外文翻译-管理持久性实体writing container-managed persistent entity beans

WRITINGCONTAINERMANAGEDPERSISTENTENTITYBEANSCONTAINERMANAGEDFIELDSACONTAINERMANAGEDPERSISTENTENTITYBEANALLOWSTHECONTAINERTOHANDLESOMEORALLOFITSDATAACCESSLOGICRATHERTHANCODINGJDBCORSQL/JOPERATIONSINYOURBEANCLASS,YOURCONTAINERIMPLICITLYPERFORMSALLDATABASEOPERATIONSBEHINDTHESCENESWITHCONTAINERMANAGEDPERSISTENCE,YOUMUSTMAKESOMEOFYOURENTITYBEANCLASSSFIELDSPUBLICSOTHATTHECONTAINERCANSETTHEFIELDSWHENITPERFORMSDATABASEOPERATIONSONBEHALFOFYOURBEANTHEFIELDSTHATYOUWANTTOBEPERSISTENTARECALLEDCONTAINERMANAGEDFIELDSYOUDONTHAVETOWORRYABOUTSETTINGTHESEFIELDSTHEEJBCONTAINERWILLAUTOMATICALLYMANIPULATETHEMFORYOUBEHINDTHESCENESWHENITPERFORMSSTORAGEOPERATIONSONERESTRICTIONOFCONTAINERMANAGEDFIELDSISTHATEVERYFIELDYOUWANTTOBEMANAGEDBYTHECONTAINERMUSTFOLLOWTHERULESFORJAVAOBJECTSERIALIZATIONWEDESCRIBETHESERULESINFULLINAPPENDIXATHISMEANSTHATPRIMITIVETYPESSUCHASDOUBLESANDBOOLEANS,ASWELLASSERIALIZABLECLASSESSUCHASPRIMARYKEYCLASSESOREJBHANDLESTOOTHERENTITYBEANS,CANBECONTAINERMANAGEDFIELDSFOREXAMPLE,THEFOLLOWINGISASNIPPETOFCODEFROMOURBANKACCOUNTENTITYBEANCLASSTHATWEWROTEINCHAPTER8WITHCONTAINERMANAGEDPERSISTENCE,THECONTAINERCANPERSISTEACHOFTHESEFIELDSFORYOUBEHINDTHESCENESWHENSAVINGYOURBEANINSTANCESFIELDS,THECONTAINERISRESPONSIBLEFORQUERYINGYOURBEANINSTANCEFORTHESEFIELDVALUESWHENLOADINGDATAINTOYOURBEANINSTANCE,THECONTAINERSETSTHESEFIELDSTHISISPOSSIBLEBECAUSEEACHOFTHEFIELDSISDECLAREDASPUBLICOFCOURSE,YOUSTILLMUSTINFORMTHECONTAINERABOUTWHICHFIELDSITSHOULDMANIPULATEYOUSPECIFYTHISINYOURBEANSDEPLOYMENTDESCRIPTORTHEEJBCONTAINERWILLINSPECTTHEDEPLOYMENTDESCRIPTORTOFIGUREOUTWHICHOFYOURENTITYBEANSFIELDSTOMANIPULATENOTETHATNOTALLFIELDSWITHINTHEBEANHAVETOBEMANAGEDBYTHECONTAINERYOUMIGHTBEPULLINGDATAMANUALLYFROMASECONDARYSOURCE,ORYOUMIGHTHAVECALCULATEDFIELDSTHEEJBCONTAINERWILLAUTOMATICALLYNOTIFYYOURBEANCLASSDURINGPERSISTENTOPERATIONS,ALLOWINGYOUTOMANAGETHESEFIELDSPRIMARYKEYCLASSASWITHBEANMANAGEDPERSISTENCE,CONTAINERMANAGEDPERSISTENCEDICTATESTHATYOURPRIMARYKEYCLASSMUSTBESERIALIZABLEBECAUSETHEEJBCONTAINERWILLWORKWITHYOURPRIMARYKEY,THEREARENEWRESTRICTIONSFORHOWYOUWRITEYOURPRIMARYKEYCLASSTHEMOSTIMPORTANTRESTRICTIONISTHATTHEFIELDSYOUHAVEINYOURPRIMARYKEYMUSTCOMEFROMTHECONTAINERMANAGEDFIELDSOFYOURENTITYBEAN,WHICHWEDESCRIBEDPREVIOUSLYTHISRESTRICTIONALLOWSTHEEJBCONTAINERTOSET,ASWELLASEXTRACT,YOURENTITYBEANSPRIMARYKEYFIELDSFOREXAMPLE,TAKEOURPRIMARYKEYCLASSFROMOURCHAPTER8SBANKACCOUNTTHISISAVALIDPRIMARYKEYCLASSFORCONTAINERMANAGEDPERSISTENCEBECAUSEITSSERIALIZABLEANDBECAUSEITSPUBLICFIELDSCOMEFROMOURBEANCLASSSCONTAINERMANAGEDFIELDSIMPLEMENTATIONGUIDELINESFORCONTAINERMANAGEDPERSISTENCETHEMETHODIMPLEMENTATIONSOFYOURENTITYBEANSSHOULDBEDIFFERENTFORCONTAINERMANAGEDPERSISTENTENTITIESNOLONGERAREYOUCONTROLLINGTHEROUTINEPERSISTENTOPERATIONSOFYOURBEANS,ANDSOMANYOFTHEMETHODSCANBELEFTEMPTYTHECONTAINERWILLDOITFORYOUTABLE91ISASUMMARYOFWHATYOUSHOULDIMPLEMENTINEACHMETHOD,ASSUMINGYOURENTITYBEANSPERSISTENCEISCONTAINERMANAGEDTAKEAQUICKGLANCEATTHECHARTFORNOWASYOUCANSEEFROMTHETABLE,MANYOFTHEDATABASEINTENSIVEOPERATIONSHAVEBEENREDUCEDINSCOPESIGNIFICANTLYYOUSHOULDREFERBACKTOTHECHARTWHENREADINGTHROUGHTHECODEINTHISCHAPTERORWHENPROGRAMMINGYOUROWNENTITYBEANCLASSESTHEORDEROFMETHODSLISTEDVERYROUGHLYMODELSTHEFLOWOFCONTROLOFANENTITYBEANINSTANCESLIFECYCLETHATWESAWATTHEENDOFCHAPTER7CONTAINERMANAGEDPERSISTENCEEXAMPLEAPRODUCTLINELETSSEEAQUICKDEMONSTRATIONOFCONTAINERMANAGEDPERSISTENCEINACTION,APPLIEDTOTHECONCEPTOFAPRODUCTLINEIFYOUREWORKINGFORAPRODUCTBASEDCOMPANY,YOURCOMPANYSPRODUCTLINEISTHESUITEOFPRODUCTSYOURCOMPANYOFFERSFOREXAMPLE,IFYOUREANAPPLIANCECOMPANY,YOUMIGHTOFFERADISHWASHER,ASTOVE,ANDADRYERIFYOUREACOMPUTERHARDWARECOMPANY,YOUMIGHTOFFERMEMORY,HARDDISKS,ANDPROCESSORSWEREGOINGTOMODELAGENERICPRODUCTASANENTITYBEANTHATUSESCONTAINERMANAGEDPERSISTENCETHEOBJECTMODELFOROURPRODUCTLINEISDETAILEDINFIGURE91LETSTAKEALOOKATEACHOFTHEFILESTHATWEMUSTCREATEFOROURENTITYBEANCOMPONENTPRODUCTJAVAOURREMOTEINTERFACEISSPECIFIEDBYPRODUCTJAVA,SHOWNINSOURCE91OURREMOTEINTERFACEISVERYSIMILARTOCHAPTER8SBANKACCOUNTREMOTEINTERFACEITHASMETHODSTOMODIFYTHEENTITYBEANINSTANCESFIELDSANDTHROWSREMOTEEXCEPTIONSTOINDICATESYSTEMLEVELERRORSPRODUCTHOMEJAVANEXT,WEHAVETHEPRODUCTSHOMEINTERFACE,PRODUCTHOMEJAVA,PRESENTEDINSOURCE92OURHOMEINTERFACEDEFINESASINGLECREATEMETHODTOCREATEANEWPRODUCTINTHEDATABASEITRETURNSAPRODUCTEJBOBJECTSOTHECLIENTCANMANIPULATETHEENTITYBEANDATAANDTHROWSAJAVAXEJBCREATEEXCEPTIONTOINDICATEANAPPLICATIONLEVELPROBLEMWEALSOEXPOSEALLSORTSOFFINDERMETHODSTOFINDEXISTINGPRODUCTSSOMEOFTHEFINDERSRETURNASINGLEEJBOBJECT,WHILEOTHERSRETURNAJAVAUTILENUMERATIONOFMULTIPLEEJBOBJECTSTHISISNEEDEDIFTHEFINDERMETHODSFINDMORETHANONEMATCHINGOBJECTNOTETHATFINDBYPRIMARYKEYSHOULDNEVERRETURNANENUMERATIONBECAUSEPRIMARYKEYSMUSTBEUNIQUEPRODUCTPKJAVAOURPRIMARYKEYCLASSISDEFINEDBYPRODUCTPKJAVA,SHOWNINSOURCE93ASWITHOURBANKACCOUNT,OURPRIMARYKEYISASIMPLESTRINGANDASWEVEFOUNDOUT,THEREARERESTRICTIONSFORWHATOURPRIMARYKEYCANBEOURPRIMARYKEYFIELDSARECOMINGFROMTHECONTAINERMANAGEDFIELDSOFTHEENTITYBEANCLASS,ASISREQUIREDWITHCONTAINERMANAGEDPERSISTENCEINPARTICULAR,OURPRIMARYKEYR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