计算机科学与技术设计论文外文翻译.docx
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计算机科学与技术设计论文外文翻译.docx
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计算机科学与技术设计论文外文翻译
本科毕业设计(论文)
外文翻译(附外文原文)
系(院):
信息科学与工程学院
课题名称:
学生信息管理系统
专业(方向):
计算机科学与技术(应用)
7.1EnterActionMappings
TheModel2architecture(seechapter1)encouragesustouseservletsandJava-
ServerPagesinthesameapplication.UnderModel2,westartbycallingaservlet.
Theservlethandlesthebusinesslogicanddirectscontroltotheappropriatepage
tocompletetheresponse.
Thewebapplicationdeploymentdescriptor(web.xml)letsusmapaURLpattern
toaservlet.Thiscanbeageneralpattern,like*.do,oraspecificpath,like
saveRecord.do.
SomeapplicationsimplementModel2bymappingaservlettoeachbusiness
operation.Thisapproachworks,butmanyapplicationsinvolvedozensorhundreds
ofbusinessoperations.Sinceservletsaremultithreaded,instantiatingsomanyservletsisnotthebestuseofserverresources.Servletsaredesignedtohandleany
numberofparallelrequests.Thereisnoperformancebenefitinsimplycreating
moreandmoreservlets.
Theservlet’sprimaryjobistointeractwiththecontainerandHTTP.Handling
abusinessoperationissomethingthataservletcoulddelegatetoanothercomponent.
StrutsdoesthisbyhavingtheActionServletdelegatethebusinessoperation
toanobject.Usingaservlettoreceivearequestandrouteittoahandlerisknown
astheFrontControllerpattern[Go3].
Ofcourse,simplydelegatingthebusinessoperationtoanothercomponent
doesnotsolvetheproblemofmappingURIs[W3C,URI]tobusinessoperations.
OuronlywayofcommunicatingwithawebbrowseristhroughHTTPrequestsand
URIs.ArrangingforaURItotriggerabusinessoperationisanessentialpartof
developingawebapplication.
Meanwhile,inpracticemanybusinessoperationsarehandledinsimilarways.
SinceJavaismultithreaded,wecouldgetbetteruseofourserverresourcesifwe
couldusethesameActionobjecttohandlesimilaroperations.Butforthisto
work,wemightneedtopasstheobjectasetofconfigurationparameterstouse
witheachoperation.
Sowhat’sthebottomline?
ToimplementModel2inanefficientandflexible
way,weneedto:
EnterActionMappings195
_Routerequestsforourbusinessoperationstoasingleservlet
_Determinewhichbusinessoperationisrelatedtotherequest
_Loadamultithreadedhelperobjecttohandlethebusinessoperation
_Passthehelperobjectthespecificsofeachrequestalongwithanyconfiguration
detailusedbythisoperation
ThisiswhereActionMappingscomein.
7.1.1TheActionMappingbean
AnActionMapping(org.apache.struts.action.ActionMapping)describeshow
theframeworkhandleseachdiscretebusinessoperation(oraction).InStruts,
eachActionMappingisassociatedwithaspecificURIthroughitspathproperty.
Whenarequestcomesin,theActionServletusesthepathpropertytoselectthe
correspondingActionMapping.ThesetofActionMappingobjectsiskeptinan
ActionMappingscollection(org.apache.struts.action.ActionMappings).
Originally,theActionMappingobjectwasusedtoextendtheActionobject
ratherthantheActionclass.WhenusedwithanAction,amappinggivesaspecific
Actionobjectadditionalresponsibilitiesandnewfunctionality.So,itwasessentially
anActiondecorator[Go4].Alongtheway,theActionMappingevolvedintoan
objectinitsownrightandcanbeusedwithorwithoutanAction.
DEFINITIONTheintentofthedecoratorpatternistoattachadditionalresponsibilitiesto
anobjectdynamically.Decoratorsprovideaflexiblealternativetosubclassing
forextendingfunctionality[Go4].
TheActionMappingsareusuallycreatedthroughtheStrutsconfigurationfile.
Formoreaboutthisfile,seechapter4.
7.1.2TheActionMappingscatalog
TheActionMappingscatalogthebusinesslogicavailabletoaStrutsapplication.
Whenarequestcomesin,theservletfindsitsentryintheActionMappingscatalog
andpullsthecorrespondingbean.
TheActionServletusestheActionMappingbeantodecidewhattodonext.It
mayneedtoforwardcontrolofftoanotherresource.Oritmayneedtopopulate
andvalidateanActionFormbean.Atsomepoint,itmayhavetopasscontroltoan
Actionobject,andwhentheActionreturns,itmayhavetolookupanAction-
Forwardassociatedwiththismapping.
196CHAPTER7
DesigningwithActionMappings
TheActionMappingworkslikearoutingslipfortheservlet.Dependingon
howthemappingisfilledout,therequestcouldgojustaboutanywhere.
TheActionMappingsrepresentthecoredesignofaStrutsapplication.Ifyou
wanttofigureouthowaStrutsapplicationworks,startwiththeActionMappings.If
youwanttofigureouthowtowriteanewStrutsapplication,startwiththeAction-
Mappings.ThemappingsareattheabsolutecenterofeveryStrutsapplication.
Inthischapter,wetakeacloselookattheActionMappingpropertiesand
explorehowtheyhelpyoudesigntheflowofaStrutsapplication.
1.0vs1.1InStruts1.1,ActionMappingsubclassesActionConfig(org.apache.
struts.config.ActionConfig)andaddsAPImethodsrequiredfor
backwardcompatibility.ActionMappingisnotdeprecated,andhowthe
hierarchywillbehandledinfuturereleaseshasnotbeendetermined.
Fornow,werefertotheActionMappingclass,butyoushouldnotethat
inStruts1.1alloftheactionpropertiesareactuallydefinedbytheActionConfig
superclass.TheActionMappingclassotherwiseworksthe
samewayinbothversions.
7.2ActionMappingproperties
Table7.1describesthebaseActionMappingproperties.Aswithotherconfiguration
components,developersmayextendActionMappingtoprovideadditional
properties.
Table7.1ThebaseActionMappingproperties
PropertyDescription
pathTheURIpathfromtherequestusedtoselectthismapping.(APIcommand)
forwardThecontext-relativepathoftheresourcethatshouldservethisrequestviaaforward.
Exactlyoneoftheforward,include,ortypepropertiesmustbespecified.
or
includeThecontext-relativepathoftheresourcethatshouldservethisrequestviaan
include.Exactlyoneoftheforward,include,ortypepropertiesmustbe
specified.
or
typeOptionallyspecifiesasubclassoforg.apache.struts.action.ActionMapping
thatshouldbeusedwheninstantiatingthismapping.
classNameThefullyqualifiednameoftheActionclassusedbythismapping.
Since
Struts1.1
ActionMappingproperties197
Inthesectionsthatfollow,wetakealookateachoftheseproperties.
7.2.1Thepathproperty
TheActionMappingURI,orpath,willlooktotheuserlikejustanotherfileon
thewebserver.Butitdoesnotrepresentafile.Itisavirtualreferencetoour
ActionMapping.
Becauseitisexposedtoothersystems,thepathisnotreallyalogicalname,like
thoseweusewithActionForward.Thepathcanincludeslashesandanextension—
asifitreferredtoafilesystem—buttheyarealljustpartofasinglename.
TheActionMappingsthemselvesarea“flat”namespacewithnotypeofinternal
hierarchywhatsoever.Theyjusthappentousethesamecharactersthatweare
usedtoseeinginhierarchicalfilesystems.
nameThenameoftheformbean,ifany,associatedwiththisaction.Thisisnottheclass
name.Itisthelogicalnameusedintheformbeanconfiguration.
rolesThelistofsecurityrolesthatmayaccessthismapping.
scopeTheidentifierofthescope(requestorsession)withinwhichtheformbean,ifany,
associatedwiththismappingwillbecreated.
validateSettotrueifthevalidatemethodoftheformbean(ifany)associatedwiththis
mappingshouldbecalled.
inputContext-relativepathoftheinputformtowhichcontrolshouldbereturnedifavalidation
errorisencountered.ThiscanbeanyURI:
HTML,JSP,VM,oranotherAction-
Mapping.
parameterGeneral-purposeconfigurationparameterthatcanbeusedtopassextrainformation
totheActionselectedbythisActionMapping.
attributeNameoftherequest-scopeorsession-scopeattributeunderwhichourformbeanis
accessed,ifitisotherthanthebean'sspecifiedname.
prefixPrefixusedtomatchrequestparameternamestoformbeanpropertynames,ifany.
suffixSuffixusedtomatchrequestparameternameswhenpopulatingthepropertiesof
ourActionFormbean,ifany.
unknownCanbesettotrueifthismappingshouldbeconfiguredasthedefaultforthisapplication
(tohandleallrequestsnothandledbyanothermapping).Onlyonemapping
canbedefinedasthedefaultunknownmappingwithinanapplication.
forwards(s)BlockofActionForwardsforthismappingtouse,ifany.
exception(s)BlockofExceptionHandlersforthismappingtouse,ifany.
Table7.1ThebaseActionMappingproperties(continued)
PropertyDescription
Since
Struts1.1
Since
Struts1.1
198CHAPTER7
DesigningwithActionMappings
Ofcourse,itcanstillbeusefultotreatyourActionMappingsasiftheywere
partofahierarchyandgrouprelatedcommandsunderthesame"folder."The
onlyrestrictionisthatthenamesmustmatchwhateverpatternisusedinthe
application’sdeploymentdescription(web.xml)fortheActionServlet.Thisisusually
either/do/*or*.do,butanysimilarpatterncanbeused.
Ifyouareworkinginateamenvironment,differentteammemberscanbe
givendifferentActionMappingnamespacestouse.Somepeoplemaybeworking
withthe/customerActionMappings,othersmaybeworkingwiththe/vendor
ActionMappings.ThismayalsorelatetotheJavapackagehierarchytheteamis
using.SincetheActionMappingURIsarelogicalconstructs,theycanbeorganized
inanywaythatsuitsyourproject.
WithStruts1.1,thesetypesofnamespacescanbepromotedtoapplication
modules.Eachteamcanworkindependentlyonitsownmodule,withitsownset
ofconfigurationfilesandpresentationpages.Configur
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