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Таврический Национальный Университет им. В.И. Вернадского

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Mastering Enterprise JavaBeans™ and the Java 2 Platform, Enterprise Edition - Roman E

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686 M A S T E R I N G E N T E R P R I S E J A V A B E A N S

Client called

create(args) on

bean instance does not

the home interface

exist



	1: Class.newInstance()	ejbRemove()
Client called a	2: setSessionContext()	ejbRemove()
Client called a	2: setSessionContext()
non-transactional	3: ejbCreate(args)
business method
on the EJB object

Client called remove() on the EJB object

client times out

		Container's limit of
		instantiated beans is
	Client times out	instantiated beans is
	Client times out	reached, so it must
		reached, so it must
		swap your bean out

ejbPassivate()

	Non-Transactional	bean instance is ready to
	Business Method	service method calls
		1: beforeCompletion()
		2: afterCompletion(true)
	afterBegin()
	Client called a	bean instance is within a
	transactional	bean instance is within a
	transactional	transaction and ready to
	business method	transaction and ready to
	business method	service method calls
	on the EJB object	service method calls
	on the EJB object
		Transactional
		Business Method

bean instance is in the passive state

ejbActivate()

Client called a method

afterCompletion(false)

on a passivated bean, so container must swap your bean back in

If transaction	If transaction
ended in a	ended in an
commit.	abort.

Client called another transactional business method on the EJB object

Figure F.5 The lifecycle of a stateful session bean (implements javax.ejb.SessionSynchronization). Each method call shown is an invocation from the container to the bean instance.

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EJB Quick Reference Guide 687

Client		Container		Bean Instance		Database

home.create(args)

beanClass.newInstance()

setSessionContext()

ejbCreate(args)

return new EJB object

Servicing a create method

ejbObject.businessMethod(args)

businessMethod(args)

Servicing a business method

ejbPassivate()

serialize bean instance,

and write serialized blob

to secondary storage

Passivating a bean instance

ejbObject.businessMethod(args)

read serialized blob

from secondary storage,

and deserialize bean instance

ejbActivate()

businessMethod(args)

Activating a bean instance

ejbObject.transactionalBusinessMethod()

afterBegin()

read database data

transactionalBusinessMethod()

Begin transaction sequence

(only if bean class implements javax.ejb.SessionSynchronization

)

beforeCompletion()

write database data

prepare

commit

If commit was successful,

afterCompletion(true)

else afterCompletion(false)

Commit transaction sequence

(only if bean class implements javax.ejb.SessionSynchronization

)

ejbObject.remove()

ejbRemove()

home.remove(...)

Servicing a remove method

Figure F.6 Sequence diagram for stateful session beans. For simplicity, the Container object represents all container subsystems, including EJB objects, home objects, transaction services, and so on.

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688 M A S T E R I N G E N T E R P R I S E J A V A B E A N S

Entity Bean Diagrams

entity bean data does not exist No client reference to EJB object

client calls home.remove(...) or direct database delete

direct database insert

client releases reference

client calls home.create(...)

client calls a finder method on home interface

entity bean data exists

No client reference to EJB object

client releases reference

if a client calls a method, a NoSuchObject exception will be thrown

entity bean data does not exist Client holds reference to EJB object

client calls ejbObject.remove(), client calls home.remove(...), or direct database delete

entity bean data exists Client holds reference to EJB object

The direct database inserts and deletes could occur

because other applications are running in your

deployment. For example, you might have a legacy client can call business methods application that a bank administrator uses to add new

bank accounts. Or you might have a simple JDBC application that doesn't use entity beans at all, but modifies the same database data your entity beans model.

Figure F.7 The client’s view of an entity bean object life cycle.

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EJB Quick Reference Guide 689

Container decided it needs another entity bean instance

bean instance does not

exist

Container decided it doesn't need your instance anymore

1: Class.newInstance()	1: unsetEntityContext()
2: setEntityContext()	2: JVM will garbage collect
	and call finalize()
	and call finalize()

Client called a finder method on the home interface.

Client called create() on the home interface (this will create new database data)

ejbCreate()

ejbPostCreate()

Container determined that the bean is out of synch with database. The bean needs to load the new database data.

ejbLoad()

Client called a business method on the EJB object

bean instance is pooled

ejbFind()

Client called remove() on the EJB object (this will destroy database data)

Passivate your state : Activate your state:
1: ejbStore()	1: ejbActivate()	ejbRemove()
2: ejbPassivate()	2: ejbLoad()

bean instance is ready to

ejbStore()

service method calls

business method

Container determined that the database is out of synch with the bean. The bean needs to store its data into the database.

Figure F.8 The life cycle of an entity bean. Each method call shown is an invocation from the container to the bean instance.

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690 M A S T E R I N G E N T E R P R I S E J A V A B E A N S

Client

Container

Bean Instance

Database

beanClass.newInstance()

setEntityContext()

Adding a new instance to the pool

home.find<METHOD>(args)

find<METHOD>(args)

search database based on args

return one or more primary keys

return one or more new EJB objects

Servicing a finder method

home.create(args)

ejbCreate(args)

create entity representation in database

ejbPostCreate(args)

return new EJB object

Servicing a create method

ejbObject.businessMethod(args)

businessMethod(args)

Servicing a business method

ejbStore()

update entity representation in database

ejbPassivate()

Passivating a bean instance

ejbObject.businessMethod(args)

ejbActivate()

ejbLoad()

read entity representation from database

businessMethod(args)

Activating a bean instance

ejbObject.remove()

ejbRemove()

home.remove(...)

remove entity representation from database

Servicing a remove method

unsetEntityContext()

Removing an instance from the pool

Figure F.9 Sequence diagram for bean-managed persistent entity beans. For simplicity, the Container object represents all container subsystems, including EJB objects, home objects, transaction services, and so on.

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EJB Quick Reference Guide

691

Client

Container

Bean Instance

Database

beanClass.newInstance()

setEntityContext()

Adding a new instance to the pool

home.find<METHOD>(args)

search database based on args

return one or more new EJB objects

Servicing a finder method

home.create(args)

ejbCreate(args)

extract container-managed field values

create entity representation in database

ejbPostCreate(args)

return new EJB object

Servicing a create method

ejbObject.businessMethod(args)

businessMethod(args)

Servicing a business method

ejbStore()

extract container-managed fields

update entity representation in database

ejbPassivate()

Passivating a bean instance

ejbObject.businessMethod(args)

ejbActivate()

read entity representation from database

set container-managed fields

ejbLoad()

businessMethod(args)

Activating a bean instance

ejbObject.remove()

ejbRemove()

home.remove(...)

remove entity representation from database

Servicing a remove method

unsetEntityContext()

Removing an instance from the pool

Figure F.10 Sequence diagram for container-managed persistent entity beans. For simplicity, the Container object represents all container subsystems, including EJB objects, home objects, transaction services, and so on.

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692 M A S T E R I N G E N T E R P R I S E J A V A B E A N S

EJB API Reference

The following section explains the Enterprise JavaBeans API, which is the javax.ejb package. This API is the essence of EJB, and defines the specific signature contracts between clients, enterprise beans, and containers. This reference is consistent with both the EJB 1.0 standard that we’ve been using throughout the book, as well as the new EJB 1.1 standard we outlined in Appendix D.

CreateException

This exception type indicates failure to create an enterprise bean. You should throw this exception in your home interface’s create(...) methods.

public class javax.ejb.CreateException extends java.lang.Exception

{

public CreateException();

public CreateException(java.lang.String);

}

DuplicateKeyException

This exception type indicates failure to create an entity bean because an entity bean with the same primary key already exists. This is a subclass of CreateException and is thrown in an entity bean home interface’s create(...) methods.

public class javax.ejb.DuplicateKeyException extends javax.ejb.CreateException

{

public DuplicateKeyException();

public DuplicateKeyException(java.lang.String);

}

EJBContext

Your bean can use an EJB context to perform callbacks to the container. These callbacks help your bean determine its current transactional status, security status, and more. Your container must make an EJB context available to your enterprise bean at runtime. Both SessionContext and EntityContext extend this interface.

public interface javax.ejb.EJBContext

{

public javax.ejb.EJBHome getEJBHome();

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EJB Quick Reference Guide 693

*This method has changed in EJB 1.1. You should

*use JNDI instead. See Appendix D.

public java.util.Properties getEnvironment();

*This method has changed in EJB 1.1. You should

*use getCallerPrincipal() instead. See Appendix D. */

public java.security.Identity getCallerIdentity();

/* This method has changed in EJB 1.1. You should

*use isCallerInRole(java.lang.String) instead.

*See Appendix D.

public boolean isCallerInRole(java.security.Identity);

*This method has changed in EJB 1.1. You should

*use JNDI instead. See Appendix D.

public javax.jts.UserTransaction getUserTransaction() throws IllegalStateException;

public void setRollbackOnly(); public boolean getRollbackOnly();

}

Table F.1 javax.ejb.EJBContext

METHOD

DESCRI PTION

USEFULNESS

getHome()	Returns a reference to your
	bean’s own home object.

Useful when your bean needs to create, destroy, or find EJB objects of its own bean class.

getEnvironment()	Returns your bean’s	Call to access deployed
	deployed environment	environment properties. Allows
	properties.	users to customize your beans via
		properties.
getCallerIdentity()	Returns the caller’s security	Useful for programmatic security
	identity.	within your bean. For example,
		you can use the caller’s distin-
		guished name as a key to unlock
		secured information in a database.
		continues

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694 M A S T E R I N G E N T E R P R I S E J A V A B E A N S

Table F.1 (Continued)

METHOD	DESCRI PTION
isCallerInRole()	Tests if a bean’s caller is in a
	particular security role (a
	group authorized to perform
	operations).

USEFULNESS

Useful for querying whether the authenticated client is authorized to perform an operation.

setRollbackOnly()	Marks the current transaction
	such that the only outcome of
	the transaction is a rollback.

Call this method to force a transaction to abort and roll back.

getRollbackOnly()	Returns a Boolean indicating	If the current transaction is going
	whether the current transac-	to abort, you may be able to
	tion has been marked for	bypass logic in your bean, saving
	rollback.	valuable computation time.
getUserTransaction()	Returns the javax.transaction	Controlling transactions explicitly
	.UserTransaction interface.	in your bean.
Note: This method is
only supported for
bean-managed
transactions.

EJBException

Your enterprise bean class should throw this exception to indicate an unexpected error, such as a failure to open a database connection, or a JNDI exception. Your container will treat this exception as a serious problem, and may take action such as logging the event or paging a system administrator, depending upon your container’s policy. The container will then throw a java.rmi.RemoteException back to the client code.

public class javax.ejb.EJBException extends java.lang.Exception

{

public javax.ejb.EJBException();

public javax.ejb.EJBException(java.lang.String); public javax.ejb.EJBException(java.lang.Exception); public java.lang.Exception getCausedByException();

}

EJBHome

Clients create, find, and remove EJB objects through home interfaces. All home interfaces extend javax.ejb.EJBHome. The container will implement the methods in javax.ejb.EJBHome when it implements your home interface as a concrete home object.

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EJB Quick Reference Guide 695

public interface javax.ejb.EJBHome extends java.rmi.Remote

{

public EJBMetaData getEJBMetaData() throws java.rmi.RemoteException;

public void remove(Handle handle) throws java.rmi.RemoteException,

javax.ejb.RemoveException;

public void remove(Object primaryKey) throws java.rmi.RemoteException,

javax.ejb.RemoveException;

*This method applies to EJB 1.1 only. It retrieves

*a home handle, which is a persistent reference to

*a home object. See Appendix D.

public javax.ejb.HomeHandle getHomeHandle()

}

Table F.2 javax.ejb.EJBHome (these methods are called by clients)

METHOD	EXPLANATION
getEJBMetaData()	Returns metadata about the enterprise bean you’re working with.
	Useful if your client code is written in a scripting language, or if you’re
	writing EJB development tools.
remove()	This method destroys an EJB object based upon an EJB object handle
	or primary key you pass in.
	Note: For entity beans, remove() also deletes the bean from the
	underlying persistent store.

EJBMetaData

This interface encapsulates metadata about an enterprise bean. Metadata is not very useful for typical client code, but it more suited towards clients that need to dynamically discover information about an enterprise bean, such as scripting languages or EJB development tools. Your client code can retrieve this metadata by calling homeObject.getEJBMetaData(). The client code will get back a serializable implementation of javax.ejb.EJBMetaData.

public interface javax.ejb.EJBMetaData

{

public javax.ejb.EJBHome getEJBHome();

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