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acachinginfrastructurecanbeleveragedforperformance.ifthedatathatthewebservicereturnsisnotdynamicallygeneratedandcanbecached，thenthecachinginfrastructurethatwebserversandotherintermediariesinherentlyprovidecanbeleveragedtoimproveperformance.however，thedevelopermusttakecarebecausesuchcachesarelimitedtothehttpgetmethodformostservers.
theserviceproducerandserviceconsumerhaveamutualunderstandingofthecontextandcontentbeingpassedalong.becausethereisnoformalwaytodescribethewebservicesinterface，bothpartiesmustagreeoutofbandontheschemasthatdescribethedatabeingexchangedandonwaystoprocessitmeaningfully.intherealworld，mostcommercialapplicationsthatexposeservicesasrestfulimplementationsalsodistributeso-calledvalue-addedtoolkitsthatdescribetheinterfacestodevelopersinpopularprogramminglanguages.
bandwidthisparticularlyimportantandneedstobelimited.restisparticularlyusefulforlimited-profiledevicessuchaspdasandmobilephones，forwhichtheoverheadofheadersandadditionallayersofsoapelementsonthexmlpayloadmustberestricted.
webservicedeliveryoraggregationintoexistingwebsitescanbeenabledeasilywitharestfulstyle.developerscanusetechnologiessuchasasynchronousjavascriptwithxml（ajax）andtoolkitssuchasdirectwebremoting（dwr）toconsumetheservicesintheirwebapplications.ratherthanstartingfromscratch，servicescanbeexposedwithxmlandconsumedbyhtmlpageswithoutsignificantlyrefactoringtheexistingwebsitearchitecture.existingdeveloperswillbemoreproductivebecausetheyareaddingtosomethingtheyarealreadyfamiliarwith，ratherthanhavingtostartfromscratchwithnewtechnology.
asoap-baseddesignmaybeappropriatewhen
aformalcontractmustbeestablishedtodescribetheinterfacethatthewebserviceoffers.thewebservicesdescriptionlanguage（wsdl）describesthedetailssuchasmessages，operations，bindings，andlocationofthewebservice.
thearchitecturemustaddresscomplexnonfunctionalrequirements.manywebservicesspecificationsaddresssuchrequirementsandestablishacommonvocabularyforthem.examplesincludetransactions，security，addressing，trust，coordination，andsoon.mostreal-worldapplicationsgobeyondsimplecrudoperationsandrequirecontextualinformationandconversationalstatetobemaintained.withtherestfulapproach，developersmustbuildthisplumbingintotheapplicationlayerthemselves.
thearchitectureneedstohandleasynchronousprocessingandinvocation.insuchcases，theinfrastructureprovidedbystandardssuchaswsrmandapissuchasjax-wswiththeirclient-sideasynchronousinvocationsupportcanbeleveragedoutofthebox.
restfulsupportinjax-ws
thejavaapiforxmlwebservices（jax-ws）providesfullsupportforbuildinganddeployingrestfulwebservices.theapiwasdevelopedthroughthejavacommunityprocessprogramasjsr224.itistightlyintegratedwiththejavaarchitectureforxmlbinding（jaxb）forbindingxmltojavatechnologydataandisincludedinboththejavaplatform，standardedition（javase）6andthejavaplatform，enterpriseedition（javaee）5.
buildingrestfulservices
theexampleusedinthissectionbuildsonthepurchaseorderservicedescribedinthejavaeeblueprintscatalogasthe"patternsanddesign"whitepapers（parts1，2，and3）.theoriginalendpointcontainedonlyonemethod--acceptpo--thatacceptedapurchaseorderandreturnedapurchaseorderstatus，bothofwhichweredefinedbyindividualschemas.
table2ssomemorecrudoperationstoaddtothisservice.
table2：additionalcrudoperations
descriptionjavatechnologymethodsignature
aneworderpublicpurchaseorderstatusacceptpo（purchaseorderorder）
retrieveanexistingorderpublicpurchaseorderretrievepo（stringorderid）
modifyanexistingorderpublicpurchaseorderpo（purchaseorderorder）
cancelanorderalreadysubmittedpublicvoidcancelpo（stringorderid）
jax-wsenablesbuildingrestfulendpointsthroughajavax.xml.ws.providerinterfaceintheapi.providerisagenericinterfacethatcanbeimplementedbyaclassasadynamicnativetoaserviceendpointinterface（sei），andaserviceimplementingthisinterfacecanbedeployedinajavaeecontainerorpublishedinastand-alonemodethroughthejax-wsendpointapi.theproviderinterfacecontainsasinglemethodwiththefollowingsignature：
tinvoke（trequest）
providerisalow-levelgenericapi，butusingitrequirestheendpointtohaveanintimateknowledgeofthedesiredmessageorpayloadstructurebeingpassedtotheservice.dependingonhowtheproviderisimplemented，thesupportedtypesfortandtheirusesarethefollowing：
☆、第五十一章惨胜
insoftwareengineering，thetermsoftwarearchitecturalstylegenerallyrefersto"asetofdesignrulesthatidentifythekindsofcomponentsandconnectorsthatmaybeusedtocomposeasystemorsubsystem."*somecommonexamplesofarchitecturalstylesincludethepipeandfilter，layered，pushbased，andsoon.inthewebservicesworld，representationalstatetransfer（rest）isakeydesignidiomthatembracesastatelessclient-serverarchitectureinwhichthewebservicesareviewedasresourcesandcanbeidentifiedbytheirurls.webserviceclientsthatwanttousetheseresourcesaccessaparticularrepresentationbytransferringapplicationcontentusingasmallgloballydefinedsetofremotemethodsthatdescribetheactiontobeperformedontheresource.restisananalyticaldescriptionoftheexistingwebarchitecture，andthustheinterplaybetweenthestyleandtheunderlyinghttpprotocolappearsseamless.
thehttpmethodssuchasgetandpostaretheverbsthatthedevelopercanusetodescribethenecessary，read，，and（crud）actionstobeperformed.somemayseeananalogytooperationsinsql，whichalsoreliesonafewcommonverbs，asnintable1.however，thereststyleandhttpprotocolaremutuallyexclusive，andrestdoesnotrequirehttp.
table1：relationshipsbetweensqlandhttpverbs
actionsqlhttp
putreadgetpost
whentouserest
architectsanddevelopersneedtodecidewhenthisparticularstyleisanappropriatechoicefortheirapplications.arestfuldesignmaybeappropriatewhen
thewebservicesarecompletelystateless.agoodtestistoconsiderwhethertheinteractioncansurvivearestartoftheserver.
acachinginfrastructurecanbeleveragedforperformance.ifthedatathatthewebservicereturnsisnotdynamicallygeneratedandcanbecached，thenthecachinginfrastructurethatwebserversandotherintermediariesinherentlyprovidecanbeleveragedtoimproveperformance.however，thedevelopermusttakecarebecausesuchcachesarelimitedtothehttpgetmethodformostservers.
theserviceproducerandserviceconsumerhaveamutualunderstandingofthecontextandcontentbeingpassedalong.becausethereisnoformalwaytodescribethewebservicesinterface，bothpartiesmustagreeoutofbandontheschemasthatdescribethedatabeingexchangedandonwaystoprocessitmeaningfully.intherealworld，mostcommercialapplicationsthatexposeservicesasrestfulimplementationsalsodistributeso-calledvalue-addedtoolkitsthatdescribetheinterfacestodevelopersinpopularprogramminglanguages.
bandwidthisparticularlyimportantandneedstobelimited.restisparticularlyusefulforlimited-profiledevicessuchaspdasandmobilephones，forwhichtheoverheadofheadersandadditionallayersofsoapelementsonthexmlpayloadmustberestricted.
webservicedeliveryoraggregationintoexistingwebsitescanbeenabledeasilywitharestfulstyle.developerscanusetechnologiessuchasasynchronousjavascriptwithxml（ajax）andtoolkitssuchasdirectwebremoting（dwr）toconsumetheservicesintheirwebapplications.ratherthanstartingfromscratch，servicescanbeexposedwithxmlandconsumedbyhtmlpageswithoutsignificantlyrefactoringtheexistingwebsitearchitecture.existingdeveloperswillbemoreproductivebecausetheyareaddingtosomethingtheyarealreadyfamiliarwith，ratherthanhavingtostartfromscratchwithnewtechnology.
asoap-baseddesignmaybeappropriatewhen
aformalcontractmustbeestablishedtodescribetheinterfacethatthewebserviceoffers.thewebservicesdescriptionlanguage（wsdl）describesthedetailssuchasmessages，operations，bindings，andlocationofthewebservice.
thearchitecturemustaddresscomplexnonfunctionalrequirements.manywebservicesspecificationsaddresssuchrequirementsandestablishacommonvocabularyforthem.examplesincludetransactions，security，addressing，trust，coordination，andsoon.mostreal-worldapplicationsgobeyondsimplecrudoperationsandrequirecontextualinformationandconversationalstatetobemaintained.withtherestfulapproach，developersmustbuildthisplumbingintotheapplicationlayerthemselves.
thearchitectureneedstohandleasynchronousprocessingandinvocation.insuchcases，theinfrastructureprovidedbystandardssuchaswsrmandapissuchasjax-wswiththeirclient-sideasynchronousinvocationsupportcanbeleveragedoutofthebox.
restfulsupportinjax-ws
thejavaapiforxmlwebservices（jax-ws）providesfullsupportforbuildinganddeployingrestfulwebservices.theapiwasdevelopedthroughthejavacommunityprocessprogramasjsr224.itistightlyintegratedwiththejavaarchitectureforxmlbinding（jaxb）forbindingxmltojavatechnologydataandisincludedinboththejavaplatform，standardedition（javase）6andthejavaplatform，enterpriseedition（javaee）5.
buildingrestfulservices
theexampleusedinthissectionbuildsonthepurchaseorderservicedescribedinthejavaeeblueprintscatalogasthe"patternsanddesign"whitepapers（parts1，2，and3）.theoriginalendpointcontainedonlyonemethod--acceptpo--thatacceptedapurchaseorderandreturnedapurchaseorderstatus，bothofwhichweredefinedbyindividualschemas.
table2ssomemorecrudoperationstoaddtothisservice.
table2：additionalcrudoperations
descriptionjavatechnologymethodsignature
aneworderpublicpurchaseorderstatusacceptpo（purchaseorderorder）
retrieveanexistingorderpublicpurchaseorderretrievepo（stringorderid）
modifyanexistingorderpublicpurchaseorderpo（purchaseorderorder）
cancelanorderalreadysubmittedpublicvoidcancelpo（stringorderid）
