Advanced Enterprise Java Programmingdoursat.free.fr/docs/teaching/CIS386_S03_Entity_Beans.pdf ·...

CIS 386 CourseAdvanced Enterprise Java Programming

Enterprise JavaBeans:BMP and CMP Entity Beans

René Doursat

Guest LecturerGolden Gate University, San Francisco

February 2003

2/2003 CIS 386 - Enterprise JavaBeans: BMP and CMP Entity Beans 2

EJB Trail

• Session Beans– Stateless– Stateful

• Entity Beans– Bean-Managed Persistence (BMP)– Container-Managed Persistence (CMP)

• Message-Driven Beans


Algorithmic Computation: No External Data

Chess PlayerSession Bean

CalculatorSession Bean

Client

Client

(a, b, c)

log(a + b)/c2

E2-E4

F7-F5

checkmate

. . .

• conversation• stateful (= chessboard)

• one-shot request• stateless


Business Computation: Manages External Data

Phone Book

Inventory,Customers,

Shopping Carts

ShoppingSession Bean

411Session Bean

Client

Client

login

ok

checkout

. . .

add item

John Doe?

555 1212• one-shot request• stateless

• conversation• stateful (= session ID)


Simple Session: Direct Data Access Possible

Phone Book411

Session BeanClient

John Doe?

555 1212

SELECT phone WHERE name=‘John Doe’

• one-shot request• stateless


Complex Session: How To Access Data?

Inventory,Customers,

Shopping Carts

ShoppingSession BeanClient

login

ok

checkout

. . .

add item

??


Complex Session: Direct Data Access Not Advised

Client

Add-Item

Log-In

Check-Out

Manage-Account

Cancel-Purchase

Shopping

Inventory

Customers

Shopping Carts

CODEDUPLICATION!


Complex Session: The Case For An Object Layer

ShoppingClient

Add-Item

Log-In

Check-Out

Manage-Account

Cancel-Purchase

ShoppingCart

Product

CustomerAccount

Inventory

Customers

Shopping Carts


Logic vs. Data: Toward Encapsulation

procedural architecture object-oriented architecture

LOGIC DATA


Logic vs. Data: Reintroducing Separation (at a higher level)

EJB architecture

session beans entity beans


Logic vs. Data: Examples

Session Beans Entity Beans

Bank teller Bank account

Credit card authorizer Credit card

DNA sequencer DNA strand

Order entry system Order, Line item

Catalog engine Product

Auction broker Bid, Item

Order approval router Purchase order

(after Mastering EJBs, Ed Roman, p231)


Logic vs. Data: Thick vs. Thin

Bank tellersession bean

Bank accountentity bean

complex bankoperations

elementary account ops(deposit, withdraw)

extensiveaccount data

simple conversationalstate (customer ID)


Definitions

Given that Enterprise Beans are server-side components deployable in a distributed multi-tier environment:

• Session Beans model the business’s processes: they perform work for clients calling them and are short-lived.

• Entity Beans model the business’s fundamental underlying data: they are persistent objects stored in permanent storage.

• Message-Driven Beans are a type of asynchronous Session Beans.


Feature Comparison

Session Beans Entity Beans

• allow shared access from multiple users

• is associated to a primary key (defining data uniqueness)

• provide an object view of data in the database

• can be long-lived

• survive container crash (automatic state reset)

• execute on behalf of a single client

• can be transaction-aware

• do not represent directly shared data in the database (but may access and update such data)

• relatively short-lived

• removed when container crashes


Concepts of Persistence

• Serialization– bit-blobs written to storage media– not practical for selective search

• Object-to-Relational Mapping– data stored to and loaded from RDBMS– generally: 1 object class = 1 table, 1 object instance = 1 row, but

not always– mapping scheme can be complex

• ODBMS– ideal for transparent object persistence, however not a wide-

spread product


Bean Class MethodsSessionBean EntityBean

setSessionContext(ctx) setEntityContext(ctx)

ejbCreate . . . ( . . . ) ejbFind . . . ( . . . )

ejbActivate() ejbHome . . . ( . . . )

ejbPassivate() ejbCreate( . . . )

ejbRemove() ejbPostCreate( . . . )

ejbActivate()

ejbLoad()

SessionBean & EntityBean ejbStore()

businessMethod( . . . ) ejbPassivate()

get . . . ( . . . ) ejbRemove()

set . . . ( . . . ) unsetEntityContext()


EJB Trail

• Session Beans– Stateless– Stateful

• Entity Beans– Bean-Managed Persistence (BMP)– Container-Managed Persistence (CMP)

• Message-Driven Beans


Without Object Pooling: Multiply And Waste

Server

Client #3

Client #1

Client #2

new Object()

if objects are “lightweight”: OK(as long as they are freed orgarbage collected)

. . . but if they are expensiveresources (connections,threads, beans, etc.): BAD!

“You don’t want to build a new taxicab and hire a new driver for each incoming customer call.”


Object Pooling: Conserve And Reuse

Server

Client #3

Client #1

Client #2

Pool

Pool.getObject() “Use a dispatch center (the pool) to assign taxicabs to customers.”


Object Pooling: Cycle

1234

234

134

2

1

345

2

145

2

1

3

45

23


Object Pooling: Cycle

5

2

4

3

5

2

4

3

2

4

3

5

23

5

2


Entity Bean’s Lifecyle: The “Easter Eggs” Lab

Does Not Exist

Pooled

Ready

1. newInstance()2. setEntityContext()

1. unsetEntityContext()2. Garbage Collect

ejbHome() ejbFind()ejbSelect()

1’. ejbStore()2. ejbLoad()

businessMethod()ejbSelect()

2’. ejbPassivate()1. ejbActivate() ejbRemove()ejbCreate()


Entity Beans: BMP & CMP

BMP Entity Beans CMP Entity Beans

• persistence logic is declared in the deployment descriptors

• smaller Java code for bean class– no persistent fields, abstract get/set– almost no JDBC

• bigger XML deployment descriptors– persistent fields– EJB-QL search queries– container-specific DB mapping

• persistence logic is programmed in the bean class

• big Java code for bean class– persistent fields & get/set methods – edit & search queries with JDBC

• small XML deployment descriptors


Entity Bean’s Business Logic: BMP

. . .

return xxx;

xxx = arg;

businessMethod( . . . )

setXxx( arg )

getXxx()

private instance fields

class MyBean

int xxx;

& CMP

. . .

abstract

abstract

businessMethod( . . . )

setXxx( arg )

getXxx()

private instance fields

class MyBeanabstract

class MyBeanSubclassextends MyBean

container-generated →


Entity Bean’s Container Methods:

ejbFind . . . ( . . . )

ejbHome . . . ( . . . )

ejbCreate( . . . )

ejbPostCreate( . . . )

ejbActivate()

ejbLoad()

ejbStore()

ejbPassivate()

ejbRemove()

setEntityContext(ctx)

unsetEntityContext()

& CMP

SELECTor ejbSelect()

ctx = ctx

EJB-QL

set . . . ()

. . .

. . .

. . .

post-SELECT

pre-UPDATE

pre-DELETE

ctx = null

JDBC

ejbFind . . . ( . . . )

ejbHome . . . ( . . . )

ejbCreate( . . . )


ejbActivate()

ejbLoad()

ejbStore()

ejbPassivate()

ejbRemove()


unsetEntityContext()JDBC

SELECT

SELECT

INSERT

SELECT

UPDATE

DELETE

ctx = ctx

ctx = null

. . .

. . .

. . .

BMP


Entity Bean’s Container Methods: CMP

ejbFind . . . ( . . . )

ejbHome . . . ( . . . )

ejbCreate( . . . )


ejbActivate()

ejbLoad()

ejbStore()

ejbPassivate()

ejbRemove()



SELECTor ejbSelect()

ctx = ctx

EJB-QL

set . . . ()

. . .

. . .

. . .

post-SELECT

pre-UPDATE

pre-DELETE

ctx = null

ejbSelect . . . ()

abstract+ EJB-QL

JDBC


Exception Handling

• MyBusinessException• . . .• CreateException• RemoveException• FinderException• ObjectNotFoundExc.

Application Exceptions System ExceptionsC

HEC

KED

RU

NTI

ME • NullPointerException• IndexOutOfBoundsExc.• IllegalArgumentExc.• . . .

• NamingException• SQLException• . . .

The caller’s fault or theinternal business logic’s fault!

The system’sinfrastructure’s fault!

• EJBException• NoSuchEntityException

Wrap in

EJBException!

Just let go...

Wrap some in

BusinessExc.!

Declare insignature


Entity Bean’s Container Methods: BMP

ejbFind . . . ( . . . )

ejbHome . . . ( . . . )

ejbCreate( . . . )


ejbActivate()

ejbLoad()

ejbStore()

ejbPassivate()

ejbRemove()

setEntityContext(ctx) public void setEntityContext(EntityContext ctx)

{this.ctx = ctx;

}

public void unsetEntityContext()

{this.ctx = null;

}




ejbFind . . . ( . . . )

ejbHome . . . ( . . . )

ejbCreate( . . . )


ejbActivate()

ejbLoad()

ejbStore()

ejbPassivate()

ejbRemove()



→ SAME

public void setEntityContext(EntityContext ctx)

{this.ctx = ctx;

}

public void unsetEntityContext()

{this.ctx = null;

}

JDBC



ejbHome . . . ( . . . )

ejbCreate( . . . )


ejbActivate()

ejbLoad()

ejbStore()

ejbPassivate()

ejbRemove()



ejbFind . . . ( . . . ) [1]

public Key ejbFind . . . ( args )throws FinderException

{

try {...get DB connection

...prepare SELECT statement

...set args in statement

...execute statement queryif (empty result) {

...throw FinderException}...return key from result

}catch (SQLException, NamingException) {

...throw EJBException}finally {

...close statement

...close connection}

}

JDBC



ejbHome . . . ( . . . )

ejbCreate( . . . )


ejbActivate()

ejbLoad()

ejbStore()

ejbPassivate()

ejbRemove()



ejbFind . . . ( . . . ) [N]

public Collection ejbFind . . . ( args )throws FinderException

{




...execute statement querywhile (not empty result) {

...fill coll. with keys from result}...return coll.



...close statement


}

JDBC



ejbHome . . . ( . . . )

ejbCreate( . . . )


ejbActivate()

ejbLoad()

ejbStore()

ejbPassivate()

ejbRemove()



ejbFind . . . ( . . . )

public Key/Collection ejbFind . . . ( args )throws FinderException

ejb-jar.xml

<entity>. . .<persistence-type>Container</persistence-type>. . .<query>

<query-method><method-name>find . . . </method-name><method-params>args</method-params>

</query-method><ejb-ql>

SELECT OBJECT(q) FROM . . .</ejb-ql>

</query>. . .

</entity>

→ IMPLEMENT IN EJB-QL

JDBC



ejbHome . . . ( . . . )

ejbCreate( . . . )


ejbActivate()

ejbLoad()

ejbStore()

ejbPassivate()

ejbRemove()



→ ABSTRACT METHOD AND EJB-QL

ejbFind . . . ( . . . )ejbSelect . . . ()

public abstract Collection ejbSelect . . . ()throws FinderException;

ejb-jar.xml

<entity>. . .<persistence-type>Container</persistence-type>. . .<query>

<query-method><method-name>ejbSelect . . . </method-name><method-params></method-params>

</query-method><ejb-ql>

SELECT q.xxx FROM . . .</ejb-ql>

</query>. . .

</entity>

JDBC



ejbCreate( . . . )


ejbActivate()

ejbLoad()

ejbStore()

ejbPassivate()

ejbRemove()



ejbFind . . . ( . . . )

ejbHome . . . ( . . . )

public Value ejbHome . . . ( args )throws BusinessException

{





...aggregate value from result}...return value



...close statement


}

JDBC



ejbCreate( . . . )


ejbActivate()

ejbLoad()

ejbStore()

ejbPassivate()

ejbRemove()



ejbFind . . . ( . . . )

ejbHome . . . ( . . . )

→ SAME OR USE ejbSelect()

public Value ejbHome . . . ( args )throws BusinessException

{





...aggregate value from result}...return value



...close statement


}

Collection c =ejbSelect()

JDBC



setEntityContext(ctx) public Key ejbCreate( args )throws CreateException

{...initialize fields with argstry {

...get DB connection

...prepare INSERT statement

...set key & fields in statement

...execute statement updateif (zero count) {

...throw CreateException}...return key



...close statement


}

ejbFind . . . ( . . . )

ejbHome . . . ( . . . )

ejbCreate( . . . )


ejbActivate()

ejbLoad()

ejbStore()

ejbPassivate()

ejbRemove()




ejbActivate()

ejbLoad()

ejbStore()

ejbPassivate()



ejbFind . . . ( . . . )

ejbHome . . . ( . . . )

ejbCreate( . . . )


ejbRemove()

JDBC

→ NO JDBC: set . . . () ONLY

public Key ejbCreate( args )throws CreateException

{...initialize fields with args, using setXxx()

...return key

}



setEntityContext(ctx) public void ejbPostCreate( args )

{...use EJBObject, if needed

}ejbFind . . . ( . . . )

ejbHome . . . ( . . . )

ejbCreate( . . . )


ejbActivate()

ejbLoad()

ejbStore()

ejbPassivate()

ejbRemove()




ejbActivate()

ejbLoad()

ejbStore()

ejbPassivate()



ejbFind . . . ( . . . )

ejbHome . . . ( . . . )

ejbCreate( . . . )


ejbRemove()

JDBC

→ SAME

public void ejbPostCreate( args )

{...use EJBObject, if needed

}



setEntityContext(ctx) public void ejbRemove()throws RemoveException

{


...prepare DELETE statement

...set key in statement


...throw RemoveException}



...close statement


}

ejbFind . . . ( . . . )

ejbHome . . . ( . . . )

ejbCreate( . . . )


ejbActivate()

ejbLoad()

ejbStore()

ejbPassivate()

ejbRemove()




ejbActivate()

ejbLoad()

ejbStore()

ejbPassivate()



ejbFind . . . ( . . . )

ejbHome . . . ( . . . )

ejbCreate( . . . )


ejbRemove()

JDBC

→ NO JDBC: pre-DELETE ONLY

public void ejbRemove()throws RemoveException

{...possible pre-DELETE processing

}



setEntityContext(ctx) public void ejbActivate()

{...acquire resources, if needed

}

public void ejbPassivate()

{...release held resources, if any

}

ejbFind . . . ( . . . )

ejbHome . . . ( . . . )

ejbCreate( . . . )


ejbActivate()

ejbLoad()

ejbStore()

ejbPassivate()

ejbRemove()




ejbLoad()

ejbStore()

ejbRemove()



ejbFind . . . ( . . . )

ejbHome . . . ( . . . )

ejbCreate( . . . )


ejbActivate()

ejbPassivate()

JDBC

→ SAME

public void ejbActivate()

{...acquire resources, if needed

}

public void ejbPassivate()

{...release held resources, if any

}



setEntityContext(ctx) public void ejbLoad()

{



...set key in statement

...execute statement queryif (empty result) {

...throw NoSuchEntityException}...get fields from result



...close statement


}

ejbFind . . . ( . . . )

ejbHome . . . ( . . . )

ejbCreate( . . . )


ejbActivate()

ejbLoad()

ejbStore()

ejbPassivate()

ejbRemove()




ejbRemove()



ejbFind . . . ( . . . )

ejbHome . . . ( . . . )

ejbCreate( . . . )


ejbActivate()

ejbPassivate()

ejbLoad()

ejbStore()

JDBC

→ NO JDBC: post-SELECT ONLY

public void ejbLoad()

{

...possible post-SELECT processing}



setEntityContext(ctx) public void ejbStore()

{


...prepare UPDATE statement

...set key & fields in statement


...throw EJBException}



...close statement


}

ejbFind . . . ( . . . )

ejbHome . . . ( . . . )

ejbCreate( . . . )


ejbActivate()

ejbLoad()

ejbStore()

ejbPassivate()

ejbRemove()




ejbRemove()



ejbFind . . . ( . . . )

ejbHome . . . ( . . . )

ejbCreate( . . . )


ejbActivate()

ejbPassivate()

ejbLoad()

ejbStore()

JDBC

→ NO JDBC: pre-UPDATE ONLY

public void ejbStore()

{...possible pre-UPDATE processing

}


EJBs Are Single-Threaded

Container Strategy 1:serialize accessto a single instance

Container Strategy 2:allow parallel accessto multiple instances


Entity Beans Are Single-Threaded

Container Strategy 2:allow parallel accessto multiple instances ejbLoad()

ejbStore()

and keep datasynchronized in DB

Container Strategy 1:serialize accessto a single instance

Advanced Enterprise Java Programmingdoursat.free.fr/docs/teaching/CIS386_S03_Entity_Beans.pdf ·...

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