外文翻译 - Web 2.0下JSP和Ajax

0外文原文JSPunderchapter1Web2.0andAjaxContentinthispaper,PersonalizedWeb2.0eraisnottheoriginalWebpersonalization,butpersonalizedservice,wewillbefacedwithanewpersonalizedInternet.FollowedisWeb2.0Webapplicationprogrammingalsowanttochange,theemergenceofAjaxhaschangedthetraditionalWebprogrammingmodel.Alotofworkisbeingquietlytransplantedtotheclient,Web2.0Webapplicationsareinanewway.AndthecombinationofJSPandAjaxtechnology,isacombinationofcross-platformandloadbalancing.Inthischapter,willbethefirsttointroducetheconceptofWeb2.0,JSPandAjaxconcepts,thenintroducedtheJSP+Ajaxcombinedwithmeaning,andthenintroducedtheJSPenvironmentanddevelopmentenvironment,atlast,intheformofcasetheuseofAjax+JSPareintroduced.LearninggoalsUnderstandthemeaningandfeaturesofWeb2.0GrasptheconceptofJSPGrasptheconceptofAjaxFamiliarwithbuildingtheJSPrunninganddevelopmentenvironmentThedifferencebetweenconnectingtheJSPandServletMasterthedevelopingAjax+JSPcaseprocessWeb2.0andJSP1.1andAjaxSincetheconceptofWeb2.0isputforward,afterseveralyearsofdevelopment,Web2.0Internetindustryhasbecomethemostpopularvocabulary.Web2.0isabasedonXML,RSS,AJAXtechnology,theintegrationofWeb1.0applicationpatternandtheemergenceofnewBlog,SNS,Wiki,etcavarietyofapplicationservicemode,many-to-manyinteractiontomeetthedemandofdifferentuserssocialization,humanizedserviceplatform.TheemergenceofWeb2.0haschangedthetraditionalWebdevelopmentmodel.In1traditionalWebdevelopment,youcanuseeitheraWebofJSP,PHPandASPtechnology,buildaWebapplication,butforaWebclienttechnologyarebeyondreach,leadtoalotofworkisdoneontheserverside,theclientonlydisplaydatalevel,thusformingthephenomenonoffatandthinclientontheserver.AndtheemergenceofWeb2.0technology,changethestatusquo.CanuseAjaxontheclientsidetocreateamiddletier,transplantingsomeworkontheservertotheclient.1.1.1Web2.0introductionTheconceptofWeb2.0producedinOReillyandMediaLiveinternationalcompanymeetingdiscussion.InternetpioneerandOReilly,vicePresidentofDaleDougherty(DaleDougherty)notice,withtheso-calledcollapseisverydifferent,theInternetismoreimportantthananyothertime,excitingnewapplicationsandwebsitesareemergingwithsurprisingregularity.Moreimportantly,thecompaniesthatsurvivedwhenthedotcombubble,seemstohavesomeincommon.SocoulditbethattheInternetcompanythatbubbleburstmarkedaturningpointintheInternet,thatcallsforWeb2.0actionhadthesignificance?Weallagreewiththispointofview,Web2.0conceptswasborn.Webversionalsohaveneverbeen,untilrecentlytheindustrytechnologyandapplicationofentrepreneurswillbeusedtopackagingrise,labeledwiththeversionofthesoftwareindustryterminology,apopularWeb2.0only.Web2.0shouldcallWeb2.0itisnotimportant,importantisnowtheconceptofWeb2.0.Web2.0,isrelativelyWeb1.0(before2003Internetmode)ofanewkindofInternetapplicationknowncollectively,isarevolutionfromthecorecontenttotheexternalapplication.BytheWeb1.0simplythroughaWebbrowsertobrowseHTMLWebpagemodeconnectingtothecontentisricher,stronger,moreinstrumentalWeb2.0thedevelopmentoftheInternetmode,Internethasbecomeanewdevelopmenttrend.Web1.0toWeb2.0,specifically,fromthemodeofpurereadtowrite,commondevelopment;BypassivelyaccepttheInternetinformationtotaketheinitiativetocreatetheInternet.Frombasiccompositionunit,isapagetodevelopmentpublished/informationrecorded;Fromthetool,itisbytheInternetbrowsertobrowser,RSSreadercontentsuchasdevelopment;Runningmechanism,bytheClientServerto2WebServices;Theauthorbytheprogrammerdevelopmentprofessionalstoallordinaryusers,suchas;Applicationsbytheprimaryapplicationoftheapplicationtothecomprehensivedevelopment.1.1.2JSPoverviewJSP(JavaServerPages)isbytheSunMicrosystemsnewtechnologythatisbasedonJavaservletsandthewholesystemofJavaWebdevelopmenttechnology.Useofthistechnologycanbuildadvanced,safetyandcross-platformdynamicwebsite.InatraditionalWebpageHTMLfiles(*.HTM,*.HTML)addedinJavaprogramfragment(scriptlets)andJSPtags(tag),constitutestheJSPpage(*.JSP),andtheWebserverincaseofaccesstotheJSPpagerequest,thefirstexecutionoftheprogramsegment,andthentheresultsreturnedtothecustomerinHTMLformat.Fragmentscanoperateonthedatabase,youcanredirectwebpages,cansendEmail,etc.,whichisneededtobuilddynamicwebsitefeatures.Alltheproceduresarecarriedoutontheserversideoperation,networktouploadtotheclientisonlytheresult,therequirementtotheclientbrowser,canrealizeNoPlugin,NoActiveXandNoJavaApplet,evenwithoutaframework.JSPallowsdynamiccontentofthepageanditsaidfurtherseparation.JSPdesigncateringtothetechnicallevelofthetwodifferent:pagegraphicdesignandthesoftwaredevelopmenttocreatedynamiccontent.JSPsmainfeaturesinclude:1.JSPisbasedonthetextofthedocument,whichisusedtohandletheclientrequest(request)andstructuralresponse(response).2.Constructtheserverclientaccessobject.3.DefineextensionmechanismofJSPlanguage.JSPisverysimilarwithMicrosoftASPtechnology.ASPprogramminglanguageisVBScriptscriptinglanguage,suchastheJSPusingJava,thisisoneofthemostobviousdifference.Inaddition,thedifferencebetweentheASPandJSPandamoreessential:twolanguagesenginewithcompletelydifferentapproachtopageembeddedintheprogramcode.UndertheASP,VBScriptcodeexplainedbyASPengineiscarriedout;UndertheJSPcodeiscompiledintoservletsandperformedbytheJavavirtualmachine,thecompilationoperationonlyintheJSPpagerequestforthefirsttime.3JSPonthecharacterofcross-platform,executionspeedhasgreattechnicaladvantages,mainlyreflectedinthefollowingaspects.1.Createanddisplaythecontentsofseparation.2.Generatethereusablecomponents.3.Anidentifiertosimplifythepage.4.Arobuststoragemanagement,andsecurity.5.Writeonce,runanywhere.1.1.3AjaxoverviewInFebruary2005,theAdaptivePathofJesseJamesGarrettcreatedthewordAjaxattheearliest.Ajaxwillchangeuserexperienceonthesite,clickthedisplaypagebeforetypeexperiencewillbeinteractive,flexibility,desktopapplicationexperience.Theusercanavoidpagereloads,avoidwaitingforthenextpartofthecontentsofthepresent.Ajaxappearancebroughttolife,totheJavaScriptapplicationandtestframeworkcoupledwithabettertoolsupport,easetheburdenofthedevelopers.Ajaxcanbeusedinmostbrowsers,anddoesnotrequireanyspecialsoftwareorhardware.Oneoftheadvantagesofthisapproachisthatdevelopersdontneedtolearnanewlanguage,alsodonthavetoditchtheoriginalmasterserversidetechnology,Ajaxisamethodoftheclientcanworkwithanyotherserverinteraction,itisnotconcernedaboutwhatisprovideservicefortheserver.AjaxisthecoreoftheJavaScriptXMLHttpRequestobject.ThisobjectwasfirstintroducedinInternetExplorer5,itisakindofsupporttechnologyofasynchronousrequests.Inshort,throughtheXMLHttpRequestobject,theJavaScriptcanmakearequesttotheserverandprocesstheresponse,andnotblocktheuser.Ajaxinteractionswiththeserverprocessasshowninfigure1-1.FIG.1-1AjaxWebapplicationmodel1.2theJSP+Ajaxstructureanditssignificance1.2.1WebapplicationsolutionsCurrentlyontheInternetthedominantthree-tierclient/servermodel,throughthecommongatewayinterfaceCGI(CommonGatewayInterface).CGIandWebappearalmostat4thesametime,wasoncetheonlywaytoprovideWebinteractivity,allstandardWebserversoftwaresupportsCGI.CGIitselfcanbeimplementedasanexecutableprogram,thiskindofWebandapplicationsystemintegrationmethodisverysimple,direct,becauseitdoesnotneedtomakeanychangesontheWebserverandbrowser.Inthisarchitecture,WebserverthroughtheCGIinterfacetocreateagatewayprocess,andpasstheuserrequeststoagateway.ApplicationgatewayhandleCGIrequests,andbyapplyingtheinterfacetoaccessspecificapplications,andthenconverttheresulttoHTMLformatandbacktotheserver.However,CGIHTTPisthefoundationofalowspeed,fragileandstatelessprotocol,sotherearesomeproblemswhenusingCGIapplicationintegration.Webserverforeachuserrequeststhegatewaymustcreateaseparateprocess,andafterreceivedbytheresultsofprocesspipelinebacktoterminatetheprocess.VisiblethroughtheCGIexecutableprogramtoconnectthedisadvantagesoftheapplicationsystemisperformanceoverhead,includingprocesscreationandterminationcosts,processthedatabetweenthecopyswitchingcostbetweenthecostandprocessetc.IfanHTMLfilecontainsalargenumberofdatabaseaccessrequest,thentheCGIWebgatewaysperformancewillbeverylow,andtheserverwillsoonreachsaturationstate,itisdifficulttosupportmoreusersrequest.AndtheCGIisnotadaptedtothewidespreadpopularityandrapiddevelopmentofemergingtechnologiessuchasJava,unabletousethehugeadvantageofthesetechnologies.Thiskindofphenomenonisverycommon,adataupdateawebpageorwebpageinapicture,youneedtotheentirewebpageinformationfromtheservertoreload,intheprocessofloading,mayhavetospendalotoftimetowait.Figure1-2traditionalWebapplicationmodelFigure1-3Web2.0applicationmode1.2.2theadvantageofAjaxsolutionWhentheuserneedsa,tospeeduptheuserinteractionanddoesnotrequirelocallyforinstallationofWebtechnology,marketwhyinmanychosetheAjax?MainlybecauseofAjaxhasthefollowingadvantages:1.Basedonopenstandards2.Highavailability53.Thecross-platform,cross-browsercompatibility4.Thehighrateof5.Technicalindependence1.3buildaJSPrunningenvironmentTheoperationoftheJSPenvironmentincludestwoparts,respectivelytheJDKdevelopmenttoolsandJSPserver.JDKinterpretdevelopmentkitisresponsibleforthecompilationandexecutionofJavafile,andtheJSPserverconvertstheJSPfiletoaJavafile,helpprovidetransactionandsecurity,etc.TheJSPserverhasmanytypes,suchasTomcat,Resin,JBoss,WebLogic,etc.TomcatisanimportantcomponentinJakaraproject,itisSunsofficialrecommendedServletandJSPcontainer,ismoresuitableforbeginners.TheJDKisaJavaDevelopmentKit(JavaDevelopmentKit).ItisakindofusedtobuildontheJavaplatformreleaseapplications,applets,andcomponentsofthedevelopmentenvironment.1.3.1installJDKdevelopmentkitTheJDKisSunMicrosystemsforJavadeveloperstoprovidesoftwaredevelopmentkit.SinceintroducedJavaJDKhasbecomethemostwidelyusedJavaSDK(Softwaredevelopmentkit).WhentheuserwriteaJavaprogram,mustusetheclasslibraryandtheJavalanguagespecification.JDKincludescompleteJRE(JavaRuntimeEnvironment,JavaRuntimeEnvironment),alsoknownasprivateRuntime.Includesvariouslibraryclassesforproductenvironment,aswellasfordevelopersusesupplementarylibrary,suchastheinternationallibrary,IDLlibrary.TheJDKincludesvarioussampleprogramstoshowpartsofJavaAPI.1.3.2TomcatserverinstallationSinceJSPrelease,introducedallkindsoftheJSPengine.ApacheGroupafterfinishingthedevelopmentofGNUJSP1.0,begintoconsiderinSUNJSWDKdevelopmentonthebasisofaJSPservercanprovideWebservicesdirectly,ofcoursealsosupportstheServlet,suchTomcatwasborn.TomcatisanimportantcomponentinJakartaproject,itisJavaWorldeditorselected2001ofthemostinnovativeJavaproducts,atthesametimeitissunsrecommendedServletandJSPcontainer,sothemoreandmorepopularwithsoftware6companiesanddevelopers.ThelatestServletandJSPspecificationscanbeachievedinthenewversionoftomcat.Second,Tomcatiscompletelyfreesoftware,anyonecanfreelydownloadfromtheInternet.TomcatisintroducedTomcatisafreeopensourceServletcontainer,itisacoreofApachefoundationsJakartaprojectproject,byApache,Sunandothercompaniesandindividualstodevelopandbecome.DuetotheSunsparticipationandsupport,thenewestServletandJSPspecificationscanalwaysreflectedintheTomcat.BecauseTomcatadvancedtechnology,stableperformance,andfree,thusdeeplyloversofJavaandgotsomesoftwaredevelopersforapproval,isnowmorepopularWebapplicationserver.Tomcatisthelatestversion6.0x,supportthelatestTomcat6Servlet2.4andJSP2.0specification.Tomcatversionprovidesavarietyofplatformsfordownloading,whichcanbedownloadedfromthesourcecodeorbinaryversion.BecauseofJavacross-platformcharacteristics,basedonJavaTomcatiscross-platform,too.Tomcatserverismadeupofaseriesofconfigurablecomponents,itscorecomponentisCatalinaServletcontainer,itisatthetopofallotherTomcatcomponentcontainer.Tomcatcomponentscanbein/conf/serverconfiguredintheXMLfile,whatarethecomponentsofeachTomcatserver.TheXMLfilecorrespondingtoaconfigurationelement.Tomcatisanopensourcesoftware,workmodecanbedividedintothreetypes:independentServletcontainer,in-processServletcontainer,theServletcontaineroutsidetheprocess.1.4buildJSPdevelopmentenvironmentTheJSPdevelopmentinthefieldofallkindsofintegrateddevelopmentenvironment(IDE)presentsthesituationofflowers,isfamouswithIBMsEclipse,theSunsNetBeansandBorlandJBuilder,etcofthecompany.IBMsEclipse,withitsopensourceandwonthemajorityofprogrammersliketousetheEclipsedevelopmentisnowoneofthemainstreamofJavaprogram.OnlyneedtoinstallMyEclipseintheEclipseplugin,youcanwriteandruntheJSPapplication.1.4.1installingEclipse7Eclipseisanopensource,extensibledevelopmentplatformbasedonJava.Inandofitself,itisjustaframeworkandasetofservices,forthroughtheplug-incomponentstobuildthedevelopmentenvironment.Fortunately,Eclipsecomeswithastandardsetofplug-ins,includingtheJavaDevelopmentTools(JavaDevelopmentTools,theJDT).SummaryofEclipesFortheEclipseplug-inarchitecture,agoodanalogyistheWebbrowser,italsohasaplug-in,Eclipseplug-inandbrowseraresimilar,istosolvetheproblemofscalability.ForaWebbrowser,ifyouwanttocanbrowsemultimediaanimation,andwanttobrowsethePDFfile,youwillneedtotwodifferentplug-ins,toensurethattwotypesofcontentcanbeshownintheWebbrowser.Eclipsetoo,throughitsmodewecaninstalldifferentpluginforHTMLeditor,databasedesign,theJSPdevelopment,c+development,etc.,allofthesedevelopmentworkinacompletelyEclipseinstallationplatform.BecauseEclipseisanopensourceproject,cangotoitsofficialwebsite,forfreetodownloadthelatestversionoftheEclipse.ThisbookUSEStheEclipseEclipseversion3.3forWindowsplatform.AlthoughEclipseitselfiswrittenintheJavalanguage,butinthedownloadpackagedoesnotincludetheJavaruntimeenvironment(namelyinstallingEclipseplatform,shouldfirstJDKinstallationkit),needusertoinstalltheJREseparately,andwanttobeintheoperatingsystemindicatetheJREbininthepathenvironmentvariable.1.4.2MyEclipseinstallationIfyouwanttoruntheJSPapplicationinEclipse,youneedtodownloadaWebplug-in,choosetouseMyEclipsepluginhere.Theplug-infees,candownloadatrialversion.MyEclipspluginprovidespowerfulfunction,candevelopuser-definedStructsframework,JSFandEJBandotherprograms.1.5therelationshipbetweentheJSPandServletTheServletisaJavatechnologyoneofCGIprogramminglanguage.WithtraditionalCGIandmanycomparedtoothersimilarCGItechnology,JavaServlethashigherefficiencyandeasiertouse,morepowerful,andhasbetterportability,moresavinginvestment.TheServletisarunonTomcatserver,JavatechnologytoautomaticallygenerateHTML8pages.TheServletisgenerallyexpandedtosupportJavaserver.ItismostcommonlyusedtoexpandtheWebserver,provideverysecure,portable,easytouseCGIalternatives.Itisakindofdynamicloadingmodule,provideserviceforarequestfromtheWebserver.ItiscompletelyruninJavavirtualmachine.Becauseittorunontheserver,soitdoesntdependonthebrowsercompatibility.AsakindofsimplifiedJSPServletdevelopmentofalternativetechnologies,sopeopletendtoformamisunderstanding,JSPisakindofmoreexcellentthantheServletandServlettechnologycanreplacecompletely.Firstofall,itmustbeadmittedthatinseparationoflogicandimplementationpagesaidtheJSPdoesbetterthantheServlet,inaddition,intheorytheJSPandServletcanreplaceeachother;Butwiththedeepeningofthestudyandapplicationexperienceinthespecificprojects,willfindthatcantsimplycomparethetwotechniques,theyallhavetheiradvantagesandadaptability.ThemaindifferencebetweentheJSPandServlet,JSPprovidesasimplesetoftags,andHTMLfusionbetter,evenifyoudontunderstandtheServletuserscanalsothroughtheJSPtomakedynamicwebpages.Asaresult,manyusersnotfamiliartotheJavalanguage,willfeeltheJSPdevelopmentmoreconvenient.TheJSPpagecanseetheeffectimmediatelyafterchange,donotneedtomanuallycompile,JSPenginewilltodothework;TheServletneedstobecompiled,restarttheServletengineandaseriesofactions.JSPtowritesimple,canbeeasilyembeddedinHTML,itiseasytoadddynamiccontent,easilyoutputHTML.IntheServletoutputHTMLwillneedtoinvokeaparticularmethod,relativetotheJSPismorecomplex.Canbeseenfromthecomparisonabove,inthepresentationlayerontheimplementationoftheJSPrelativetotheServlethasgreatadvantage.But,ifyouwanttodevelopWebapplicationshaveaneedtoimplementcomplexcontrollogic,thenusetheServletcanbeveryclearandeasytoencapsulatethecontrollogic.InfactmanyWeblayerapplicationframework(suchasStrutsframework)istouseaServlettorealizethecontrollogic.9中文翻译第1章Web2.0下JSP和Ajax内容摘要Web2.0时代的个性化不是原来的网页个性化，而是服务个性化，我们面对的将是一个全新的个性化互联网。随之而来就是Web2.0时代的Web程序编程也要发生变化，Ajax的出现改变了传统Web编程的模式。大量的工作正在悄悄的移植到客户端，Web2.0时代的Web程序正在以新的方式出现。而JSP和Ajax技术的结合，是跨平台和负载平衡的结合。在本章中，将首先介绍Web2.0的概念、JSP概念和Ajax概念，接下来介绍JSP+Ajax结合的意义，然后介绍JSP的运行环境和开发环境，最后以案例的方式介绍了Ajax+JSP的使用。学习目标理解Web2.0的产生意义和特点掌握JSP概念掌握Ajax概念熟练掌握构建JSP运行和开发环境连接JSP和Servlet的区别掌握开发Ajax+JSP案例流程1.1Web2.0与JSP、Ajax简介自从Web2.0的概念提出以来，经过几年的发展，Web2.0已经成为互联网行业最受关注的词汇。Web2.0是一种以XML、RSS、AJAX等技术为基础，融合了Web1.0的应用模式及新出现的Blog、SNS、Wiki等多种多对多互动应用服务模式，来满足不同用户社会化、人性化需求的服务平台。Web2.0的出现改变了传统Web开发模式。在传统的Web开发中，可以使用JSP、PHP和ASP的任一种Web技术，构建Web程序，但对于Web客户端技术都是鞭长莫及，导致大量的工作都是在服务器端完成，客户端仅仅只是显示数据的层面，从而形成了胖服务器端和瘦客户端现象。而Web2.0技术的出现，改变了这种现状。可以利用Ajax技术在客户端创建一个中间层，将服务器端一些工作移植到客户端。1.1.1Web2.0简介“Web2.0”的概念产生于OReilly公司和MediaLive国际公司的会议讨论中。互联网先驱和OReilly公司副总裁的戴尔多尔蒂(DaleDougherty)注意到，同所谓的“崩溃”迥然不同，互联网比其他任何时候都更重要，令人激动的新应用程序和网站正在以令人惊讶的规律性涌现出来。更重要的是，那些幸免于当初网络泡沫的公司，看起来有一些共同之处。那么会不会是互联网公司那场泡沫的破灭标志了互联网的一种转折，以至于呼吁“Web2.0”的行动有了意义？我们都认同这种观点，Web2.0概念由10此诞生。Web本来也从来也没有版本之分，直到近来业界的创业者将以前的技术和应用重新“包装”起来，贴上了软件行业的版本术语标签，Web2.0才大行其道了。Web2.0是否该叫Web2.0这并不重要，重要的是现在的Web2.0的概念。Web2.0，是相对Web1.0（2003年以前的互联网模式）的新的一类互联网应用的统称，是一次从核心内容到外部应用的革命。由Web1.0单纯通过网络浏览器浏览html网页模式向内容更丰富、联系性更强、工具性更强的Web2.0互联网模式的发展，已经成为互联网新的发展趋势。Web1.0到Web2.0的转变，具体的说，是从模式上单纯的“读”向“写”、“共同建设”发展；由被动地接收互联网信息向主动创造互联网信息迈进。从基本构成单元上，是由“网页”向“发表/记录的信息发展”；从工具上，是由互联网浏览器向各类浏览器、rss阅读器等内容发展；运行机制上，由“ClientServer”向“WebServices”转变；作者由程序员等专业人士向全部普通用户发展；应用上由初级的应用向全面大量应用发展。1.1.2JSP概述JSP（JavaServerPages）是由SunMicrosystem公司推出的新技术，是基于JavaServlet以及整个Java体系的Web开发技术。利用这一技术可以建立先进、安全和跨平台的动态网站。在传统的网页HTML文件(*.htm,*.html)中加入Java程序片段(Scriptlet)和JSP标记(tag)，就构成了JSP网页(*.jsp)，Web服务器在遇到访问JSP网页的请求时，首先执行其中的程序片段，然后将执行结果以HTML格式返回给客户。程序片段可以操作数据库、可以重新定向网页、可以发送Email等等，这就是建立动态网站所需要的功能。所有程序操作都在服务器端执行，网络上传送给客户端仅是得到的结果，对客户浏览器的要求最低，可以实现NoPlugin、NoActiveX和NoJavaApplet，甚至无框架。JSP使得页面的动态内容与它的表示进一步分离。JSP的设计迎合了两个不同的技术层面：页面的图形设计和创建动态内容的软件开发。JSP的主要特性包括：1.JSP是基于文本的文档，用来处理客户端请求（request）和构造响应（response）。2.构造server端访问的对象。3.定义扩展JSP语言的机制。JSP与Microsoft的ASP技术非常相似。ASP的编程语言是VBScript之类的脚本语言，JSP使用的是Java，这是两者最明显的区别。此外，ASP与JSP还有一个更为本质的区别：两种语言引擎用完全不同的方式处理页面中嵌