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1、JavaandtheInternetIfJavais,infact,yetanothercomputerprogramminglanguage,youmayquestionwhyitissoimportantandwhyitisbeingpromotedasarevolutionarystepincomputerprogramming.Theanswerisn’timmediatelyobviousifyou’recomingfromatraditionalprogrammingperspective.Althoug
2、hJavaisveryusefulforsolvingtraditionalstandaloneprogrammingproblems,itisalsoimportantbecauseitwillsolveprogrammingproblemsontheWorldWideWeb.WhatistheWeb?TheWebcanseemabitofamysteryatfirst,withallthistalkof“surfing,”“presence,”and“homepages.”It’shelpfultostepbac
3、kandseewhatitreallyis,buttodothisyoumustunderstandclient/serversystems,anotheraspectofcomputingthat’sfullofconfusingissues.Client/ServercomputingTheprimaryideaofaclient/serversystemisthatyouhaveacentralrepositoryofinformation—somekindofdata,ofteninadatabase—tha
4、tyouwanttodistributeondemandtosomesetofpeopleormachines.Akeytotheclient/serverconceptisthattherepositoryofinformationiscentrallylocatedsothatitcanbechangedandsothatthosechangeswillpropagateouttotheinformationconsumers.Takentogether,theinformationrepository,thes
5、oftwarethatdistributestheinformationandthemachinewheretheinformationandsoftwareresideiscalledtheserver.Thesoftwarethatresidesontheremotemachine,communicateswiththeserver,fetchestheinformation,processesit,andthendisplaysitontheremotemachineiscalledtheclient.Theb
6、asicconceptofclient/servercomputing,then,isnotsocomplicated.Theproblemsarisebecauseyouhaveasingleservertryingtoservemanyclientsatonce.Generally,adatabasemanagementsystemisinvolved,sothedesigner“balances”thelayoutofdataintotablesforoptimaluse.Inaddition,systemso
7、ftenallowaclienttoinsertnewinformationintoaserver.Thismeansyoumustensurethatoneclient’snewdatadoesn’twalkoveranotherclient’snewdata,orthatdataisn’tlostintheprocessofaddingittothedatabase(thisiscalledtransactionprocessing).Asclientsoftwarechanges,itmustbebuilt,d
8、ebugged,andinstalledontheclientmachines,whichturnsouttobemorecomplicatedandexpensivethanyoumightthink.It’sespeciallyproblematictosupportmultipletypesofcomputersandoperatings
