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Chapter 6. Conversational state
Chapter 6. Conversational state
Head First Servlets and JSP By Bert Bates, Kathy Sierra, Bryan Basham ISBN: 0596005407 Publisher: O'Reilly Prepared for Stephen Goss, Safari ID:
Print Publication Date: 8/1/2004 User number: 747221 Copyright 2007, Safari Books Online, LLC.
This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior
written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that
otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 6. Conversational state
Chapter 6. Conversational state
Head First Servlets and JSP By Bert Bates, Kathy Sierra, Bryan Basham ISBN: 0596005407 Publisher: O'Reilly Prepared for Stephen Goss, Safari ID:
Print Publication Date: 8/1/2004 User number: 747221 Copyright 2007, Safari Books Online, LLC.
This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior
written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that

otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 6. Conversational state
Chapter 6. Conversational state
Head First Servlets and JSP By Bert Bates, Kathy Sierra, Bryan Basham ISBN: 0596005407 Publisher: O'Reilly Prepared for Stephen Goss, Safari ID:
Print Publication Date: 8/1/2004 User number: 747221 Copyright 2007, Safari Books Online, LLC.
This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior
written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that
otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 6. Conversational state
Chapter 6. Conversational state
Head First Servlets and JSP By Bert Bates, Kathy Sierra, Bryan Basham ISBN: 0596005407 Publisher: O'Reilly Prepared for Stephen Goss, Safari ID:
Print Publication Date: 8/1/2004 User number: 747221 Copyright 2007, Safari Books Online, LLC.
This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior
written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that
otherwise violates the Safari Terms of Service is strictly prohibited.
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SESSIONMATCHINGTHESESSION)$
CREATEANEWSESSION
!LLTHECOOKIEWORKHAPPENSBEHINDTHESCENES
Whoa! The method for GETTING a
session ID cookie (and matching it
with an existing session) is the same
as SENDING a session ID cookie.
You never actually SEE the session
ID yourself (although you can ask
the session to give it to you).
Chapter 6. Conversational state
Chapter 6. Conversational state
Head First Servlets and JSP By Bert Bates, Kathy Sierra, Bryan Basham ISBN: 0596005407 Publisher: O'Reilly Prepared for Stephen Goss, Safari ID:
Print Publication Date: 8/1/2004 User number: 747221 Copyright 2007, Safari Books Online, LLC.
This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior
written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that
otherwise violates the Safari Terms of Service is strictly prohibited.
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ITFROMTHE3ERVLET#ONTEXT
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7HENYOUCALLGET3ESSIONONTHE#ONTAINERYOURESAYING
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MATCHESTHESESSION)$THISCLIENTSENTORANEWONE"UTIN
EITHERCASETHESESSIONISFORTHECLIENTASSOCIATEDWITHTHIS
REQUESTv
"UTTHEREISANOTHERWAYTHATYOUCANGETASESSIONFROM
ASESSIONEVENTOBJECT2EMEMBERALISTENERCLASSISNTA
SERVLETOR*30ITSJUSTACLASSTHATWANTSTOKNOWABOUT
THEEVENTS&OREXAMPLETHELISTENERMIGHTBEANATTRIBUTE
TRYINGTOFINDOUTWHENITTHEATTRIBUTEOBJECTWASADDED
TOORREMOVEDFROMASESSION
4HEEVENTHANDLINGMETHODSDEFINEDBYTHELISTENER
INTERFACESRELATEDTOSESSIONSTAKEANARGUMENTOFTYPE
(TTP3ESSION%VENTORITSSUBCLASS(TTP3ESSION"INDING%VENT
!ND(TTP3ESSION%VENTHASAGET3ESSIONMETHOD
3OIFYOUIMPLEMENTANYOFTHEFOURLISTENERINTERFACES
RELATEDTOSESSIONSWELLGETTOTHATLATERINTHECHAPTER
YOUCANACCESSTHESESSIONTHROUGHTHEEVENTHANDLING
CALLBACKMETHODS&OREXAMPLETHISCODEISFROMACLASS
THATIMPLEMENTSTHE(TTP3ESSION,ISTENERINTERFACE
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SESSIONREGARDLESSOFWHETHERTHERESAPREEXISTINGSESSION3INCEYOUALWAYSGET
AN(TTP3ESSIONINSTANCEBACKFROMTHATMETHODTHEONLYWAYTOKNOWIF
THESESSIONISNEWISTOASKTHESESSION
SXEOLFYRLGGR*HW+WWS6HUYOHW5HTXHVWUHTXHVW+WWS6HUYOHW5HVSRQVHUHVSRQVH
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getSession() returns a session no matter
what but you canÕt tell if itÕs a new
session unless you ask the session.
isNew() returns true if the
client has not yet responded
with this session ID.
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Chapter 6. Conversational state
Chapter 6. Conversational state

Head First Servlets and JSP By Bert Bates, Kathy Sierra, Bryan Basham ISBN: 0596005407 Publisher: O'Reilly Prepared for Stephen Goss, Safari ID:
Print Publication Date: 8/1/2004 User number: 747221 Copyright 2007, Safari Books Online, LLC.
This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior
written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that
otherwise violates the Safari Terms of Service is strictly prohibited.
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CREATEDSESSION)TMIGHTNOTMAKESENSEFORTHECHECKOUTSERVLETFOREXAMPLE
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3OTHERESANOVERLOADEDGET3ESSIONBOOLEANMETHODJUSTFORTHATPURPOSE
)FYOUDONTWANTTOCREATEANEWSESSIONCALLGET3ESSIONFALSEANDYOULLGET
EITHERNULLORAPREEXISTING(TTP3ESSION
4HECODEBELOWCALLSGET3ESSIONFALSETHENTESTSWHETHERTHERETURNVALUEWAS
NULL)FITWASNULLTHECODEOUTPUTSAMESSAGEANDTHENCREATESANEWSESSION
SXEOLFYRLGGR*HW+WWS6HUYOHW5HTXHVWUHTXHVW+WWS6HUYOHW5HVSRQVHUHVSRQVH
WKURZV,2([FHSWLRQ6HUYOHW([FHSWLRQ^
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`
Passing ÒfalseÓ means the method
returns a pre-existing session,
or null if there was no session
associated with this client.
Now we can test for whether
there was already a session
(the no-arg getSession()
would NEVER return null).
Here we KNOW weÕre making a new session.
4
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)SNTTHECODEABOVEJUSTASTUPIDINEFlCIENTWAY
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YOUSTILLCREATEDANEWSESSION
$
9OURERIGHT4HECODEABOVEISJUSTFORTESTINGHOW
THETWODIFFERENTVERSIONSOFGET3ESSIONWORK)NTHEREAL
WORLDTHEONLYTIMEYOUDWANTTOUSEGET3ESSIONFALSEIS
IFYOUDO./4WANTTOCREATEANEWSESSION)FYOURGOALIS
TOCREATEANEWSESSIONBUTSTILLRESPONDDIFFERENTLYIFYOU
KNOWTHISISANEWVERSUSPREEXISTINGSESSIONTHENUSE
THENOARGGET3ESSIONMETHODANDSIMPLYASKTHESESSION
IFITSNEWUSINGTHE(TTP3ESSIONIS.EWMETHOD
4
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3OITLOOKSLIKEGET3ESSIONTRUEISEXACTLYTHE
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$


2IGHTAGAIN4HENOARGVERSIONISACONVENIENCE
FORTHOSETIMESWHENYOUKNOWTHATYOUALWAYSWANTA
SESSIONNEWOREXISTING4HEVERSIONTHATTAKESABOOLEANIS
USEFULWHENYOUKNOWTHATYOUDONTWANTANEWSESSION
ORWHENTHEDECISIONOFWHETHERTOMAKEANEWSESSION
HAPPENSATRUNTIMEANDYOUREPASSINGAVARIABLEINTOTHE
GET3ESSIONSOME"OOLEANMETHOD
Chapter 6. Conversational state
Chapter 6. Conversational state
Head First Servlets and JSP By Bert Bates, Kathy Sierra, Bryan Basham ISBN: 0596005407 Publisher: O'Reilly Prepared for Stephen Goss, Safari ID:
Print Publication Date: 8/1/2004 User number: 747221 Copyright 2007, Safari Books Online, LLC.
This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior
written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that
otherwise violates the Safari Terms of Service is strictly prohibited.
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)FYOURAPPDEPENDSONSESSIONSYOUNEEDADIFFERENTWAY
FORTHECLIENTAND#ONTAINERTOEXCHANGESESSION)$INFO
,UCKYFORYOUTHE#ONTAINERCANHANDLEACOOKIEREFUSING
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METHODWILLALWAYSRETURNTRUE
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Chapter 6. Conversational state
Chapter 6. Conversational state
Head First Servlets and JSP By Bert Bates, Kathy Sierra, Bryan Basham ISBN: 0596005407 Publisher: O'Reilly Prepared for Stephen Goss, Safari ID:
Print Publication Date: 8/1/2004 User number: 747221 Copyright 2007, Safari Books Online, LLC.
This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior
written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that
otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 6. Conversational state
Chapter 6. Conversational state
Head First Servlets and JSP By Bert Bates, Kathy Sierra, Bryan Basham ISBN: 0596005407 Publisher: O'Reilly Prepared for Stephen Goss, Safari ID:
Print Publication Date: 8/1/2004 User number: 747221 Copyright 2007, Safari Books Online, LLC.
This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior
written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that
otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 6. Conversational state
Chapter 6. Conversational state
Head First Servlets and JSP By Bert Bates, Kathy Sierra, Bryan Basham ISBN: 0596005407 Publisher: O'Reilly Prepared for Stephen Goss, Safari ID:
Print Publication Date: 8/1/2004 User number: 747221 Copyright 2007, Safari Books Online, LLC.
This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior
written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that
otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 6. Conversational state
Head First Servlets and JSP By Bert Bates, Kathy Sierra, Bryan Basham ISBN: 0596005407 Publisher: O'Reilly Prepared for Stephen Goss, Safari ID:
Print Publication Date: 8/1/2004 User number: 747221 Copyright 2007, Safari Books Online, LLC.
This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior

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Chapter 6. Conversational state
Head First Servlets and JSP By Bert Bates, Kathy Sierra, Bryan Basham ISBN: 0596005407 Publisher: O'Reilly Prepared for Stephen Goss, Safari ID:
Print Publication Date: 8/1/2004 User number: 747221 Copyright 2007, Safari Books Online, LLC.
This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior
written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that
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Chapter 6. Conversational state
Chapter 6. Conversational state
Head First Servlets and JSP By Bert Bates, Kathy Sierra, Bryan Basham ISBN: 0596005407 Publisher: O'Reilly Prepared for Stephen Goss, Safari ID:
Print Publication Date: 8/1/2004 User number: 747221 Copyright 2007, Safari Books Online, LLC.
This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior
written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that
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Chapter 6. Conversational state
Chapter 6. Conversational state
Head First Servlets and JSP By Bert Bates, Kathy Sierra, Bryan Basham ISBN: 0596005407 Publisher: O'Reilly Prepared for Stephen Goss, Safari ID:
Print Publication Date: 8/1/2004 User number: 747221 Copyright 2007, Safari Books Online, LLC.
This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior
written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that
otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 6. Conversational state
Chapter 6. Conversational state
Head First Servlets and JSP By Bert Bates, Kathy Sierra, Bryan Basham ISBN: 0596005407 Publisher: O'Reilly Prepared for Stephen Goss, Safari ID:
Print Publication Date: 8/1/2004 User number: 747221 Copyright 2007, Safari Books Online, LLC.
This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior
written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that
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Chapter 6. Conversational state
Chapter 6. Conversational state
Head First Servlets and JSP By Bert Bates, Kathy Sierra, Bryan Basham ISBN: 0596005407 Publisher: O'Reilly Prepared for Stephen Goss, Safari ID:
Print Publication Date: 8/1/2004 User number: 747221 Copyright 2007, Safari Books Online, LLC.
This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior
written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that
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Chapter 6. Conversational state
Chapter 6. Conversational state
Head First Servlets and JSP By Bert Bates, Kathy Sierra, Bryan Basham ISBN: 0596005407 Publisher: O'Reilly Prepared for Stephen Goss, Safari ID:
Print Publication Date: 8/1/2004 User number: 747221 Copyright 2007, Safari Books Online, LLC.
This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior
written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that

otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 6. Conversational state
Head First Servlets and JSP By Bert Bates, Kathy Sierra, Bryan Basham ISBN: 0596005407 Publisher: O'Reilly Prepared for Stephen Goss, Safari ID:
Print Publication Date: 8/1/2004 User number: 747221 Copyright 2007, Safari Books Online, LLC.
This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior
written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that
otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 6. Conversational state
Chapter 6. Conversational state
Head First Servlets and JSP By Bert Bates, Kathy Sierra, Bryan Basham ISBN: 0596005407 Publisher: O'Reilly Prepared for Stephen Goss, Safari ID:
Print Publication Date: 8/1/2004 User number: 747221 Copyright 2007, Safari Books Online, LLC.
This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior
written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that
otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 6. Conversational state
Chapter 6. Conversational state
Head First Servlets and JSP By Bert Bates, Kathy Sierra, Bryan Basham ISBN: 0596005407 Publisher: O'Reilly Prepared for Stephen Goss, Safari ID:
Print Publication Date: 8/1/2004 User number: 747221 Copyright 2007, Safari Books Online, LLC.
This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior
written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that
otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 6. Conversational state
Chapter 6. Conversational state
Head First Servlets and JSP By Bert Bates, Kathy Sierra, Bryan Basham ISBN: 0596005407 Publisher: O'Reilly Prepared for Stephen Goss, Safari ID:
Print Publication Date: 8/1/2004 User number: 747221 Copyright 2007, Safari Books Online, LLC.
This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior
written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that
otherwise violates the Safari Terms of Service is strictly prohibited.
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TIMEHERETURNSTOTHEBEERSITE3OHESETSTHECOOKIETHE
lRSTTIMEHERECEIVESTHECLIENTSNAMEANDIFHEGETSTHE
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Chapter 6. Conversational state
Chapter 6. Conversational state
Head First Servlets and JSP By Bert Bates, Kathy Sierra, Bryan Basham ISBN: 0596005407 Publisher: O'Reilly Prepared for Stephen Goss, Safari ID:
Print Publication Date: 8/1/2004 User number: 747221 Copyright 2007, Safari Books Online, LLC.
This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior
written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that
otherwise violates the Safari Terms of Service is strictly prohibited.

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The Cookie constructor takes
a name/value String pair.
setMaxAge is deÞ ned in SECONDS. This code says Òstay
alive on the client for 30*60 secondsÓ (30 minutes).
Setting max age to -1 makes the cookie disappear when

the browser exits. So, if you call getMaxAge() on the
ÒJSESSIONIDÓ cookie, what will you get back?
ThereÕs no getCookie(String) method
you can only get cookies in a Cookie
array, and then you have to loop over
the array to Þ nd the one you want.
Chapter 6. Conversational state
Chapter 6. Conversational state
Head First Servlets and JSP By Bert Bates, Kathy Sierra, Bryan Basham ISBN: 0596005407 Publisher: O'Reilly Prepared for Stephen Goss, Safari ID:
Print Publication Date: 8/1/2004 User number: 747221 Copyright 2007, Safari Books Online, LLC.
This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior
written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that
otherwise violates the Safari Terms of Service is strictly prohibited.
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NAME4HEFORMCALLSASERVLETTHATGETSTHEUSERNAMEREQUESTPARAMETER
ANDUSESTHENAMEVALUETOSETACOOKIEINTHERESPONSE
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ANDTHEBUSINESSLOGICKNOWSNOTTOASKTHEUSERTOINPUTHISNAMEAGAIN
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Chapter 6. Conversational state
Chapter 6. Conversational state
Head First Servlets and JSP By Bert Bates, Kathy Sierra, Bryan Basham ISBN: 0596005407 Publisher: O'Reilly Prepared for Stephen Goss, Safari ID:
Print Publication Date: 8/1/2004 User number: 747221 Copyright 2007, Safari Books Online, LLC.
This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior
written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that
otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 6. Conversational state
Chapter 6. Conversational state
Head First Servlets and JSP By Bert Bates, Kathy Sierra, Bryan Basham ISBN: 0596005407 Publisher: O'Reilly Prepared for Stephen Goss, Safari ID:
Print Publication Date: 8/1/2004 User number: 747221 Copyright 2007, Safari Books Online, LLC.
This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior
written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that
otherwise violates the Safari Terms of Service is strictly prohibited.