翻译文献java servlets的概要

外文原文0VERVIEWOFJAVASERVLETSSERVLETSAREPROTOCOLANDPLATFORMINDEPENDENTSERVERSIDECOMPONENTSWRITTENINJAVA，WHICHDYNAMICALLYEXTENDJAVAENABLEDSERVERSTHEYPROVIDEAGENERALFRAMEWORKFORSERVICESBUILTUSINGTHEREQUESTRESPONSEPARADIGM。THEIRINITIALUSEISTOPROVIDESECUREWEBBASEDACCESSTODATAWHICHISPRESENTEDUSINGHTMLWEBPAGES，INTERACTIVELYVIEWINGORMODIFYINGTHATDATAUSINGDYNAMICWEBPAGEGENERATIONTECHNIQUESSINCESERVLETSRUNINSIDESERVERS，THEYDONOTNEEDAGRAPHICALUSERINTERFACEOTHERWISE，THEYARETHESERVERSIDECOUNTERPARTTOAPPLETSWHICHAREUSEDONLYONTHECLIENTSIDEOFSYSTEMSTHEYAREJAVAAPPLICATIONCOMPONENTSWHICHAREDOWNLOADED，ONDEMAND，TOTHEPARTOFTHESYSTEMWHICHNEEDSTHEMFIGURE1CLIENTSTALKINGTOJAVASERVLETSINSERVERSCLIENTSMAYRANGEINCOMPLEXITYFROMSIMPLEHTMLFORMSTOSOPHISTICATEDJAVAAPPLETSSERVLETSWILLFREQUENTLYUSESOMEKINDOFPERSISTENTSTORAGE，SUCHASFILESORADATABASESERVLETSAREMOSTOFTENPROVIDEDBYORGANIZATIONSWHICHPROVIDECUSTOMIZEDMULTIUSERSERVICESTOTHEIRCUSTOMERBASESHOWEVER，SERVLETSAREALSOFLEXIBLEENOUGHTOSUPPORTSTANDARDIZEDSERVICESSUCHASSERVINGSTATICWEBPAGESTHROUGHTHEHTTPORHTTPSPROTOCOLS，ANDPROXYINGSERVICESSINCETHEYAREUSEDFORDYNAMICEXTENSIBILITY，THEYMAYBEUSEDINAPLUGINSTYLE，SUPPORTINGFACILITIESSUCHASSEARCHENGINESANDSEMICUSTOMAPPLICATIONSSERVLETSALSOPROVIDEASTRONGPLATFORMFORSEMICUSTOMAPPLICATIONS，SUCHASWEBBASEDORDERENTRYORINVENTORYSYSTEMSALTHOUGHALLSERVLETSAREWRITTENINJAVA，THEIRCLIENTSMAYBEWRITTENINANYLANGUAGEWHENSERVLETSAREUSEDINTHEMIDDLETIERSOFDISTRIBUTEDAPPLICATIONSYSTEMS，THEYCANINTURNBECLIENTSTOOTHERSERVICES，WRITTENINANYLANGUAGEFOREXAMPLESERVLETSCANUSEJDBCTOCONTACTANAPPLICATIONSHIGHLYTUNEDRELATIONALDATABASESCOMMUNICATINGWITHOTHERKINDSOFCURRENTORLEGACYSYSTEMSMAYCALLFORALTERNATESOFTWAREPACKAGES，ASREQUIREDBYTHOSESYSTEMSMANYWAYSTOUSESERVLETSAFEWOFTHEMANYAPPLICATIONSFORSERVLETSINCLUDEASIMPLESERVLETCANPROCESSDATAWHICHWASPOSTEDOVERHTTPSUSINGANHTMLFORM，PASSINGDATASUCHASAPURCHASEORDERWITHCREDITCARDDATATHISWOULDBEPARTOFANORDERENTRYANDPROCESSINGSYSTEM，WORKINGWITHPRODUCTANDINVENTORYDATABASESANDPERHAPSANONLINEPAYMENTSYSTEMSINCESERVLETSHANDLEMULTIPLEREQUESTSCONCURRENTLY，THEREQUESTSCANBESYNCHRONIZEDWITHEACHOTHERTOSUPPORTCOLLABORATIVEAPPLICATIONSSUCHASONLINECONFERENCINGONECOULDDEFINEACOMMUNITYOFACTIVEAGENTS，WHICHSHAREWORKAMONGEACHOTHERTHECODEFOREACHAGENTWOULDBELOADEDASASERVLET，ANDTHEAGENTSWOULDPASSDATATOEACHOTHERONESERVLETCOULDFORWARDREQUESTSOTHERSERVERSTHISTECHNIQUECANBALANCELOADAMONGSEVERALSERVERSWHICHMIRRORTHESAMECONTENTOR，ITCOULDBEUSEDTOPARTITIONASINGLELOGICALSERVICEBETWEENSEVERALSERVERS，ROUTINGREQUESTSACCORDINGTOTASKTYPEORORGANIZATIONALBOUNDARIESAPIAVAILABILITY_JTHEJAVASERVLETAPIISASTANDARDJAVAEXTENSIONAPITHISMEANSTHATWHILEITISNOTPARTOFTHECOREJAVAFRAMEWORKWHICHMUSTALWAYSBEPARTOFALLPRODUCTSBEARINGTHEJAVABRAND，ITWILLBEMADEAVAILABLEWITHSUCHPRODUCTSBYTHEIRVENDORSASANADDONPACKAGESUNHASPROVIDEDAPACKAGEWHICHMAYBEUSEDTOEMBEDSERVLETSUPPORTINOTHERWEBSERVERS，INCLUDINGAPACHEANDDERIVEDSERVERSSUCHASSTRONGHOLDNETSCAPEFASTTRACKANDENTERPRISESERVERS，ANDMICROSOFTSIISSERVLETSWEREINITIALLYSUPPORTEDINTHEJAVAWEBSERVERFROMSUNSINCETHEN，ANUMBEROFOTHERJAVABASEDWEBSERVERSHAVESUPPORTEDTHEAPI，ORCOMMITTEDTOSUPPORTINGITFEATURESOFTHEJAVASERVLETAPITHESERVLETAPIISALREADYSUPPODEDBYMOSTJAVABASEDWEBSERVERS,ANDIMPLEMENTALIONSAREAVAILABLEFOROTHERPOPULARWEBSERVERSTHISMEANSTHATYOUGETTHEJAVAADVANTAGEWHENYOUUSETHESERVLETAPINOTONLYWILLYOURCODENOTHAVEMEMORYLEAKSANDSUFFERFROMHARDTOFINDPOINTERBUGS。BUTYOURCODERUNSONPLATFORMSFROMMANYSERVERVENDORSYOUDONTNEEDTOLOCKYOURSELFINTOASINGLEVENDORSERVEREXTENSIONAPI，USINGERRORPRONELANGUAGESSUCHASCORSCRIPTINGLANGUAGESINSTEAD，YOUCANDOALLOFYOURSERVERANDCLIENTDEVELOPMENTINASINGLEDEVELOPMENTLANGUAGENOLONGERDOESYOURTEAMNEEDTOJUGGLEMULTIPLELANGUAGES，ANDCOPEWITHTHEMAINTAINABILITYPROBLEMSINHERENTINSCRIPTINGLANGUAGESNOLONGERDOYOURWEBBASEDAPPLICATIONSNEEDTOSUFFERTHEPERFORMANCEANDPORTABILITYPENALTIESOFCGIJAVAISTHEPROFESSIONALPROGRAMMINGTOOLYOUNEEDTOPROVIDEROBUSTSERVERSOLUTIONSTHISSECTIONPROVIDESYOUANOVERVIEWOFTHEKEYFEATURESOFJAVASERVLETS，ADDRESSINGTHESEMAINTOPICSWHATDOSERVLETSLOOKLIKESERVLETLIFECYCLESECURITYFEATURESHTMLAWARESERVLETSHTTPSPECIFICSERVLETSPERFORMANCEFEATURESWHATDOSERVLETSLOOKLIKESERVLETSSUPPORTTHEFAMILIARPROGRAMMINGMODELOFACCEPTINGREQUESTSANDGENERATINGRESPONSESTHISMODELISUSEDWITHAVARIETYOFDISTRIBUTEDSYSTEMPROGRAMMINGTOOLSETS，RANGINGFROMREMOTEPROCEDURECALLSTOTHEHTTPREQUESTSMADETOWEBSERVERSSERVLETSIMPLEMENTTHESERVLETINTERFACE，USUALLYBYEXTENDINGEITHERTHEGENERICORANHTTPSPECIFICIMPLEMENTATIONTHESIMPLESTPOSSIBLESERVLETDEFINESASINGLEMETHOD，SERVICETHESERVICEMETHODISPROVIDEDWITHREQUESTANDRESPONSEPARAMETERSTHESEENCAPSULATEFHEDATASENTBYTHECLIENT，PROVIDINGACCESSTOPARAMETERSANDALLOWINGSERVLETSTOREPODSTATUSINCLUDINGERRORSSERVLETSNORMALLYRETRIEVEMOSTOFTHEIRPARAMETERSTHROUGHANINPUTSTREAM，ANDSENDTHEIRRESPONSESSINGANOUTPUTSTREAM、THESEINPUTANDOUTPUTSTREAMSMAYBEUSEDWITHDATANWHATEVERFORMATISAPPROPRIATEFOREXAMPLEANAPPLETANDSERVICEMIGHTEXCHANGEDATAUSINGOBJECTSERIALIZATION；HTML，ANDNUMEROUSIMAGEFORMATS，MAYALSOBEAPPROPRIATEDATAFORMATSSERVLETANDENVIRONMENTSTATESINCESERVLETSAREJAVAOBJECTS，THEYHAVEINSTANCESPE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VLET的生命周期安全功能HTML是SERVLET的页面HTTP的特定对象是SERVLET性能特点SERVLET是什么SERVLET是支持熟悉的编程模型的接受要求，并生成RESPONSESTHIS模型是用各种各样的分布式系统编程工具，从远程过程打电话给HTTP请求作出WEB服务器。SERVLET是贯彻落实SERVLET的接口，通常是通过扩大无论是通用或一个HTTP特定IMPLEMENTATIONTHE最简单可行的SERVLET定义了一个方法，服务服务方法是提供与要求，并响应PARAMETERSTHESE概括数据派出由客户提供了机会，参数，并允许SERVLET是为了REPOD地位，其中包括错误SERVLET是一般取回他们的大部分参数，通过输入流，并发送他们的反应的输出流这些输入和输出流，可用于与DATAN什么格式是APPROPRIATEFOR例子一个APPLET与服务，可能交换数据使用对象序列化HTML及许多形象格式，也可适当的数据格式。SERVLET和环境状况由于SERVLET是是JAVA对象，他们有举例具体DATATHIS也就是说，在效果SERVLET是正独立运行的应用程序内部的服务器，而无需使用复杂性增加的班级。（这是需要一些替代服务器延伸对SERVLET的使用）SERVLET是已进入某些SERVLET的具体配置数据，在初始化TIMETHIS允许不同的事例，同时SERVLET的级别被初始化不同的数据，并加以管理不同名称SERVLETSTHE提供的数据，在初始化的时候将包括一个领域，每个举例来说，将保持其持久性，例如特定STATESERVLETS也有能力进行互动他们的环境，通过SERVLETCONTEXT中的物体。SERVLET是已进入某些SERVLET的具体配置数据，在初始化TIMETHIS允许不同的事例，同时SERVLET的班级被初始化不同的数据，并加以管理不同名称SERVLETSTHE提供的数据，在初始化的时候将包括一个领域，每个举例来说，将保持其持久性，例如特定STATESERVLETS也有能力进行互动他们的环境，通过SERVLETCONTEXT中的的语句。什么是SERVLET服务器也各有不同，他们如何知道什么时候负荷SERVLETSWHEN请求进来时，服务器知道如何绘制它以一个SERVLET，它可能必须先予以LOADEDTHAT映射通常会做一取消，这些常见的方式服务器管理员可以指定一些类型的客户的要求，始终地图某一SERVLETFOR举一个例子，其中会谈到一个特定的数据库。服务器管理员可能会指明这部分的客户的要求是名字的SERVLETAS发现一个经管SERVLET是DIRECTORYAT许多网站，该目录将分担服务器分担负载的处理，为现场的客户。有些伺服器或许能够自动调用SERVLET是过滤输出的其他SERVLET是根据他们的行政CONFIGURATIONFOR例如，特定类型的SERVLET的产量就可能触发后处理，由其他SERVLET是，或许履行格式转换。适当授权客户可指定的SERVLET是被引用过，在没有行政干预。防伪特征SERVLELS有机会获得信息约其CLIENTSWHEN使用安全协议，如SSL了。同行的身份可以判定RELIABLYSERVLETS依靠HTTP的，也有进入的HTTP特定认证数据。SERVLET是有JAVA的优势记忆体存取行为，并有强烈的延续行为。错误的SERVLET是不会雕刻的手法是，在大部分C语言服务器扩建环境。不同于其它任何当前服务器扩展API的JAVASERVLET是提供强有力的安全策略SUPPORTTHIS是因为所有的JAVA环境提供一个安全限制可以用来控制是否将行动，例如网络或文件访问，以PERMITTEDBY默认情况下，所有SERVLET是不可信的，并不得执行操作，如存取网络服务或本地文件。不过，SERVLET是“建在“服务器内部或SERVLET是已进行数字签名，因为他们把到JAVA进程的档案，可能会受到信任和给予更多的权限，由保安MANAGERA数字签名就可执行代码表明，该组织的出现就意味“先天不足，加上管理松散它“在一些SENSESUCH签名，不能够支持问责制本身，但他们的确显示一定程度的保证，将被放置在使用该CODEFOR举例来说，某一特定签字，从MIS的组织可能需要的所有守则，这是理所当然的一般接触网络服务在一个企业INTRANETTHAT签名可能只用于守则，这是强烈认为，不特别是对违反安全政策。WEB应用的生命周期一个网络应用软件的网页元件，静态资源文件，如影像，并帮手班和图书馆。该WEB容器提供了许多配套服务，致力提升能力的网络组件，使它们更容易DEVELOPHOWEVER，因为一个WEB应用程序必须考虑这些服务到，这一过程，为创建和运行WEB应用是不同的是传统的独立的JAVACLASSESTHE过程中，用于创建，部署和执行一个网站应用可归纳如下1发展了WEB组件代码。2扩展了WEB应用部署描述符。3编译WEB应用组件和HELPER类参照由组件四可选包申请成为伸展单元，5扩展并应用到WEB容器6获得一个URL，提及WEB应用网络模块在JAVAEE的架构，WEB组件和静态网页内容的文件，如图像称为WEB的资源。一个网络模块是最小的部署和使用单位的网站RESOURCESAJAVAEE的网站单元对应一个WEB应用作为定义在JAVASERVLET的规范。此外，以WEB组件和网络资源，网络模块可包含其他文件。服务器端实用班（数据库类等）。通常，这些符合需要J