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1、JavaandtheInternetIfJavais,infact,yetanothercomputerprogramminglanguage,youmayquestionwhyitissoimportantandwhyitisbeingpromotedasarevolutionarystepincomputerprogramming.Theanswerisn’timmediatelyobviousifyou’recomingfromatraditionalprogrammingperspect
2、ive.AlthoughJavaisveryusefulforsolvingtraditionalstandaloneprogrammingproblems,itisalsoimportantbecauseitwillsolveprogrammingproblemsontheWorldWideWeb.WhatistheWeb?TheWebcanseemabitofamysteryatfirst,withallthistalkof“surfing,”“presence,”and“homepages
3、.”It’shelpfultostepbackandseewhatitreallyis,buttodothisyoumustunderstandclient/serversystems,anotheraspectofcomputingthat’sfullofconfusingissues.Client/ServercomputingTheprimaryideaofaclient/serversystemisthatyouhaveacentralrepositoryofinformation—so
4、mekindofdata,ofteninadatabase—thatyouwanttodistributeondemandtosomesetofpeopleormachines.Akeytotheclient/serverconceptisthattherepositoryofinformationiscentrallylocatedsothatitcanbechangedandsothatthosechangeswillpropagateouttotheinformationconsumers
5、.Takentogether,theinformationrepository,thesoftwarethatdistributestheinformation,andthemachine(s)wheretheinformationandsoftwareresideiscalledtheserver.Thesoftwarethatresidesontheremotemachine,communicateswiththeserver,fetchestheinformation,processesi
6、t,andthendisplaysitontheremotemachineiscalledtheclient.Thebasicconceptofclient/servercomputing,then,isnotsocomplicated.Theproblemsarisebecauseyouhaveasingleservertryingtoservemanyclientsatonce.Generally,adatabasemanagementsystemisinvolved,sothedesign
7、er“balances”thelayoutofdataintotablesforoptimaluse.Inaddition,systemsoftenallowaclienttoinsertnewinformationintoaserver.Thismeansyoumustensurethatoneclient’snewdatadoesn’twalkoveranotherclient’snewdata,orthatdataisn’tlostintheprocessofaddingittotheda
8、tabase(thisiscalledtransactionprocessing).Asclientsoftwarechanges,itmustbebuilt,debugged,andinstalledontheclientmachines,whichturnsouttobemorecomplicatedandexpensivethanyoumightthink.It’sespeciallyproblematictosupportmultipletypesofcomputersandoperat
