Adoption of Latest Frameworks & APIs for the development of Enterprise Application in the Software Industry using Java Platform

8/14/2019 Adoption of Latest Frameworks & APIs for the development of Enterprise Application in the Software Industry usin

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Adoption of Latest Frameworks & APIs for the development of MS Research SurveyEnterprise Application in the Software Industry using Java Platform By: Muhammad Ali Ameer MS-SPM (06-0802)National University of Computer Emerging Sciences FAST, Karachi

SpringisalayeredJEEapplicationframeworkincludesthemostcompletelightweight

container,acommonabstractionlayerfortransactionmanagement,aJDBCabstraction

layer,IntegrationwithToplink,Hibernate,JDO,andiBATISSQLMaps,AOPfunctionality,

aflexibleMVCwebapplicationframework.

Howthese

frameworks

ease

out

Enterprise

Application

development

which

not

only

cut

down

development&maintenancecyclebutfacilitatereusability,separationanddevelopmentof

scalableapplications.

HowSoftwarefirmsevaluatetheseframeworksfortheiradoptioninspecificenterprise

applicationsandwhatbenefittheywilleventuallyget.

TheframeworksmentionedabovelikeJSF,Struts,Tapestry,SpringandHibernatefallintbroad

categoryoffamousDesignPatternsofEnterpriseApplicationArchitecture:

WebPresentation

Patterns

Data

Source

Architectural

Patterns

basedonModelViewControllerPattern

JSF,Struts,Tapestry&Spring

basedonPatternslikeTableDataGateway,

RowDataGateway,ActiveRecord&Data

Mapper

Hibernate,APIslikeJDO,JPA&JTA

Thefirstpartofthedocumentwilldiscussaboutthetechnicalitiesofframeworksthatarebasedon

WebPresentationPatterns,howtheyfacilitatesEnterpriseApplicationDevelopmentandhow

SoftwareDevelopment

Organizations

evaluate

then

for

their

adoption

in

specific

enterprise

applications&whatbenefittheyeventuallyget.

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1. FrameworksbasedonWebPresentationPatterns1.1. StrutsFramework

Strutsisthemostfamousandwidelyused&acceptedenterpriseapplicationframework

onJEEplatform.ItisbasedonModelViewController(MVC)Architecture.

Struts2Architecture


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TheRequestInitiation

Therequestresponsecyclestartsandfinishesfromtheuserswebbrowser.AURLthatrepresentsan

actioncanbeenteredasaURLdirectlyintothebrowsersaddressbar,oritcanbegeneratedbythe

frameworkwhentheuserclicksonalinkorsubmitsaform.TheURLwilllooksomethinglike

http://localhost:8080/app/index.action.

ConfigurationfilesforthewebapplicationdeterminewhichURLsarehandledbytheStruts2frameworkandwhicharent.Usually,allrequestsforanentirewebcontextorinstalled

applicationareforwardedtotheStruts2servletfilter,anditmakesthedecision.

TheStruts2ServletFilter

Whenrequestsarereceivedattheservletcontainer,theyareforwardedtoeitheraservletorafilter

thatwillhandleprocessingtherequest.InStruts2,afilterisused,andtheclassforhandlingtherequest

istheFilterDispatcherclass.

ThefilterandaDispatcherclass(towhichmanyofthetasksaredelegated)aretheheartoftheStruts2

framework.Together,theyprovideaccesstotheinfrastructurethatwillbeneededtoprocessthe

request.Uponstartup,implementationsofconfigurableelementsintheframework,including

ConfigurationManager,ActionMapper

and

ObjectFactory

are

loaded.

With

respect

to

processing

the

request,theStruts2filterperformsthefollowing:

Servesstaticcontent:Dojocontent,JavaScript,anduserconfigurablefilescanbeservedfromthe

Struts2orthewebapplicationsJARfile,allowingalltheelementsforawebapplicationtobepackaged

together.

Determinestheactionconfiguration:ThefilterusestheConfigurationManagerandthe

ActionMapperimplementationstodeterminewhichactionmapstotheURLfromtheincomingrequest;

bydefault,actionsaredeterminedbylookingforanactionextension.

Creates

the

action

context:

Because

actions

are

generic

and

not

specific

to

HTTP,

the

information

containedinthewebrequestneedstobeconvertedtoaprotocolindependentformatfortheactionsto

use;thisincludesextractingdatafromtheHttpServletRequestandtheHttpSessionobjects.

Createstheactionproxy:Thereisanadditionallayerofindirectionintheprocessingintheformof

anActionProxyclass.Thisclasscontainsalltheconfigurationandcontextinformationtoprocessthe

requestandwillcontaintheexecutionresultsaftertherequesthasbeenprocessed.

Performscleanup:Toensurethatnomemoryleaksoccur,thefilterautomaticallyperforms

cleanupoftheActionContextobject.WhentheActionProxyclassinstanceiscreatedandconfigured,the

execute()methodisinvoked.Thissignalsthatthepreparationoftheactioniscomplete,andthereal

processingoftheactionisabouttostart.

TheActionInvocation

TheActionInvocationobjectmanagestheexecutionenvironmentandcontainstheconversationalstate

oftheactionbeingprocessed.ThisclassisthecoreoftheActionProxyclass.Theexecution

environmentismadeupofthreedifferentcomponents:actions,interceptorsandresults.

Inadditiontotheseelements,actionscanhavemethodsconfiguredaslifecyclecallbacks.The

ActionInvocationclassinvokesthesecallbackmethodsattheappropriatetimes.

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TheAction

OneofthefirsttasksthattheActionInvocationperformsistoconsulttheconfigurationbeingusedand

tocreateaninstanceoftheaction.UnlikeStrutsandotherframeworksthatreuseactioninstances,

Struts2createsanewactionobjectinstanceforeachandeveryrequestthatisreceived.Thereisaslight

performanceoverheadwiththisapproach,buttheadvantagegainisthattheobjectcanbehaveasa

PlainOldJavaObject(POJO).

Interceptors

Interceptorsprovideasimplewaytoaddprocessinglogicaroundthemethodbeingcalledonthe

action.Theyallowforcrossfunctionalfeaturestobeappliedtoactionsinaconvenientandconsistent

way,avoidingtheneedforaddingcodetoeachandeveryactionthatovertimewouldcreateadditional

maintenanceoverhead.ThefunctionalityissimilartothatprovidedbyservletfiltersandtheJDKProxy

object.Eachactionwillhavemanyinterceptorsconfigured.Theseinterceptorsareinvokedintheorder

thattheyareconfigured.Aftertheyareallappliedtotherequest,theactionsmethodthatprocesses

thelogicfortherequestiscalled.Byconvention,thisistheexecute()method;however,anyno

argumentmethodintheclassthatreturnsaStringoraResultobjectmaybeused.

Aftertheactionlogicisexecuted,thecallreturnsthroughtheconfiguredinterceptorsinthereverse

order,allowing

for

post

processing

of

the

action.

TheResults

Aftertheprocessingoftheactioniscomplete,themethodoftheactionclassthatprocessesthe

requestreturnsaStringastheresult,whichismappedviaconfigurationtoanimplementationofthe

Resultinterface,ortheactioncandirectlyreturnaResultobjectinstance.TheResultinterfaceisvery

similartoanactionclass;itcontainsasinglemethodthatgeneratesaresponsefortheuser.The

responsegeneratedcanvarydramaticallybetweendifferentconcreteclassimplementations(knowas

resulttypes).ItcouldmodifytheHTTPresponsecodes,generateabytearrayforanimage,orrendera

JSP.WhenreturningaStringastheresult,thedefaultconfiguredResultimplementationrendersJSPs

totheuser.

The

final

step

is

to

return

the

response

(if

one

is

generated)

back

to

the

user,

which

completes

the

currentrequestprocessingcycle.

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Struts2TheCoreComponents

The

interactions

and

relationships

between

Struts

2

core

components

Actions

ActionsarethecoreoftheStruts2framework,astheyareforanyMVC(ModelViewController)

framework.EachURLismappedtoaspecificaction,whichprovidestheprocessinglogicnecessaryto

servicetherequestfromtheuser.

TheonlyrequirementforactionsinStruts2isthattheremustbeonenoargumentmethodthatreturns

eitheraStringorResultobject.Ifthenoargumentmethodisnotspecified,thedefaultbehavioristo

usetheexecute()method.Otherwise,anadditionalconfigurationtospecifythemethodnameis

needed.

WhentheresultisaStringobject,thecorrespondingResultisobtainedfromtheactionsconfiguration

andinstantiated.Thisisthenusedtogeneratearesponsefortheuser.Eventhoughthereisno

requirementthat

an

action

implements

an

interface

or

extends

another

class,

sometimes

it

makes

sensetoextendhelperclassesorinterfaces.Struts2providestwosuchhelpersthatcanbeused.

ThefirsthelperistheActioninterface.Thisinterfacedoesnothingmorethansupplythecommon

stringbasedreturnvaluesasconstantsandenforcethatimplementingclassesprovidethedefault

execute()method.

TheActionSupportclassismoreinteresting.ItimplementstheActioninterfaceandprovidesan

implementationfortheexecute()methodthatreturnstheSUCCESSvalue.


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Fourotherinterfacesarealsoimplemented.TheValidateableandValidationAwareinterfacesprovide

supportforvalidation.Theseallowtheactiontoprovideprogrammatic,annotationbased,and

declarativeXMLbasedvalidation.TheTextProviderandLocaleProvideinterfacesprovidesupportfor

localizationandinternationalization.

Interceptors

Interceptorsallowforcrosscuttingfunctionalitytobeimplementedseparatelyfromtheactionaswellastheframework.Thismakesthecoreframeworkcodeleanerthanitmayhaveoriginallybeenandable

toadapttonewframeworkfeaturesmuchfaster.Infact,theloosecouplingmeansthatusersnolonger

havetowaitfortheframeworktoimplementthenewfeaturetheyrequire;instead,theycan

implementandapplytheneededfeaturesthemselveswithoutmodifyingtheunderlyingframework

sourcecode.

Usinginterceptors,thefollowingcanbeachieved:

Providingpreprocessinglogicbeforetheactioniscalled.

Interacting

with

the

action,

providing

execution

information,

such

as

Spring

managed

objects,

and

settingtherequestparameterontheaction.

Providingpostprocessinglogicaftertheactioniscalled.

Modifyingtheresultbeingreturned,hencechangingwhatisrenderedtotheuser.

Catchingexceptionssothatalternateprocessingcanbeperformedoradifferentresultcanbe

returned.

TheValueStackandOGNL

The

Value

Stack

is

a

central

concept

in

the

Struts2

framework.

All

of

the

core

components

interact

with

itinonewayoranothertoprovideaccesstocontextinformationaswellastoelementsofthe

executionenvironment.

Underneath,theValueStackisexactlywhatitsaysastackimplementation.However,thereare

differencesbetweenatraditionalstackimplementationandtheValueStack.Thefirstdifferenceisthat

thecontentsofthestackaremadeupoffourlevels:

Temporaryobjects:Theseobjectsneedtemporarystorageduringtheprocessingofarequest,for

example,thecurrentelementinacollectionthatisbeingiteratedover.

Modelobject:WhentheactionimplementstheModelDriveninterface,themodelobjectisplacedon

thestackinfrontoftheactionthatisbeingexecuted;thislevelwillnotbepresentiftheinterfaceisnot

implementedby

the

action.

Actionobject:Thisistheactionthatiscurrentlybeingexecuted.

Namedobjects:Anyobjectcanbeassignedanidentifier,makingitanamedobject.Namedobjects

canbedevelopercreatedbutalsoincludedare#application,#session,#request,#attr,andparameters

eachcorrespondingtoanequivalentHTTPscopedobjectcollection.

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Anotherdifferenceishowthestackisused.Traditionally,whenusingastack,objectscanbepushedon

andpoppedoffwhenwantedtousethem.TheValueStackusesOGNL(ObjectGraphNavigational

Language)syntaxforsearchingorevaluatingaparticularexpression.

Likeotherexpressionlanguages,suchasJSTL(JSPStandardTagLibrary)orMVEL(MVFLEX

ExpressionLanguage),OGNLprovidesamechanismtonavigateobjectgraphsusingadotnotationand

evaluateexpressions,includingcallingmethodsontheobjectsbeingretrieved.

Searchingisalsonotsomethingthatisgenerallyassociatedwithstacks.FortheValueStack,theOGNLexpressionistestedateachlevel,intheordertheyarelistedatthestartofthesection.Iftheexpression

canbeevaluated,theresultisreturned.Otherwise,thenextleveldownistested.Whenallthelevels

havebeenexhausted,andaresultstillcannotbeevaluated,anullvalueisreturned.

ResultsandResultTypes

Afteranactionhasbeenprocessed,itstimetosendtheresultinginformationbacktotheuser.

InStruts2,thistaskissplitintotwoparts:theresulttypeandtheresultitself.

Theresulttypeprovidestheimplementationdetailsforthetypeofinformationthatisreturnedtothe

user.ResulttypesareusuallypreconfiguredinStruts2orprovidedviaplugins,butdeveloperscan

providecustomresulttypesaswell.Configuredasthedefaultresulttypeisthedispatcher,whichusesa

JSPto

render

the

response

to

the

user.

After

aresult

type

is

defined,

it

can

be

used

many

times

by

differentactionresults.

TagLibraries

Taglibrariesprovidetheintersectionbetweenactionsandviews,allowingdynamicinformationfrom

theactionstoberenderedaswellasmakingrenderingdecisionsontheinformationtodisplayat

runtime.Thisisnothingunusual,andtaglibrariesinoneformoranotherareavailableinmostweb

applicationframeworks.

ThedifferencebetweentheStruts2taglibrariesandothertaglibraries(suchasJSTL)isthattheStruts2

taglibrarieshaveatightintegrationwiththeframework.TheytakefulladvantageoftheValueStackto

accessactionmethods,andtheytakeadvantageofOGNLtoevaluateexpressions,projectinto

collection

properties,

and

perform

on

the

fly

object

creation

and

collection

generation.

Thefourdifferentcategoriesfortaglibrariesarelistedhere:

Controltags:Thisgroupprovidestagsthatcontrolwhatinformationisrenderedinthefinalview,as

wellaswaystomanipulatecollectionsofelementsthatcanthenbefurtherutilized.

Datatags:Thisgroupprovidestagsthatrenderdynamicallygeneratedinformation(suchasdata)

fromtheactionthathasjustexecuted,internationalizedtext,andgeneratedURLsandlinks.Theycan

alsoprovidedebuginformationforthedeveloper.

Formtags:ThisgroupprovideswrappersforHTMLformtags,aswellasadditionaluserinterface

widgets.They

include

the

option

transfer

group,

date

and

time

pickers,

and

check

box

lists.

Nonformtags:Thetagsinthisgroupareusedinformsbutarenotdirectlyformentryelements.

Theyincludeerrormessagedisplays,tabbedpanels,andtreeviews.

ThebiggestdifferencebetweentheStruts2taglibrariesandothertaglibrariesisinthearchitecture.

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TheMVCstructureofStruts2taglibraries

FollowingarethethreemaincomponentsthatmakeuptheStruts2tagarchitecture:

Model:ThemodelcomponentinthediagramistheComponentclass.Fortagsthatareform

elementsorthosethatprovideagreatdealofHTML,thereisalsotheUIBeanclass.TheUIBeanclass

providesadditionalfeaturestoallowthetagsspecificFreemarkerrenderingtemplatestobemerged

intotheoutputstream.Eachnewtagrequiresamodelclasstobeimplementedthatextendsoneof

thesetwoclasses.Theclassissimple,providingthegettersandsettersforpropertiesthatareavailable

tobeused.TheparentComponentclasshasaccesstotheValueStackforretrievingextraparameters

orforwhenOGNLexpressionsneedtobeevaluated.

View:Theviewconsistsofeitheroneortwotemplates(bydefault,theseareFreemarkertemplates);

onlyoneneedstobespecifiedifthetagdoesnthaveenclosedtags.Thetemplatesprovidea

mechanismtokeepformattingawayfromthelogicandawaytochangewhatispresentedtotheuser

onaperprojectbasiswithoutrecompilingtheframework.

Controller:ThecontrollerallowstagstobeaccessedviaJSP,Velocity,orFreemarkerresulttemplates.

Thisisamajordeviationfromtraditionaltags.Normally,taglibrariesareavailabletoJSPtemplatesbut

nottootherviewtechnologies.Struts2fixesthisbymakingtaglibraryobjectsavailableinnonJSP

templates.Foreachviewtechnologythatwewanttosupport,anewsubclassofTagModel,

AbstractDirective,or

ComponentTagSupport

needs

to

be

created.

These

classes

provide

acustom

mechanismtopopulatethenecessaryfieldsinthemodelobject.


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1.2 TapestryFrameworkTapestryisacomponentbasedwebapplicationframework,writteninJava.Tapestryismore

thanasimpletemplatingsystem;TapestrybuildsontheJavaServletAPItobuildaplatformfor

creatingdynamic,interactivewebsites.Morethanjustanothertemplatinglanguage,Tapestryisareal

frameworkforbuildingcomplexapplicationsfromsimple,reusablecomponents.Tapestryoffloads

muchof

the

error

prone

work

in

creating

web

applications

into

the

framework

itself,

taking

over

mundanetaskssuchasdispatchingincomingrequests,constructingandinterpretingURLsencoded

withinformation,handlinglocalizationandinternationalizationandmuchmorebesides.

WhyisTapestrySpecial?Tapestryisaframeworkthatwascreatedkeepingthedeveloperinmind.Firstofall,itsparadigmis

veryclosetothatoftheRADenvironment.AbuttonontheTapestrypagehasaneventhandler

methodassociatedwithitinadeclarativeway,andthemethodisinvokedwhenthebuttonispressed.

TheTapestrywebdeveloperdoesn'tneedtorememberthatthebuttononthepageinauser'sweb

browserandthecodeoftheeventhandlermethodonthewebservercanbethousandsmilesapart,

anddoesn'tneedtocareaboutwhichcommunicationprotocolisbeingused.Thisnaturalapproach

makesTapestry

significantly

easier

to

learn

than

any

other

web

development

framework,

and

it

makes

theprocessofdevelopmentmuchmoreefficient.However,thereareanumberofotherattractive

features,thecombinationofwhichmakesTapestryunique.

PerhapsthehardestpartofunderstandingTapestryisthefactthatitiscomponentcentricnot

operationcentric.Mostwebtechnologies(Struts,Servlets,PHP,etc.)areoperationcentric.Wecreate

ServletsorActionsthatareinvokedwhenauserclicksalinkorsubmitsaform.Weareresponsiblefor

selectinganappropriateURL,andthenameandtypeofanyqueryparameters,sothatwecanpass

alongtheinformationweneedintheURL.Wearealsoresponsibleforconnectingouroutputpages

(whethertheyareJSPs,Velocitytemplates,orsomeotherformoftemplatingtechnology)tothose

operations.ThisrequiresustoconstructthoseURLsandgetthemintothehrefattributeofour

(hyperlinks)

tag,

or

into

the

action

attribute

of

our

tag.

EverythingisdifferentinsideTapestry.Tapestryapplicationsconsistofpages;pagesareconstructed

fromsmallercomponents.Componentsmaythemselvesbeconstructedfromothercomponents.Every

pagehasauniquename,andeverycomponentwithinapagehasitsownuniqueid.Thisisacomponent

objectmodel.Effectively,everycomponenthasanaddressthatcaneasilybeincorporatedintoaURL.

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RequestResponseCycleinTapestryFramework

TapestryApplicationisasetofInteractivePagesItisnaturalforauserofawebapplicationtothinkofitasasetofpages.Theusermightclickona

button,

select

a

value

in

a

drop

down

list

or

do

something

else,

and

the

page

would

display

different

data,orevenacompletelydifferentpagemightbeshownbytheapplicationasaresultofuseractions.

ThedesignofTapestryisveryclosetothisnaturalparadigm,asaTapestryapplicationactuallyconsists

ofanumberofTapestrypages.ATapestrypageisquiteacleverentity.Itremembersthevalues

enteredbytheuser,andiftheuserinitiatessomeaction,likeclickingonalinkorclickingonabutton,

thepagewillreacttothatactionbyrunninganappropriatefragmentofcodeaneventhandler

method.Itisfordeveloperstodecidewhatkindofcodeitwillbeandhowitwillusetheinputprovided

bytheuser.

Thiswillsoundveryfamiliartothosewhohaveexperienceofdevelopingdesktopapplicationswith

someRapidApplicationDevelopmentenvironments,suchasBorlandDelphiorMicrosoftVisualBasic.

However,webapplicationsareverydifferentfromdesktopapplications,andalthoughworkingwith

Tapestrywe

do

not

need

to

deal

with

complexities

that

arise

from

this

difference,

it

is

useful

to

understandhowthingswork,atleastingeneralterms.

TapestryPagesarePooled

Tapestrywasdesignedwithgreatscalabilityinmind.ThismeansthataTapestryapplicationshouldbe

abletoeasilyhandleahugeamountofconcurrentusers,andforthis,itshouldspendminimaleffortsto

serveeveryindividualrequest.


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Say,auserrequeststheStartpage.ShouldTapestrycreateaninstanceofthispageespeciallyforthis

useranddiscarditassoonastheuserwillgotoanotherpage?Thiswouldn'tbeefficient,asthenext

moment,twentyotheruserswillcomeandrequestaninstanceoftheStartpage.Itwouldbe

reasonablenottodiscard,buttoreusetheinstancethatwasjustusedforthefirstuser.However,there

isapotentialproblem.Thepagemighthavesomesensitivedataputintoitbythefirstusersaya

password,oranythingelse.Toavoidthisproblem,Tapestrywillwipecleantheinstanceusedbythe

firstuserbeforegivingittoanyotheruser.Itwillresetallvariablesonthepageclasstotheirinitialvalues.

Inreality,Tapestrymaintainsapoolofinstancesforeverypage,andwhenapageisrequested,ittakes

aninstancefromtheappropriatepooltoservethatrequest,andthenreturnstheinstancetoitspool.At

theendoftherequest,Tapestrywillwipecleanthevariablesoftheinstanceofanyuserspecificdata.

ThismechanismmakesTapestryveryefficient.Butwehavetorememberthatevenifwethinkthatwe

aredealingwiththesamepage,inmostcasesthepagewillberepresentedbyadifferentinstance(may

beevencomingfromacompletelydifferentserver,inaclusteredenvironment),andthenextinstance

willhavenoideaofwhatwehavejusttoldthepreviousinstance.Thatis,unlesswetakespecialcare

andmakesurethattheinformationispassedbetweeninstancesproperly.

WhathappenedwhenwetriedtopassamessagetotheAnotherpageisthatwetookaninstanceofit,

andputourmessageintoit.ThenwetoldTapestrytoshowtheAnotherpagetothisuser.What

Tapestry5doesisthatittellstheuser'sbrowserthatithassuccessfullyhandleduserssubmission;now

goon.WhenthebrowserrequestsfortheAnotherpage,ittakesafreshinstanceofthatpagefromthe

poolandusesittoproducetheoutput.Unfortunately,thatfreshinstancewillknownothingaboutthe

messagewewantedtopass.

Sohowcanwemakeourapplicationworkwithallthisinstancepooling?Shouldtherebeawaytomake

Tapestryremembertheinformationwehaveputintothepage,nomatterwhichinstanceofthatpage

isbeingused?

Thereare

actually

two

approaches

to

this:

Wecanmakeapagefieldpersistent.Thisisaverysimpleapproach,butithassomedownsides.

Wecanusepageactivationcontext.Thisisasuperiorapproach,butnotforeverycase,andit

involvesmorecoding.

TheEngineisacentralobject,itoccupiesthesamesemanticspaceinTapestrythattheHttpSession

doesintheServletAPI.TheEngineisultimatelyresponsibleforstoringthepersistentstateofthe

application(propertiesthatexistfromonerequesttothenext),andthisisaccomplishedbystoringthe

EngineintotheHttpSession.EngineservicesarethebridgebetweenServletsandURLsandtherestof

Tapestry.Engine

services

are

responsible

for

encoding

URLs,

providing

query

parameters

that

identify,

totheframework,theexactoperationthatshouldoccurwhenthegeneratedURListriggered(bythe

enduserclickingalinkorsubmittingaform).Servicesarealsoresponsiblefordispatchingthose

incomingrequests.ThisencapsulationofURLencodinganddecodinginsideasingleobjectiskeyto

howTapestrycomponentscanflexiblyoperatewithoutconcernforhowtheyarecontainedandon

whichpagetheservicestakeintoaccountpageandlocationwhenformulatingURLs.

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TheVisitobjectisanapplicationdefinedobjectthatactsasafocalpointforallserversidestate(not

associatedwithanysinglepage).IndividualapplicationsdefineforthemselvestheclassoftheVisit

object.TheVisitisstoredasapropertyoftheEngine,andsoisultimatelystoredpersistentlyinthe

HttpSession.

TheGlobal

object

is

also

application

specific.

It

stores

information

global

to

the

entire

application,

independentofanyparticularuserorsession.AcommonusefortheGlobalobjectistocentralizelogic

thatperformsJNDIlookupsofsessionEJBs.

TapestryistightlyintegratedwithOGNL,theObjectGraphNavigationLanguage.OGNLisaJava

expressionlanguage,whichisusedtopeekintoobjectsandreadorupdatetheirproperties.OGNLis

similarto,andmustmorepowerfulthan,theexpressionlanguagebuiltintotheJSP2.0standardtag

library.OGNLnotonlysupportpropertyaccess,itcanincludemathematicalexpressionsandmethod

invocations.Itcanreferencestaticfieldsofpublicclasses.Itcancreatenewobjects,includinglistsand

maps.OGNLisprimarilyusedtoallowtwodifferentobjects(suchasapageandacomponent

containedbythatpage)toshareinformation.

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1.3. SpringFrameworkTheSpringFrameworkisanopensourcelightweightapplicationframeworkthataimstomake

JEEdevelopmenteasier. UnlikesingletierframeworkssuchasStrutsorHibernate,Springaimstohelp

structurewholeapplicationsinaconsistent,productivemanner,pullingtogetherbestofbreedsingle

tierframeworks

to

create

acoherent

architecture.

Since

Spring

is

alightweight

framework,

it

not

only

aimstoreducecomplexityinapplicationcode,butavoidunnecessarycomplexityintheirown

functioning.Soitdoesnthaveahighstartuptime,doesntinvolvehugebinarydependencies,willrun

inanyenvironment,anddoesntplaceobstaclesinthewayoftesting.

Springisboththemostpopularandmostambitiousofthelightweightframeworks.Itisthe

onlyonetoaddressallarchitecturaltiersofatypicalJEEapplication,andtheonlyonetooffera

comprehensiverangeofservices,aswellasalightweightcontainer.ThefollowingarethekeySpring

modules:

InversionofControlcontainer:Thecore"container"Springprovides,enablingsophisticated

configurationmanagementforPOJOs.TheSpringIoCcontainercanmanagefineorcoarse

grainedPOJOs

(object

granularity

is

amatter

for

developers,

not

the

framework),

and

work

withotherpartsofSpringtoofferservicesaswellasconfigurationmanagement.

AspectOrientedProgramming(AOP)framework:AOPenablesbehaviorthatwould

otherwisebescatteredthroughdifferentmethodstobemodularizedinasingleplace.Spring

usesAOPunderthehoodtodeliverimportantoutoftheboxservicessuchasdeclarative

transactionmanagement.SpringAOPcanalsobeusedtoimplementcustomcodethatwould

otherwisebescatteredbetweenapplicationclasses.

Dataaccessabstraction:Springencouragesaconsistentarchitecturalapproachtodata

access,andprovidesauniqueandpowerfulabstractiontoimplementit.Springprovidesarich

hierarchyofdataaccessexceptions,independentofanyparticularpersistenceproduct.Italso

providesarangeofhelperservicesforleadingpersistenceAPIs,enablingdeveloperstowrite

persistenceframeworkagnosticdataaccessinterfacesandimplementthemwiththetoolof

theirchoice.

JDBCsimplification:SpringprovidesanabstractionlayeroverJDBCthatissignificantlysimpler

andlesserrorpronetousethanJDBCwhenweneedtouseSQLbasedaccesstorelational

databases.

Transactionmanagement:SpringprovidesatransactionabstractionthatcansitoverJTA

"global"transactions(managedbyanapplicationserver)or"local"transactionsusingtheJDBC,

Hibernate,JDO,oranotherdataaccessAPI.Thisabstractionprovidesaconsistent

programmingmodelinawiderangeofenvironmentsandisthebasisforSpring'sdeclarative

andprogrammatictransactionmanagement.

MVCwebframework:SpringprovidesarequestbasedMVCwebframework.Itsuseofshared

instancesofmultithreaded"controllers"issimilartotheapproachofStruts,butSpring'sweb

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frameworkismoreflexible,andintegratesseamlesslywiththeSpringIoCcontainer.Allother

SpringfeaturescanalsobeusedwithotherwebframeworkssuchasStrutsorJSF.

SimplificationforworkingwithJNDI,JTA,andotherJ2EEAPIs:Springcanhelpremovethe

needformuchoftheverbose,boilerplatecodethat"doesn'tdoanything."WithSpring,wecan

continueto

use

JNDI

or

EJB,

if

we

want,

but

we'll

never

need

to

write

another

JNDI

lookup.

Instead,simpleconfigurationcanresultinSpringperformingthelookuponourbehalf,

guaranteeingthatresourcessuchasJNDIcontextsareclosedevenintheeventofanexception.

Lightweightremoting:SpringprovidessupportforPOJObasedremotingoverarangeof

protocols,includingRMI,IIOP,andHessian,Burlap,andotherwebservicesprotocols.

JMSsupport:SpringprovidessupportforsendingandreceivingJMSmessagesinamuch

simplerwaythanprovidedthroughstandardJ2EE.

JMXsupport:SpringsupportsJMXmanagementofapplicationobjectsitconfigures.

Supportfor

acomprehensive

testing

strategy

for

application

developers:

Spring

not

only

helpstofacilitategooddesign,allowingeffectiveunittesting,butprovidesacomprehensive

solutionforintegrationtestingoutsideanapplicationserver.

SpringsValue

ThekeySpringvaluescanbesummarizedasfollows:

Springisanoninvasiveframework.Thisisthekeydeparturefrommostpreviousframeworks.

Whereastraditional

frameworks

such

as

EJB

or

Apache

Avalon

force

application

code

to

be

aware

of

theframework,implementingframeworkspecificinterfacesorextendingframework specificclasses,

Springaimstominimizethedependenceofapplicationcodeontheframework.ThusSpringcan

configureapplicationobjectsthatdon'timportSpringAPIs;itcanevenbeusedtoconfiguremany

legacyclassesthatwerewrittenwithoutanyknowledgeofSpring.Thishasmanybenefits.For

example:

ApplicationcodewrittenaspartofaSpringapplicationcanberunwithoutSpringoranyother

container.

LockintoSpringisminimized.Forexample,wecouldmigratetoanotherlightweightcontainer,or

possiblyeven

reuse

application

objects

in

an

EJB

3.0

EJB

container,

which

supports

asubset

of

Spring's

DependencyInjectioncapability.

MigrationtofutureversionsofSpringiseasier.Thelesscodedependsontheframework,thegreater

thedecouplingbetweentheimplementationofourapplicationandthatoftheframework.Thusthe

implementationofSpringcanchangesignificantlywithoutbreakingcode,allowingtheframeworkto

beimprovedwhilepreservingbackwardcompatibility.

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Ofcourseinsomeareas,suchasthewebframework,it'simpossibletoavoidapplicationcode

dependingontheframework.ButSpringconsistentlyattemptstoreachthenoninvasiveidealwhere

configurationmanagementisconcerned.

Springprovidesaconsistentprogrammingmodel,usableinanyenvironment.Manyweb

applicationssimply

don't

need

to

run

on

expensive,

high

end,

application

servers,

but

are

better

off

runningonawebcontainersuchasTomcatorJetty.It'salsoimportanttorememberthatnotall

applicationsareserversideapplications.Springprovidesaprogrammingmodelthatinsulates

applicationcodefromenvironmentdetailssuchasJNDI,makingcodelessdependentonitsruntime

context.

Springaimstopromotecodereuse.Springhelpstoavoidtheneedtomakesomeimportanthard

decisionsupfront,likewhetherourapplicationwilleveruseJTAorJNDI;Springabstractionswillallow

todeployourcodeinadifferentenvironmentifweeverneedto.ThusSpringenablesustodefer

architecturalchoices,potentiallydeliveringbenefitssuchastheneedtopurchaseanapplicationserver

licenseonlywhenweknowexactlywhatourplatformrequirementsare,followingtestsofthroughput

andscalability.

SpringaimstofacilitateObjectOrienteddesigninJEEapplications.Inreality,manyJEE

applicationsdonotdeservethenameofOOapplications.Springaimstoremovesomeofthe

impedimentsinplaceofOOintraditionaldesigns.

Springaimstofacilitategoodprogrammingpractice,suchasprogrammingtointerfaces,rather

thanclasses.UseofanIoCcontainersuchasSpringgreatlyreducesthecomplexityofcodingto

interfaces,ratherthanclasses,byelegantlyconcealingthespecificationofthedesiredimplementation

classandsatisfyingitsconfigurationrequirements.Callersusingtheobjectthroughitsinterfaceare

shieldedfromthisdetail,whichmaychangeastheapplicationevolves.

Springpromotespluggability.Springencouragestothinkofapplicationobjectsasnamedservices.

Ideally,thedependenciesbetweensuchservicesareexpressedintermsofinterfaces.Thuswecan

swaponeserviceforanotherwithoutimpactingtherestofourapplication.Thewayinwhicheach

serviceisconfiguredisconcealedfromtheclientviewofthatservice.

SpringfacilitatestheextractionofconfigurationvaluesfromJavacodeintoXMLorproperties

files.WhilesomeconfigurationvaluesmaybevalidlycodedinJava,allnontrivialapplicationsneed

someconfigurationexternalizedfromJavasourcecode,toallowitsmanagementwithout

recompilationorJavacodingskills.Springencouragesdeveloperstoexternalizeconfigurationthat

might

otherwise

have

been

inappropriately

hard

coded

in

Java

source

code.

More

configurable

code

is

typicallymoremaintainableandreusable.

Springisdesignedsothatapplicationsusingitareaseasyaspossibletotest.Asfaraspossible,

applicationobjectswillbePOJOs,andPOJOsareeasytotest;dependenceonSpringAPIswill

normallybeintheformofinterfacesthatareeasytostubormock.UnlikethecaseofJNDI,for

example,stubbingormockingiseasy;unlikethecaseofStruts,forexample,applicationclassesare

seldomforcedtoextendframeworkclassesthatthemselveshavecomplexdependencies.

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Springisconsistent.Bothindifferentruntimeenvironmentsanddifferentpartsoftheframework,

Springusesaconsistentapproach.

Springpromotesarchitecturalchoice.WhileSpringprovidesanarchitecturalbackbone,Springaims

tofacilitatereplaceabilityofeachlayer.Forexample,withaSpringmiddletier,weshouldbeableto

switchfrom

one

O/R

mapping

framework

to

another

with

minimal

impact

on

business

logic

code,

or

switchfrom,say,StrutstoSpringMVCorWebWorkwithnoimpactonthemiddletier.

Springdoesnotreinventthewheel.Despiteitsbroadscope,Springdoesnotintroduceitsown

solutioninareassuchasO/Rmappingwheretherearealreadygoodsolutions.Similarly,itdoesnot

implementitsownloggingabstraction,connectionpool,distributedtransactioncoordinator,

remotingprotocols,orothersystemservicesthatarealreadywellservedinotherproductsor

applicationservers.However,Springdoesmaketheseexistingsolutionssignificantlyeasiertouse,and

placestheminaconsistentarchitecturalapproach.

RelationshiptoOtherFrameworks

Springdoesnotreinventthewheel.Springaimstoprovidethegluethatenablestobuilda

coherentandmanageableapplicationarchitectureoutofdisparatecomponents.Springrelatesto

someofthemanyproductsitintegrateswith.

PersistenceFrameworks

SpringdoesnotprovideitsownO/Rmappingframework.ItprovidesanabstractionoverJDBC,but

thisisalesspainfulwayofdoingexactlythesamethingasmightotherwisehavebeendonewith

JDBC.

Springprovides

aconsistent

architectural

model,

but

allows

to

choose

the

O/R

mapping

framework

of

anychoice(oranSQLbasedapproachwhereappropriate).Forthemanyapplicationsthatbenefit

fromusingO/Rmapping,weshouldintegrateanO/RmappingframeworkwithSpring.Spring

integrateswellwithallleadingO/Rmappingframeworks.Supportedchoicesinclude:

Hibernate:TheleadingopensourceO/Rmappingtool.HibernatewasthefirstO/Rmappingtoolfor

whichSpringofferedintegration.Spring'sHibernateintegrationmakesHibernatesignificantlyeasier

touse,throughtheHibernateTemplatewe'vebrieflydiscussedandthroughintegrationwithSpring's

transactionmanagement.

JDOimplementations:SpringprovidessupportforJDO1.0andJDO2.0standards.SeveralJDO

vendorsalsoshiptheirownSpringintegration,implementingSpring'sJdoDialectinterface,giving

applicationdevelopersaccesstocommoncapabilitiesthatgobeyondtheJDOspecificationwithout

lockingintoaparticularJDOvendor.

TopLink:TopLinkistheoldestO/Rmappingtoolonthemarket,datingbacktothemid1990s.

TopLinkisnowanOracleproduct,andOraclehaswrittenaSpringintegrationthatenablesSpring

userstoworkasseamlesslywithTopLinkaswithHibernateoraJDOimplementation.

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ApacheOJB:AnO/RmappingproductfromApache.

iBATIS:iBATISSQLMapsisnot,strictlyspeaking,anO/Rmappingproduct.However,itdoesoffera

convenientwayofdefiningSQLstatementsinadeclarativefashion,mappingobjectstostatement

parametersandresultsetstoobjects.IncontrasttofullblownO/Rmappingsolutions,though,SQL

Mapsdoes

not

aim

to

provide

an

object

query

language

or

automatic

change

detection.

AlltheseintegrationsareconsistentinthatSpringfacilitatestheuseofDAOinterfaces,andall

operationsthrowinformativesubclassesofSpring'sDataAccessException.Springprovideshelpers

suchastemplatesforalltheseAPIs,enablingaconsistentprogrammingstyle.Spring'scomprehensive

architecturaltemplatemeansthatalmostanypersistenceframeworkcanbeintegratedwithinthis

consistentapproach.IntegrationeffortsfromseveralJDOvendorsthefactthattheSpring/TopLink

integrationwasdevelopedbytheTopLinkteamatOracle,andthatthepopularCayenneopensource

O/RmappingprojectitselfdevelopedSpringintegrationforCayenneshowsthatSpring'sdata

accessabstractionisbecomingsomethingofadefactostandardforconsistentapproachto

persistenceinJava/JEEapplications.

Spring'sownJDBCframeworkissuitablewhenwewantSQLbasedaccesstorelationaldata.Thisis

notanalternativetoO/Rmapping,butit'snecessarytoimplementatleastsomescenariosinmost

applicationsusingarelationaldatabase.(Also,O/Rmappingisnotuniversallyapplicable,despitethe

claimsofitsmoreenthusiasticadvocates.)

Importantly,SpringallowstomixandmatchdataaccessstrategiesforexampleHibernatecodeand

JDBCcodesharingthesameconnectionandtransaction.Thisisanimportantbonusforcomplex

applications,whichtypicallycan'tperformallpersistenceoperationsusingasinglepersistence

framework.

WebFrameworks

Again,thefundamentalphilosophyistoenableuserstochoosethewebframeworkoftheirchoice,

whileenjoyingthefullbenefitofaSpringmiddletier.Popularchoicesinclude:

Struts:StillthedominantMVCwebframework(althoughindecline).ManySpringusersuseStruts

withaSpringmiddletier.Integrationisfairlyclose,anditisevenpossibletoconfigureStrutsActions

usingSpringDependencyInjection,givingtheminstantaccesstomiddletierobjectswithoutanyJava

coding.

WebWork:IntegrationwithWebWorkisparticularlyclosebecauseofWebWork'sflexibledesignand

thestronginterestintheWebWorkcommunityinusingWebWorkalongwithaSpringmiddletier.Itis

possibleto

configure

WebWork

Actions

using

Spring

Dependency

Injection.

SpringMVC:Spring'sownMVCwebframework,whichofcourseintegratesparticularlywellwitha

Springmiddletier.

Tapestry:AcomponentorientedframeworkfromApache'sJakartagroup,Tapestryintegrateswell

withSpringbecausedeclarativepagemetadatamakesiteasyforTapestrypagestoaccessSpring

providedserviceswithoutanycodelevelcouplingtoSpring.

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JSF:SpringintegratesverywellwithJSF,giventhatJSFhastheconceptof"namedbeans"anddoes

notaimtoimplementmiddletierservicesitself.

Spring'sapproachtowebframeworksdiffersfromthattopersistence,inthatSpringprovidesitsown

fullyfeaturedwebframework.Ofcourse,wearenotforcedtousethisifwewishtouseaSpring

middletier.

While

Spring

integrates

well

with

other

web

frameworks,

there

are

afew

integration

advantagesavailableonlywithSpring'sownMVCframework,suchastheabilitytousesome

advancedfeaturesofSpringDependencyInjection,ortoapplyAOPadvicetowebcontrollers.

Nevertheless,asSpringintegrateswellwithotherwebframeworks,weshouldchooseSpring'sown

MVCframeworkonitsmerits,ratherthanbecausethere'sanyelementofcompulsion.SpringMVCis

anappealingalternativetoStrutsandotherrequestdrivenframeworksasitishighlyflexible,helpsto

ensurethatapplicationcodeinthewebtieriseasilytestable,andworksparticularlywellwithawide

varietyofviewtechnologiesbesidesJSP.

AOPFrameworks

SpringprovidesaproxybasedAOPframework,whichiswellsuitedforsolvingmostproblemsinJ2EE

applications.

However,sometimesweneedcapabilitiesthataproxybasedframeworkcannotprovide,suchasthe

abilitytoadviseobjectscreatedusingthenewoperatorandnotmanagedbyanyfactory;ortheability

toadvisefields,aswellasmethods.

Tosupportsuchrequirements,SpringintegrateswellwithAspectJandApectWerkz,thetwoleading

classweavingbasedAOPframeworks.It'spossibletocombineSpringDependencyInjectionwith

suchAOPframeworksforexample,configuringAspectJaspectsusingthefullpoweroftheSpring

IoCcontainerasiftheywereordinaryclasses.

Springdoes

not

attempt

to

replicate

the

power

of

afull

blown

AOP

solution

such

as

AspectJ;

this

wouldproducenobenefitstoSpringusers,whoareinsteadfreetomixSpringAOPwithAspectJas

necessarytoimplementsophisticatedAOPsolutions.

OtherFrameworks

SpringintegrateswithotherframeworksincludingtheQuartzscheduler,JasperReports,andVelocity

andFreeMarkertemplateengines.

Again,thegoalistoprovideaconsistentbackboneforapplicationarchitecture.

Allsuchintegrationsaremodules,distinctfromtheSpringcore.WhilesomeshipwiththemainSpring

distribution,

some

are

external

modules.

Spring's

open

architecture

has

also

resulted

in

numerous

otherprojects(suchastheCayenneO/Rmappingframework)providingtheirownSpringintegration,

orprovidingSpringintegrationwiththirdpartyproducts.

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1.4. JavaServerFaces(JSF)FrameworkJSFbringsacomponentbasedmodeltowebapplicationdevelopmentthat'ssimilartothemodel

that'sbeenusedinstandaloneGUIapplicationsforyears.Thetechnologybuildsontheexperience

gainedfromJavaServlets,JavaServerPages,andnumerouscommercialandopensourceweb

applicationframeworksthatsimplifythedevelopmentprocess.InJavaServerFaces,developerslearn

howtousethisnewframeworktobuildrealworldwebapplications.JavaServerFacespaysparticular

attentiontosimpletasksthatareeasilyignored,butcrucialtoanyrealapplication:workingwith

tabulardata,forexample,orenablinganddisablingbuttons.

JSFisnewstandardframework,developedthroughJavaCommunityProcess(JCP),thatmakesiteasy

tobuilduserinterfacesforjavawebapplications byassemblingreusablecomponentsinapage.We

canthinkof JSFframeworkasatoolbox thatisfullof readytousecomponentswherewecanquickly

andeasilyaddandreuse thesecomponentsmanytimesinapageandcaptureeventsgeneratedby

actionsonthesecomponents.SoJSFapplicationsareeventdriven.Wetypicallyembedcomponents

inajsp

page

using

custom

tags

defined

by

JSF

technology

and

use

the

framework

to

handle

navigation

fromonepagetoanother.Componentscanbenestedwithinanothercomponent,forexample,input

box,buttoninaform.

JSFisbasedonwellestablishedModelViewController(MVC)designpattern.Applicationsdeveloped

usingJSFframeworksarewelldesignedandeasytomaintainthenanyotherapplicationsdevelopedin

JSPandServlets.JSFeasesthedevelopmentofwebapplicationsbasedonJavatechnologies.The

followingsaresomeofbenefitsofusingJSF:

JSFprovidesstandard,reusablecomponentsforcreatinguserinterfacesforwebapplications.

JSFprovides

many

tag

libraries

for

accessing

and

manipulating

the

components.

Itautomaticallysavestheformdataandrepopulatestheformwhenitisdisplayedatclient

side.

JSFencapsulatestheeventhandlingandcomponentrenderinglogicfromprogrammers,

programmersjustusethecustomcomponents.

JSFisaspecificationandvendorscandeveloptheimplementationsforJSF.

TherearemanyGUIsavailablethesedaystosimplifythedevelopmentofwebbased

applicationbasedonJSFframework.

TheJSFframeworkisresponsibleforinteractingwithclientdevices,anditprovidestoolsfor

tyingtogetherthevisualpresentation,applicationlogic,andbusinesslogicofawebapplication.

However,thescopeofJSFisrestrictedtothepresentationtier.Databasepersistence,webservices,

andotherbackendconnectionsareoutsidethescopeofJSF.

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Page 21 of 29

Highlevel

overview

of

the

JSF

framework

JSFconnectstheviewandthemodelandoperatesasthecontrollerthatreactstotheuserby

processingactionandvaluechangeevents,routingthemtocodethatupdatesthemodelortheview.

Whentheusersubmitsformtothese

rver,theJSFimplementationinvokesthecheckmethodofthe

userbean.Thatmethodcantakearbitraryactionstoupdatethemodel,anditreturnsthenavigation

DataconversionUsersenterdataintowebformsastext.Businessobjectswantdataasnumbers,

ld

isrequired"or"thisfieldmustbeanumber".Ofcourse,whenusersenterinvaliddata,weneedto

InternationalizationJSFmanagesinternationalizationissuessuchascharacterencodingsandthe

psophisticatedcomponentsthatpage

designerssimplydropintotheirpages.Forexample,supposeacomponentdeveloperproducesa

Alternativerenderers

By

default,

JSF

generates

markup

for

HTML

pages.

But

it

is

easy

to

extend

the

ToolsupportJSFisoptimizedforusewithautomatedtools.Asthesetoolsmatureinthecoming

years,webelievethatJSFwillbethemusthaveframeworkfordevelopingwebinterfaceswithJava.

IDofthenextpagetobedisplayed.

dates,orotherdatatypes.

Validationand

error

handling

JSF

makes

it

easy

to

attach

validation

rules

for

fields

such

as

"this

fie

displayappropriateerrormessages.JSFtakesawaymuchofthetediumofthisprogrammingtask.

selectionofresourcebundles.

CustomcomponentsComponentdeveloperscandevelo

calendarcomponentwithalltheusualbellsandwhistles.

JSFframeworktoproducemarkupforanotherpagedescriptionlanguagesuchasWMLorXUL.


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Page 22 of 29

TheJSFlifecycle

TheRestoreViewphaseretrievesthecomponenttreefortherequestedpageifitwasdisplayed

previouslyorconstructsanewcomponenttreeifitisdisplayedforthefirsttime.Ifthepagewas

displayedpreviously,allcomponentsaresettotheirpriorstate.ThismeansthatJSFautomatically

retainsforminformation.Forexample,whenauserpostsillegaldatathatisrejectedduringdecoding,

theinputsareredisplayedsothattheusercancorrectthem.

Iftherequesthasnoquerydata,theJSFimplementationskipsaheadtotheRenderResponsephase.

Thishappens

when

apage

is

displayed

for

the

first

time.

Otherwise,thenextphaseistheApplyRequestValuesphase.Inthisphase,theJSFimplementation

iteratesoverthecomponentobjectsinthecomponenttree.Eachcomponentobjectcheckswhich

requestvaluesbelongtoitandstoresthem.

IntheProcessValidationsphase,thesubmittedstringvaluesarefirstconvertedto"localvalues,"

whichcanbeobjectsofanytype.WhenwedesignaJSFpage,wecanattachvalidatorsthatperform


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correctnesschecksonthelocalvalues.Ifvalidationpasses,theJSFlifecycleproceedsnormally.

However,whenconversionorvalidationerrorsoccur,theJSFimplementationinvokestheRender

Responsephasedirectly,redisplayingthecurrentpagesothattheuserhasanotherchancetoprovide

correctinputs.

Afterthe

converters

and

validators

have

done

their

work,

it

is

assumed

that

it

is

safe

to

update

the

modeldata.DuringtheUpdateModelValuesphase,thelocalvaluesareusedtoupdatethebeansthat

arewiredtothecomponents.

IntheInvokeApplicationphase,theactionmethodofthebuttonorlinkcomponentthatcausedthe

formsubmissionisexecuted.Thatmethodcancarryoutarbitraryapplicationprocessing.Itreturnsan

outcomestringthatispassedtothenavigationhandler.Thenavigationhandlerlooksupthenext

page.

Finally,theRenderResponsephaseencodestheresponseandsendsittothebrowser.Whenauser

submitsaform,clicksalink,orotherwisegeneratesanewrequest,thecyclestartsanew.

WebDevelopmentusingJSF

AlthoughJSFisdesignedtobeindependentofspecificprotocolsandmarkuplanguages,mostJava

developerswilluseitinconcertwithJavaservletsandJSPstocreateHTMLbasedWebapplications.

TheseapplicationscancommunicatewithJavaapplicationserversviathenowubiquitousand

venerableHTTP.TheauthorsoftheJSFspecificationareawareofthisdemographic,sooneoftheir

primarygoalsistoresolveanumberofissuesrelatedtousingthestatelessHTTPprotocolinconcert

withHTMLclients.ThespecificationhighlightsanumberofJSFfeaturesrelatedtothisgoal:

UIComponent

State:

JSF

specifically

addresses

saving

user

interface

component

state

between

requestsinaWebclientsession.

ComponentRendering:HTMLisjustoneofmanymarkuplanguages,andeachWebclientssupport

ofaparticularmarkuplanguagemayvary.JSFprovidesarenderingmechanismforaddressingthis

varietyoftargetWebclients.

FormProcessing:MostWebapplicationsareformbased.JSFprovidesanumberofconvenient

featuresforprocessingmultipageandsinglepageformbasedrequests.

FormValidation:Alongwithformprocessing,validatingformdataisacriticalneed.JSFhelps

automate

this

process

and

provide

the

necessary

error

reporting.

EventModel:JSFprovidesastronglytypedcomponenteventmodelforrespondingtoclient

generatedeventswithserversidehandlers.

TypeConversion:SinceWebclientrequestsviaHTTPprovideformdataasstrings,amechanismfor

convertingthesestringstoandfromtheapplicationmodelwouldbeveryuseful.JSFprovidesafacility

forenablingtypeconversion.

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ErrorHandling:Allapplicationsmustdealwithapplicationerrorsandexceptions.JSFprovidesa

mechanismforhandlingerrorconditionsandreportingthembacktotheuserinterface.

Internationalization:MultilanguagesupportisoftenakeyrequirementinWebapplications,whichare

easilyaccessiblefromaroundtheworld.JSFprovidesnativesupportofinternationalization.

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2. Frameworks&APIsbasedonDataSourceArchitecturalPatterns2.1. HibernateFramework

Workingwithobjectorientedsoftwareandarelationaldatabasecanbecumbersomeandtime

consumingintoday'senterpriseenvironments.Hibernateisanobject/relationalmappingtoolforJava

environments.Thetermobject/relationalmapping(ORM)referstothetechniqueofmappingadata

representationfromanobjectmodeltoarelationaldatamodelwithaSQLbasedschema.

HibernatenotonlytakescareofthemappingfromJavaclassestodatabasetables(andfrom

JavadatatypestoSQLdatatypes),butalsoprovidesdataqueryandretrievalfacilitiesandcan

significantlyreducedevelopmenttimeotherwisespentwithmanualdatahandlinginSQLand

JDBC.Hibernatesgoalistorelievethedeveloperfrom95percentofcommondatapersistencerelated

programmingtasks.Hibernatemaynotbethebestsolutionfordatacentricapplicationsthatonlyuse

storedprocedurestoimplementthebusinesslogicinthedatabase,itismostusefulwithobject

orienteddomainmodelsandbusinesslogicintheJavabasedmiddletier.However,Hibernatecan

certainlyhelp

us

to

remove

or

encapsulate

vendor

specific

SQL

code

and

will

help

with

the

common

taskofresultsettranslationfromatabularrepresentationtoagraphofobjects.

2.2. JavaDataObjects(JDO)APIJDOspecifiesapersistenceserviceforthoseobjectswhosestateoutlivesthelifetimeofasingle

invocationofaJavaVirtualMachine(JVM).Nearlyeveryprogramsavesthestateofsomeobjectsand

eitherrestoresthisstateonasubsequentinvocationorsharesitwithanotherconcurrentlyrunning

program.Thestatepreservedisboththestatewithinobjectsandtherelationshipsbetweenobjects.

JDOisapersistenceservicebecauseitconnectsJavaobjectsinmemorytothelongtermstorageof

theirstate.

By

using

aservice

that

is

concerned

only

with

persistence,

applications

can

isolate

the

work

ofmovingstatebetweenmemoryandadatastoretooneareaofcode.Withoutapersistenceservice,

thecodetointerfacewiththedatastoreisspreadthroughouttheapplication.ByusingJDO,the

applicationprogrammercanmakepersistenceamodularcomponent.Asaresult,themaintainability

oftheapplicationimproves.Itiseasiertofindbugs,fixthem,avoidintroducingnewbugs,and

upgradethecapabilitiesoftheapplication.

Althoughmostapplicationsneedtopersistsomeobjects,notallobjectsrequirepersistence.Many

objectsinaprogramaresimplytransient,whichmeanstheirstateiscreatedasneededanddiscarded

whentheprogramstopsexecuting,ifnotbefore.Someobjectsaretransientbutusepersistentobjects

ortheinformationinthem.Forexample,anobjectthatsumsthesalesfiguresfromacollectionof

persistentinvoices

may

itself

be

transient.

JDOSpecifiesaUniformPersistenceService

JDOspecifiesanApplicationProgrammingInterface(API)toalibraryofservicesthatthe

applicationprogramcanuseforpersistence.JDOalsospecifiesthepersistentservicesthatare

providedtransparentlytoallpersistentobjects.JDOshipswithareferenceimplementationofthisAPI

thatmaybesuitableforprototypedevelopment.Numerousvendorshavecreatednewproductsor

Page 25 of 29


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adaptedexistingproductstosupporttheJDOspecification.Theseproductswillcompeteagainsteach

otherintermsofrobustness,performance,supporteddatastores,supportforoptionalJDOfeatures,

andeaseofconfiguration,flexibility,andsoforth.

JDOencapsulatesandsimplifiestheprogrammingissuesthatareuniquetopersistentobjects.It

providesaservice

to

find,

update,

and

delete

existing

persistent

objects

and

to

store

new

persistent

objects.Itencapsulatesthemappingofobjectstateinmemorytopersistentstateinthedatastore.It

ensuresthatmultiplechangesmadetopersistentobjectsinmemoryarestoredinanallornothing

fashioninthedatastore.Lastly,itallowsmultipleconcurrentlyexecutingapplicationsandthreadsto

shareaccesstothepersistentstate.

JDOoffersauniformsetofpersistenceservicesthatdonotvarywiththedatastoreusedorthe

deploymentenvironmentchosen.JDOimplementationscanbebuiltforavarietyofdatastore

architectures,suchasfiles,objectdatabases,relationaldatabases,andgeneralizedtransaction

processingservices.BecauseJDOencapsulatesthedatastore,itallowstheapplicationtousethesame

setofservicesregardlessofthedatastoreselected.TheuniformityofJDOallowstheapplicationto

remainblissfully

ignorant

of

the

differences

in

query

languages,

data

models,

and

access

interfaces

betweenthevariousdatastores.Whenitcomestodeploymentarchitectures,applicationcodethat

usesJDOmaybedeployedinstandaloneapplications,client/serverapplications,servlets,and

EnterpriseJavaBeans(EJBs).Forthemostpart,thesamesetofJDOservicesisavailableinallofthese

environments.

ALargePartofJDO'sPersistenceServiceisTransparent

WhenusingJDO,theapplicationprogrammerdoesnotwritepersistencerelatedcodeinthe

applicationdataclassesthesearetheclassesthatdefinetheobjectsthathavepersistentstate.

Instead,theprogrammercreatestheapplicationdataclassesasifpersistencewerenotanissue.He

declaresthefieldsthatcontaintheobject'sstateandwritesthemethodstoaccessandmodifythe

stateoftheobjectinmemory.

JDOrequiresanenhancementstepforallapplicationdataclasses.TheJDOvendorsuppliesatool,

calledtheenhancer,thattheprogrammerusestoaddthepersistencerelatedcodetoapplicationdata

classes.Asaresultofenhancement,JDOcanmanagetheapplicationdataobjectsaspersistent

objects.Becauseenhancementusuallyoccursaftercompilation,persistencerelatedcodeisusually

notvisibleinthesourcecodeoftheapplicationdataclasses.

Transparentpersistenceispowerfulbecauseitrequiresnocodingbytheapplicationprogrammerand

because

it

imposes

few

design

and

coding

constraints.

When

an

application

uses

JDO,

persistence

codeiseffectivelyabsentinthesourcecodeofapplicationdataclasses.Yet,atruntime,thedata

objectsarealive.Theycanbefetchedfromthedatastorebyqueriesoridentity.Ifonepersistent

objectreferencesanother,thereferenceisinstantiatedtransparentlywhenused.Whenatransaction

isactive,thedataobject'spersistentstateistransactionallyconsistentwiththedatastore,and

modificationsmadetoitwillbereflectedinthedatastorewhenthetransactioniscommitted.

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2.3. JavaTransactionAPI(JTA)DistributedtransactionservicesinEnterpriseJavamiddlewareinvolvefiveplayers:

Thetransactionmanager

Theapplication

server

Theresourcemanager

Theapplicationprogramand

Thecommunicationresourcemanager

Eachoftheseplayerscontributestothedistributedtransactionprocessingsystembyimplementing

differentsetsoftransactionAPIsandfunctionalities.

Atransactionmanagerprovidestheservicesandmanagementfunctionsrequiredtosupport

transactiondemarcation,

transactional

resource

management,

synchronization,

and

transaction

contextpropagation.

Anapplicationserver(orTPmonitor)providestheinfrastructurerequiredtosupporttheapplication

runtimeenvironmentwhichincludestransactionstatemanagement.Anexampleofsuchan

applicationserverisanEJBserver.

Aresourcemanager(througharesourceadapter1)providestheapplicationaccesstoresources.The

resourcemanagerparticipatesindistributedtransactionsbyimplementingatransactionresource

interfaceusedbythetransactionmanagertocommunicatetransactionassociation,transaction

completionandrecoverywork.Anexampleofsucharesourcemanagerisarelationaldatabaseserver.

Acomponentbasedtransactionalapplicationthatisdevelopedtooperateinamodernapplication

serverenvironmentreliesontheapplicationservertoprovidetransactionmanagementsupport

throughdeclarativetransactionattributesettings.Anexampleofthistypeofapplicationsisan

applicationdevelopedusingtheindustrystandardEnterpriseJavaBeans(EJB)component

architecture.Inaddition,someotherstandaloneJavaclientprogramsmaywishtocontroltheir

transactionboundariesusingahighlevelinterfaceprovidedbytheapplicationserverorthe

transactionmanager.

Acommunicationresourcemanager(CRM)supportstransactioncontextpropagationandaccessto

thetransactionserviceforincomingandoutgoingrequests.TheJTAdocumentdoesnotspecify

requirementspertained

to

communication.

Fromthetransactionmanagersperspective,theactualimplementationofthetransaction

servicesdoesnotneedtobeexposed;onlyhighlevelinterfacesneedtobedefinedtoallowtransaction

demarcation,resourceenlistment,synchronizationandrecoveryprocesstobedrivenfromtheusersof

thetransactionservices.ThepurposeofJTAistodefinethelocalJavainterfacesrequiredforthe

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transactionmanagertosupporttransactionmanagementintheJavaenterprisedistributedcomputing

environment.

RelationshiptoOtherJavaAPIs

EnterpriseJavaBeans

TheEnterpriseJavaBeansarchitecturerequiresthatanEJBContainersupportapplicationlevel

transactiondemarcation

by

implementing

the

javax.transaction.UserTransaction

interface.

The

UserTransactioninterfaceisintendedtobeusedbyboththeEJBBeanimplementer(for

TX_BEAN_MANAGEDBeans)andbytheclientprogrammerwhowantstoexplicitlydemarcate

transactionboundarieswithinprogramsthatarewrittenintheJavaprogramminglanguage.


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JDBC2.0StandardExtensionAPI

OneofthenewfeaturesincludedintheJDBC2.0ExtensionSpecificationissupportfordistributed

transactions.TwonewJDBCinterfaceshavebeencreatedforJDBCdriverstosupportdistributed

transactionsusingtheJavaTransactionAPIsXAResourceinterface.ThenewJDBC2.0interfacesare

javax.sql.XAConnectionand

javax.sql.XADataSource.

A

JDBC

driver

that

supports

distributed

transactionsimplementsthejavax.transaction.xa.XAResourceinterface,thejavax.sql.XAConnection

interface,andthejavax.sql.XADataSourceinterface.

JavaMessageService

TheJavaTransactionAPImaybeusedbyaJavaMessageServiceprovidertosupportdistributed

transactions.AJMSproviderthatsupportstheXAResourceinterfaceisabletoparticipateasaresource

managerinadistributedtransactionprocessingsystemthatusesatwophasecommittransaction

protocol.Inparticular,aJMSproviderimplementsthejavax.transaction.xa.XAResourceinterface,the

javax.jms.XAConnectionandthejavax.jms.XASessioninterface.

JavaTransactionService

JavaTransactionService(JTS)isaspecificationforbuildingatransactionmanagerwhichsupportsthe

JTAinterfacesatthehighlevelandthestandardJavamappingoftheCORBAObjectTransaction

Service1.1specificationatthelowlevel.JTSprovidestransactioninteroperabilityusingtheCORBA

standardIIOPprotocolfortransactionpropagationbetweenservers.JTSisintendedforvendorswho

providethetransactionsysteminfrastructureforenterprisemiddleware.

Documents

Adoption of Latest Frameworks & APIs for the development of Enterprise Application in the Software Industry using Java Platform