英文文献 科技类 原文及翻译 65文档格式.docx

英文文献 科技类 原文及翻译 65文档格式.docx

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DbFormsbuildsontopofJavaServlets2.2andJavaServerPages1.1technologiesbySunMicrosystems.ItmakesextensiveuseoftheJSPTagLibraryextensionintroducedintheJSP1.1specification.

Theproject'

shomepageislocatedathttp:

//www.dbforms.organdcontainsacompleteusermanual,severaltechnicalarticles,sourceandbinarydistributions,onlineexamples,aCVS,mailinglists,andlotsofotherinformationrelatedtoDbForms.

DbFormsimplementstheconceptsoftheModel-View-Controller（MVC）designpattern.（SeeDesignPatterns:

ElementsofReusableObject-OrientedSoftware,ErichGamma,RichardHelm,RalphJohnson,andJohnVlissides,AddisonWesley,October1994.）YoudonotneedtoprovideanyController-relatedcode;

justfocusondefiningtheModelandcreatingtheJSPviewcomponentsoftheapplication（mainlyusingDbFormscustomtags）.

ThefollowingdiscusseshowModel,ViewandControllerinteractinDbForms.

TheModel:

DatabaseObjectsDescribedbyDatabaseMetadata

TheuseofDbFormsistoperformoperationsondatabases.ThedatabasetablesaccessedbyaDbFormsapplicationmustbedeclaredinaXMLconfigurationfile（usuallystoredasWEB-INF/dbforms-config.xml）,whichisparsedandevaluatedatWeb-applicationstartuptime.

AsshowninListing1,everytable（orview）tobeaccessedbyDbFormshastobedeclaredinsideofa<

table>

element.Allrelevanttablefieldsneedtobedeclaredinsideofa<

field>

elementnestedwithinitsrespective<

element.

ThereexistsatoolforgeneratingthisXMLdataautomatically.Thetoolreadsdatabasemetadataofaspecifieddatabaseandconstructsaconfigurationfile,asshowninListing1.TheController:

Parsing,Dispatching,andExecutingEvents

Aspointedoutabove,youdonotneedtoprovideanyController-relatedcodewhentheControllerisatrueinfrastructuralcomponent.However,it'

susefulifyouhaveanideaofwhat'

sgoingoninsidetheController.Thefollowinglinesprovidethatinformation.

TheControllerincludesseveralcomponents:

ControllerServlet:

thisservletisthesinglepointofentryforallincomingHTTPrequestsfromclients.

EventEngine:

anassistanttotheControllerServlet,itfocusesonfilteringHTTPrequestsforWebEventsandinstantiatesthem.

WebEventObjects:

allObjectsderivedfromtheabstractsuper-classWebEventhavetheabilitytoinitializethemselvesbyreadingagivenHTTPrequest.Theseeventsgetexecuted,eitherdirectlybytheControllerorbytheView.

Thefollowingdescriptionoftheexecutionofatypicaluseractionshouldgiveyouabetterpictureofwhatthecontrollerdoesandhowitinteractswiththeothercomponents:

1.Userpressesthebutton"

deleterow"

onhis/herDbFormsapplication.

2.ClientbrowsersubmitsdataviaHTTP-POSTtotheController-servlet.

3.TheControllerServletdelegatestheincomingrequesttotheEventEngine,whichdeterminesthemainevent（theuserexplicitlytriggeredtheeventbyclickingabutton）.However,theremayoccurimplicitevents,too--i.e.,automaticupdatingofallchangedinputfieldsofalldatarows.

4.TheEventEnginecomponentparsesthatrequestanddeterminesthekindofactiontheuserwantstobeexecuted.

5.ItthencreatestheappropriateWebEvent（inourcase,aDeleteEvent）anddelegatestherequestObjecttothisnewly-createdWebEvent,whichfinalizesitsowninitialization.Afterthat,theEventEnginereturnstherecently-createdand-initializedeventbacktotheControllerServlet.

6.TheControllerServlettellstheeventtoexecuteitsbuilt-inoperation,ifitisaDatabaseEvent.Otherevents（NavigationEvent,etc.）aredelegatedtotheappropriateViewcomponent.

7.TheControllerServletinvokesEventEngineagaintocheckifthereareadditional（implicit）eventstobeexecuted.Ifso,theappropriatedWebEventObjectsarecreatedandexecutedinthesamemannerasthemaineventdescribedabove.

8.TheControllerServletdeterminestheViewcomponenttowhichtherequestshouldbeforwarded.Iffound,theControllerServletinvokesthecomponentandforwardstherequest.

9.IftheViewcomponentisaJSPpagecontainingDbFormstags,thosetagswillsearchfornavigationeventstobeexecuted,andwillfinallygeneratetheresponsefortheuser.

10.Theresponseisrenderedbytheuser'

sWebbrowser.

TheView:

JSPTemplatesProvidedbytheApplicationDeveloper

TheViewportionofaDbFormsapplicationisgenerallyconstructedusingJSPtechnology.JSPfilesmaycontainstaticHTMLelements,aswellasdynamicelementscontainingJavacode（definitions,statements,expressions）.FormoreinformationaboutJSP,pleaseseeSun'

sJSPpage.

Withrelease1.1oftheJSPAPI,apowerfulfacilitycalledJSPtaglibrarieswasadded.Withthesecustomtags,youcanencapsulateevenmostsophisticatedJavacodeintolightweightJSPtags.

DbFormsmakesuseofthegreatpotentialofJSPtaglibraries.Itcontainsanextensivecustomtagslibraryforrenderingandmanipulatingdatabasedata.

TheStructureofaDbFormsView

Figure1givesaconceptualoverviewofthemaincomponentsofatypicalDbFormsview.

TheBasicConceptsofForms

EachDbForms-viewJSPmayhaveoneormoreroottagsofthetypeform.Everyformtaghastocontainexactlyoneheadertag,exactlyonebodytag,andexactlyonefootertag,inexactlythatorder.

Eachofthosetagsmaycontainsub-elementslikedatafields,inputfields,actionbuttons,and--ofcourse--plainHTMLtextandJSPcode.

headerandfootertagsarecommonlyusedfortitlesofpages,labellingtables,placingactionandnavigationbuttons,inputfieldstoenternewdata,etc.headerandfootertagsgetevaluatedonlyonce.

Thebodytagisusedforshowingdatarowscomingfromthedatabase,andforprovidingtheuserwiththefunctionalitytoeditthatdata.Howmanytimesthebodytaganditssub-elementsgetrendereddependsonthevalueofthemaxRowsattributeoftheformelement（andofcourse,onthenumberofdatasetsactuallyfetchedfromthedatabase）.

maxRows=n--bodygetsexecutedntimesatmaximum（withninN）

maxRows="

*"

--bodygetsexecutedforeveryrowinthetable（"

endless"

form）

NestedForms

Everyformmaycontainoneormorenestedsub-formsinsideitsbodyelement.

The"

orders"

formisnestedwithinthebodyelementofthe"

customer"

form,asshowninFigure2.Theuserwillseeonecustomerperpage（becausemaxRowsissetto"

1"

）andalltheorders（becausemaxRows="

）thecustomerhastaken.Theusermaynavigatethroughthelistofcustomersbyclickingthenavigationbuttons.

OK,Let'

sSeeSomeCode!

Asstatedbefore,JSPviewsaretheonlypartsofaDbFormsapplicationadeveloperusuallyneedstoputhis/herhandson.DbFormsprovidesanextensivecustomtaglibrarywhichmakesthisaneasytask,sothatitcanbeperformedevenbynon-programmers.

Aswewillseelater,muchofthiscodecanbegeneratedautomaticallybytoolsincludedinDbForms.However,itisusefultounderstandthebasicsofDbFormsviews,evenifmuchoftheworkcanbedoneautomatically.

ThefollowingtwosectionswillshowasimpleandamoreadvancedexampleofaDbFormsview.BothexamplescanbethoughtasbeingpartsofalittleCRMapplicationofa（virtual）agency.

ASimpleExample

Description:

ThisJSPview（service.jsp）enablestheuser（s）toadministertheservicestheagencyprovidestoitscustomers.Theuser（anemployeeoftheagencyorcallcenteragent）shouldgetalistofalltheexistingservices,alongwithtextfieldsandbuttonstoupdateanddeletedata.Finally,anemptyinputmaskforinsertingnewservicesisneeded.

WehavesetmaxRowsto"

whichhastheeffectthatallrowswillbeshownatonce.Ifthereexisthundredsofservices,wewouldliketosetmaxRowsto"

10,"

"

20,"

oranotherlimitednumber,andwewouldinstantiatenavigationbuttonsforscrollingbetweenthepages.Wewillusethatpatternlater.

Theerrorstagshowsalistoferrors,ifanyoccurred（i.e.duplicatekeyerror,etc.）.

TheupdateButtonanddeleteButtontagsareplacedinthebodyandthereforerenderedforeachrow.

AnExampleofNestedForms

Thefollowingpage（customer_order.jsp）givesyouthefunctionalitytomanagetheincomingordersofacustomer.Youareabletoeditbothordersofacustomerandthecustomerdataitself.Furthermore,youdonotneedtostrugglewithplainserviceIDs,butwillbeabletoconvenientlyselecttheservicesfromaselectboxbyname.

Withthispage,wehavedemonstratedanothercoupleofm