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1、JavaandtheInternetIfJavais,infact,yetanothercomputerprogramminglanguage,youmayquestionwhyitissoimportantandwhyitisbeingpromotedasarevolutionarystepincomputerprogramming.Theanswerisn’timmediatelyobviousifyou’recomingfromatraditionalprogrammingperspective.A
2、lthoughJavaisveryusefulforsolvingtraditionalstandaloneprogrammingproblems,itisalsoimportantbecauseitwillsolveprogrammingproblemsontheWorldWideWeb.WhatistheWeb?TheWebcanseemabitofamysteryatfirst,withallthistalkof“surfing,”“presence,”and“homepages.”It’shelp
3、fultostepbackandseewhatitreallyis,buttodothisyoumustunderstandclient/serversystems,anotheraspectofcomputingthat’sfullofconfusingissues.Client/ServercomputingTheprimaryideaofaclient/serversystemisthatyouhaveacentralrepositoryofinformation—somekindofdata,of
4、teninadatabase—thatyouwanttodistributeondemandtosomesetofpeopleormachines.Akeytotheclient/serverconceptisthattherepositoryofinformationiscentrallylocatedsothatitcanbechangedandsothatthosechangeswillpropagateouttotheinformationconsumers.Takentogether,thein
5、formationrepository,thesoftwarethatdistributestheinformationandthemachinewheretheinformationandsoftwareresideiscalledtheserver.Thesoftwarethatresidesontheremotemachine,communicateswiththeserver,fetchestheinformation,processesit,andthendisplaysitontheremot
6、emachineiscalledtheclient.Thebasicconceptofclient/servercomputing,then,isnotsocomplicated.Theproblemsarisebecauseyouhaveasingleservertryingtoservemanyclientsatonce.Generally,adatabasemanagementsystemisinvolved,sothedesigner“balances”thelayoutofdataintotab
7、lesforoptimaluse.Inaddition,systemsoftenallowaclienttoinsertnewinformationintoaserver.Thismeansyoumustensurethatoneclient’snewdatadoesn’twalkoveranotherclient’snewdata,orthatdataisn’tlostintheprocessofaddingittothedatabase(thisiscalledtransactionprocessin
8、g).Asclientsoftwarechanges,itmustbebuilt,debugged,andinstalledontheclientmachines,whichturnsouttobemorecomplicatedandexpensivethanyoumightthink.It’sespeciallyproblematictosupportmultipletypesofcomputersandoperatings
