订单管理系统中英文对照外文翻译文献.docx

订单管理系统中英文对照外文翻译文献.docx

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订单管理系统中英文对照外文翻译文献

中英文对照外文翻译

（文档含英文原文和中文翻译）

MySQLandJSPWebapplications

JSPdevelopersencounteruniqueproblemswhenbuildingwebapplicationsthatrequireintensedatabaseconnectivity.MySQLandJSPWebApplicationsaddressesthechallengesofbuildingdata-drivenapplicationsbasedontheJavaServerPagesdevelopmentmodel.MySQLandJSPWebApplicationsbeginswithanoverviewofthecoretechnologiesrequiredforJSPdatabasedevelopment--JavaServerPages,JDBC,andthedatabaseschema.ThebookthenoutlinesandpresentsanInternetcommerceapplicationthatdemonstratesconceptssuchasreceivingandprocessinguserinput,designingandimplementingbusinessrules,andbalancingtheuserloadontheserver.ThroughtheJDBC（JavaDataBaseConnector）,thedevelopercancommunicatewithmostcommercialdatabases,suchasOracle.ThesolutionspresentedinMySQLandJSPWebApplicationscenterontheopensourcetoolsMySQLandTomcat,allowingthereaderanaffordablewaytotestapplicationsandexperimentwiththebook'sexamples.

SoWhatIsJSPAllAbout?

Ifyoumeettherequirementsmentioned,youshouldalreadyhaveaprettygoodideawhattheanswertothisquestionis.JSPisallaboutdoinghighlyobject-orientedWebsitesthatcanleverageallthebestpracticesofmodernsoftwareengineering.ThesepracticesincludethingssuchasSQLdatabasesandUML-baseddesign.Thisisn'ttosaythatJSPisacure-allandthatusingitwillautomaticallymakeyourWebsiteaparagonofengineeringart.It'sjustaspossibletodesignbadWebsitesinJSPaswithanyothertechnology.That'swhy,asyougothroughthetext,youwillseehowtoincorporatethebestpracticesandhowtoavoidthepitfallsofconveniencewhenprojectsgetstressful.JSPitselfisanevolutionarystepalongthepaththatstartedwiththefirststaticWebservers,movedthroughCGI-enabledservers,andfinallythefirstgenerationofscript-enabledservers.JSPislessaWebserverwithaJavacomponentthanitisaJavaenginethatunderstandstheWeb.

JSPgrewoutofJavaservlets.ServletsallowthedevelopertohandletheincomingWebrequestsusingaJavaprogramthathasaccesstoallthenormalinformationthataCommonGatewayInterface（CGI）programwould.Inaddition,theservlethasaccesstosession-persistentobjects.TheseareJavaobjectsthatareassociatedwithaspecificusersessionandcanbeusedtostorestatebetweenrequests.Servletprogrammingwasamajorstepforwardinallowingdeveloperstowritewell-structuredmodularWebapplicationsusinganobject-orientedlanguage.Italsosolvedtheproblemofstatepersistence,allowingmoreinformationtoresideontheserverduringatransactionandlesstohavetopassbackandforthbetweentheuserandtheserver.Servletsstillsufferedfromonemajorproblem.BecausetheyeventuallyneedtospitoutHTML,theHTMLcodinghadtobeembeddedintheservletcode.Thisledtocodefragmentsliketheoneshownhere:

Out.println（"\n\n\n"）;

Out.println（""）;

Thiskindofembeddinggetsveryoldveryfastwhenyouhavetocodealotofpages.Inaddition,havingtoescapeallofthequotationmarkscanleadtoalotofconfusingandhard-to-finderrorsifyouleaveoutabackslash.Eventually,astill-betterideaemerged.SupposethatyoucouldcombinethebestofstaticHTMLpagesandwiththeinteractivecapabilitiesofservlets.TheresultwasJavaServerPages（ontheMicrosoftside,theresultwasActiveServerPages）.AsFigureI.1shows,JSPisacomplicatedbeast.Inthenextchapter,you'llwalkthroughthisflowindetail,butforthemoment,herearethemajorsteps:

1.ArequestcomesinfromabrowserusingthenormalHTTPrequestformat.

2.TheWebserverhandsofftherequesttoJSP.JSPlooksatthefilenameandfindstheappropriateJSPfile.

3.The.jspfileisconvertedintoa.javafile,containingJavacodethatwillcreateaclasswhosenameisderivedfromthe.jspfilename.

4.JSPthencompilesthe.javafileusingjavactoproducea.classfile.Notethatthetwopreviousstepsareskippedifa.classfilealreadyexistsandisnewerthanthe.jspfile.

5.Aninstanceofthenewlycreatedclassisinstantiatedandsentthe_jspServicemessage.

6.Thenewinstancelookstoseeifthereisalreadyaninstanceofthestuff.Userobjectcalleduserexistinginthesessionobjectspaceforthecurrentlyconnecteduser.Ifnot,oneisinstantiated.

7.Aspartofservicingstuff.jsp,theuserinstanceiscalledwiththegetUserName（）method.

8.IftheJSPprocessingrequiresaccesstoinformationinadatabase,itusesJDBCtomaketheconnectionandhandletheSQLrequests.

Asyoucansee,atremendousamountofpowerisavailableintheJSPworld.DevelopersarefreetowriteWebpagesthatlookmostlylikeHTML,exceptwherecalloutstoJavaarerequired.But,atthesametime,theyarefreetodevelopfullyfleshed-outobject-orientedapplicationsusingallthefeaturesthatJavacanbringtobear.Theyalsogetallthebenefitsofservlets,includingsessionpersistence.

WhyDoWeNeedDatabases?

Well,onereasonissothatLarryEllisonofOraclecanaffordtokeephimselfonProzacwhenhethinksaboutBillGates.Amoreseriousansweristhesamereasonthatdrovemantofirstpressastickagainstapieceofwetmud:

becauseit'sgoodtowritethingsdown.Webserversaremarvelouscreatures,butthey'reabitlikeidiotsavants.AskthemtoserveaWebpageorrunapieceofJava,andtheyperformlikeachamp.Butstartaskingthemtorememberwhattheydidfiveminutesago,andtheydevelopamnesiafasterthanacharacterinasoapopera.

Thefirstandmostimportantreasonthatyouusedatabasesisthatthere'salotinane-commercetransactionthatyouneedtorememberandtrack:

•Auser'sname,address,creditcard,andotherinformationpreviouslyenteredonaregistrationpage

•hattheusermighthaveputintoashoppingcartandleftfromaprevioustransaction

•Whatitemsareinstock,alongwiththeirprice,description,andsoon

•Ordersthatneedtobefulfilled,ordersthathavebeenshipped,anditemsthathavebeenbackordered.

Now,youcouldstoreallthisinformationinaflatfileontheserver'sharddisk,butthereareotherimportantpropertiesthatyouwanttohaveforthisdata:

•Youwanttobeabletobackoutatransactionifpartofitfails.

•YouwanttobeabletolocatethedatasomewheremoresecurethantheWebserver,whichcouldbeinaDMZoroutsidethefirewallaltogether.

•Youwanttobeabletoaccessdatasuchasuserdataorproductsquickly,eveniftherearethousandsormillionsofthem.

Whenyouaddtheseitemstotheshoppinglist,onlyarelationaldatabasewillreallydothejobeffectively.

MySQL

Manysitesdon'tneedthebattleshipstrength（andpricetag）ofOracle.MySQLisanopen-sourceSQLdatabaseavailableforanyonetouse,withmany（althoughnotall）ofthefeaturesofitsbigbrothers,suchasOracle.

MySQLisavailableforjustaboutanycomputerthathasdecentpower—itisfairlylightweightontheprocessorandeasytoinstall（10minutes,asopposedtomultiplehoursforOracle）.

So,perhapsyouarewondering,what'sthecatch?

WhatareyounotgettinginMySQLthatmakespeopleturntoOracle?

Well,MySQLisaneatlittlepackage,butitismissingsomethingsthatwouldbenicetohaveinaperfectworld.

AmajorfeaturethatMySQLdoesnotofferisdatabaseconsistencychecking.Youcanuseforeignkeytagsinyourschema,butMySQLcheerfullyignoresthem.AlotofDBAsIknowwouldconsiderthisaverybadthing.

Aforeignkeyconstraintpreventsyoufromcreatinginconsistentdata.Forexample,let'ssupposethatyouhadaschemethatlookedlikethis:

CREATETABLEUSER（

USERIDINTEGER,

FIRST_NAMEVARCHAR（80）,

LAST_NAMEVARCHAR（80））;

CREATETABLEPURCHASE（

USERIDFOREIGNKEYUSER（USERID）,

ITEMINTEGER,

QUANTITYINTEGER）;

InadatabasesuchasOracle's,ifyoucreatedanentryinthePURCHASEtablewithauserIDof3,therewouldhavetoalreadybeauserIDof3intheUSERtableoranerrorwouldoccur.Similarly,youcouldn'tdeleteuser3fromUSERifitwasreferencedinPURCHASE.TheMySQLfolksmakeaprettyimpassionedargumentintheirdocumentationthatdependingonforeignkeysfordataintegrityisabadideaanyway,butconvincingyourDBAofthisphilosophyislikelytodegradeintoareligiousdebate.

Inaddition,someotherfeaturesaremissing,suchassubselectsandselectinto.Butprobablytheothermajorpiecethatyouwillmissistherollback/commitfunctionality.MySQLdoesimplementrollbackandcommitforcertaintypesoftables,butnotallofthem.Again,theMySQLfolksoffertheirownspinonwhythisisokay,butbeingabletorollbacktransactionsis（inmyopinion）importantenoughtomakesurethatyouhaveitavailable.

Rollbackallowsyoutosetasavepointonthedatabasebeforestartingtodoaseriesoftransactionswithit,andbeabletoeitherrollbacktotheoriginalstateorcommitthechangesattheend.Forexample,whenrecordingapurchase,youneedtorecordadebitagainsttheuser'saccountandenterarecordintotheshippingtablesothatyou'llknowlatertoshiptheitem.Let'ssaythatthesecondpartfails.Youwouldn'twanttochargetheuserbutnotshiptheitem.Thus,you'dwanttorollbacktothestatebeforethetransactionbegan.

So,MySQLisn'tafull-blownproductiondatabase—atleast,notyet.It'sstillgoodenoughforprobably90%ofthee-commercesitesintheworld,however.Andversion4.0,whichisinalphaasofthiswriting,addressesanumberoftheseconcerns,including