jsp技术网站设计外文翻译Word下载.docx

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EarlydynamicpagesmainlyCGI（CommonGatewayInterface,publicGatewayInterface）technology,youcanusedifferentlanguagesoftheCGIprograms,suchasVB,C

/C++orDelphi,andsoon.ThoughthetechnologyofCGIisdevelopedandpowerful,becauseofdifficultiesinprogramming,andlowefficiency,modifycomplexshortcomings,

itisgraduallybeingreplacedbythetrend.Ofallthenewtechnology,JSP/Servletwithmoreefficientandeasytoprogram,morepowerful,moresecureandhasagoodportability,theyhavebeenmanypeoplebelievethatthefutureisthemostdynamicsiteofthefuturedevelopmentoftechnology.

SimilartoCGI,Servletsupportrequest/responsemodel.Whenacustomersubmitarequesttotheserver,theserverpresentedtherequestServlet,Servletresponsibleforhandlingrequestsandgeneratearesponse,andthengavetheserver,andthenfromtheserversenttothecustomer.AndtheCGIisdifferent,Servletnotgenerateanewprocess,butwithHTTPServeratthesameprocess.Itthreadsthroughtheuseoftechnology,reducetheservercosts.Servlethandlingoftherequestprocessisthis:

Whenreceivedfromtheclient'

srequest,callingservicemethods,themethodofServletarrivalofthefirstjudgementiswhattypeofrequest（GET/POST/HEAD…）,thencallstheappropriatetreatment（DoGet/doPost/doHead…）andgeneratearesponse.

Althoughsuchacomplex,infact,simplysaidtoServletisaJavaclass.AndthegeneralcategoryofthedifferenceisthatthistypeoperatinginaServletcontainer,whichcanprovidesessionmanagementandtargetedlife-cyclemanagement.SothatwhenyouusetheServlet,youcangetallthebenefitsoftheJavaplatform,includingthesafetyofthemanagement,useJDBCaccessthedatabaseandcross-platformcapability.Moreover,Servletusingthread,andcandevelopmoreefficientWebapplications.

JSPtechnologyisakeyJ2EEtechnology,itatahigherlevelofabstractionofaServlet.

ItallowsconventionalstaticanddynamicHTMLcontentgeneratedbycombininganHTMLpagelookslike,butasaServlettorun.TherearemanycommercialapplicationserversupportJSPtechnology,suchasBEAWebLogic,IBMWebSphere,JRun,andsoon.JSPandServletusemorethansimple.IfyouhaveaJSPsupportforWebservers,andaJSPdocument,youcanputitFangdaoanystaticHTMLfilescanbeplaced,donothavetocompile,donothavetopack,donothavetoClassPathsettings,youcanvisitasordinaryWebItdidvisit,theserverwillautomaticallyhelpyoutodootherwork.

JSPdocumentlookslikeanordinarystaticHTMLdocument,butinsidecontainsanumberofJavacode.Ituses.Jspthesuffix,usedtotelltheserverthisdocumentinneedofspecialtreatment.WhenwevisitaJSPpage,thedocumentwillfirstbetranslatedintoa

JSPengineJavasourcefiles,isactuallyaServlet,andcompiler,andthen,likeotherServlet,fromServletenginetohandle.Servletengineofthistypeloading,handlingrequestsfromcustomers,andtheresultsreturnedtothecustomer,asshownbelow:

Figure1:

CallingtheprocessofJSPpages

Afteranothervisitthispagetothecustomer,aslongasthepapertherehavebeennochanges,JSPenginehasbeenloadeddirectlycalltheServlet.Ifyouhavealreadybeenmodified,itwillbeonceagaintheimplementationoftheaboveprocess,translate,compileandload.Infact,thisistheso-called"

firstpersontopunishment."

Becausewhenthefirstvisittotheimplementationofaseriesoftheaboveprocess,sowillspendsometimeaftersuchavisitwouldnot.

JavaservletsofferapowerfulAPIthatprovidesaccesstoalltheinformationabouttherequest,thesession,andtheapplication.combiningJSPwithservletsletsyouclearlyseparatetheapplicationlogicfromthepresentationoftheapplication;

inotherwords,itletsyouusethemostappropriatecomponenttypefortherolesofModel,ViewandController.

Servlets,Filters,andListeners

AservletisaJavaclassthatextendsaserverwithfunctionalityforprocessingarequestandproducingaresponse.It'

simplementedusingtheclassesandinterfacesdefinedbytheServletAPI.TheAPIconsistsoftwopackages:

thejavax.servletpackagecontainsclassesandinterfacesthatareprotocol-independent,whilethejavax.servlet.httppackageprovidesHTTP-specificextensionsandutilityclasses.

Whatmakesaservletaservletisthattheclassimplementsaninterfacenamedjavax.servlet.Servlet,eitherdirectlyorbyextendingoneofthesupportclasses.Thisinterfacedefinesthemethodsusedbythewebcontainertomanageandinteractwiththe

servlet.AservletforprocessingHTTPrequeststypicallyextendsthejavax.servlet.http.HttpServletclass.ThisclassimplementstheServletinterfaceandprovidesadditionalmethodssuitableforHTTPprocessing.

ServletLifecycle

Thewebcontainermanagesallaspectsoftheservlet'

slifecycle.Itcreatesaninstanceoftheservletclasswhenneeded,passesrequeststotheinstanceforprocessing,andeventuallyremovestheinstance.ForanHttpServlet,thecontainercallsthefollowingmethodsattheappropriatetimesintheservletlifecycle.

BesidesthedoGet（）anddoPost（）methods,therearemethodscorrespondingtotheotherHTTPmethods:

doDelete（）,doHead（）,doOptions（）,doPut（）,anddoTrace（）.Typicallyyoudon'

timplementthesemethods;

the HttpServletclassalreadytakescareofHEAD,OPTIONS,andTRACErequestsinawaythat'

ssuitableformostservlets,andtheDELETEandPUTHTTPmethodsarerarelyusedinawebapplication.

It'

simportanttorealizethatthecontainercreatesonlyoneinstanceof eachservlet.

Thismeansthattheservletmustbethreadsafe--abletohandlemultiplerequestsatthesametime,eachexecutingasaseparatethreadthroughtheservletcode.Withoutgettinglostindetails,yousatisfythisrequirementwithregardstoinstancevariablesifyoumodifythereferencedobjectsonlyintheinit（）anddestroy（）methods,andjustreadthemintherequestprocessingmethods.

CompilingandInstallingaServlet

Tocompileaservlet,youmustfirstensurethatyouhavetheJARfilecontainingallServletAPIclassesintheCLASSPATHenvironmentvariable.TheJARfileisdistributedwithallwebcontainers.Tomcatincludesitinafilecalledservlet.jar,locatedinthecommon/libdirectory.OnaWindowsplatform,youincludetheJARfileintheCLASSPATH.

.ReadingaRequest

OneoftheargumentspassedtothedoGet（）anddoPost（）methodsisanobjectthatimplementstheHttpServletRequestinterface.Thisinterfacedefinesmethodsthatprovideaccesstoawealthofinformationabouttherequest.

GeneratingaResponse

Besidestherequestobject,thecontainerpassesanobjectthatimplementstheHttpServletResponseinterfaceasanargumenttothedoGet（）anddoPost（）methods.Thisinterfacedefinesmethodsforgettingawriterorstreamfortheresponsebody.Italsodefinesmethodsforsettingtheresponsestatuscodeandheaders.

UsingFiltersandListeners

Theservletspecificationdefinestwocomponenttypesbesideservlets:

filtersandlisteners.ThesetwotypeswereintroducedintheServlet2.3specification,soifyou'

reusingacontainerthatdoesn'

tyetsupportthisversionofthespecification,I'

mafraidyou'

re

outofluck.

Filters

Afilterisacomponentthatcaninterceptarequesttargetedforaservlet,JSPpage,orstaticpage,aswellastheresponsebeforeit'

ssenttotheclient.Thismakesiteasytocentralizetasksthatapplytoallrequests,suchasaccesscontrol,logging,andchargingforthecontentortheservicesofferedbytheapplication.Afilterhasfullaccesstothebodyandheadersoftherequest andresponse,soitcanalso performvarioustransformations.OneexampleiscompressingtheresponsebodyiftheAccept-Languagerequestheaderindicatesthattheclientcanhandleacompressedresponse.

AfiltercanbeappliedtoeitheraspecificservletortoallrequestsmatchingaURLpattern,suchasURLsstartingwiththesamepathelementsorhavingthesameextension.

Listeners

Listenersallowyourapplicationtoreacttocertainevents.PriortoServlet2.3,youcouldhandleonlysessionattributebindingevents（triggeredwhenanobjectwasaddedorremovedfromasession）.Youcoulddothisbylettingtheobjectsavedasasessionattribute（using the HttpSession.setAttribute（） method）implement theHttpSessionBindingListenerinterface.Withthenewinterfacesintroducedinthe2.3versionofthespecification,