计算机专业文献翻译XML与JSP联手Word文档格式.docx

计算机专业文献翻译XML与JSP联手Word文档格式.docx

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justuseatexteditor,ratherthanacomplicateddatabasetool.XMLfilesarealsoeasiertobackup,tosharewithyourfriends,ortodownloadtoyourclients.Youcanalsoeasilyuploadnewdatatoyoursite,usingFTP.

AmoreabstractadvantageofXMListhat,beingahierarchicalratherthanarelationalformat,itcanbeusedinamuchmorestraightforwardmannertodesigndatastructuresthatfityourneeds.Youdon'

tneedtouseanentityrelationshipeditornornormalizeyourschema.Ifyouhaveoneelementthatcontainsanotherelement,youcanrepresentthatdirectlyintheformat,ratherthanusingajointable.

Notethatformanyapplications,afilesystemwillnotsuffice.Ifyouhaveahighvolumeofupdates,afilesystemmaygetconfusedorcorruptedbysimultaneouswrites;

databasesusuallysupporttransactions,whichallowconcurrencywithoutcorruption.Further,adatabaseisanexcellenttoolifyouneedtomakecomplicatedqueries,especiallyiftheywillvaryfromtimetotime.Databasesbuildindexes,andareoptimizedforkeepingtheindexesuptodatewithaconstantlychangingdataset.Relationaldatabasesalsohavemanyotheradvantages,includingarichquerylanguage,matureauthoringandschemadesigntools,provenscalability,fine-grainedaccesscontrol,andsoon.

（Note:

Youcanusesimplefilelockingtoprovideapoorman'

stransactionserver.AndyoucanalsoimplementanXMLindex-and-searchtoolinJava,butthat'

satopicforanotherarticle.）

Inthiscase,asinmostlow-to-mediumvolume,publishing-basedWebsites,youcanassumethefollowing:

mostofthedataaccessisreads,notwrites;

thedata,thoughpotentiallylarge,isrelativelyunchanging;

youwon'

tneedtodocomplicatedsearches,butifyoudo,you'

lluseaseparatesearchengine.TheadvantagesofusingamatureRDBMSfade,whiletheadvantageofusinganobject-orienteddatamodelcometothefore.

Finally,it'

sentirelypossibletoprovideawrapperforyourdatabasethatmakesSQLqueriesandtranslatesthemintoXMLstreams,soyoucouldhaveitbothways.XMLbecomesamorerobust,programmer-friendlyfrontendtoamaturedatabaseforstoringandsearching.（Oracle'

sXSQLservletisoneexampleofthistechnique.）

Theapplication:

Anonlinephotoalbum

Everybodylovesphotos!

Peopleloveshowingpicturesofthemselves,theirfriends,theirpets,andtheirvacations.TheWebistheultimatemediumforself-indulgentshutterbugs--theycanannoytheirrelativesfromthousandsofmilesaway.Whileafull-fledgedphotoalbumsitewouldrequireacomplicatedobjectmodel,I'

llfocusondefiningasinglePictureobject.（ThesourcecodeforthisapplicationisavailableinResources.）Theobjectrepresentingapictureneedsfieldsrepresentingitstitle,thedateitwastaken,anoptionalcaption,and,obviously,apointertotheimagesource.

Animage,inturn,needsafewfieldsofitsown:

thelocationofthesourcefile（aGIForJPEG）andtheheightandwidthinpixels（toassistyouinbuilding<

img>

tags）.Herethereisoneneatadvantagetousingthefilesystemasyourdatabase:

youcanstoretheimagefilesinthesamedirectoryasthedatafiles.

Finally,let'

sextendthepicturerecordwithanelementdefiningasetofthumbnailimagesforuseinthetableofcontentsorelsewhere.HereIusethesameconceptofimageIdefinedearlier.

TheXMLrepresentationofapicturecouldlooksomethinglikethis:

<

picture>

<

title>

AlexOnTheBeach<

/title>

date>

1999-08-08<

/date>

caption>

Tryinginvaintogetatan<

/caption>

image>

src>

alex-beach.jpg<

/src>

width>

340<

/width>

height>

200<

/height>

/image>

thumbnails>

alex-beach-sm.jpg<

72<

alex-beach-med.jpg<

150<

99<

/thumbnails>

/picture>

NotethatbyusingXML,youputalltheinformationaboutasinglepictureintoasinglefile,ratherthanscatteringitamongthreeorfourseparatetables.Let'

scallthisa.pixfile--soyourfilesystemmightlooklikethis:

summer99/alex-beach.pix

summer99/alex-beach.jpg

summer99/alex-beach-sm.jpg

summer99/alex-beach-med.jpg

summer99/alex-snorkeling.pix

etc.

Techniques

There'

smorethanonewaytoskinacat,andthere'

smorethanonewaytobringXMLdataontoyourJSPpage.Hereisalistofsomeofthoseways.（Thislistisnotexhaustive;

manyotherproductsandframeworkswouldserveequallywell.）

DOM:

YoucanuseclassesimplementingtheDOMinterfacetoparseandinspecttheXMLfile

XMLEntryList:

YoucanusemycodetoloadtheXMLintoajava.util.Listofname-valuepairs

XPath:

YoucanuseanXPathprocessor（likeResin）tolocateelementsintheXMLfilebypathname

XSL:

YoucanuseanXSLprocessortotransformtheXMLintoHTML

Cocoon:

YoucanusetheopensourceCocoonframework

Rollyourownbean:

YoucanwriteawrapperclassthatusesoneoftheothertechniquestoloadthedataintoacustomJavaBean

NotethatthesetechniquescouldbeappliedequallywelltoanXMLstreamyoureceivefromanothersource,suchasaclientoranapplicationserver.

JavaServerPages

TheJSPspechashadmanyincarnations,anddifferentJSPproductsimplementdifferent,incompatibleversionsofthespec.IwilluseTomcat,forthefollowingreasons:

Itsupportsthemostup-to-dateversionsoftheJSPandservletspecs

It'

sendorsedbySunandApache

YoucanrunitstandalonewithoutconfiguringaseparateWebserver

sopensource

（FormoreinformationonTomcat,seeResources.）

YouarewelcometouseanyJSPengineyoulike,butconfiguringitisuptoyou!

BesurethattheenginesupportsatleasttheJSP1.0spec;

thereweremanychangesbetween0.91and1.0.TheJSWDK（JavaServerWebDevelopmentKit）willworkjustfine.

TheJSPstructure

WhenbuildingaJSP-drivenWebsite（alsoknownasaWebapp）,Iprefertoputcommonfunctions,imports,constants,andvariabledeclarationsinaseparatefilecalledinit.jsp,locatedinthesourcecodeforthisarticle.

IthenloadthatfileintoeachJSPfileusing<

%@includefile="

init.jsp"

%>

.The<

%@include%>

directiveactsliketheClanguage'

s#include,pullinginthetextoftheincludedfile（here,init.jsp）andcompilingitasifitwerepartoftheincludingfile（here,picture.jsp）.Bycontrast,the<

jsp:

include>

tagcompilesthefileasaseparateJSPfileandembedsacalltoitinthecompiledJSP.

Findingthefile

WhentheJSPstarts,thefirstthingitneedstodoafterinitializationisfindtheXMLfileyouwant.Howdoesitknowwhichofthemanyfilesyouneed?

TheanswerisfromaCGIparameter.TheuserwillinvoketheJSPwiththeURLpicture.jsp?

file=summer99/alex-beach.pix（orbypassingafileparameterthroughanHTMLform）.

However,whentheJSPreceivestheparameter,you'

restillonlyhalfwaythere.Youstillneedtoknowwhereonthefilesystemtherootdirectorylies.Forexample,onaUnixsystem,theactualfilemaybeinthedirectory/home/alex/public_html/pictures/summer99/alex-beach.pix.JSPsdonothaveaconceptofacurrentdirectorywhileexecuting,soyouneedtoprovideanabsolutepathnametothejava.iopackage.

TheServletAPIprovidesamethodtoturnaURLpath,relativetothecurrentJSPorServlet,intoanabsolutefilesystempath.ThemethodServletContext.getRealPath（String）doesthetrick.EveryJSPhasaServletContextobjectcalledapplication,sothecodewouldbe:

Stringpicturefile=

application.getRealPath（"

/"

+request.getParameter（"

file"

））;

or

getServletContext（）.getRealPath（"

whichalsoworksinsideaservlet.（Youmustappenda/becausethemethodexpectstobepassedtheresultsofrequest.getPathInfo（）.）

Oneimportantnote:

wheneveryouaccesslocalresources,beverycarefultovalidatetheincomingdata.Ahacker,oracarelessuser,cansendbogusdatatohackyoursite.Forinstance,considerwhatwouldhappenifthevaluefile=../../../../etc/passwdwereentered.Theusercouldinthiswayreadyourserver'

spasswordfile.

TheDocumentObjectModel

DOMstandsfortheDocumentObjectModel.ItisastandardAPIforbrowsingXMLdocuments,developedbytheWorld