Enterprise Java Beans

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Enterprise Java Beans (EJB

)

By

Janaranjani K

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Outline



 _{Introduction of EJBs.}_{Introduction of EJBs.} 

 _{EJB as a Business Tier Component.}_{EJB as a Business Tier Component.} 

 _{EJB fundamentals.}_{EJB fundamentals.}



 _{Enterprise Beans.}_{Enterprise Beans.}



 Foundation of EJB.Foundation of EJB.



 _{What constitutes Enterprise Bean?}_{What constitutes Enterprise Bean?}



 _{Session beans.}_{Session beans.}



 _{Components of a Session beans.}_{Components of a Session beans.}



 The Session EJB Lifecycle (includes stateful and stateless).The Session EJB Lifecycle (includes stateful and stateless).



 _{An example of stateless session bean (which includes both}_{An example of stateless session bean (which includes both}

remote and local interface). remote and local interface).

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Introduction to EJBs

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Introduction to EJBs



 _{EJB is a standard for building server side component in java. It}_{EJB is a standard for building server side component in java. It}

defines a contract between the component and application server defines a contract between the component and application server that enables the component to run in any application server.

that enables the component to run in any application server.



 _{EJB components (called as enterprise beans}_{EJB components (}_{called as enterprise beans) are}_{) are}

  _deployable_deployable   _imported_imported   _loaded_loaded

into an application server, which host all these components. into an application server, which host all these components.

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Continued…



Common Service includes:



 _{Transaction Management}_{Transaction Management}



 Resource ManagementResource Management



 _{Connection pooling}_{Connection pooling}



 SecuritySecurity



 _Networking_Networking



 _{Persistant Management}_{Persistant Management}



 ConcurrencyConcurrency



 Location transparencyLocation transparency



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EJB as a Business Tier

Component



 _{Enterprise beans are intended for server side component}_{Enterprise beans are intended for server side component}

development not for client side (which lies in presentation tier development not for client side (which lies in presentation tier and components like thick clients, web service clients

and components like thick clients, web service clients etc areetc are used for its development). So it lies in

used for its development). So it lies in Business Tier.Business Tier.



 _{EJB component can perform the following tasks:}_{EJB component can perform the following tasks:}



 _{Perform business logic.}_{Perform business logic.}



 Access to the database.Access to the database. 

 _{E.g., Submitting an order for books.}_{E.g., Submitting an order for books.}



 _{Enterprise bean can achieve database access using}_{Enterprise bean can achieve database access using JDBC.}_JDBC.



 Access another system.Access another system. 

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EJB Fundamentals

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Enterprise Beans



 _{An enterprise bean}_An _{enterprise bean is a server side software component that}_{is a server side software component that}

can be deployed in a distributed environment. can be deployed in a distributed environment.



 _{It compose of one or more java objects.}_{It compose of one or more java objects.}



 _{The client to an enterprise bean can be one of the following:}_{The client to an enterprise bean can be one of the following:}



 _{A servlet}_{A servlet}



 _{An applet}_{An applet}



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Continued…



_{Types of Beans:}



 _{Session beans.}_{Session beans.}



 _{Stateful session beans.}_{Stateful session beans.} 

 _{Stateless session beans.}_{Stateless session beans.}



 Entity beans.Entity beans.



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Enterprise java Enterprise java beans beans BMP BMP CMP CMP Stateless Stateless Stateful Stateful Entity beans Entity beans MDBs MDBs Session Beans Session Beans

Diagrammatic

Representation

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Session Beans



_{Session beans model business process.}



_{They are perform actions. Like,}



Adding numbers



Accessing database



Unlike entity beans, they are

Unlike entity beans, they are non-persistant.

non-persistant.



_Types:



 Stateful session beans.Stateful session beans.



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Stateful Session Beans



_{A stateful session bean maintains a}

_{A stateful session bean maintains a conversational state}

_{conversational state}



_{The state is relevant only for a single client}

_{The state is}

_{relevant only for a single client}



Cannot be seen by other clients



_{The state is not persistent}

_{The state is}

_{not persistent}



Expires after a certain timeout



_{It has performance hit due to}

_{It has performance hit due to resource pooling.}

_{resource pooling.}



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Stateless Session Beans



 _{Conceptually, the same as stateful session beans.}_{Conceptually, the same as stateful session beans.} 

 _{No need to save the conversational state, so called Stateless.}_{No need to save the conversational state, so called Stateless.}



 _Can_{Can have fields, but they are not unique to}_{have fields, but they are not unique to any client}_{any client}



 _{Since the container knows the bean has no state, it can:}_{Since the container knows the bean has no state, it can:}



 _{Use a single bean instance (While each client thinks it has its}_{Use a single bean instance (While each client thinks it has its}

own copy) own copy)



 Destroy/re-instantiate on the flyDestroy/re-instantiate on the fly



 _{Redirect requests to different instances (load balancing)}_{Redirect requests to different instances (load balancing)}



 _{Client does not care on which server the bean is stored}_{Client does not care on which server the bean is stored}



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Entity Beans



 _{Entity beans model Business Data.}_{Entity beans model Business Data.} 

 _{Object-oriented view of entities stored in}_{Object-oriented view of entities stored in persistent storage}_{persistent storage}



 Normally, each instance represents a row in a relational DBNormally, each instance represents a row in a relational DB

table table



 _{Persistence code can be written manually (bean-managed}_{Persistence code can be written manually (bean-managed}

persistence,

persistence, BMP BMP ) or automatically (container-managed) or automatically (container-managed persistence,

persistence, CMP CMP ))



 _{A single bean instance (on the server) can be accessed by}_{A single bean instance (on the server) can be accessed by}

multiple clients multiple clients 

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Message Driven Beans



_{New in EJB 2.0 standard}



_{Built on top of JMS to send m}

_{Built on top of JMS to send messages to clients, which in}

_{essages to clients, which in}

turn would be received by

turn would be received by MDB.

MDB.



_{It is invoked by the container upon arrival of message at}

the destination that is serviced by

the destination that is serviced by the message-driven

the message-driven

bean.



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Foundation of EJB

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

 _{EJB components are based on Distributed Objects}_{EJB components are based on Distributed Objects} 

 _{A distributed object is an object that is callable from a remote}_{A distributed object is an object that is callable from a remote}

system. system.



 _{The client can be in-process, out-of-process or a client located}_{The client can be in-process, out-of-process or a client located}

elsewhere on the network. elsewhere on the network.



 _{It does the invocation with the help of the followings:}_{It does the invocation with the help of the followings:}



 _{Stubs (client side proxy object):}_{Stubs (client side proxy object):}



 _{It masks the network communication from t}_{It masks the network communication from the client.}_{he client.}



 _{It knows how to call over the network using the sockets,}_{It knows how to call over the network using the sockets, massaging}_massaging

parameters as necessary into their network representation. parameters as necessary into their network representation. 

 Skeleton (server side proxy object):Skeleton (server side proxy object):



 _{It masks the network communication from t}_{It masks the network communication from the distributed object.}_{he distributed object.}



 _{It understands how to receive calls on a network.}_{It understands how to receive calls on a network.}



 _{Also knows how to massage parameters from the network}_{Also knows how to massage parameters from the network}

representation to their java r

representation to their java representations.epresentations. 

 _{It then delegates the call to the appropriate implementation object.}_{It then delegates the call to the appropriate implementation object.}

Distributed Architecture

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What constitutes Enterprise

Bean?

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

 _{Enterprise Bean class:}_{Enterprise Bean class:}



 It contains the implementation of your business logic.It contains the implementation of your business logic.



 _{It can be session or entity or MDB.}_{It can be session or entity or MDB.}



 _{Component Interface:}_{Component Interface:}



 _{Remote Interface:}_{Remote Interface:}



 _{It is the java interface that enumerates the business}_{It is the java interface that enumerates the business}

methods of your bean class. methods of your bean class.



 _{Client code always go through the remote or local interface}_{Client code always go through the remote or local interface}

and never interacts with the bean directly. and never interacts with the bean directly.



 _{It obeys the rules for}_{It obeys the rules for java RMI-IIOP.}_{java RMI-IIOP.}

Continued…

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Continued…



 Local Interface:Local Interface:



 _{It’s a high performing version of remote version.}_{It’s a high performing version of remote version.} 

 _{Used when you are calling the bean that presents in the}_{Used when you are calling the bean that presents in the}

same process. same process.



 _{Unlike remote interface, it will not undergo stubs, skeleton,}_{Unlike remote interface, it will not undergo stubs, skeleton,}

marshaling/demarshaling of parameters. marshaling/demarshaling of parameters.



 _{EJB object:}_{EJB object:}



 It is container generated implementations of the remoteIt is container generated implementations of the remote

interface. interface. 

 _{All client invoications go through this.It delegates the}_{All client invoications go through this.It delegates the call to}_{call to}

bean and implements the remote interface bean and implements the remote interface



 _{Local home object:}_{Local home object:}



 High performing version of home object.High performing version of home object.



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Continued…



 _{Home interface:}_{Home interface:}



 _{Java interface, acts as a EJB factory.}_{Java interface, acts as a EJB factory.}



 _{Provides a handle of bean class to client}_{Provides a handle of bean class to client}



 _{Local Home interface:}_{Local Home interface:}



 _{High version of Home interface.}_{High version of Home interface.}



 _{Home object:}_{Home object:}



 _{Container generated implementation of home interface.}_{Container generated implementation of home interface.}



 Obeys RMI-IIOP rules.Obeys RMI-IIOP rules.



 _{Local home object:}_{Local home object:}



 High performing version of home object.High performing version of home object.



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Continued…



 _{Deployment Descriptor:}_{Deployment Descriptor:}



 _{An XML file, specifies the middleware requirements of your}_{An XML file, specifies the middleware requirements of your}

bean to the container. bean to the container.



 _{Vendor specific files:}_{Vendor specific files:}



 _{Enables you to take the advantage of vendor specific features}_{Enables you to take the advantage of vendor specific features}



 _{EJB-jar file:}_{EJB-jar file:}



 A complete zip of the above said A complete zip of the above said files.files.



 _{Given to the application server.}_{Given to the application server.}



 Application server unpacks the jar file and Application server unpacks the jar file and loads the bean into theloads the bean into the

container. container.

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Session Beans

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Components of a Session

Beans



 _{To define session bean X, you must create three classes:}_{To define session bean X, you must create three classes:}



 _{The remote (local) component interface, called}_{The remote (local) component interface, called X}_X (or_(or X_X Local)_Local)



 _Extends_Extends _EJBObject_EJBObject _(or_(or_{EJBLocalObject}_{EJBLocalObject}₎₎



 _{(All extended types are from}_{(All extended types are from} _javax.ejb_javax.ejb₎₎



 The home interface, calledThe home interface, called X X Home (or Home (or X X LocalHome)LocalHome)



 _Extends_Extends _EJBHome_EJBHome _(or_(or_EJBLocalHome_EJBLocalHome₎₎



 _{The bean class itself, called}_{The bean class itself, called X}_X Bean_Bean



 _Extends_Extends _SessionBean_SessionBean



 _{Should implement}_{Should implement} _{java.io.Serializable}_{java.io.Serializable} _{(for stateful beans)}_{(for stateful beans)}



 _{Implements business methods from the component interface}_{Implements business methods from the component interface}



 _Implements_{Implements lifecycle}_lifecycle _{methods (}_{methods (}_ejb_ejb_XXX_XXX₎₎



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Stateful Session Bean’s

Lifecycle

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Lifecycle Methods



 _{Lifecycle methods are defined in the}_{Lifecycle methods are defined in the X}_{X Bean class}_{Bean class} 

 _{They are named ejb XXX}_{They are named ejb}_XXX



 _ejbCreate_ejbCreate,, _ejbActivate_ejbActivate, etc. plus, etc. plus _{setSessionContext}_{setSessionContext}



 _{No other method name should begin with ‘}_{No other method name should begin with ‘}_ejb_ejb_’’



 _{Some lifecycle methods also appear in the}_{Some lifecycle methods also appear in the X}_{X Home interface}_{Home interface}



 _{For session beans, only the}_{For session beans, only the create}_{create methods appear in the}_{methods appear in the}

home interface home interface 

 In the home interface, the ‘In the home interface, the ‘_ejb_ejb’ prefix is not used’ prefix is not used



 _{i.e., method should be named ‘}_{i.e., method should be named ‘}_create_create_’’ 

 _{Lifecycle methods are}_{Lifecycle methods are invoked by the container}_{invoked by the container}_{when changing}_{when changing}

state during the bean’s life state during the bean’s life

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ejbCreate Methods in

Stateful Session Beans



 _{A stateful session bean can contain several}_{A stateful session bean can contain several} _ejbCreate_ejbCreate

methods methods



 _{The methods can have zero or more parameters}_{The methods can have zero or more parameters} 

 _{They can be called as}_{They can be called as} _ejbCreate_ejbCreate_{(...) or}_{(...) or}_ejbCreate_ejbCreate_XXX (...),_XXX_(...),

for more descriptive names for more descriptive names 

 _e.g.,_e.g., _{ejbCreateByName(String name)}_{ejbCreateByName(String name)}



 _{Must be}_{Must be} _{public void}_{public void} 

 _{Should throw}_{Should throw} _{javax.ejb.CreateException}_{javax.ejb.CreateException}_{if creation fails}_{if creation fails}

for whatever reason (invalid arguments, etc.) for whatever reason (invalid arguments, etc.)

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Continued…



 _{Must be reflected in the}_{Must be reflected in the X}_{X Home interface (local or remote) by a}_{Home interface (local or remote) by a}

method with identical parameters, that is called ‘

method with identical parameters, that is called ‘createcreate’ or ’ or ‘‘createcreateXXX’XXX’



 Returns the bean component interface type (Returns the bean component interface type ( X _X ))



 For remote homes, throwsFor remote homes, throws _{java.rmi.RemoteException}_{java.rmi.RemoteException}



 _e.g.,_e.g., _public_public _X_X _{createByName(String name) throws}_{createByName(String name) throws}

... ...

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Activation and Passivation



 _{During the bean’s lifecycle, the container may decide to}_{During the bean’s lifecycle, the container may decide to}

passivate

passivate itit



 _{Normally done to free up memory and other resources}_{Normally done to free up memory and other resources} 

 _{Bean is notified immediately before passivation by lifecycle}_{Bean is notified immediately before passivation by lifecycle}

method

method ejbPassivateejbPassivate()()



 _{In this method, the bean should:}_{In this method, the bean should:}



 Release any resources it might be Release any resources it might be holdingholding



 _{Sockets, Open files, database connections, etc.}_{Sockets, Open files, database connections, etc.}



 Nullify fields that should not be serialized (Nullify fields that should not be serialized (cache, etc.)cache, etc.)



 _{If the bean is referenced by client while passivated, the container}_{If the bean is referenced by client while passivated, the container}

activates

activates it.it.



 _{Bean is notified by}_{Bean is notified by} _ejbActivate_ejbActivate_{() immediately after de-}_{() immediately after}

de-serialization serialization



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The Lifecycle of Stateless

Session EJBs



 _{Session EJBs have no state, so activation and}_{Session EJBs have no state, so activation and passivation are}_{passivation are} meaningless

meaningless



 The container simply destroys instances when low on memory,The container simply destroys instances when low on memory,

and creates new ones as needed and creates new ones as needed



 Still,Still, _ejbActivate_ejbActivate andand _ejbPassivate_ejbPassivate must be implementedmust be implemented

in

in X X Bean (as empty methods)Bean (as empty methods)



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ejbCreate Methods in

Stateless Session Beans



 _{For stateless session beans, there can be}_{For stateless session beans, there can be only one}_{only one} _ejbCreate_ejbCreate method, accepts zero parameters

method, accepts zero parameters



 _{Reflected normally in the home interface as create.}_{Reflected normally in the home interface as create.}



 _{Must be}_{Must be} _{public void}_{public void}



 _{Should throw}_{Should throw} _{javax.ejb.CreateException}_{javax.ejb.CreateException} _{if creation fails for}_{if creation fails for} whatever reason (invalid arguments, etc).

whatever reason (invalid arguments, etc).



 _{Must be reflected in the}_{Must be reflected in the X}_{X Home interface (local or remote) by a}_{Home interface (local or remote) by a} method with identical parameters, that is called ‘

method with identical parameters, that is called ‘ createcreate’.’.



 _{Returns the bean component interface type (}_{Returns the bean component interface type ( X}_X ))



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Sample Session Bean

Deployment Descriptors

  _{…. <enterprise-beans>}_{…. <enterprise-beans>}   _<session>_<session>   _{<ejb-name>HelloWorldLocalBean</ejb-name>}_{<ejb-name>HelloWorldLocalBean</ejb-name>}   _{<home>examples.webservices.basic.localHome_Object.HelloWo}_{<home>examples.webservices.basic.localHome_Object.HelloWo} rldHome</home> rldHome</home>   _{<remote>examples.webservices.basic.localHome_Object.HelloW}_{<remote>examples.webservices.basic.localHome_Object.HelloW} orldRemote</remote> orldRemote</remote>   _<ejb- <ejb-class>examples.webservices.basic.localHome_Object.HelloWorl class>examples.webservices.basic.localHome_Object.HelloWorl dLocalBean</ejb-class> dLocalBean</ejb-class> 

 _{<session-type>Stateless(stateful)}_{<session-type>}_{Stateless(stateful)}_{</session-type>}_{</session-type>}   _{<transaction-type>Container</transaction-type>}_{<transaction-type>Container</transaction-type>}   _</session>_</session>   _{</enterprise-beans> ….}_{</enterprise-beans> ….}

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An example of stateless

session bean.

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Session Bean Class

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

 _{package examples.webservices.basic.localHome_Object;}_{package examples.webservices.basic.localHome_Object;}



 _{import javax.ejb.SessionBean;}_{import javax.ejb.SessionBean;} 

 _{import javax.ejb.CreateException;}_{import javax.ejb.CreateException;} 

 _{import javax.ejb.SessionContext;}_{import javax.ejb.SessionContext;}



 _{public class HelloWorldLocalBean implements SessionBean{}_{public class HelloWorldLocalBean implements SessionBean{} 

 _{private SessionContext ctx;}_{private SessionContext ctx;} 

 

 _{public void ejbCreate() {}}_{public void ejbCreate() {}} 

 _{public void ejbActivate() {}}_{public void ejbActivate() {}} 

 _{public void ejbPassivate() {}}_{public void ejbPassivate() {}} 

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

 _{public void setSessionContext(SessionContext ctx) {}_{public void setSessionContext(SessionContext ctx) {} 

 _{this.ctx = ctx;}_{this.ctx = ctx;} 

 _}} 

 _{public String sayHelloMethod(int num, String s) {}_{public String sayHelloMethod(int num, String s) {} 

 

 _{System.out.println("sayHello in webservices.basic.javaclass}_{System.out.println("sayHello in webservices.basic.javaclass}

webservice has "+ webservice has "+



 _{"been invoked with arguments " + s + " and " + num+" the}_{"been invoked with arguments " + s + " and " + num+" the}

context is : "+ctx); context is : "+ctx);



 _{String returnValue = "HelloWorldLocalBean....:This message}_{String returnValue = "HelloWorldLocalBean....:This message}

brought to you by the "+ brought to you by the "+



 _{"letter "+s+" and the number "+num+" the context is : "+ctx;}_{"letter "+s+" and the number "+num+" the context is : "+ctx;} 

 _{return returnValue;}_{return returnValue;} 

 _}} 

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

 _{package examples.webservices.basic.localHome_O}_package_{examples.webservices.basic.localHome_Object;}_bject;



 _{import javax.ejb.EJBHome;}_{import javax.ejb.EJBHome;}



 _{import javax.ejb.CreateExcepti}_import_{javax.ejb.CreateException;}_on;



 _{import java.rmi.RemoteExcepti}_import_{java.rmi.RemoteException;}_on;



 _{public interface HelloWorldHome extends EJBHome{}_{public interface HelloWorldHome extends EJBHome{}



 _{HelloWorldRemote create() throws CreateException,}_{HelloWorldRemote create() throws CreateException,} RemoteException ; RemoteException ;   _}}

Home Interface

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Remote Interface



 _{package examples.webservices.basic.localHome_Object;}_{package examples.webservices.basic.localHome_Object;}



 _{import java.rmi.RemoteException;}_{import java.rmi.RemoteException;} 

 _{import javax.ejb.EJBObject;}_{import javax.ejb.EJBObject;}



 _{public interface HelloWorldRemote extends EJBObject {}_{public interface HelloWorldRemote extends EJBObject {}



 public String sayHelloMethod(int num, String s) throwspublic String sayHelloMethod(int num, String s) throws

RemoteException; RemoteException;     _}}

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Local Home Interface



 _{package examples.webservices.basic.localHome_Object;}_{package examples.webservices.basic.localHome_Object;} 

 _{import javax.ejb.EJBLocalHome;}_{import javax.ejb.EJBLocalHome;} 

 _{import javax.ejb.CreateException;}_{import javax.ejb.CreateException;} 

 _{public interface HelloWorldLocalHome extends EJBLocalHome{}_{public interface HelloWorldLocalHome extends EJBLocalHome{} 

 _{HelloWorldLocal create() throws CreateException;}_{HelloWorldLocal create() throws CreateException;} 

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Local Interface



 _{package examples.webservices.basic.localHome_Object;}_{package examples.webservices.basic.localHome_Object;} 

 _{import javax.ejb.EJBLocalObject;}_{import javax.ejb.EJBLocalObject;} 

 _{public interface HelloWorldLocal extends EJBLocalObject {}_{public interface HelloWorldLocal extends EJBLocalObject {} 

 _{public String sayHelloMethod(int num, String s);}_{public String sayHelloMethod(int num, String s);} 

   _}}

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Deployment Descriptor



 _{<?xml version="1.0" encoding="UTF-8"?>}_{<?xml version="1.0" encoding="UTF-8"?>} 

 _{<!DOCTYPE ejb-jar PUBLIC "-//Sun Microsystems, Inc.//DTD}_{<!DOCTYPE ejb-jar PUBLIC "-//Sun Microsystems, Inc.//DTD}

Enterprise JavaBeans 2.0//EN" Enterprise JavaBeans 2.0//EN" "http://java.sun.com/dtd/ejb- jar_2_0.dtd"> jar_2_0.dtd">   _<ejb-jar>_<ejb-jar>   _{<enterprise-beans>}_{<enterprise-beans>}   _<session>_<session>   _{<ejb-name>HelloWorldLocalBean</ejb-name>}_{<ejb-name>HelloWorldLocalBean</ejb-name>}   _{<home>examples.webservices.basic.localHome_Object.HelloWo}_{<home>examples.webservices.basic.localHome_Object.HelloWo} rldHome</home> rldHome</home>   _{<remote>examples.webservices.basic.localHome_Object.HelloW}_{<remote>examples.webservices.basic.localHome_Object.HelloW} orldRemote</remote> orldRemote</remote>

(42)

Continued…

  _<local- <local-home>examples.webservices.basic.localHome_Object.HelloWorl home>examples.webservices.basic.localHome_Object.HelloWorl dLocalHome</local-home> dLocalHome</local-home>   _{<local>examples.webservices.basic.localHome_Object.HelloWor}_{<local>examples.webservices.basic.localHome_Object.HelloWor} ldLocal</local> ldLocal</local>   _<ejb- <ejb-class>examples.webservices.basic.localHome_Object.HelloWorl class>examples.webservices.basic.localHome_Object.HelloWorl dLocalBean</ejb-class> dLocalBean</ejb-class>   _{<session-type>Stateless</session-type>}_{<session-type>Stateless</session-type>}   _{<transaction-type>Container</transaction-type>}_{<transaction-type>Container</transaction-type>}   _</session>_</session>   _{</enterprise-beans>}_{</enterprise-beans>}   _</ejb-jar>_</ejb-jar>