ejbe slides

Copyright © 2000, BEA Systems Inc.EJBE-1Developing Enterprise Applications with BEA WebLogic Server

Module

EJBEEntity EJBs

At the end of this module you will be able to:• understand how entity EJBs stay persistent• write entity EJBs from scratch• connect an entity EJB to a data source


Section

1Entity EJB Basics

At the end of this section you will be able to:• design an entity EJB that is mapped to a datasource• describe the differences between CMP and BMP• write a container managed entity EJB


What is an Entity EJB?What is an Entity EJB?

§ Entity EJBs have the following behavior:Ø they are a representation of persistent dataØ they can survive a crashØmultiple clients can be using EJBs that

represent the same dataØ the EJB instance contains a “copy” of the data

in the persistent store


Persistence ManagementPersistence Management

§ The attributes of the object must be stored using a persistent mechanism.§ Examples of persistence management

include:Ø serialization to a fileØ relational database mappings through JDBC

Client-clientID-corporateName-address-town-postcode

Persistent Storage

database,files, etc...

Object in memory


Shared Entity EJBsShared Entity EJBs

§When multiple clients share an entity EJB they:Ø receive their own instanceØ share the underlying dataØ do not have to handle synchronization

Client

Client

Persistent StorageClient

Server

Entity EJB

Client Context

Container


Primary KeysPrimary Keys

§ Every entity EJB has a set of attributes that are unique when aggregated together.§ The aggregated attributes are called the

primary key of an entity EJB.


ObjectObject--Relational MappingRelational Mapping

§ An O-R mapping stores each object in a single row of a table.§ A database column is associated with each

attribute of the class. Client

••Client IdClient Id•Corporatename•Address•Town•Postcode

clientIdclientId Corporate Name Address Town Postcode

411MEB MEB 1, Lichfield Road B ’ham B7 4TU411PIT PITCH 34, London Road Chester C60 7YJ411WC World Company 1, The Strand London W1 8PL

Primarykey


Identical Identical Enitity Enitity EJBsEJBs

§ Two entity EJBs are identical if the contents of their primary keys are identical.

Client

Client

Persistent StorageClient

Server

Entity EJB

Client Context

Container

Primary Key


Types of PersistenceTypes of Persistence

§ There are two types of persistent EJBs:ØContainer-Managed Persistence (CMP)Ø Bean-Managed Persistence (BMP)

Client

Persistent Storage

Client

Server

Entity EJB

Client Context

Container

CMP

BMP

The Logic is here!


Entity vs. Session EJB AuthoringEntity vs. Session EJB Authoring

Differences Between Writing Entity EJBs and Session EJBs:1. You must write a primary key class.2. The home interface must have a findByPrimaryKey(<PrimaryKey>)

method.3. The home interface can have other find(…) methods.4. The bean class must implement the javax.ejb.EntityBean interface.5. The bean class must provide an ejbCreate(…) AND an

ejbPostCreate(…) for each create(…) listed in the home interface.

Differences Between Writing Entity EJBs and Session EJBs:1. You must write a primary key class.2. The home interface must have a findByPrimaryKey(<PrimaryKey>)

method.3. The home interface can have other find(…) methods.4. The bean class must implement the javax.ejb.EntityBean interface.5. The bean class must provide an ejbCreate(…) AND an

ejbPostCreate(…) for each create(…) listed in the home interface.


Primary Key ClassesPrimary Key Classes

§ A primary key object is the unique identifier of an EJB.§ A primary key class must:Ø be declared publicØ implement java.io.SerializableØ have a no-argument constructorØ have all of its attributes be declared public

Sample Primary Key Class:public class AlarmClockPK implements java.io.Serializable {

public int serialNumber;public String currentStation;

}

Sample Primary Key Class:public class AlarmClockPK implements java.io.Serializable {


}


Primary Key AttributesPrimary Key Attributes

§ The EJB class must contain the same parameters listed in the primary key.

AlarmClockBean

••int serialNum;int serialNum;••String currentStation;String currentStation;•long currentVolume;•Date wakeUpTime;•boolean isFm;

AlarmClockPK

••int serialNum;int serialNum;••String currentStation;String currentStation;


CMP EJB CreationCMP EJB Creation

: Client EJBHome instance

create(args)

Container-Provided Classes

EJBObject Entity Context Synchronization database

new

extract container managed fields

create entity representation in DB

ejbCreate(args)

ejbPostCreate(args)

Return remote stub containing primary key

instance!

Create primary key

instance with values

extracted!


Home InterfacesHome Interfaces

§ Entity EJB home interfaces must include one or more find(…) methods.

Syntax for findByPrimaryKey(…) Method:

Syntax for Other find(…) Methods:

Syntax for findByPrimaryKey(…) Method:

Syntax for Other find(…) Methods:

public <RemoteIF> findByPrimaryKey(<PrimaryKey> pk) throws FinderException, RemoteException;

public <RemoteIF> findWhatever(…) throws FinderException, RemoteException;

public Enumeration findWhatever(…)throws FinderException, RemoteException;


Attribute and Attribute and find(…)find(…) Method MappingMethod Mapping


Finder ExpressionsFinder ExpressionsSyntax for Expressions:

Available Operators:

Available Operands:

Syntax for Expressions:

Available Operators:

Available Operands:

operator operand1 operand2

(), =, <, >, <=, >=, !, &, |, like

1. Another Expression2. An EJB Attribute3. A find(…)Method Parameter (Must precede with $)

Finder Expression Examples:Finder Expression Examples:(> balance $amount)

(& (> bal $amount) (! (= accountType ‘checking’)))

(= 1 1)

(like lastName M%)


Writing the Bean ClassWriting the Bean Class

§ The bean class must implement the EntityBean interface.

The EntityBean Interface:public interface EntityBean extends EnterpriseBean {public void ejbActivate();public void ejbPassivate();public void ejbLoad();public void ejbStore();public void setEntityContext(EntityContext ctx);public void unsetEntityContext()public void ejbRemove();

}

Some Other Guidelines:1. Your ejbCreate(…) methods should return void for CMP.2. You do not have to implement any ejbFind(…) methods for CMP.

The EntityBean Interface:public interface EntityBean extends EnterpriseBean {public void ejbActivate();public void ejbPassivate();public void ejbLoad();public void ejbStore();public void setEntityContext(EntityContext ctx);public void unsetEntityContext()public void ejbRemove();

}

Some Other Guidelines:1. Your ejbCreate(…) methods should return void for CMP.2. You do not have to implement any ejbFind(…) methods for CMP.


Entity EJB Life CycleEntity EJB Life Cycle

does not exist

pooled

ready

instance throws system exception from any method

unsetEntityContext()newInstance()setEntityContext(ec)

ejbStore()ejbLoad()

ejbPassivate()ejbActivate()

ejbFind<METHOD>()

ejbRemove()

ejbCreate(args)ejbPostCreate(args)

business method


PassivationPassivation


business method


EJBObject Entity Context

Synchro-nization database

extract container managed fields

updated entity state in DB

business method

Container

ejbStore()

ejbPassivate()


ActivationActivation


business method


EJBObject Entity Context

Synchro-nization database

set container-managed fields

read entity state in DB

ejbActivate()

Container

ejbLoad()

business method


Standard Entity EJB ExceptionsStandard Entity EJB Exceptions

§ The EJB specification defines five standard EJB application exceptions:Ø javax.ejb.CreateExceptionØ javax.ejb.DuplicateExceptionØ javax.ejb.FinderExceptionØ javax.ejb.ObjectNotFoundExceptionØ javax.ejb.RemoveException


Finally, An Example!Finally, An Example!

§ Let’s write an entity EJB that tracks different alarm clock settings.§ The EJB will track:Ø the time the alarm is supposed to go offØ the current radio station selectedØAM/FM radio selection


The Remote InterfaceThe Remote Interface

The AlarmClock Remote Interface:

public interface AlarmClock extends Remote, EJBObject {public Date getAlarmTime() throws RemoteException;public String getRadioStation() throws RemoteException;public boolean isFmSet() throws RemoteException;public void isFmSet(boolean fm) throws RemoteException;public void setAlarmTime(Date time) throws RemoteException;public void setRadioStation(String station)

throws RemoteException;}

The AlarmClock Remote Interface:

public interface AlarmClock extends Remote, EJBObject {public Date getAlarmTime() throws RemoteException;public String getRadioStation() throws RemoteException;public boolean isFmSet() throws RemoteException;public void isFmSet(boolean fm) throws RemoteException;public void setAlarmTime(Date time) throws RemoteException;public void setRadioStation(String station)

throws RemoteException;}


The Home Interface and Primary KeyThe Home Interface and Primary Key

The AlarmClockHome Home Interface:public interface AlarmClockHome extends EJBHome {AlarmClock create() throws CreateException, RemoteException;AlarmClock create(Date time, String station, boolean fm)

throws CreateException, RemoteException;AlarmClock findByPrimaryKey(AlarmClockPK id)

throws FinderException, RemoteException;Enumeration findAllFMSettings()

throws FinderException, RemoteException;}

The AlarmClockHome Home Interface:public interface AlarmClockHome extends EJBHome {AlarmClock create() throws CreateException, RemoteException;AlarmClock create(Date time, String station, boolean fm)

throws CreateException, RemoteException;AlarmClock findByPrimaryKey(AlarmClockPK id)

throws FinderException, RemoteException;Enumeration findAllFMSettings()

throws FinderException, RemoteException;}

AlarmClockPK Primary Key Class:public class AlarmClockPK implements java.io.Serializable {


}

AlarmClockPK Primary Key Class:public class AlarmClockPK implements java.io.Serializable {


}


The Bean Class Finally!The Bean Class Finally!

The AlarmClockBean EJB Class:public class AlarmClockBean implements EntityBean {

public int id;

transient protected EntityContext context;

// Container managed fieldspublic String station;public String wakeUpTime;public boolean isFm;

The AlarmClockBean EJB Class:public class AlarmClockBean implements EntityBean {

public int id;

transient protected EntityContext context;

// Container managed fieldspublic String station;public String wakeUpTime;public boolean isFm;


The Bean Class Finally!The Bean Class Finally!The AlarmClockBean EJB Class Continued:public void ejbActivate() {}public void ejbLoad() {}public void ejbPassivate() {}public void ejbRemove() {}public void ejbStore() {}

public void ejbCreate() {// Generate a unique ID for this EJB.// Most EJBs pass receive this value as a parameter.this.id = (int)(Math.random()*100000);

// Get the station and time from the environment// properties.Properties props = context.getEnvironment();this.station = props.getProperty("Station");this.isFm = props.getProperty("isFM");this.wakeUpTime = props.getProperty("Time");

}

The AlarmClockBean EJB Class Continued:public void ejbActivate() {}public void ejbLoad() {}public void ejbPassivate() {}public void ejbRemove() {}public void ejbStore() {}

public void ejbCreate() {// Generate a unique ID for this EJB.// Most EJBs pass receive this value as a parameter.this.id = (int)(Math.random()*100000);

// Get the station and time from the environment// properties.Properties props = context.getEnvironment();this.station = props.getProperty("Station");this.isFm = props.getProperty("isFM");this.wakeUpTime = props.getProperty("Time");

}


The AlarmClockBean EJB Class Continued:

public void ejbCreate(String time, String station, boolean isFm){// Generate a unique ID for this EJB.// Most EJBs pass this value in.this.id = (int)(Math.random()*100000);

this.wakeUpTime = time;this.station = station;this.isFm = new Boolean(isFm).toString();

}

public void ejbPostCreate() {}public void ejbPostCreate(String time, String station,

boolean isFm) {}

The AlarmClockBean EJB Class Continued:

public void ejbCreate(String time, String station, boolean isFm){// Generate a unique ID for this EJB.// Most EJBs pass this value in.this.id = (int)(Math.random()*100000);

this.wakeUpTime = time;this.station = station;this.isFm = new Boolean(isFm).toString();

}

public void ejbPostCreate() {}public void ejbPostCreate(String time, String station,

boolean isFm) {}

The Bean Class Finally!The Bean Class Finally!EJBE-1, 2


BMP ConsiderationsBMP Considerations

Things you Have to do For BMP Entity EJBs:1. You must code the persistence management for the ejbCreate(…),

ejbRemove(), ejbLoad(), and ejbStore() methods.2. The ejbCreate(…) methods must return a primary key instance.3. The ejbFind(…) methods must be implemented.

Things you Have to do For BMP Entity EJBs:1. You must code the persistence management for the ejbCreate(…),

ejbRemove(), ejbLoad(), and ejbStore() methods.2. The ejbCreate(…) methods must return a primary key instance.3. The ejbFind(…) methods must be implemented.


BMP EJB CreationBMP EJB Creation


create(args)


EJBObject Entity Context Synchronization database

new

create representation in DB

ejbCreate(args)

ejbPostCreate(args)

Return remote stub containing primary key

instance!

Return primary key instance with unique values inserted


The Alarm With BMPThe Alarm With BMP


The Alarm With BMPThe Alarm With BMPEJBE-3


TransactionsTransactions

§ Transactions can group multiple statements into an atomic unit to ensure integrity.§ EJBs can have their transaction

demarcation level set:Ø for the entire EJBØ per method


EJB Transaction AttributesEJB Transaction Attributes

§ The following entities can demarcate transactions:Ø an EJB clientØ the container (automatic demarcation)Ø the EJB component itself

§ The EJB specification defines 6 transaction attributes:Ø TX_NOT_SUPPORTEDØ TX_SUPPORTSØ TX_MANDATORYØ TX-REQUIREDØ TX_REQUIRES_NEWØ TX_BEAN_MANAGED


Container

TX_NOT_SUPPORTEDTX_NOT_SUPPORTED

§ TX_NOT_SUPPORTED transactions cause client transactions to be suspended during the EJB’s execution.

method

EJBContainer

Active Transaction

EJBContainer

Client

1-begin2-method3-commit

method

method

Scenario 1:

Scenario 2: No Transaction Active

Client


TX_SUPPORTSTX_SUPPORTS

§ TX_SUPPORTS implies that the EJB will be included in any client-started transactions.

Container

method

EJBContainer

Active Transaction

EJBContainer

Client


method

method

Scenario 1:


Client


TXTX__MANDATORYMANDATORY

§ TX_MANDATORY transactions require the client to pass a global transaction to the EJB.

Container EJBContainer

Active Transaction

EJBContainer

Client


method

method

Scenario 1:


Client

TransactionRequiredException


TX_REQUIREDTX_REQUIRED

§ TX_REQUIRED transactions force the EJB to be executed within a transaction started either by the client or the container.


Active Transaction

Container

Client


method

method

Scenario 1:


Client


EJB


TX_REQUIRES_NEWTX_REQUIRES_NEW

§ TX_REQUIRES_NEW transactions force the EJB to execute within a new transaction that can only be started by the container.


Active Transaction

Container

Client


method

Scenario 1 (try to avoid):

Scenario 2:No Transaction Active

Client


EJB


Localized Transaction


TX_BEAN_MANAGEDTX_BEAN_MANAGED

§ TX_BEAN_MANAGED transactions are demarcated within the EJB only.


Active Transaction

Container

Client


method

Scenario 1 (try to avoid):

Scenario 2:No Transaction Active

Client


Localized Transaction

method

EJB1-begin2-method3-commit

method


The The UserTransactionUserTransaction InterfaceInterface

§ Use the javax.jts.UserTransactionobject to demarcate transactions within a client or EJB.

UserTransaction

begin()commit()rollback()setRollbackOnly()getStatus()setTransactionTimeout()

<<Interface>>

To Obtain a New javax.jts.UserTransaction Instance From JNDI:To Obtain a New javax.jts.UserTransaction Instance From JNDI:UserTransaction trans =

(UserTransaction)ctx.lookup(“javax.jts.UserTransaction”);


Other Transaction IssuesOther Transaction Issues

§ An EJB’s conversational state is NOTencompassed in a transaction.§ A rollback() on a transaction that

encompasses an EJB will not revert the EJB’s attributes!§ Container and client managed transaction

objects can be accessed by the context:

To Obtain Change the Status of the Current Transaction Within an EJB:To Obtain Change the Status of the Current Transaction Within an EJB:contextObject.setRollbackOnly();boolean setForRollback = contextObject.getRollbackOnly();


Reverting Conversational StateReverting Conversational State

§ You can have your EJB implement the SessionSynchronization interface.

SessionSynchronization Interface Methods:// Called by the application server right after the start of a new transaction. If you // store attributes that may need to be reverted, do it here.public void afterBegin();

// Called immediately before the completion of the transaction. It is NOT known if// is committed or rolled back at this point.public void beforeCompletion();

// Called immediately after the completion of a transaction. If the committed// variable is true, then the transaction was successful. If the committed value// is false, the transaction was rolled back. You can recover EJB state from // within this method if you need to.public void afterCompletion(boolean committed);

}

SessionSynchronization Interface Methods:// Called by the application server right after the start of a new transaction. If you // store attributes that may need to be reverted, do it here.public void afterBegin();

// Called immediately before the completion of the transaction. It is NOT known if// is committed or rolled back at this point.public void beforeCompletion();

// Called immediately after the completion of a transaction. If the committed// variable is true, then the transaction was successful. If the committed value// is false, the transaction was rolled back. You can recover EJB state from // within this method if you need to.public void afterCompletion(boolean committed);

}


ReviewReview

§ In this section we talked about :Ø container-managed and bean-managed

persistenceØ the differences between session and entity

EJBsØ primary key classesØ transactions and their demarcation levels


ReviewReview

§ In this module we talked about:Ø container and bean managed persistenceØ primary key classesØ differences between session and entity EJBsØwriting ejbPostCreate(…) and ejbFind(…) methods

Øwriting ejbLoad() and ejbStore()methods

Ø transactions

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