外文翻譯 外文資料和譯文

外文翻譯外文資料和譯文_文檔視界..

XX大學XXXXXXX

外文資料和譯文

專業(yè)：軟件工程

班級：軟件XXXXX

姓名：XXXXX

學號：XXXXXXXXXXXXXX

指導教師：XXXXXXXX

2009年12月17日

原文

1.1AJSPtechnologyoverview

Let'sbeginbytalkingalittleabouthowJSPpageswork.We'regoingtokeepitsimpleandfocusonsomeofthebasics.Formoreinformation,seeResourcesforlinkstoadditionalJSPtechnologyinformation.

Inthetraditionalsense,JSPpageslookverymuchlikeHTMLpages,withafewextratags.ThesetagsallowthedesignertoembedJavacode(notJavaScript)inthepageitself.AWebapplicationserver,liketheIBMWebSphereApplicationServer,willinterceptrequestsforJSPpages.It'stippedofftotheirexistencebythepage'sextension:.jsp(not.html).TheWebapplicationserverthenpreprocessestheJSPpage,takingouttheJSPtagsandanyembeddedJavacode,leavingonlytheHTML.TheextractedJSPtagsandembeddedJavacodeareusedtobuildaJavaservlet(JSPpageservlet)thatrunsthecodeandinsertstheresultsbackintotheoriginalpagewheretheJSPtagsusedtobe.TheresultispureHTML.TheJavaisstrippedoutandrunontheserverbeforetherequestingbrowserseesanyresult.

WecanapplythesameprincipletoanXMLpage.BeforetherequesteroftheJSPpagecontainingXMLeverseestheXML(beitabrowserorsomeotherB2Bapplication),theJavacodeisstrippedoutoftheJSPpageandusedtogenerateadditionalcontent,whichisinsertedbackintothepageatthepointswheretheJSPtagsusedtoreside.Thisfeaturegivesyoutheabilitytocontrolexactlywherenewcontentistobeinserted,downtothecharacter.

We'lllookathowtomakethisworkinaminute.First,let'sconsiderwhyyoumightwanttocreatedynamicXMLusingJSP.WhynotsimplywriteaJavaapplicationorservlettogeneratetheentiredocument?WhybotherwithJSPatall?Themostimportantreason,providingonlyportionsofanXMLdocumentaredynamic,isthatitmakessensenottoregeneratethat

staticcontentforeveryrequest.UsingaJSPpage,thestaticXMLwithinthepageactsasatemplatethatisfilledoutbythedynamiccontent.YourJavacodeistaskedwithgeneratingonlythecontentthatmightchangeovertime--amoreefficientapproach.

Asapracticalmatter,JSPpagesallowyoutoseparatetasksforwhichdifferentdeveloperswillberesponsible.Inparticular,theyallowyoutobetterseparatethedatafromtheview,allowingyoutoaddnewpresentationswithoutaffectingthelogic.ImaginehavingoneJavaservletthatperformsthebusinesslogicandredirectstheresultingdatatoanappropriateJSPpagebasedonthenatureoftherequest.Forexample,aservletmightredirectdatatoaJSPpagecontainingWMLwhenitdetectsaWAPphonebrowsermakingtherequest.ItcouldalsoredirectthedatatoaJSPpagecontainingHTMLforstandardbrowserrequests.

1.2BenefitsofJSP

JSPpagesaretranslatedintoservlets.So,fundamentally,anytaskJSPpagescanperformcouldalsobeaccomplishedbyservlets.However,thisunderlyingequivalencedoesnotmeanthatservletsandJSPpagesareequallyappropriateinallscenarios.Theissueisnotthepowerofthetechnology,itistheconvenience,productivity,andmaintainabilityofoneortheother.Afterall,anythingyoucandoonaparticularcomputerplatformintheJavaprogramminglanguageyoucouldalsodoinassemblylanguage.Butitstillmatterswhichyouchoose.

JSPprovidesthefollowingbenefitsoverservletsalone:1.ItiseasiertowriteandmaintaintheHTML.YourstaticcodeisordinaryHTML:noextrabackslashes,nodoublequotes,andnolurkingJavasyntax.2.YoucanusestandardWeb-sitedevelopmenttools.EvenHTMLtoolsthatknownothingaboutJSPcanbeusedbecausetheysimplyignoretheJSPtags.3.Youcandivideupyourdevelopmentteam.TheJavaprogrammerscanworkonthedynamiccode.TheWebdeveloperscanconcentrateonthepresentationlayer.

Onlargeprojects,thisdivisionisveryimportant.Dependingonthesizeofyourteamandthecomplexityofyourproject,youcanenforceaweakerorstrongerseparationbetweenthestaticHTMLandthedynamiccontent.Now,thisdiscussionisnottosaythatyoushouldstopusingservletsanduseonlyJSPinstead.Bynomeans.Almostallprojectswilluseboth.Forsomerequestsinyourproject,youwilluseservlets.Forothers,youwilluseJSP.Forstillothers,youwillcombinethemwiththeMVCarchitecture.Youwanttheappropriatetoolforthejob,andservlets,bythemselves,donotcompleteyourtoolkit.

1.3AdvantagesofJSP

OverCompetingTechnologiesAnumberofyearsago,Martywasinvitedtoattendasmall20-personindustryroundtablediscussiononsoftwaretechnology.SittingintheseatnexttoMartywasJamesGosling,inventoroftheJavaprogramminglanguage.Sittingseveralseatsawaywasahigh-levelmanagerfromaverylargesoftwarecompanyinRedmond,Washington.Duringthediscussion,themoderatorbroughtupthesubjectofJini,whichatthattimewasanewJavatechnology.Themoderatoraskedthemanagerwhathethoughtofit,andthemanagerrespondedthatitwastooearlytotell,butthatitseemedtobeanexcellentidea.Hewentontosaythattheywouldkeepaneyeonit,andifitseemedtobecatchingon,theywouldfollowhiscompany'susual"embraceandextend"strategy.Atthispoint,Goslinglightheartedlyinterjected"Youmeandisgraceanddistend."

Now,thegrievancethatGoslingwasairingwasthathefeltthatthiscompanywouldtaketechnologyfromothercompaniesandsubornitfortheirownpurposes.Butguesswhat?Theshoeisontheotherfoothere.TheJavacommunitydidnotinventtheideaofdesigningpagesasamixtureofstaticHTMLanddynamiccodemarkedwithspecialtags.Forexample,ColdFusiondidityearsearlier.EvenASP(aproductfromtheverysoftwarecompany

oftheaforementionedmanager)popularizedthisapproachbeforeJSPcamealonganddecidedtojumponthebandwagon.Infact,JSPnotonlyadoptedthegeneralidea,itevenusedmanyofthesamespecialtagsasASPdid.

So,thequestionbecomes:whyuseJSPinsteadofoneoftheseothertechnologies?Ourfirstresponseisthatwearenotarguingthateveryoneshould.Severalofthoseothertechnologiesarequitegoodandarereasonableoptionsinsomesituations.Inothersituations,however,JSPisclearlybetter.Hereareafewofthereasons.

1.3.1Versus.NETandActiveServerPages(ASP).

NETiswell-designedtechnologyfromMicrosoft.http://./doc/40ef6fe2ab8271fe910ef12d2af90242a995ab21.htmlisthepartthatdirectlycompeteswithservletsandJSP.TheadvantagesofJSParetwofold.

First,JSPisportabletomultipleoperatingsystemsandWebservers;youaren'tlockedintodeployingonWindowsandIIS.Althoughthecore.NETplatformrunsonafewnon-Windowsplatforms,theASPpartdoesnot.Youcannotexpecttodeployserioushttp://./doc/40ef6fe2ab8271fe910ef12d2af90242a995ab21.htmlapplicationsonmultipleserversandoperatingsystems.Forsomeapplications,thisdifferencedoesnotmatter.Forothers,itmattersgreatly.

Second,forsomeapplicationsthechoiceoftheunderlyinglanguagemattersgreatly.Forexample,although.NET'sC#languageisverywelldesignedandissimilartoJava,fewerprogrammersarefamiliarwitheitherthecoreC#syntaxorthemanyauxiliarylibraries.Inaddition,manydevelopersstillusetheoriginalversionofASP.Withthisversion,JSPhasaclearadvantageforthedynamiccode.WithJSP,thedynamicpartiswritteninJava,notVBScriptoranotherASP-specificlanguage,soJSPismorepowerfulandbettersuitedtocomplexapplicationsthatrequirereusablecomponents.

YoucouldmakethesameargumentwhencomparingJSPtothepreviousversionofColdFusion;withJSPyoucanuseJavaforthe"realcode"and

arenottiedtoaparticularserverproduct.However,thecurrentreleaseofColdFusioniswithinthecontextofaJ2EEserver,allowingdeveloperstoeasilymixColdFusionandservlet/JSPcode.

1.3.2VersusPHP

PHP(arecursiveacronymfor"PHP:HypertextPreprocessor")isafree,open-source,HTML-embeddedscriptinglanguagethatissomewhatsimilartobothASPandJSP.OneadvantageofJSPisthatthedynamicpartiswritteninJava,whichalreadyhasanextensiveAPIfornetworking,databaseaccess,distributedobjects,andthelike,whereasPHPrequireslearninganentirelynew,lesswidelyusedlanguage.AsecondadvantageisthatJSPismuchmorewidelysupportedbytoolandservervendorsthanisPHP.

1.3.3VersusPureServlets

JSPdoesn'tprovideanycapabilitiesthatcouldn't,inprinciple,beaccomplishedwithservlets.Infact,JSPdocumentsareautomaticallytranslatedintoservletsbehindthescenes.Butitismoreconvenienttowrite(andtomodify!)regularHTMLthantouseazillionprintlnstatementstogeneratetheHTML.Plus,byseparatingthepresentationfromthecontent,youcanputdifferentpeopleondifferenttasks:yourWebpagedesignexpertscanbuildtheHTMLbyusingfamiliartoolsandeitherleaveplacesforyourservletprogrammerstoinsertthedynamiccontentorinvokethedynamiccontentindirectlybymeansofXMLtags.DoesthismeanthatyoucanjustlearnJSPandforgetaboutservlets?Absolutelynot!JSPdevelopersneedtoknowservletsforfourreasons:

(1).JSPpagesgettranslatedintoservlets.Youcan'tunderstandhowJSPworkswithoutunderstandingservlets.

(2).JSPconsistsofstaticHTML,special-purposeJSPtags,andJavacode.WhatkindofJavacode?Servletcode!Youcan'twritethatcodeifyoudon'tunderstandservletprogramming.

(3).SometasksarebetteraccomplishedbyservletsthanbyJSP.JSPisgoodatgeneratingpagesthatconsistoflargesectionsoffairlywellstructuredHTMLorothercharacterdata.Servletsarebetterforgeneratingbinarydata,buildingpageswithhighlyvariablestructure,andperformingtasks(suchasredirection)thatinvolvelittleornooutput.

(4).SometasksarebetteraccomplishedbyacombinationofservletsandJSPthanbyeitherservletsorJSPalone.

1.3.4VersusJavaScript

JavaScript,whichiscompletelydistinctfromtheJavaprogramminglanguage,isnormallyusedtodynamicallygenerateHTMLontheclient,buildingpartsoftheWebpageasthebrowserloadsthedocument.ThisisausefulcapabilityanddoesnotnormallyoverlapwiththecapabilitiesofJSP(whichrunsonlyontheserver).JSPpagesstillincludeSCRIPTtagsforJavaScript,justasnormalHTMLpagesdo.Infact,JSPcanevenbeusedtodynamicallygeneratetheJavaScriptthatwillbesenttotheclient.So,JavaScriptisnotacompetingtechnology;itisacomplementaryone.

ItisalsopossibletouseJavaScriptontheserver,mostnotablyonSunONE(formerlyiPlanet),IIS,andBroadVisionservers.However,Javaismorepowerful,flexible,reliable,andportable.VersusWebMacroorVelocity

JSPisbynomeansperfect.Manypeoplehavepointedoutfeaturesthatcouldbeimproved.Thisisagoodthing,andoneoftheadvantagesofJSPisthatthespecificationiscontrolledbyacommunitythatdrawsfrommanydifferentcompanies.So,thetechnologycanincorporateimprovementsinsuccessivereleases.However,somegroupshavedevelopedalternativeJava-basedtechnologiestotrytoaddressthesedeficiencies.This,inourjudgment,isamistake.Usingathird-partytoollikeApacheStruts

thataugmentsJSPandservlettechnologyisagoodideawhenthattooladdssufficientbenefittocompensatefortheadditionalcomplexity.ButusinganonstandardtoolthattriestoreplaceJSPisabadidea.Whenchoosingatechnology,youneedtoweighmanyfactors:standardization,portability,integration,industrysupport,andtechnicalfeatures.TheargumentsforJSPalternativeshavefocusedalmostexclusivelyonthetechnicalfeaturespart.Butportability,standardization,andintegrationarealsoveryimportant.Forexample,theservletandJSPspecificationsdefineastandarddirectorystructureforWebapplicationsandprovidestandardfiles(.warfiles)fordeployingWebapplications.AllJSP-compatibleserversmustsupportthesestandards.FilterscanbesetuptoapplytoanynumberofservletsorJSPpages,butnottononstandardresources.ThesamegoesforWebapplicationsecuritysettings.Besides,thetremendousindustrysupportforJSPandservlettechnologyresultsinimprovementsthatmitigatemanyofthecriticismsofJSP.Forexample,theJSPStandardTagLibraryandtheJSP2.0expressionlanguageaddresstwoofthemostwell-foundedcriticisms:thelackofgooditerationconstructsandthedifficultyofaccessingdynamicresultswithoutusingeitherexplicitJavacodeorverbosejsp:useBeanelements.

1.4MisconceptionsAboutJSP

ForgettingJSPIsServer-SideTechnologyHerearesometypicalquestionsMartyhasreceived(mostofthemrepeatedly).

?OurserverisrunningJDK1.4.So,howdoIputaSwingcomponentinaJSPpage?

?HowdoIputanimageintoaJSPpage?IdonotknowtheproperJavaI/Ocommandstoreadimagefiles.

?SinceTomcatdoesnotsupportJavaScript,howdoImakeimagesthatarehighlightedwhentheusermovesthemouseoverthem?

?OurclientsuseolderbrowsersthatdonotunderstandJSP.Whatshouldwedo?

?Whenourclientsuse"ViewSource"inabrowser,howcanIpreventthemfromseeingtheJSPtags?Allofthesequestionsarebasedupontheassumptionthatbrowsersknowsomethingabouttheserver-sideprocess.Buttheydonot.Thus:

?ForputtingappletswithSwingcomponentsintoWebpages,whatmattersisthebrowser'sJavaversion—theserver'sversionisirrelevant.IfthebrowsersupportstheJava2platform,youusethenormalAPPLET(orJavaplug-in)tagandwoulddosoevenifyouwereusingnon-Javatechnologyontheserver.

?YoudonotneedJavaI/Otoreadimagefiles;youjustputtheimageinthedirectoryforWebresources(i.e.,twolevelsupfromWEB-INF/classes)andoutputanormalIMGtag.

?Youcreateimagesthatchangeunderthemousebyusingclient-sideJavaScript,referencedwiththeSCRIPTtag;thisdoesnotchangejustbecausetheserverisusingJSP.

?Browsersdonot"support"JSPatall—theymerelyseetheoutputoftheJSPpage.So,makesureyourJSPoutputsHTMLcompatiblewiththebrowser,justasyouwoulddowithstaticHTMLpages.

?And,ofcourseyouneednotdoanythingtopreventclientsfromseeingJSPtags;thosetagsareprocessedontheserverandarenotpartoftheoutputthatissenttotheclient.ConfusingTranslationTimewithRequestTimeAJSPpageisconvertedintoaservlet.Theservletiscompiled,loadedintotheserver'smemory,initialized,andexecuted.Butwhichstephappenswhen?Toanswerthatquestion,remembertwopoints:?TheJSPpageistranslatedintoaservletandcompiledonlythefirsttimeitisaccessedafterhavingbeenmodified.

?Loadingintomemory,initialization,andexecutionfollowthe

normalrulesforservlets.Table1givessomecommonscenariosandtellswhetherornoteachstepoccursinthatscenario.Themostfrequentlymisunderstoodentriesarehighlighted.Whenreferringtothetable,notethatservletsresultingfromJSPpagesusethe_jspServicemethod(calledforbothGETandPOSTrequests),notdoGetordoPost.Also,forinitialization,theyusethejspInitmethod,nottheinitmethod.

中文翻譯

1.1JSP技術概述

讓我們先對JSP頁面的工作方式作一些簡單的討論。我們將力求簡單，只將注意力集中于一些基本的方面。有關詳細信息，請參閱參考資料中到其他JSP技術信息的。

從傳統(tǒng)意義上講，JSP頁面與HTML頁面很相似，只是多了一些標記。這些標記使設計人員能夠將Java代碼（不是JavaScript）嵌入到頁面中。Web應用程序服務器（如IBMWebSphereApplicationServer）將截取對JSP頁面的請求。頁面的擴展名.jsp（不是.html）向應用程序服務器暗示了這些標記的存在。Web應用程序服務器隨后對JSP頁面進行預處理，提取其中的JSP標記和任何嵌的Java代碼，而只保留HTML。提取出來的JSP標記和嵌Java代碼用來構建Javaservlet（JSP頁面servlet），Javaservlet運行該代碼并將結果插入到原頁面中JSP標記所在的位置。得到的結果是純HTML。在請求瀏覽器看到任何結果之前，Java代碼被剝離并在服務器上運行。

我們可以將同樣的原理應用于XML頁面。在包含XML的JSP頁面的請求者（可能是一個瀏覽器，也可能是某個企業(yè)對企業(yè)的應用程序）看到XML之前，Java代碼被剝離JSP頁面并用來生成其他容，生成的容被插入到JSP標記原來所在的頁面位置。這種特性使您能夠精確地控制將新容插入到什么位置，甚至可以精確到單個字符。

過一會兒我們將考慮如何使用以上的特性。首先，讓我們考慮為什么您可能會想到用JSP創(chuàng)建動態(tài)XML。為什么不只是編寫Java應用程序或servlet來生成整個文檔？為什么要費心去使用JSP呢？最重要的原因是無須為每個請求重新生成靜態(tài)容是有意義的（假定XML文檔只有部分容是動態(tài)的）。通過使用JSP頁面，頁面的靜態(tài)XML就可以充當一個模板，該模板是用動態(tài)容填充的。Java代碼的任務僅僅是生成可能隨時間變化的容--這是一種更有效的方法。

非?，F(xiàn)實的一個問題是，JSP頁面使您能夠將不同開發(fā)人員負責的任務分開。特別是，它們允許您更好地將數(shù)據(jù)與視圖分離開，從而允許您在不影響邏輯的情況下添加新表示。設想這樣一個Javaservlet，它執(zhí)行業(yè)務邏輯，并根據(jù)請求

的性質(zhì)將生成的結果重定向到適當?shù)腏SP頁面。例如，當servlet檢測到WAP瀏覽器發(fā)出請求時，它就可以將數(shù)據(jù)重定向到一個包含WML的JSP頁面。對于標準瀏覽器請求，它可以將數(shù)據(jù)重定向到包括HTML的JSP頁面。

1.2JSP的好處

JSP頁面最終會轉換成servler。因而，從根本上，JSP頁面能夠執(zhí)行的任何任務都可以用servler來完成。然而，這種底層的等同性并不意味著servler和JSP頁面對于所有的情況都等同適用。問題不在于技術的能力，而是二者在便利性、生產(chǎn)率和可維護性上的不同。畢竟，在特定平臺上能夠用Java編程語言完成的事情，同樣可以用匯編語言來完成，但是選擇哪種語言依舊十分重要。和單獨使用servler相比，JSP提供下述好處：1.JSP中HTML的編寫與維護更為簡單。JSP中可以使用常規(guī)的HTML：沒有額外的反斜杠，沒有額外的雙引號，也沒有暗含的Java語法。2.能夠使用標準的開發(fā)工具。即使對那些對JSP一無所知的HTML工具，我們也可以使用，因為它們會忽略JSP標簽（JSPtags）。3.可以對開發(fā)團隊進行劃分。Java程序員可以致力于動態(tài)代碼。Web開發(fā)人員可以將經(jīng)理集中在表示層（presentationlayer）上。對于大型的項目，這種劃分極為重要。依據(jù)開發(fā)團隊的大小，及項目的復雜程度，可以對靜態(tài)HTML和動態(tài)容進行弱分離（weakerseparation）和強分離（strongerseparation）。在此，這個討論并不是讓您停止使用servlets，只使用JSP。幾乎所有的項目都會同時用到這兩種技術。針對項目中的某些請求，您可能會在MVC構架下組合使用這兩項技術。我們總是希望用適當?shù)墓ぞ咄瓿上鄬墓ぷ?，僅僅是servlet并不能填滿您的工具箱。

1.3JSP相對于競爭技術的優(yōu)勢

許多年前，Marty受到邀請,參加一個有關軟件技術的小型(20個人)研討會.做在Marty旁邊的人是JamesGoslingJava編程語言的發(fā)明者。隔幾個位置,是來自華盛頓一家大型軟件公司的高級經(jīng)理。在討論過程中,研討會的主席提出了Jini的議題,這在當時是一項新的Java技術.主席向該經(jīng)理詢問他的想法.他繼續(xù)說,他們會持續(xù)關注這項技術,如果這項技術變得流行起來,他們會遵循公司的“接受并擴充(embraceandextend)”的策略.此時,Gosling隨意地插話說“你的意思其實就是不接受且不擴充(disgraceanddistend)?！?/p>

在此,Gosling的抱怨顯示出，他感到這個公司會從其他公司那里拿走技術,用于他們自己的目的.但你猜這次怎么樣?這次鞋子穿在了另一只腳上。Java社團沒有發(fā)明這一思想將頁面設計成由靜態(tài)HTML和用特殊標簽標記的動態(tài)代碼混合組成.。ColdFusion多年前就已經(jīng)這樣做了。甚至ASP(來自于前述經(jīng)理所在公司的一項產(chǎn)品)都在JSP出現(xiàn)之前推廣了這種方式。實際上,JSP不只采用了這種通用概念,它甚至使用許多和ASP相同的特殊標簽。因此,問題變成:為什么使用JSP,而不使用其他技術呢?我們的第一反應是我們不是在爭論所有的人應該做什么。其他這些技術中,有一些也很不錯,在某些情況下也的確是合情合理的選擇.然而,在其他情形中,JSP明顯要更好一些。下面給出幾個理由。

1.3.1與.NET和ActiveServerPages(ASP)相比.

NET是Microsoft精心設計的一項技術。http://./doc/40ef6fe2ab8271fe910ef12d2af90242a995ab21.html是與servlets和JSP直接競爭的技術。JSP的優(yōu)勢體現(xiàn)在兩個方面。

首先,JSP可以移植到多種操作系統(tǒng)和Web服務器,您不必僅僅局限于部署在Windows和IIS上盡管核心.NET平臺可以在好幾種非Windows平臺上運行，但ASP這一部分不可以。您不能期望可以將重要的http://./doc/40ef6fe2ab8271fe910ef12d2af90242a995ab21.html應用部署到多種服務器和操作系統(tǒng)。對于某些應用，這種差異沒有什么影響。但有些應用，這種差異卻非常重要。

其次，對于某些應用，底層語言的選擇至關重要。例如，盡管.NET的C#語言設計優(yōu)良，且和Java類似，但熟悉核心C#語法和眾多工具庫的程序員很少。此外,許多開發(fā)者依舊使用最初版本的ASP。相對于這個版本,JSP在動態(tài)代碼方面擁有明顯的優(yōu)勢。使用JSP,動態(tài)部分是用Java編寫的,而非VBScript過其他ASP專有的語言,因此JSP更為強勁,更適合于要求組件重用的復雜應用。

當將JSP與之前版本的ColdFusion對比時，您可能會得到相同的結論。應用JSP，您可以使用Java編寫“真正的代碼”，不必依賴于特定的服務器產(chǎn)品。然而，當前版本的ColdFusion滿足J2EE服務器的環(huán)境，允許開發(fā)者容易的混合使用ColdFusion和Servlet/JSP代碼。

1.3.2與PHP相比

PHP（“PHP：HypertextPreprocessor”的遞歸字母縮寫詞）是免費的、開放源代碼的、HTML嵌入其中的腳本語言，與ASP和JSP都有某種程度的類似。JSP

的一項優(yōu)勢是動態(tài)部分用Java編寫，而Java已經(jīng)在聯(lián)網(wǎng)、數(shù)據(jù)庫訪問、分布式對象等方面擁有廣泛的API，而PHP需要學習全新的、應用相對廣泛的語言。JSP的第二項優(yōu)勢是，和PHP相比，JSP擁有極為廣泛的工具和服務器提供商的支持。

與純Servlet相比原則上，JSP并沒有提供Servlet不能完成的功能。實際上，JSP文檔在后臺被自動轉換成Servlet。但是編寫（和修改）常規(guī)的HTML，要比無數(shù)println語句生成HTML要方便得多。另外，通過將表示與容分離，可以為不同的人分配不同的任務：網(wǎng)頁設計人員使用熟悉的工具構建HTML，要么為Servlet程序員留出空間插入動態(tài)容，要么通過XML標簽間接調(diào)用動態(tài)容。這是否表示您只可以學習JSP，將Servlet丟到一邊呢？當然不是！由于以下4種原因，JSP開發(fā)人員需要了解Servlet：

（1）JSP頁面會轉換成Servlet。不了解Servlet就無法知道JSP如何工作。（2）JSP由靜態(tài)HTML、專用的JSP標簽和Java代碼組成。哪種類型的Java代碼呢？當然是Servlet代碼！如果不了解Servlet編程，那么就無法編寫這種代碼。