计算机专业文献翻译Jsp最佳实践Word格式.docx

计算机专业文献翻译Jsp最佳实践Word格式.docx

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1.SeparateHTMLfromJava

2.PlacebusinesslogicinJavaBeans

3.Factorgeneralbehavioroutofcustomtaghandlerclasses

4.FavorHTMLinJavahandlerclassesoverJavainJSPs

5.Useanappropriateinclusionmechanism

6.UseaJSPtemplatemechanism

7.Usestylesheets

8.UsetheMVCpattern

9.Useavailablecustomtaglibraries

10.UseJSPcommentsinmostcases

11.FollowHTMLbestpractices

12.UtilizetheJSPexceptionmechanism

ThesetipswillhelpyouwriteJSPsthatarereusableandeasytomaintain.

（1）SeparateHTMLfromJava

ItcanbetemptingtothrowallJavaandHTMLcodenecessaryforaWebpageintoasingleJSPfile.Insimplesystemdevelopment,suchanapproachmakesiteasyforsomeonenewtothesystemtolocateallrelevantcodeinoneplaceandunderstandhowitallinteracts.However,thisapproachbecomesburdensomeandcostlywhentheapplicationgrowsmorecomplexandmoredevelopersbecomeinvolved.

CombiningHTMLandJavainthesamesourcecodecanmakethecodesignificantlylessreadable.Toenhancesoftwarereadability,developersoftenuseindentation;

butmixingHTMLandJavascriptletsinthesamefilecanmakeusefulindentationextremelydifficulttomaintain.

ManyWebdevelopmentmethodologiesandarchitecturesnowemphasizetheseparationofHTMLfromJavacodesodifferentdeveloperscanfocusontheirstrengths.ProperlyseparatingJavaandHTML,includingHTML-likeJSPtagsandcustomtags,allowsWebdesignersandHTMLcoderstoworkontheHTML（presentation）aspects,whileJavadevelopersworkontheapplication′sJava（processinglogic）portions.Javadevelopersfocusonbusinesslogicastheyimplementthebehaviorbehindthecustomtags;

WebdesignersthenusethesecustomtagsjustastheyuseordinaryHTMLtags.

（2）PlacebusinesslogicinJavaBeans

JavacodeincludeddirectlyinsideaJSPisnotasreadilyaccessibletootherJSPsasJavacodecontainedwithinaJavaBean.CommonbehaviorandbusinesslogicplacedinJavaBeanscannotonlybeusedbyotherJSPsbutalsobyotherportionsoftheapplication.ThatisbecauseJavaBeansaremerelyJavaclassesthatsatisfysomebasicconventions（suchasaconstructorwithnoargumentsandpublicget/setmethodsforprivatedatamembers）andcanbeusedasanyotherJavaclass.NotethatEnterpriseJavaBeans（EJBs）arealsousefulforstoringbehaviorsanddatacommontoallcomponentsoftheapplication.

（3）Factorgeneralbehavioroutofcustomtaghandlerclasses

Javaclassesknownascustomtaghandlersimplementcustomtags.UnlikeJavaBeans,customtaghandlerclassesarenotreadilyusedlikeordinaryJavautilityclasses.Instead,customtaghandlerclassesimplementspecificinterfaces--orextendclassesthatprovidetheseinterfaces′basicimplementations.BecausetheyarenotreadilyreusedoutsideJSPs,customtaghandlersshouldcontainonlyspecificbehaviorthatwouldnotbeusefuloutsidethatcustomtag--thatis,outsidetheJSP.CustomtagsoftenrequiresupportforcommonbehaviorsorbusinesslogicandcanutilizeJavaBeansorEJBsthatperformthosecommonbehaviors.

（4）FavorHTMLinJavahandlerclassesoverJavainJSPs

SometimescleanlyseparatingHTML,JSPtags,andHTML-likecustomtagsfromJavarequiresunnecessarilyconvolutedcode.Inthesecases,youeitherincludeJavascriptletsandexpressionsintheJSPorputsomeHTMLcodeintheJavataghandlerclass.

I′dratherseeasmallamountofHTMLcodeintheJavaclassthanseeJava,suchasscriptletsandexpressions,intheJSP.Sincecustomtaghandlersarespecifictothecustomtagstheyimplement（andnotreusableoutsideJSPs）,placingnecessaryHTMLthereisnottroublesome.Sun′sJava2Platform,EnterpriseEdition（J2EE）Blueprintsdocumentationdiscussesthisissuefurther.

（5）Useanappropriateinclusionmechanism

Itisrarelygooddesigntoreproducecodecommonlyusedbydifferentapplicationpieceseachtimeanotherpieceofthatapplicationneedsthatfunctionality.FactoringcommonJSPorHTMLcodeoutofmultiplepagesandintoasinglefileimprovesmaintainability（youneedtomakechangesinonlyonelocation）andreusability.

TwoJSPincludemechanismsreducecoderedundancyandpromotereusability;

toensurethatyouusetheappropriateincludemechanism,itisimportanttoknowthedifferencesbetweenthetwo.Generally,IusetheincludedirectiveunlessIcanjustifyaneedfortheincludeaction.Question7intheBlueprints′"

WebTier"

sectionprovidesagoodresourceforunderstandingthedifferencesbetweenthetwoincludemechanismsanddeterminingwhichtouseinaparticularsituation.

（6）UseaJSPtemplatemechanism

AtemplatemechanismallowsforacommonfiletocontrolWebpage,orJSP,layout.Then,whenyouwanttochangethelayout,youneedtomodifyonlyonefile,andalltheotherpageswillreflectthelayoutchange.Thisdoesn′tjustmakeformoremaintainablecode;

usingtemplatestocontrollayoutalsomakesWebpagesmoreaestheticallypleasingtouserswhoseeconsistentlayoutsforallanapplication′spages.

（7）Usestylesheets

Justastemplatesenabledeveloperstoplacelayoutcontrolinasinglelocation,stylesheetsenabledeveloperstoplaceappearancecontrolinasinglelocation.IuseCascadingStyleSheets（CSS）tocontrolsuchitemsasfontfamilies,fontsizes,andtablecharacteristics.Liketemplates,stylesheetsallowthedevelopertomakechangesinonelocation;

thosechangesimmediatelyreflectonallappropriatepages,resultinginincreasedmaintainabilityandconsistentappearancetousers.

（8）UsetheMVCpattern

WhileotherdesignpatternscanbeusedeffectivelywithJSPs,IoftenusetheModel-View-Controller（MVC）architecturewithJSPtechnology.MVCenablesthedevelopmentofapplicationsthatareeasiertocreate,test,maintain,andenhance.InJSPterminology,implementationofanMVCarchitectureisoftenreferredtoasModel2（fromanearlyJSPspecification）.TheJ2EEBlueprintssamplesarebasedonMVC.

（9）Useavailablecustomtaglibraries

Whyshoulddevelopersspendtimereinventingthewheelandworryingabouttestinganddebuggingwhencustomtaglibrariesarereadilyavailableformanydifferentpurposes?

Somevendorsprovidecustomtaglibrariestotheircustomersforfreeorforindividualpurchase,butmanycustomtagscanbefoundonline.Resourcesprovidesagoodstartingpointforlocatingpotentiallyusefultaglibraries.

Whilethesethird-partycustomtaglibrariesoccasionallyhavebugs,mostlikelysuchproblemswillbediscovered,sincemanydevelopersusetheselibrariesandtestthemintheirownapplications.Also,manycustomtagsareopensource,soyoucaneditthemtomeetyourneeds.

Ifinditwellworthmytimetokeepinformedofavailablecustomtags,sincetheselibrariesoftenprovidefunctionalitycommontomostWebapplications.Whilelearningaboutavailablecustomtaglibrariesrequiresasmalltimeinvestment,reusingalready-availablecustomtagssavesthetimeofwriting,testing,anddebuggingmyowncustomtags.Asmentionedabove,manytaglibrariesarealsoopensource;

inthesecases,Icanreadilyadaptgeneralbehaviortomyspecificproject′ssituation.

（10）UseJSPcommentsinmostcases

Appropriatecommentingseemstochallengesoftwaredevelopers.JSPs,likeothertypesofcode,shouldincludecommentsthatdescribecomplexorextraordinaryfunctionality,thepages′purpose,andothergeneralinformationtypicallycommentedoutinsourcecode.

SinceJSPsallowdeveloperstointermixJava,JSPtags,andHTMLtagsinthesamepage,therearemultiplewaystocommentaJSPpage.Developersshouldcarefullyconsiderwhichtypeofcommenttoemployinthepage.HTMLcommentswillbeviewableinthecompiledJSP′sHTMLsourcecode,andbothmajorbrowsersmakeviewingthissourceeasy.JSPcomments,ontheotherhand,arenotplacedintheHTMLdocumentcreatedbytheJSPcompilationprocess.Thesecommentscannotbeviewedaspartofthepage′ssourcethroughthebrowser,andtheydonotincreasethesizeoftherenderedpage′sgeneratedsource.JavacommentscanalsooccurinaJSPinsideJavascriptletsections.Thesearenotviewableinthebrowsereither,butincludingJavacommentsintheJSPpageviolatestheprincipleofseparatingJavafromtheHTML.

Codecommentsareusuallymeantfordeveloperswhowriteandmaintaincode.Therefore,useJSPcommentsunlessthereisacompellingreasontohavethecommentsdisplayinthebrowseruponrequest.

（11）FollowHTMLbestpractices

WhenJavaisfactoredoutoftheJSPandintoJavaBeansandcustomtaghandlers,theJSPconsistsmostlyofJSPtags,includingcustomtags,andHTMLtags.TomaketheJSPeasiertounderstandandmaintain,followbestpracticesrelatedtoHTMLdevelopment.

（12）UtilizetheJSPexceptionmechanism

Whileathrownexception′sstacktraceprovesextremelyusefulfordeveloperswhendebuggingtheircode,itisrarelydesirabletoshareanentireexceptionstack