.com/channel_content/jw-ejbs-index.shtmlhttp://www.javaworld.com/channel_content/jw-ejbs-index.shtmlhttp://www.javaworld.com/channel_content/jw-ejbs-index.shtmlhttp://www.java.net/

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