New riders java for the web with servlets JSP and EJB a developers guide to J2EE solutions apr 2002 ISBN 073571195x

JavafortheWebwithServlets,JSP,and
EJB:ADeveloper'sGuidetoJ2EE
Solutions
ByBudiKurniawan


Publisher :NewRidersPublishing
PubDate :April12,2002
ISBN :0-7357-1195-X
Pages :976



JavafortheWebwithServlets,JSPandEJBistheonebookyou
needtomasterJavawebprogramming.Itcoversallthe
technologiesneededtoprogramwebapplicationsinJavausing
Servlets2.3,JSP1.2,EJB2.0andclient-sideprogrammingwith
JavaScript.Thesetechnologiesareexplainedinthecontextof
real-worldprojects,suchasane-commerceapplication,a
documentmanagementprogram,fileuploadandprogrammable
filedownload,andanXML-basedonlinebookproject.


Tableof
•
Contents Inadditiontoexcellentcontent,thisbookincludeslicensesto
• Examples twoJavawebcomponentsfromBrainySoftware.com.You

receiveafulllicenseoftheProgrammableFileDownload
componentforcommercialandnon-commercialdeployment.
Youarealsograntedtoalicensetodeploytheauthor'spopular

FileUploadbeanfornon-commercialuse,whichhasbeen
licensedbytheFortune500companyCommerceOneand
purchasedbymajorcorporationssuchasSaudiBusiness
Machine,Ltd.andBaxterHealthcareCorporation.

777
Copyright


AbouttheAuthor



AbouttheTechnicalReviewers



Acknowledgments



TellUsWhatYouThink



Introduction



TheHypertextTransferProtocol(HTTP)

SystemArchitecture



Java2,EnterpriseEdition(J2EE)



DevelopingWebApplicationsinJava



OverviewofPartsandChapters







PartI:BuildingJavaWebApplications
Chapter1.TheServletTechnology



TheBenefitsofServlets

ServletApplicationArchitecture



HowaServletWorks



TheTomcatServletContainer



SixStepstoRunningYourFirstServlet



Summary




Chapter2.InsideServlets



Thejavax.servletPackage

AServlet'sLifeCycle



ObtainingConfigurationInformation



PreservingtheServletConfig



TheServletContext



SharingInformationAmongServlets



RequestsandResponses



TheGenericServletWrapperClass



CreatingThread-SafeServlets

Summary




Chapter3.WritingServletApplications



TheHttpServletClass



TheHttpServletRequestInterface



HttpServletResponse



SendinganErrorCode



SendingSpecialCharacters

BufferingtheResponse



PopulatingHTMLElements



RequestDispatching



Summary




Chapter4.AccessingDatabaseswithJDBC



Thejava.sqlPackage



FourStepstoGettingtotheDatabase

ADatabase-BasedLoginServlet



TheSingleQuoteFactor



InsertingDataintoaTablewithRegistrationServlet



DisplayingAllRecords



SearchPage



AnOnlineSQLTool



ShouldIKeeptheConnectionOpen?



Transactions

ConnectionPooling



Summary




Chapter5.SessionManagement



WhatIsSessionManagement?



URLRewriting



HiddenFields



Cookies

SessionObjects



KnowingWhichTechniquetoUse



Summary




Chapter6.ApplicationandSessionEvents



ListeningtoApplicationEvents



ListeningtoHttpSessionEvents



Summary

Chapter7.ServletFiltering



AnOverviewoftheAPI



ABasicFilter



MappingaFilterwithaURL



ALoggingFilter



FilterConfiguration



AFilterthatChecksUserInput

FilteringtheResponse



FilterChain



Summary




Chapter8.JSPBasics



What'sWrongwithServlets?



RunningYourFirstJSP



HowJSPWorks

TheJSPServletGeneratedCode



TheJSPAPI



TheGeneratedServletRevisited



ImplicitObjects



Summary




Chapter9.JSPSyntax



Directives



ScriptingElements

StandardActionElements




Comments



ConvertingintoXMLSyntax



Summary




Chapter10.DevelopingJSPBeans



CallingYourBeanfromaJSPPage



ABriefTheoryofJavaBeans

MakingaBeanAvailable



AccessingPropertiesUsingjsp:getPropertyandjsp:setProperty



SettingaPropertyValuefromaRequest



JavaBeansCodeInitialization



TheSQLToolBeanExample



Summary




Chapter11.UsingJSPCustomTags

WritingYourFirstCustomTag



TheRoleoftheDeploymentDescriptor



TheTagLibraryDescriptor



TheCustomTagSyntax



TheJSPCustomTagAPI



TheLifeCycleofaTagHandler



Summary

Chapter12.ProgrammableFileDownload



KeystoProgrammableFileDownload



UsingtheBrainysoftware.comFileDownloadBean



Summary




Chapter13.FileUpload



TheHTTPRequest



Client-SideHTML

HTTPRequestofanUploadedFile



UploadingaFile



FileUploadBean



MultipleFileUpload



Summary




Chapter14.SecurityConfiguration



ImposingSecurityConstraints



AllowingMultipleRoles

Form-BasedAuthentication



DigestAuthentication




MethodsRelatedtoSecurity



RestrictingCertainMethods



Summary




Chapter15.Caching



CachingDataintoaTextFile

CachinginMemory



Summary




Chapter16.ApplicationDeployment



ApplicationDirectoryStructure



DeploymentDescriptor



ServletAliasandMapping



JSPAliasandMapping

PackagingandDeployingaWebApplication



Summary




Chapter17.ArchitectingJavaWebApplications



Model1Architecture



Model2Architecture



Summary




Chapter18.DevelopingE-CommerceApplications

ProjectSpecification



TheDatabaseStructure



PageDesign



Preparation



ApplicationDesign



BuildingtheProject



Summary

Chapter19.XML-BasedE-Books



TheTableofContents



TranslatingXMLintotheObjectTree



TheProject



Pre-RendertheTableofContents



Summary




Chapter20.Web-BasedDocumentManagement

TheDocmanProject



Summary








PartII:Client-SideProgrammingwithJavaScript



Chapter21.JavaScriptBasics



IntroductiontoJavaScript



AddingJavaScriptCodetoHTML



JavaScriptObjectModel

EventHandler



WindowandStringObjects



Summary




Chapter22.Client-SideProgrammingBasics



CheckingWhetherJavaScriptIsEnabled



HandlingJavaScript-UnawareBrowsers



HandlingDifferentVersionsofJavaScript

IncludingaJavaScriptFile



CheckingtheOperatingSystem



CheckingtheBrowserGeneration



CheckingtheBrowserType



CheckingtheBrowserLanguage



HandlingDynamicVariable-Names



Summary

Chapter23.Redirection



AnticipatingFailedRedirection



UsingtheRefreshMetaTag



UsingthelocationObject



GoingBacktothePreviousPage



MovingForward



NavigationwithaSELECTElement



Summary

Chapter24.Client-SideInputValidation



TheisEmptyFunction



ThetrimFunction



ThetrimAllFunction



TheisPositiveIntegerFunction



TheisValidPhoneNumberFunction



TheisMoneyFunction

TheisUSDateandisOZDateFunctions



ConvertingDateFormats



DataTypeConversion:StringtoNumeric




DataTypeConversion:NumerictoString



UsingtheValidationFunctions



Summary




Chapter25.WorkingwithClient-SideCookies

CreatingCookieswitha<META>Tag



CreatingCookieswithdocument.cookie



CreatingCookieswiththesetCookieFunction



ReadingCookiesontheBrowser



DeletingaCookieontheBrowser



CheckingIftheBrowserCanAcceptCookiesUsingJavaScript



CheckingIftheBrowserAcceptsCookiesWithoutJavaScript

Summary




Chapter26.WorkingwithObjectTrees



TheArrayObject



TrulyDeletinganArrayElement



CreatinganObject



AHierarchyofObjects



Summary

Chapter27.ControllingApplets



IsJavaEnabled?



IstheAppletReady?



ResizinganApplet



CallinganApplet'sMethod



GettinganApplet'sProperty



SettinganAppletProperty



UsingJavaClassesDirectly

Applet-to-JavaScriptCommunication



AccessingtheDocumentObjectModelfromanApplet



InvokingJavaScriptFunctionsfromanApplet



EvaluatingaJavaScriptStatementfromanApplet



SettingtheAppletParameter



Applet-to-AppletCommunicationThroughJavaScript



DirectApplet-to-AppletCommunication

Summary






PartIII:DevelopingScalableApplicationswithEJB
Chapter28.EnterpriseJavaBeans




WhatIsanEnterpriseJavaBean?



BenefitsofEJB



EJBApplicationArchitecture



TheSixEJBRoles



TypesofEnterpriseBeans

WritingYourFirstEnterpriseBean



EJBExplained



WritingClientApplications



CreatingaBean'sInstance



Summary




Chapter29.TheSessionBean

WhatIsaSessionBean?



StatefulandStatelessSessionBeans



WritingaSessionBean



TheTassieOnlineBookstoreExample



Summary




Chapter30.EntityBeans



WhatIsanEntityBean?



TheRemoteInterface

TheHomeInterface



ThePrimaryKeyClass



TheEntityBean



TwoTypesofEntityBeans



WritingaBMPEntityBean



WritingaCMPEntityBean



Summary

Chapter31.EJBQueryLanguage



EJBQLSyntax



EJBQLBNF



Summary




Chapter32.JavaMessageService



IntroductiontoMessaging



TheJMSAPI

TheJMSAPIMessagingDomains



TheJMSObjectModel



WritingJMSClients




Summary




Chapter33.Message-DrivenBeans



WhatIsaMessage-DrivenBean?



TheApplicationProgrammingInterface

WritingaMessage-DrivenBean



Summary






PartIV:Appendixes
AppendixA.TomcatInstallationandConfiguration



TomcatInstallation



TomcatDirectories



ChangingthePort



ConstructingaJSPApplication

AppendixB.Thejavax.servletPackageReference



Interfaces



Classes



Exceptions



Interfaces



Classes



Exceptions

AppendixC.Thejavax.servlet.httpPackageReference



Interfaces



Classes




AppendixD.Thejavax.servlet.jspPackageReference



Interfaces



Classes




AppendixE.Thejavax.servlet.jsp.tagextPackageReference

Interfaces



Classes




AppendixF.JBossInstallationandConfiguration



SystemRequirements



InstallingJBoss



DirectoryStructure




Configuration

RunningJBoss



Deployment



JBossandTomcat



Summary




AppendixG.RelatedResources



J2EE



Servlet

JSP





TagLibrary



Servlet/JSPContainers



JDBC



JNDI



JMS



EJB

J2EEServer




AppendixH.What'sOntheCD-ROM?



ReadThisBeforeOpeningtheSoftware



GNULESSERGENERALPUBLICLICENSE



GNULESSERGENERALPUBLICLICENSE



NOWARRANTY




Copyright
Copyright©2002byNewRidersPublishing

FIRSTEDITION:April,2002
Allrightsreserved.Nopartofthisbookmaybereproducedortransmittedinany
formorbyanymeans,electronicormechanical,includingphotocopying,
recording,orbyanyinformationstorageandretrievalsystem,withoutwritten
permissionfromthepublisher,exceptfortheinclusionofbriefquotationsina
review.
LibraryofCongressCatalogCardNumber:2001093802
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Interpretationoftheprintingcode:Therightmostdouble-digitnumberisthe
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printingofthebookoccurredin2002.

Trademarks
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totheaccuracyofthisinformation.Useofaterminthisbookshouldnotbe
regardedasaffectingthevalidityofanytrademarkorservicemark.

WarningandDisclaimer
ThisbookisdesignedtoprovideinformationaboutJavaforthewebworking
withservlets,jsp,andejb.Everyefforthasbeenmadetomakethisbookas
completeandasaccurateaspossible,butnowarrantyoffitnessisimplied.


Theinformationisprovidedonanas-isbasis.TheauthorsandNewRiders
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AbouttheAuthor
BudiKurniawanisanITconsultantspecializinginInternetandobject-oriented
programmingandhastaughtbothJavaandMicrosofttechnologies.Heisthe
authorofthemostpopularJavaUploadbeanfromBrainySoftware.com,which
islicensedbyCommerceOne(NASDAQ:CMRC)andpurchasedbymajor
corporations,suchasSaudiBusinessMachineLtd(www.sbm.com.sa),Baxter
HealthcareCorporation(www.baxter.com),andothers.
BudihasaMastersofResearchdegreeinElectricalEngineeringfromSydney
University,Australia.Hisresearchtopicwasondigitalimageprocessing.Budi
haswrittenanumberofcomputerbooks,aswellaspublishedarticlesformore
than10publications—includingprestigiousJavamagazines,suchasJava-Pro,
JavaWorld,JavaReport,andO'Reilly'swww.onjava.com.Budiisnowthe
weeklycontributorfortheServlets/JSPsectionofJavaInsightandcanbe
contactedat


AbouttheTechnicalReviewers
Thesereviewerscontributedtheirconsiderablehands-onexpertisetotheentire
developmentprocessforJavafortheWebwithServlets,JSP,andEJB.Asthe
bookwasbeingwritten,thesededicatedprofessionalsreviewedallthematerial
fortechnicalcontent,organization,andflow.Theirfeedbackwascriticalto
ensuringthatJavafortheWebwithServlets,JSP,andEJBfitsourreader'sneed
forthehighest-qualitytechnicalinformation.

ChrisCraneiscurrentlyteachingatMemorialUniversityofNewfoundland,
whereheoffersprogrammingcoursescoveringawiderangeofprogramming
conceptsandlanguages,suchasdesktopapplicationdevelopmentusingVisual
Basic,C++,andJavatoDistributedEnterpriseApplicationsusingEJB,and
Microsoft.NetWebServices.Outsideofhisteachingduties,Chrisrunshisown
consultingcompany,developingEnterprise-levelapplicationsforcompanies
throughoutCanadaandtheU.S.HeisalsocertifiedasanMCP,MCSD,MCT,
CCNA,CCAIandSCP/Java2.
LanWujoinedPersistenceSoftwareinSiliconValleyafterreceivingher
Master'sDegreeinComputerScience.Lan'seffortsatPersistencewerefocused
onJavawithEJBs.Later,shemovedontomyCFOCorporation,wheresheis
involvedwiththedesigninganddevelopingoftheautomationsystem.Sheis
nowwithBlueMartiniSoftwareandresponsibleforautomationwithJavaand
webprogramming.


Acknowledgments
Somanypeopleareinvolvedintheprocessofdeliveringthisbook,without
whomthisbookwouldneverbeareality.
FirstandforemostI'dliketothankDeborahHittel-Shoaf,myAcquisitions
Editor,forherprofessionalismandflexibility.Really,shetakescareofher
authors.
ThanksalsogotoGrantMunroe,myDevelopmentEditor,forhispatienceand
forgettingallthechapterstogether.
Twoexcellenteditorshelpedmewithtechnicalreviewandprovidedinvaluable
feedbackandmadethecontentmuch,muchbetter:LanWuandChrisCrane.I
wouldalsoliketothankthem.
Finally,allthefolksatNewRiderswhohelpedmewiththediagrams,
proofreading,index,layout,andsoon.Thankyou.
SpecialthanksgotomybestfriendKenforprovidingmewithexcellent

accommodation(andInternetaccess)duringmyChristmasvisittoVancouver,
BC—afterbeingknockedoutexhaustedinthemiddleofthewritingofthis
book.Hispartyandthetoursrefreshedme.


TellUsWhatYouThink
Asthereaderofthisbook,youarethemostimportantcriticandcommentator.
Wevalueyouropinionandwanttoknowwhatwe'redoingright,whatwecould
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AstheAssociatePublisherforNewRidersPublishing,Iwelcomeyour
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PleasenotethatIcannothelpyouwithtechnicalproblemsrelatedtothetopicof
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Whenyouwrite,pleasebesuretoincludethisbook'stitleandauthoraswellas
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Fax:

317-581-4663

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StephanieWall
AssociatePublisher
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Indianapolis,IN46290USA


Introduction
TheInternetisstillyoungandvulnerable.Therefore,itshistoryisnotalengthy
one.Thewebstartedwheneverythingwasjuststaticpages.Unlessyouarea
six-year-oldwhizkidreadingthisbookbecauseyouaremoreinterestedinJava
webprogrammingthanPlayStation2,itismostlikelythatyouexperiencedthe
timewhenawebsitewasnomorethanHTMLpages.Intheearlierdays,aweb
sitehadatmostonepageanditmoreoftenthannotwascalledahomepage.
Theterms"Internetapplication"or"webapplication"werecoinedwhen
dynamiccontentwasintroduced.Looselyinterpreted,awebapplicationisaweb
sitewhosecontentsaregenerateddynamicallybeforebeingsenttothebrowser.
YoushouldfirstunderstandhowtheInternetworksbeforelearninghowaweb
applicationworks.
WhenyousurftheInternet,youbasicallyrequestforacertainfilelocatedina
particularcomputerinthelocationyouspecifyintheUniformResourceLocator
(URL).Thecomputerwherethefileisstorediscalledthewebserver.This
computer'smainfunctionistoserveanybodyontheInternetwhorequestsfiles
ithosts.Becauseyouneverknowwhenauserwillvisitanduseyourweb
application,yourwebservermustbeupandrunningallthetime.
WhenyouclickortypeinaURLintheLocationorAddressboxofyour
browser,thefollowingthingshappen:
TheclientbrowserestablishesaTCP/IPconnectionwiththeserver.
Thebrowsersendsarequesttotheserver.

Theserversendsaresponsetotheclient.
Theserverclosestheconnection.
Notethataftersendingtherequestedpagetothebrowser,theserveralways
closestheconnection,whetherornottheuserrequestsotherpagesfromthe
server.


WhatIsHappeningintheIndustry
SincetheemergenceoftheInternet,webtechnologieshavebecomemoreand
moreimportant,andwebapplicationsaremoreandmorecommon.Theuseofa
webbrowserisnolongerrestrictedtosurfingstaticpagesontheInternet.Itis
nowverycommonplacetoseeawebbrowserusedasanapplication'sclient.
Whatthismeansis,somepeoplebelieve,whoevercontrolstheInternetcontrols
thefutureofcomputing—oreventhefutureitself.Attheveryleast,the
evidencehasbeendemonstratedbythestrugglesofafewcompaniestograbthe
webbrowsers'dominationinthelate1990s.Asthebestexample,Microsoft
Corporation—stillthenumberoneplayerinthesoftwarebusinessupuntilnow
—feltitwasimportanttohaveeveryoneontheplanetusingitsInternet
Explorerbrowser.That'swhyitexerteditsoverwhelmingpowerinsoftware
technologytocreatethefastestandsmartestbrowsereveranddistributeitfor
free.WiththesurrenderofNetscape,Microsofthaswonthebattleofbrowsers.
Inthenextfiveyears,itisstillhardtoimaginehowanybrowsercouldsurpass
thepopularityofMicrosoftInternetExplorer.
Ontheserverside,it'sadifferentstory,though.Thewarisfarfromover.
Microsoftcan'tpushitsservertechnologyaseasilyasitforcedNetscapetogive
up.Infact,themostpopularservertechnologyisJava.Tobeprecise,it'sSun
Microsystems'Java2,EnterpriseEdition(J2EE).Microsoftisstilltryingto
catchupwithitsnew.NETinitiativethatisareplacementofitsprevious
DistributedinterNetApplications(DNA)platformfordevelopingenterprise
applications.Releasedinearly2002,.NETwillcollidehead-onwithJ2EE.The

nextfewyearswillstillseeJ2EEand.NETasthetwocompetingserver
technologies.Rightnow,it'sstilltooprematuretopredictwhowillcomeoutthe
winner.
Strategy-wise,MicrosofttakesafardifferentapproachfromSunintryingto
win.Microsoftprovidesasingle-vendorsolution,sellingfromtheoperating
systemtothedatabaseserver.J2EE,ontheotherhand,issupportedbythe
entireindustry.(ForalistofvendorswhoprovideJ2EEcompliantservers,see
AppendixG,"RelatedResources.")AnalystshavetriedtocompareJ2EEand
.NETinmanywhitepaperspublishedontheInternet.Unfortunately,the
conclusionsvaryagreatdeal.TofindoutmoreabouthowJ2EEand.NET
compare,youcanconsultthefollowingarticles,whichareavailableonline:
Microsoft.NETvs.J2EE:HowDoTheyStackUp?,


/>Java2EnterpriseEdition(J2EE)versusThe.NETPlatform:TwoVisions
foreBusiness,
DotNet.doc
J2EEvs.Microsoft.NET:AComparisonofBuildingXML-BasedWeb
Services,
/>CompareMicrosoft.NETtoJ2EETechnology,
/>Atthispoint,youshouldhavegottenthebigpictureofwhatishappeninginthe
industry.Youcanfindoutmoreabout.NETat.J2EE
ispresentedinthesection,"Java2."
Alsonotethatthetermwebservercanalsobeusedtorefertothesoftware
packageusedinthewebservercomputertohandlerequestsandrespondto
them.Infact,throughoutthisbook,thetermwebserverisusedtorefertothis
software.
Thefirstpopularwebserver—NCSAHTTPd—wascreatedbyRobMcCoolat
theNationalCenterforSupercomputingApplications.And,McCool'sinvention
wasreallycoolbecauseithelpedtheInternetrevolutionizeourlivesandwent

ontobecomethefoundationfortheApachewebserver—themostusedweb
serverontheInternettoday.

TheHypertextTransferProtocol(HTTP)
HTTPistheprotocolthatallowswebserversandbrowserstoexchangedata
overtheweb.Itisarequestandresponseprotocol.Theclientrequestsafileand
theserverrespondstotherequest.HTTPusesreliableTCPconnections—by
defaultonTCPport80.HTTP(currentlyatversion1.1atthetimeofthis
writing)wasfirstdefinedinRFC2068.ItwasthenrefinedinRFC2616,which
canbefoundat />

InHTTP,it'salwaystheclientwhoinitiatesatransactionbyestablishinga
connectionandsendinganHTTPrequest.Theserverisinnopositiontocontact
aclientormakeacallbackconnectiontotheclient.Eithertheclientortheserver
canprematurelyterminateaconnection.Forexample,whenusingaweb
browseryoucanclicktheStopbuttononyourbrowsertostopthedownload
processofafile,effectivelyclosingtheHTTPconnectionwiththewebserver.

HTTPRequests
AnHTTPtransactionbeginswitharequestfromtheclientbrowserandends
witharesponsefromtheserver.AnHTTPrequestconsistsofthreecomponents:
Method——URI—Protocol/Version
Requestheaders
Entitybody
AnexampleofanHTTPrequestisthefollowing:

GET/servlet/default.jspHTTP/1.1
Accept:text/plain;text/html
Accept-Language:en-gb
Connection:Keep-Alive

Host:localhost
Referer:http://localhost/ch8/SendDetails.htm
User-Agent:Mozilla/4.0(compatible;MSIE4.01;Windows
Content-Length:33
Content-Type:application/x-www-form-urlencoded
Accept-Encoding:gzip,deflate
LastName=Franks&FirstName=Michael
Themethod—URI—protocolversionappearsasthefirstlineoftherequest.


GET/servlet/default.jspHTTP/1.1
whereGETistherequestmethod,/servlet/default.jsprepresents
theURIandHTTP/1.1theProtocol/Versionsection.
Therequestmethodwillbeexplainedinmoredetailsinthenextsection,"HTTP
requestMethods."
TheURIspecifiesanInternetresourcecompletely.AURIisusuallyinterpreted
asbeingrelativetotheserver'srootdirectory.Thus,itshouldalwaysbeginwith
aforwardslash/.AURLisactuallyatypeofURI(see
TheProtocolversionrepresentstheversion
oftheHTTPprotocolbeingused.
Therequestheadercontainsusefulinformationabouttheclientenvironmentand
theentitybodyoftherequest.Forexample,itcouldcontainthelanguagethe
browserissetfor,thelengthoftheentitybody,andsoon.Eachheaderis
separatedbyacarriagereturn/linefeed(CRLF)sequence.
Betweentheheadersandtheentitybody,thereisablankline(CRLF)thatis
importanttotheHTTPrequestformat.TheCRLFtellstheHTTPserverwhere
theentitybodybegins.InsomeInternetprogrammingbooks,thisCRLFis
consideredthefourthcomponentofanHTTPrequest.
InthepreviousHTTPrequest,theentitybodyissimplythefollowingline:

LastName=Franks&FirstName=Michael
TheentitybodycouldeasilybecomemuchlongerinatypicalHTTPrequest.

HTTPrequestMethods
EachHTTPrequestcanuseoneofthemanyrequestmethodsasspecifiedinthe
HTTPstandards.TheHTTP1.1requestmethodsandthedescriptionsofeach
methodaregiveninTableI.1.
TableI.1.HTTP1.1requestMethods


Method

Description

GET

GETisthesimplest,andprobably,mostusedHTTPmethod.GETsimply
retrievesthedataidentifiedbytheURL.IftheURLreferstoascript(CGI,
servlet,andsoon),itreturnsthedataproducedbythescript.

HEAD

TheHEADmethodprovidesthesamefunctionalityasGET,butHEADonly
returnsHTTPheaderswithoutthedocumentbody.

POST

LikeGET,POSTisalsowidelyused.Typically,POSTisusedinHTML
forms.POSTisusedtotransferablockofdatatotheserverintheentity
bodyoftherequest.

OPTIONS TheOPTIONSmethodisusedtoqueryaserveraboutthecapabilitiesit
provides.Queriescanbegeneralorspecifictoaparticularresource.

PUT

ThePUTmethodisacomplementofaGETrequest,andPUTstoresthe
entitybodyatthelocationspecifiedbytheURI.ItissimilartothePUT
functioninFTP.

DELETE TheDELETEmethodisusedtodeleteadocumentfromtheserver.The
documenttobedeletedisindicatedintheURIsectionoftherequest.

TRACE

TheTRACEmethodisusedtotractthepathofarequestthroughfirewall
andmultipleproxyservers.TRACEisusefulfordebuggingcomplex
networkproblemsandissimilartothetraceroutetool.

Warning
HTTP1.0onlyhasthreerequestmethods:GET,HEAD,andPOST.

Ofthesevenmethods,onlyGETandPOSTarecommonlyusedinanInternet
application.


HTTPResponses
Similartorequests,anHTTPresponsealsoconsistsofthreeparts:
Protocol—Statuscode——Description
Responseheaders

Entitybody
ThefollowingisanexampleofanHTTPresponse:

HTTP/1.1200OK
Server:Microsoft-IIS/4.0
Date:Mon,3Jan199813:13:33GMT
Content-Type:text/html
Last-Modified:Mon,11Jan199813:23:42GMT
Content-Length:112
<HTML>
<HEAD>
<TITLE>HTTPResponseExample</TITLE></HEAD><BODY>
WelcometoBrainySoftware
</BODY>
</HTML>
Thefirstlineoftheresponseheaderissimilartothefirstlineoftherequest
header.ThefirstlinetellsyouthattheprotocolusedisHTTPversion1.1,the
requestsucceeded(200=success),andthateverythingwentokay.
Theresponseheaderscontainusefulinformationsimilartotheheadersinthe
request.TheentitybodyoftheresponseistheHTMLcontentoftheresponse
itself.TheheadersandtheentitybodyareseparatedbyasequenceofCRLFs.

SystemArchitecture


Thissectionismeanttogiveyouthebigpictureofasoftwareapplicationsystem
utilizingJavaorothertechnologies.Thissectiontakesthecommonapproachof
introducingsoftwaresystemarchitecturebyobservinghowithasevolved.
Awell-designedsoftwareapplicationispartitionedintoseparatelogicalparts
calledlayers.Eachlayerhasadifferentresponsibilityintheoverallarchitecture.

Theselayersarepurelyabstractions,anddonotcorrespondtophysical
distribution.
Typicallayersinasoftwaresystemareasfollows:
Presentationlayer.Inthislayerarepartsthathandletheuserinterfaceand
userinteraction.
Businesslogiclayer.Thislayercontainscomponentsthathandlethe
programminglogicoftheapplication.
Datalayer.Thislayerisusedbythebusinesslogiclayertopersiststate
permanently.Thislayernormallyconsistsofoneormoredatabaseswhere
dataisstored.However,othertypesofdatastorecouldalsobeused.For
example,itisnowverycommontouseXMLdocumentsasstoragetokeep
data.

TheTwo-TierArchitecture
Atwo-tieredapplicationisasimpleclient-serverapplicationinwhichthe
processingworkloadfallsontotheclientcomputer'sshouldersandtheserver
simplyactsasatrafficcontrollerbetweentheclientandthedata.Theterm"fat
client"forthistypeofarchitectureisduetothebulkofprocessingrequirements
attheclientside.Inthisarchitecture,thepresentationlayerandthebusiness
logiclayerarehostedinonetierandthedatalayerisonanothertier.FigureI.1
showsatwo-tierarchitecture.
FigureI.1.Atwo-tieredapplication.