EJB'S

7/29/2019 EJB'S

http://slidepdf.com/reader/full/ejbs 1/72

EJB notes.

E

J

BC

al

lb

a

c

k

s

(j

a

v

a

x.ej

b

p

a

c

k

a

g

e)

E

ntit

y

B

ea

n

(e

xt

e

n

ds

E

nter

pr

is

e

B

ea

n)

Def ines

7 contain

er callbacks :

1• voidsetEntit

yContext(Ent

ityContextctx)

2• voidunsetEntityContext()

3• voidejbActivate()

4• voidejbPassivate()

5• voidejbLoad

()

6• voidejbStore()

7• voidejbRemove ()

SessionBean

(extends

EnterpriseBea

n)

Defines 4

container

callbacks :

1• voidsetSessionContext(SessionContextctx)

2• voidejbActivate()

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3• voidejbP

assivate()

4• void

ejbRemove()

S

es

sio

n

S

y

n

c

hr

o

ni

za

ti

o

n

D

ef

in

es

3

c

o

nt

ai

ner

ca

ll

b

ac

ks :

1• voidafterBegin()

2• voidbeforeCompletion()

3• voidafterCompletion(booleancommitted)

EJB API

(javax.ejb

package)

EJBHome(extends

java.rmi.Remote)

1• EJBMetaDatagetE

JBMetaData() HomeHandle getHomeHandle () // EJB1.1 or

void

remove

(Handle h)

//

invalidates

void

remove

(Object primaryKey)

//

invalidates

EJBObject

(extends

java.rmi.Rem

ote)

1• EJBHomegetEJBHome()

Handle getHandle () // Serialize

Object getPrimaryKey ()

// RemoteExcept

bean

1• booleanisIdentical(EJBObjecto)

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voidremove(

)//invali

datesclientstu

b

E

J

B

C

o

nt

e

xt

(S

es

sio

n

C

o

nt

e

xt

,

E

nt

it

y

C

o

nt

e

xt

)

1• PrincipalgetCallerPri

ncipal() /booleanisCallerInRole(Stringname)


EJBObject getEJBObject () //

SessionC

xt Object getPrimaryKey () // EntityCon

1• voidsetRollbackO

nly() /booleangetRollbackOnly()

EJBMetaData


Class

getHomeInterfaceClass

() //

N.B. n

Class

getPrimaryKeyClass() // never

1• ClassgetRemoteInterfa

ceClass()

2• booleanisSessio

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nboole

anisStatelessSession ()

//EJB1.1orabove

1

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EJB Notes

List the

required

classes/interfac

es that must be

provided foran EJB

component.

Common

1• Home

interfac

e

(extend

s

javax.ej

b.EJBH

ome) -

defines

the

create

method

s (+

finders

for

Entity)

2• Remote

Interface

(extends javax.ej b.EJBO bject) -definesthe

business logicinterface

3• Bean

class -implements theEJBcallbacks,“implied” EJBcallbacks and

business

methods

4• Primar

y Keyclass – Entity

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beansonly

Entity Beans.

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D

es

cr

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ip

ti

o

n

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R

e

m

o

t

e

D

e

f

i

n

e

s

t

h

e

b

u

s

i

n

e

s

s

m

e

th

o

d

s

i

n

t

e

r

f

a

c

e

HomeDefines

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the factory and

locator

methods :

interface//requiredmethods<REMOTE_IF>findByPrimaryK

ey(<PK>pk)

// optional methods

<REMOTE_IF> create (<PARAMS>)// multiple creat

allowed

<REMOTE_IF> find<METHOD_NAME> (<PARAMS>)

Collection find<METHOD_NAME> (<PARAMS>)//EJB

Enumeration find<METHOD_NAME> (<PARAMS>)

//

EJB

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Entity

Implemen

ts

javax.ejb.

EntityBea

n

(ejbLoad

(), etc)

and the

business

methods

defined in

the Bean

remote

interface.

class Alsoimplementsthe “implied”EJB callbacksdefined in thehome interface:

<REMOTE_I

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F>create(<PARAMS>)

becomes<PK>ejbCreate(<PARAMS>)

F

o

r

e

a

c

h

e

jbCreate (<PARAMS>)

t

h

e

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NAME>(<PAR

AMS>)

becomes<P

K>

ej bFind<METHOD _ N

AME>(<PAR AMS>)

F

i

n

de

r

s

t

h

a

t

r

e

t

u

r

n

a

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c

o

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c

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p

r

i

m

a

r

y

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k

e

y

s

i

n

t

h

e

b

e

a

n

.

ejbCreate has

different return

values/types

depending on

the EJB version

and persistence

type :

1•EJ

B

1

.

1

,

C

M

P

:<PRIMARY_KEY

>ejbCreat

e(<PARAM

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(<PARAMS>

) –

r

e

t

u

r

n

s

p

ri

m

ar

y

k

e

y

3•EJ

B1.0

,CMP:voi

dejbCr

eate(<PARAMS>

)

-(contai

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ner k now

sPK )

T

h

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e

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d

o

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a

ct

i

v

a

t

i

o

n

ejbFind

methodsthatreturna

collectionhavediff er entre

turnsde

pendingontheEJ

Bversion:

1•

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EJ

B

1

.

1

:

if

no

m

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ll

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c

ti

o

n2•EJ

B1.0:if nom

atches

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f ound,r

etur nnull

Primary

You can

use an existing

class (e.g.String) or

create one.

Key class

The

pr im

ar ykeyclassmust :

1•imp

le

m

e

n

t

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j

a

v

a.

i

o

.

Se

ri

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7/29/2019 EJB'S


r

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7/29/2019 EJB'S


o

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7/29/2019 EJB'S


r

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7/29/2019 EJB'S


s

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.

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.

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e

7/29/2019 EJB'S


y

s

–

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7/29/2019 EJB'S


t

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r

.

2

EJB Notes

Session Beans.

Description Remot e Defines the business methodsinterfa

ce

Home Define the factory method :

Interfa

ce(Statel ess // required method

Sessio

n

// multiple create methods are not allow

<REMOTE_IF> create ()

Bean)

Home Defines the factory methods : Interfa

ce// required methods(Statef

ul

<REMOTE_IF> create () Sessio

n <REMOTE_IF> create (<PARAMS>)

Bean)// multiple create methods are allowed, at least o

Session Implements javax.ejb.SessionBean (ejbActivate (), etc) and t

Bean the remote interface.

class Also implements the “implied” EJB callbacks defined in the SLSB : <REMOTE_IF> create () becomes void ejbCreate ( SFSB : <REMOTE_IF> create (<PARAMS>) becomes void ejb

ejbActivate () / ejbPassivate () : SLSB : these methods are meaningless, SLSB aren’t swapp

SFSB – the following types are maintained on activate/pas

EJB1.x : primitives, serializable objs, SessionContext, rem

EJB1.1 : JNDI naming contexts, home refs

Any other types must be labelled as transient or set to nul

restored

7/29/2019 EJB'S


in ejbActivate () – e.g. on passivate, close socket client a

open

and set var.

N.B. transient fields won’t be reset on activate – they may

that used them left them as. Therefore, transient vars shoul

EJB 2.0

As of EJB2.0,local versionsare available :

1• Local

Home/

Local

interfac

es

(extend

javax.ej b.EJBL

ocalHo

me/EJB

LocalO

bject)

2• BeanS

t

i

l

l

i

m

p

l

e

m

e

n

t

ja

v

a

x

.

e

j

b

.

S

es

s

i

o

n

7/29/2019 EJB'S


B

e

a

n

/

E

n

t

i

t

y

B

e

a

n

b

u

t

h

a

v

e

t

o

u

se

t

h

e

l

o

c

a

l

c

o

n

t

e

x

t

–

e

.

g

.

c

7/29/2019 EJB'S


t

x

.

g

e

t

E

J

B

L

o

c

a

l

H

o

m

e

(

)

EJB2.0 also

introduces the

MessageDriven

Bean :

1• no

local/re

moteinterfac

e

2• Bean

implements

javax.ej b.MessageDrivenBean and

javax.j

ms.MessageListener

3

EJB Notes

Distinguish

between

7/29/2019 EJB'S


stateful and

stateless

session beans

Stateful SessionBean

1• models

business

logic, processe

s,

workflow, etc.

2• associated witha singleclientfor thelife-timeof the bean.

3• maintain

s client-specificstate betweenmethodcalls – i.e. theinteraction issomewhat drawnout

4• can be

viewedas anextension/agentof theclient

5• resource

management :swapped

6• createsless

network traffic

thanstateless

– noneed to

passstate

every

time

Stateless SessionBean

1• models

a service

as a re-usable

object

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2• associat

ed witha singleclientfor thedurationof the

methodcall.

3• no

client-specific statemaintained,state passedin as parameters

andtheresultreturned – i.e. theinteraction isshort

4• resource

management : pooled

5• more

scalable

thanstateful

as asmall

number

canservice a

large

number of

clients

Distinguish

between

session and

entity beans

“like .. a script

for a play .. and

the actors that

perform the

play .. entity

beans are the

actors and props, the

session bean is

the script”

Session Bean

1• “owned

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” by a

singleclient

2• models

a shortlived business

process(onlylasts aslong astheclientsession;dies onsystemcrash)

Entity Bean

1• shared

by manyclients

2• obj

ect

“view

”(pr

ovides

saf e/c

ons

istent

acc

ess) of

alon

g-liv

ed/ per

sistent

busine

ssent

ity(su

rvives

a

sys

tem

crash)

3• resource

management : pooled

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4• more re-

usable

than

session beans

Recognize

appropriateuses for entity,

stateful session

and stateless

session beansEntity Bean

1• User,

Customer,

Account, Order

Stateful session.1• Shoppin

g cart,Account

Manager

Stateless session.

1• Credit

card

authorization,

currency

converter,SocketC

lientSer

vice

State the

benefits and

costs of

container-

managed

persistence

Pros.1• producti

vity –

don’thave to

write/de bug

tediousdatabase

mappingcode

2• cleaner

code – beanisn’t boggeddownwith persiste

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nce code

3• perform

ance – thecontainer canimpleme

ntcaching

4• po

rtability – asDBcode

ishandled bythecontainer,CMP beanscan bemovedtoot

her containersand be persist

ent(

P J C :

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d on’ t a

gr ee

,d e

pl o

yment isn’ t

por

tabl e)

Cons.

1• portabili

ty – in

EJB1.x,deploym

ent of

CMPwasn’t

portable

2• simplisti

cmapping – inEJB1.x,CMPdidn’tsupportrelationships,dependentobjects,etc.

3• lack of control

4• legacysupport – noteverydatastore isadatabase but mostvendorsonlysupportDBmapping

4

7/29/2019 EJB'S


EJB Notes

State the

transaction

al

behaviour

in a given

scenario

for an

enterprise

bean

method

with a

specified

transaction

al attribute

as defined

in the

deploymen

t

descriptor

BMT (Bean

Managed

Transactions).

EJB1.x : clients

can manage TX

using JTA; TXisolation level

can be set for each specific

resourcemanager, e.g.

JDBC EJB1.1 :session beans

can manage TXusing JTA and

setting<transaction-type>Bean<transaction-

type>EJB1.0 : session

& entity beanscan manage TX

using JTA andsetting the TX

attribute toTX_BEAN_MANAGED

CMT

(Container

Managed

Transactions)The

recommended

practice for

EJB is to use

CMT :

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1• cleaner

code –

bean

isn’t

cluttere

d with

transact

ional

code

2• distribu

tedsupport

– thecontainer canorganisemultipl

eResour ceManagers

3• reusabl

e - beanscan bereusedindifferent

circumstances bychanging thedeploymentdescriptor

4• flexible

– can be

specified per method, per

bean(N.B. if anymethoduseBMP,allmust)

The

transaction

al context

(a.k.a.

scope)

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defines

what beans

are

participatin

g in the

current

transaction

. When

using CMT

the

container

starts and

ends the

transaction

when a

transaction

al method

is called

(i.e.declared as

starting a

transaction

in the

deploymen

t

descriptor)

.

Conseque

ntly, the

transactional

context

will be

propagate

d to all

targets

(methods/

beans

used

within the

method

that

“started”

the

transactio

n).

The targets

can control

their

participatio

n in the

propagated

transaction

by setting

one of 6

transaction

7/29/2019 EJB'S


al

attributes

in the

deployment

descriptor

(e.g.

<trans-attribute

>Required

</trans-

attribute

>) :

Attribute Description

NotSupported Current TX suspended until called method compl(TX_NOT_SUPPORTED)

Supports If caller bean part of a TX, called method/bean jo

(TX_SUPPORTS) Otherwise, called method executes as is.

Requires If caller bean part of a TX, called method/bean jo(TX_REQUIRED) Otherwise called method/bean starts a new TX (a

any other methods/beans it calls). After the calle

TX scope ends.RequiresNew Called method/bean always starts a new TX (app

(TX_REQUIRES_NEW) other methods/beans it calls). After the called mescope ends.

If caller bean part of a TX, current TX is suspendMandatory If caller bean part of a TX, called method/bean jo

(TX_MANDATORY) Otherwise called bean throws javax.transaction.T Never If caller bean part of a TX, throw RemoteExcepti

(EJB1.1 only) Other, called bean/method executes as is.TX_BEAN_MANAGED Caller bean/method creates a new TX using JTA,

(EJB1.0 only) the called method completes.

In EJB1.0

CMT, it was

possible to

control

transaction

further by

setting the

transaction

isolation levelin the

deployment

descriptor on

a per method

basis

In EJB1.1

CMT, it’s still

possible to

change the

isolation level

but it’s

container dependent.

7/29/2019 EJB'S


5

EJB Notes

Miscellaneous

A transaction

represents a

unit-of-work

(one or more

tasks that must

all complete)

and embodies

the concept of

an exchange

between two parties. In EJB

each task is

represented as

a method so

the unit-of-

work is

represented as

one or more

method calls

on one or more

beans.

A transactionalsystem must

enforce the ACID

properties :

Propert y DescriptionAtomic All or nothing – if any task fails the transaction if rolled back; if all

committed (i.e. made Durable).Consistent The state of the system must reflect the real world. This is enforced

1. the transactional system ensures that data is Atomic, Isolated and2. the application developer ensures the system has appropriate cons

violation, referential integrity, etc.Isolated The transactional system ensures that data involved in a current tran

transactions until the current transaction completes.

The degree of isolation is controlled by setting the “isolation level”.Durable The transactional system must ensure that the data is persistent befo

to be complete – i.e. until committed, the data is still isolated.

Additionally, the transactional system ensures that the data survives

phase commit) and transaction logging.

A transactional system has to be able to deal with concurrency issues :

Issue DescriptionDirtyread TX2 reads uncommitted changes made by another TX1; if TX1

E.g. TX1 attempts to book the last seat but fails on payment; T

sold out. Non- “Lost update”repeatable

read TX1 reads; TX2 reads and updates; TX1 updates and blats over

Phantom read TX1 gets a list of seats; TX2 adds a seat; TX1 is unaware of the

7/29/2019 EJB'S


Concurrency

issues can becontrolled using

one of 4 transaction

isolation levels :

Re

Isolation Level Dirty Re

TRANSACTION_READ_UNCOMMITTED Y

TRANSACTION_READ_COMMITTED N

TRANSACTION_REPEATABLE_READ N

TRANSACTION_SERIALIZABLE N

These isolation levels have to be viewed from the perspective of eachclient :

Isolation Level DescriptionREAD_UNCOMMITTED Reader & Writer

No locks/waiting; anything goes.Reader picks up all column changes (synched at ro

READ_COMMITTED Reader - only wants “real” data (i.e. that made durab

Writer

Wait until others have finished reading before maki

If writer gets there first, readers wait until writer has

REPEATABLE_READ Reader - Blocks writer until finished reading or wait

Writer

No updates or deletions to existing rows; insert of ro

updates / deletions to stuff writer is working on – wr

SERIALIZABLE Reader - Blocks writer until finished reading or wait

Writer

No updates, deletions or insertions except by the wri

EJB Notes

Given a

requirements

specificationdetailing

security and

flexibility

needs,

identify

architectures

that would

fulfill those

requirements

Architectures.Refer to the

“Common

Architecture”

and “Security”

documents.

7/29/2019 EJB'S


In summary :

1• a

modula

r

architec

ture is

the

mostflexible

but

require

s more

effort

to

manage

2• securityisrequire

d at alllevelsand amodular architecturesupports this

3• Javahasgood

securitysupport – JVM,securityAPIs,etc

4• typ

ica

l

ele

me

nts

that

sup

por

t

sec

urit

y

an

d

fle

xib

ility

are

:

fire

wa

7/29/2019 EJB'S


lls,

loa

d

bal

anc

ers,

clu

stered

ap

pli

cat

ion

ser

ver

s,

etc

5• EJB

security is

flexib

le –

declar

ative

so can

be

adjust

ed as

requir

ed;

can be

mapp

ed to

enviro

nment

specif

ics

(LDA

P,

mainf

rame,

etc.)

J2EE Security.

Within an

EJB

component

security roles

are defined - a

role is a

logical user

(e.g. admin,

customer).

When the

component is

deployed, the

role is

mapped to

7/29/2019 EJB'S


“real” J2EE

users/groups

(e.g. PJC is

able to

assume the

admin role).

To accesssecure

resources, the

Subject (client)

must be

authenticated

and authorized :

1• Authen

tication

.

T

o

a

u

t

h

e

n

t

i

c

a

te

,

t

h

e

S

u

b

j

ec

t

m

u

s

t

p

r

e

s

e

n

t

t

7/29/2019 EJB'S


h

e

i

r

C

r

ed

e

n

t

i

a

l

s

(

e

.

g

.

u

s

e

r

n

a

m

e/

p

a

s

s

w

o

r

d

)

to

t

h

e

c

o

n

t

a

in

e

r

.

7/29/2019 EJB'S


If the

authent

ication

is

success

ful, the

Subject

isassociat

ed with

one or

more

Princip

al

objects.

N

.

B.

a

u

t

h

e

n

ti

c

a

ti

o

n

i

s

n

o

t

c

u

r r

e

n

tl

y

p

a

r

t

o f

t

h

e

E

7/29/2019 EJB'S


J

B

s

p

e

cif

i

c

a

ti

o

n

–

e

. g

.

t

h

e

c

r

e

d

e

n

ti

a

l

s

m

a

y

b

e

pa

s

s

e

d

a

s

p

r

o p

e

r

ti

e

7/29/2019 EJB'S


s

t

o

a

n

I

nit

i

a

l

C

o

n

t

e

xt,

J

A

A

S

m

a

y

b

e

u

s

e

d

,

e

t

c

.

2• Authorisation.

O

n

c

e

a

u

t

h

e

nt

i

c

a

t

7/29/2019 EJB'S


e

d

,

t

h

e

P

r

i

n

c

i

p

a

l

(

s

)

c

a

n

b

e

c

h

ec

k

e

d

a

g

a

i

n

s

t

t

h

e

R

o

l

e

t

o

d

e

c

i

7/29/2019 EJB'S


d

e

i

f

t

he

c

l

i

e

n

t

i

s

a

u

t

h

o

r

i

s

e

d

t

o

a

c

c

e

s

s

t

he

s

e

c

u

r

e

r

e

so

u

r

c

e

7/29/2019 EJB'S


.

Role

based

author

isatio

n is

fully

suppo

rted

by

J2EE

–

securi

ty

constr

aints

in

web.xml,

metho

d

level

securi

ty in

EJB

deplo

yment

descri

ptor,

“runA

s” in

deplo

yment

descri

ptor.

N

.

B

.

i

n

s

t

a

n

c

e

b

a s

e

d

7/29/2019 EJB'S


7/29/2019 EJB'S


’

s

a

c

c

ou

n

t

)

i

s

n

’

t y

e

t

s

p

e

c

i

f

ie

d

J2EE also has

other built-in

security

features :

1• web-

tier

authent

ication

– viaHTTP

authent

ication,

FORM/

j_securi

ty_chec

k,

client

certific

ates

2•secure

communications – SSL;web-tier

7/29/2019 EJB'S


authenticationcan useSSL for HTTP/FORMauth

3• security packages – digests,digitalsignatures,ciphers,certificates,etc.

EJB securityEJB supports

declarative

security

(programmatic

security is also

supported) by

setting the

appropriate

values in the

deployment

descriptor :<method

-permission> <ro

le-name>admin</rol

e> <metho

7/29/2019 EJB'S


d>

<ejb-name>Account</ejb-name>

<method-name>*</method-name>

</meth

od>

</met

h

od-

permi

ssio

n>

Not very

portable at the

moment –

authentication

and “runAs”

are container

specific;

container to

container

security

propagation is

undefined.

7

EJB Notes

Identify

costs and

benefits of

using an

intermediate

data access

object

between an

entity bean

and the data

resource

Pros.

7/29/2019 EJB'S


1• transpa

rency –

specific

s of

data

access

are

hidden

from

the

entity

bean

2• modula

r – theDAOcould

beswappe

d for another withlittledisruption totheentity

beancode

3• cleaner

code -

dataaccessfactored out sosimplifiesentity

beancode

4• reusabl

e – DAO

could be re-used ina “FastLaneReader ”

Cons.

1• only

suitable

for

BMP2• extra

code -have towriteDAO

7/29/2019 EJB'S


7/29/2019 EJB'S


class

modifier must be

public(abstract

, finalnot

allowed); no

finalize()

2• business&callback methodsmethod

modifier must be

public

(static,

final notallowed);

arguments must

be legalRMI

types

Exceptions

A

pp

lic

ation

ex

ce

pti

on

s

re

pr

es

en

t

busi

ne

ss

lo

gi

c

fai

lu

re

s

so

ar e

ex

pe

ct

ed

7/29/2019 EJB'S


to

be

ret

ur

ne

d

to

the

re

m

ot

e

cli

en

t.

So

m

e

com

m

on

ap

pli

ca

tio

n

ex

ce

pti

ons

ar

e

pr

ov

id

ed

in

th

e

ja

vax.

ej

b

pa

ck

ag

e

bu

t

ca

n

also

be

us

er

-

7/29/2019 EJB'S


de

fi

ne

d.

System

exceptions

represent systemlevel failures andare excepted to

be caught by thecontainer.

The container handles the

exception and re-

packages it asRemoteExceptio

n before

returning it to theclient.

The container

will deal with all

unchecked

exceptions – e.g. NullPointerExce

ption

B

e

a

n

m

e

th

o

d

s

c

a

n

c

a

t

c

h

e

x

c

e

p

t

i

o

n

s

a

r

er

e

-

t

h

r

7/29/2019 EJB'S


o

w

w

i

t

h

in

a

m

e

t

h

o

d

–

e

.

g

.c

a

t

c

h

J

D

B

C

e

r

r

o

r

a

n

d

r

e

-

t

h

r

ow

a

s

E

J

B

E

x

c

e

p

ti

o

n

.

I

7/29/2019 EJB'S


n

E

J

B

1

.

0,

m

e

t

h

o

d

s

c

ou

l

d

t

h

r

o

w

R

e

m

o

t

e

E

x

c

e

p

t

i

o

n

t

o

i

n

d

i

c

a

t

e

a

s

7/29/2019 EJB'S


y

s

t

e

m

/

n

on

-

a

p

p

l

i

c

a

t

i

on

e

r

r

o

r

.

I

n

E

J

B

1

.

1

,

m

e

t

h

o

d

s

a

r

e

n

o

w

e

x

p

e

c

7/29/2019 EJB'S


t

e

d

t

o

th

r

o

w

E

J

B

E

x

c

e p

t

i

o

n

(

o

r

a

n

o

t

h

e

r

R

u

n

t

i

m

e

E

x

c

e

p

t

i

o

n

)

.

H

o

w

e

7/29/2019 EJB'S


v

e

r

,

a

l

l

o

f

t

h

e

s

a

m

pl

e

c

o

d

e

(

i

n

c

l

u

d

i

n

g

P

e

t

s

t

o

r

e

)

s

t

i

l

l

u

s

e

s

R

7/29/2019 EJB'S


e

m

o

t

e

E

x

ce

p

t

i

o

n

.

The bean method

implementations

must match the

interfacedefinitions interms of

exceptions apartfrom : RemoteException - the container handles remote exception iss

EJBException- extends RuntimeException so doesn’t have“throws”

clause.

Method Application Exceptions

Any Application/custom exceptions

create () CreateException, DuplicateKeyException

findXXX ()

FinderException, ObjectNotFoundException (sing

remove () RemoveException

business methods, NoSuchEntityException (object has been removed

ejbLoad, ejbStore

Primary Services.

There are 7

primary services

provided by the

container :

concurrency (to

maintainsafe/consistent

access to shared

entity bean),

lifecycle

management

(pooling/swappi

ng), persistence

(CMP),

distributed

objects (EJB

uses RMI-IIOP),

naming

(JNDI canhookup to a

number of

naming

services),

transactions

7/29/2019 EJB'S


(CMT) and

security (EJB

builds on

Java2

security to

add method

level

security).

8

Date post:	14-Apr-2018
Category:	Documents
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EJB'S

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