外文翻译Struts 开发的最佳实践Word文件下载.docx
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外文翻译Struts 开发的最佳实践Word文件下载.docx
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First,we'
llexplaintheStrutscomponentsinthecontextofbestpracticesandtheroleeachoneplaysinyourWebapplicationdevelopment.
Action
Every
Action
ofyourapplicationextendsStruts'
org.apache.struts.action.Action.These
classesprovideaninterfacetotheapplication'
sModellayer,actingasawrapperaroundthebusinesslogic.Each
classmustprovideitscase-specificimplementationtothe
perform()
method.The
methodalwaysreturnsavalueoftype
ActionForward.
ActionForm
ActionForm
org.apache.struts.action.ActionForm.
ActionFormsaresimpleJavaBeansthatencapsulateandvalidaterequestparameters.Tovalidateyourrequestdata,your
ActionForm'
s
validate()
methodmustgiveacase-specificimplementation.
ActionFormsserveasacarrierofrequestdatatothe
class.AJSPobjectcombineswitharespective
toformyourapplication'
sViewlayer,wherealmosteveryformfieldoftheJSPobjectmapstoanattributeofthecorresponding
ActionForm.
JSPcustomtaglibraries
TheJSPcustomtaglibrariesareacollectionofactionspresentedastags.ThisisapowerfulfeatureoftheJSPSpecification1.1;
itallowsyoutoseparatepresentationfromotherapplicationtiers.ThelibrariesareeasytouseandyoucanreadtheminXML-likefashion.YoucaneasilymaintaintheJSPcomponentsbyminimizingtheuseofJavascriptletsinthem.TheJSPtagsthatStrutsprovidesincludeHTML,logic,andbeantags.
ActionErrors
Youuse
ActionErrorstosupportexceptionhandling.An
ActionError
trapsandpropagatesanapplicationexceptiontotheViewlayer.Eachoneisacollectionof
instances.
ActionErrorsencapsulateerrormessages,whilethe
<
/html:
errors>
inthePresentationlayerrendersallerrormessagesinthe
collection.
BestPractice1.ReusedataacrossmultipleActionForms
NowthatyouarefamiliarwiththeStrutscomponents,wewillcontinuebyshowingyouwaystogetthemostoutoftheframework.First,StrutsrecommendsthatyouassociateeveryJSPobjectwithan
ActionForm,whichencapsulatesdatarepresentedinthescreen.YouaccesstheformdataintheJSPobjectusingaccessorymethodsfoundin
ActionForm.Listing1showstheconventionaluseof
tagintheViewlayer.
Listing1.UsingActionForminJSP
html:
formaction="
/bp1"
>
<
textproperty="
attrib1"
/>
form>
The
called"
BP1AForm"
includestheattribute
attrib1,aswellasitsgetterandsettermethods.Intheconfigurationfilestruts-config.xml,theaction"
mapsto
bp1AForm
usingthe
name
attribute.ThisfacilitatesdatadisplayintheJSP.
Toimplementthisbestpractice,Strutsrecommendsyoudotwothings:
1.CreateaJavaBean(BP1BForm)withattributesthatformanattributesubsetin
BP1AForm,alongwiththeattributes'
getterandsettermethods.
2.Replacetheattributesin
BP1AForm
withthebean
BP1BForm
byassociatingthebeanwith
BP1AForm.Nowyoucanaccessthisattributesubsetin
through
BP1BForm.Listing2showsyouhow.
Listing2.AccessingformattributesinJSP
bean:
definename="
bp1AForm"
property="
bp1BForm"
id="
bp1B"
type="
com.ibm.dw.webarch.struts.BP1BForm"
textname="
subsetAtt1"
BestPractice2.UseActionclasstohandlerequests
TypicallywhenusingtheStrutsframework,foreveryactiontheJSPcomponentrequestsyourapplicationtoexecute,theapplicationmustextendStruts'
org.apache.struts.action.Action
tocreatean
class.Thisindividual
classinterfaceswiththeapplication'
sModellayerwhileprocessingtherequest.
Toimplementthispractice,Strutsrecommendsyoufollowthesesteps:
1.Createan
class,say
BP2Action,byextending
org.apache.struts.action.Action.
2.Createallother
classesinyourWebapplicationbyextending
BP2Action.
3.In
BP2Action,createamethod
performTask(),asinpublicabstract
ActionForwardperformTask(ActionMappingmapping,ActionFormform,HttpServletRequestrequest,HttpServletResponseresponse)throwsIOException,ServletException.
4.In
BP2Action
addoneormoregenericmethodstotheapplication,forexample
serverSideValidate().Youcandecideonthemethod'
saccessmodifierbyconsideringthefollowingfactors:
oIfall
classesmustimplementthismethod,makeitabstract.
oIfsome
classeswillprovideacase-specificimplementation,declarethemethodprotectedandgiveitadefaultimplementation.
5.In
BP2Action,declaremethod
asfinal.Invoketheabovegenericmethod,whichmustalwaysbecalledbeforeprocessingtherequest.Nowcallthemethod
performTask()
createdin
step3.
6.Inevery
classextending
BP2Action,addmethod
withacase-specificimplementation.
Advantages
Thispracticehastwomainadvantages.First,ithelpsyouavoidredundantcodeinevery
classofyourWebapplication.Second,itgivestheapplicationmorecontrolovergenerictasksbycentralizingthebehaviorinone
class.
BestPractice3.UseActionFormtoworkonsessiondata
InaStruts-basedWebapplication,each
extends
org.apache.struts.action.ActionForm.These
ActionFormsencapsulatepagedataandprovideavalidationframeworktovalidaterequestparameters.
MostWebapplicationsmaintaindatainsessiontomakethemavailablethroughouttheapplication.ThisbestpracticeaddressesthisWebapplicationfeature.Itallowsmethods
toSession()
and
fromSession()
tomovesessiondatatoandfromtheformdata.Thus,itaddressessessiondatamaintenanceinaWebapplication.
Toadheretothispractice,followthesesteps:
1.Createanabstractclassnamed
BP3Form
byextending
org.apache.struts.action.ActionForm.
2.In
BP3Form,addmethodswithaccessmodifiersasinpublicabstract
voidtoSession(SessionDatasessionData)
voidfromSession(SessionDatasessionData).
3.Inevery
ActionForm,extend
andimplementtheabstractmethodsinwhichtheformdataistransportedtoandfromthesession.
4.Thecorresponding
classmaydeterminetheorderinwhichthesemethodsarecalled.Forexample,youcouldinvokemethod
onthe
justbefore
actionForward
isdetermined.
Whentousethispractice
Thispracticeismostusefulwhensessiondataismaintainedasasingleobjectand/oreverypagemanipulatesorusessessiondata.
BestPractice4.Handleexceptionseffectively
Conventionally,whenanapplicationexceptionoccursinan
class,theexceptionisfirstlogged.ThentheclasscreatesanActionError
andstoresitintheappropriatescope.This
classthenforwardscontroltotheappropriate
ActionForward.Listing3showshow
classhandlesexceptions.
Listing3.ExceptionhandlinginanActionclass
try{
//CodeinActionclass
}
catch(ApplicationExceptione){
//logexception
ActionErrorsactionErrors=newActionErrors();
ActionErroractionError=newActionError(e.getErrorCode());
actionErrors.add(ActionErrors.GLOBAL_ERROR,actionError);
saveErrors(request,actionErrors);
Whileconventionalexceptionhandlingproceduressaveexceptioninformationinevery
class,bestpractice4aimstoavoidredundantcodewhilehandlingexceptions.
Tousethispractice,Strutsrecommendsfollowingthesesteps:
BP4Action,byextending
BP4Action.
BP4Action,declarevariable
ActionErrorsactionErrors=newActionErrors();
.
BP4Action,createamethod
asinpublicabstract
ActionForwardperformTask(ActionMappingmapping,ActionFormform,HttpServletRequestrequest,HttpServletResponseresponse,ActionErrorsactionErrors)throwsIOException,ServletException.
BP4Action,declaremethod
asfinal.Theninvokegenericmethods,whichmustalwaysbecalledbeforeprocessingtherequest.Nowyoucancallthemethod
createdinthepreviousstep.
6.Whileimplementingmethod
inevery
class(byextending
BP4Action),handleapplicationexceptionsasshowninListing4.
Listing4.UsingActionErrorseffectively
try{
catch(ApplicationExceptionappException){
//Logexception
//AdderrortoactionErrors
actionErrors.add(ActionErrors.GLOBAL_ERROR,
newActionError(appException.getErrorCode()));
In
BP4Action,afterinvokingthemethod
performTask(),savethe
ActionErrors
using
saveErrors(request,errors).
Thispractice'
smainadvantageisthatitavoidscoderedundancyinevery
classthathandles
ActionErrors.
Inconclusion
BuildinganeasilymaintainableWebapplicationcanbeoneofthemostchallengingtasksforadevelopmentt
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