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Chapter 1. Why use Servlets & JSPs? Head First Servlets and JSP By Bert Bates, Kathy Sierra, Bryan Basham ISBN: 0596005407 Publisher: O'Reilly Prepared for Stephen Goss, Safari ID: stephengoss@gmx.net Print Publication Date: 8/1/2004 User number: 747221 Copyright 2006, 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 web consists of gazillions ofilla or clients (using browsers like Moz server Safari) and servers (using web through apps like Apache) connected Our goal is wires and wireless networks. clients that ion icat appl to build a web to around the globe can access. And become obscenely rich.

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Chapter 2. Web App Architecture Head First Servlets and JSP By Bert Bates, Kathy Sierra, Bryan Basham ISBN: 0596005407 Publisher: O'Reilly Prepared for Stephen Goss, Safari ID: stephengoss@gmx.net Print Publication Date: 8/1/2004 User number: 747221 Copyright 2006, 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 2. Web App Architecture

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0W_ Q\ TWWS[ QV KWLM _PI\ UISM[ I [MZ ^TM\ I [MZ ^TM\ In the real world, 99.9% of all t() servlets override either the doGe or doPost() method. LPSRUW MDYD[ VHUYOHW LPSRUW MDYD[ VHUYOHW KWWS LPSRUW MDYD LR

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Chapter 2. Web App Architecture

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Chapter 2. Web App Architecture

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Chapter 2. Web App Architecture

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*]\ _IQ\ <PMZM¼[ UWZM aW] KIV LW _Q\P \PM ,, "ESIDES MAPPING 52,S TO ACTUAL SERVLETS YOU CAN USE THE $$ TO CUSTOMIZE OTHER ASPECTS OF YOUR WEB APPLICATION INCLUDING SECURITY ROLES ERROR PAGES TAG LIBRARIES INITIAL CONlGURATION INFORMATION AND IF IT S A FULL * %% SERVER YOU CAN EVEN DECLARE THAT YOU LL BE ACCESSING SPECIlC ENTERPRISE JAVABEANS $ON T WORRY ABOUT THE DETAILS YET 4HE CRUCIAL POINT FOR NOW IS THAT THE $$ GIVES YOU A WAY TO DECLARATIVELY MODIFY YOUR APPLICATION WITHOUT CHANGING SOURCE CODE 4HINK ABOUT THIS IT MEANS THAT EVEN THOSE WHO AREN T *AVA PROGRAMMERS CAN CUSTOMIZE YOUR *AVA WEB APPLICATION WITHOUT HAVING TO DRAG YOU BACK FROM YOUR TROPICAL VACATION

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Chapter 2. Web App Architecture

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Chapter 2. Web App Architecture

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Chapter 2. Web App Architecture

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Chapter 3. Mini MVC Tutorial Head First Servlets and JSP By Bert Bates, Kathy Sierra, Bryan Basham ISBN: 0596005407 Publisher: O'Reilly Prepared for Stephen Goss, Safari ID: stephengoss@gmx.net 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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here, just displaying test information.

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Chapter 3. Mini MVC Tutorial

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+ WUXQTQVO LMXTWaQVO IVL \M[\QVO \PM KWV\ZWTTMZ [MZ^TM\ /K WE VE BUILT DEPLOYED AND TESTED OUR (4-, AND WE VE BUILT AND DEPLOYED OUR $$ WELL WE PUT THE WEB XML INTO THE DEPLOYMENT ENVIRONMENT BUT TECHNICALLY THE $$ WON T BE DEPLOYED UNTIL WE RESTART 4OMCAT .OW IT S TIME TO COMPILE THE l RST VERSION OF THE SERVLET DEPLOY IT AND TEST IT VIA THE (4-, FORM .OW WE LL RESTART 4OMCAT TO MAKE SURE THAT IT hSEESv THE WEB XML AND SERVLET CLASS

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*]QTLQVO IVL \M[\QVO \PM UWLMT KTI[[ )N -6# THE MODEL TENDS TO BE THE hBACK ENDv OF THE APPLICATION )T S OFTEN THE LEGACY SYSTEM THAT S NOW BEING EXPOSED TO THE WEB )N MOST CASES IT S JUST PLAIN OLD *AVA CODE WITH NO KNOWLEDGE OF THE FACT THAT IT MIGHT BE CALLED BY SERVLETS 4HE MODEL SHOULDN T BE TIED DOWN TO BEING USED BY ONLY A SINGLE WEB APP SO IT SHOULD BE IN ITS OWN UTILITY PACKAGES

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-VPIVKQVO \PM [MZ^TM\ \W KITT \PM UWLMT [W \PI\ _M KIV OM\ :-)4 IL^QKM )N THIS VERSION TWO SERVLET WE LL ENHANCE THE DO0OST METHOD TO CALL THE MODEL FOR ADVICE VERSION THREE WILL MAKE THE ADVICE COME FROM A *30 4HE CODE CHANGES ARE TRIVIAL BUT THE IMPORTANT PART IS UNDERSTANDING THE REDEPLOYMENT OF THE ENHANCED WEB APP 9OU CAN TRY TO WRITE THE CODE RECOMPILE AND DEPLOY ON YOUR OWN OR YOU CAN TURN THE PAGE AND FOLLOW ALONG

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Chapter 3. Mini MVC Tutorial

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Chapter 3. Mini MVC Tutorial

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Chapter 3. Mini MVC Tutorial

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+ZMI\M \PM 2;8 Âš^QM_Âş \PI\ OQ^M[ \PM IL^QKM $ON T GET YOUR HOPES UP 9OU RE GOING TO HAVE TO WAIT FOR A FEW CHAPTERS BEFORE WE REALLY START TALKING ABOUT *30S 4HIS *30 ISN T ACTUALLY A PARTICULARLY GOOD ONE EITHER BECAUSE OF ITS SCRIPTLET CODE WHICH WE LL TALK ABOUT LATER IN THE BOOK &OR NOW IT SHOULD BE PRETTY EASY TO READ AND IF YOU WANT TO EXPERIMENT A LITTLE GO FOR IT !LTHOUGH WE COULD TEST THIS *30 NOW FROM THE BROWSER WE LL WAIT UNTIL AFTER WE MODIFY THE SERVLET VERSION THREE TO SEE IF IT WORKS

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Chapter 3. Mini MVC Tutorial

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Chapter 3. Mini MVC Tutorial

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Chapter 3. Mini MVC Tutorial

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Chapter 4. Being a Servlet

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Chapter 4. Being a Servlet Head First Servlets and JSP By Bert Bates, Kathy Sierra, Bryan Basham ISBN: 0596005407 Publisher: O'Reilly Prepared for Stephen Goss, Safari ID: stephengoss@gmx.net 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 5. Being a Web App Head First Servlets and JSP By Bert Bates, Kathy Sierra, Bryan Basham ISBN: 0596005407 Publisher: O'Reilly Prepared for Stephen Goss, Safari ID: stephengoss@gmx.net 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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ent nit-param> elem We took the <iervlet> element. out of the <s

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Chapter 5. Being a Web App

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5M NO .OT UNLESS YOU HAVE A REALLY SMALL SIMPLE WEB APP 4HERE ARE MUCH BETTER WAYS TO DO LOGGING 4HE MOST POPULAR ROBUST LOGGING MECHANISM IS ,OG J YOU CAN FIND IT ON THE !PACHE SITE AT KWWS MDNDUWD DSDFKH RUJ ORJ M 9OU CAN ALSO USE THE LOGGING !0) FROM JAVA UTIL LOGGING ADDED TO * 3% IN VERSION )T S FINE TO USE THE 3ERVLET#ONTEXT LOG METHOD FOR SIMPLE EXPERIMENTS BUT IN A REAL PRODUCTION ENVIRONMENT YOU WILL ALMOST CERTAINLY WANT TO CHOOSE SOMETHING ELSE 4HERE S A GOOD REFERENCE ON WEB APP LOGGING WITH AND WITHOUT ,OG J IN THE *AVA 3ERVLET *30 #OOKBOOK FROM / 2EILLY ,OGGING IS NOT PART OF THE EXAM OBJECTIVES BUT IT S IMPORTANT &ORTUNATELY YOU LL FIND THE !0)S EASY TO USE

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Chapter 5. Being a Web App

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A context listener is simple: implement ServletContextListener.

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Chapter 5. Being a Web App

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Chapter 5. Being a Web App

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<]\WZQIT" I [QUXTM ;MZ ^TM\+WV\M`\4Q[\MVMZ .OW WE LL WALK THROUGH THE STEPS OF MAKING AND RUNNING A 3ERVLET#ONTEXT,ISTENER 4HIS IS JUST A SIMPLE TEST CLASS SO THAT YOU CAN SEE HOW ALL THE PIECES WORK TOGETHER WE RE NOT USING THE DATABASE CONNECTION EXAMPLE BECAUSE YOU D HAVE TO SET UP A DATABASE TO MAKE IT WORK "UT THE STEPS ARE THE SAME REGARDLESS OF THE CODE YOU PUT IN YOUR LISTENER CALLBACK METHODS )N THIS EXAMPLE WE LL TURN A 3TRING INIT PARAMETER INTO AN ACTUAL OBJECTÂ&#x2C6;A $OG 4HE LISTENER S JOB IS TO GET THE CONTEXT INIT PARAMETER FOR THE DOG S BREED "EAGLE 0OODLE ETC THEN USE THAT 3TRING TO CONSTRUCT A $OG OBJECT 4HE LISTENER THEN STICKS THE $OG OBJECT INTO A 3ERVLET#ONTEXT ATTRIBUTE SO THAT THE SERVLET CAN RETRIEVE IT 4HE POINT IS THAT THE SERVLET NOW HAS ACCESS TO A SHARED APPLICATION OBJECT IN THIS CASE A $OG AND DOESN T HAVE TO READ THE CONTEXT PARAMETERS 7HETHER THE SHARED OBJECT IS A $OG OR A DATABASE CONNECTION DOESN T MATTER 4HE KEY IS TO USE THE INIT PARAMETERS TO CREATE A SINGLE OBJECT THAT ALL PARTS OF THE APP WILL SHARE

In this example, weĂ&#x2022;ll put a Dog into a ServletContext.

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Chapter 5. Being a Web App

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go.... (This isnĂ&#x2022;t the ONLY place itsevecan ral WEB-INF/classes is one of for places the Container can lookrs in the classes. WeĂ&#x2022;ll cover the othe Deployment chapter.)

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Chapter 5. Being a Web App

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Chapter 5. Being a Web App

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?ZQ\QVO \PM TQ[\MVMZ KTI[[ )T WORKS JUST LIKE OTHER TYPES OF LISTENERS YOU MIGHT BE FAMILIAR WITH SUCH AS 3WING '5) EVENT HANDLERS 2EMEMBER ALL WE NEED TO DO IS GET THE CONTEXT INIT PARAMETERS TO l ND OUT THE DOG BREED MAKE THE $OG OBJECT AND PUT THE $OG INTO THE CONTEXT AS AN ATTRIBUTE

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Implement javax.servlet.ServletCo

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xt. Ask the event for the ServletConte Use the context to get the init parameter.

Use the context to set an attribute (a name/object pair) that is the Dog. Now other parts of the app will be able to get the value of the attribute (the Dog).

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The Dog doesnĂ&#x2022;t need to be cleaned up... when the context goes away, it means the whole app is going down, including the Dog.

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Chapter 5. Being a Web App

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Nothing special here. Just a plain old Java class.

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(WeĂ&#x2022;ll use the co parameter as thentext init the Dog constructargument for or.)

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) THOUGHT ) READ SOMEWHERE THAT SERVLET ATTRIBUTES HAD TO BE 3ERIALIZABLE

)NTERESTING QUESTION 4HERE ARE SEVERAL DIFFERENT ATTRIBUTE TYPES AND WHETHER THE ATTRIBUTE SHOULD BE 3ERIALIZABLE ONLY MATTERS WITH 3ESSION ATTRIBUTES !ND THE SCENARIO IN WHICH IT MATTERS IS ONLY IF THE APPLICATION IS DISTRIBUTED ACROSS MORE THAN ONE *6- 7E LL TALK ALL ABOUT THAT IN THE 3ESSIONS CHAPTER 4HERE S NO TECHNICAL NEED TO HAVE ANY ATTRIBUTES INCLUDING 3ESSION ATTRIBUTES BE 3ERIALIZABLE ALTHOUGH YOU MIGHT CONSIDER MAKING ALL OF YOUR ATTRIBUTES 3ERIALIZABLE BY DEFAULT UNLESS YOU HAVE A REALLY GOOD REASON ./4 TO 4HINK ABOUT ITÂ&#x2C6;ARE YOU REALLY CERTAIN THAT NOBODY WILL EVER WANT TO USE OBJECTS OF THAT TYPE AS ARGUMENTS OR RETURN VALUES AS PART OF A REMOTE METHOD CALL #AN YOU REALLY GUARANTEE THAT ANYONE WHO USES THIS CLASS $OG IN THIS CASE WILL NEVER RUN IN A DISTRIBUTED ENVIRONMENT 3O ALTHOUGH YOU AREN T REQUIRED TO MAKE ANY ATTRIBUTES 3ERIALIZABLE YOU PROBABLY SHOULD IF YOU CAN

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Chapter 5. Being a Web App

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Chapter 5. Being a Web App

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Chapter 5. Being a Web App

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9ES THERE ARE SEVERAL OTHER TYPES OF LISTENERS THAT WE LL TALK ABOUT IN A MINUTE

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Chapter 5. Being a Web App

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Chapter 5. Being a Web App

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<ZW]JTM[PWW\QVO )F YOU GET A .ULL0OINTER%XCEPTION YOU DIDN T GET A $OG BACK FROM GET!TTRIBUTE #HECK THE 3TRING NAME USED IN SET!TTRIBUTE AND MAKE SURE IT MATCHES THE 3TRING NAME YOU RE USING IN GET!TTRIBUTE 2ECHECK YOUR WEB XML AND MAKE SURE THE LISTENER IS REGISTERED 4RY LOOKING AT THE SERVER LOGS AND SEE IF YOU CAN l ND OUT IF THE LISTENER IS ACTUALLY BEING CALLED 4O MAKE IT AS CONFUSING AS POSSIBLE WE GAVE EVERYTHING A SUBTLY DIFFERENT NAME 7E WANT TO MAKE SURE YOU RE PAYING ATTENTION TO HOW THESE NAMES ARE USED AND WHEN YOU NAME EVERYTHING THE SAME IT S TOUGH TO TELL HOW THE NAMES AFFECT YOUR APP 3ERVLET CLASS NAME ,ISTENER4ESTER CLASS 7EB APP DIRECTORY NAME LISTENER4EST 52, PATTERN MAPPED TO THIS THE SERVLET ,ISTEN4EST DO

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Chapter 5. Being a Web App

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4Q[\MVMZ[" VW\ R][\ NWZ KWV\M`\ M^MV\[ 7HERE THERE S A LIFECYCLE MOMENT THERE S USUALLY A LISTENER TO HEAR ABOUT IT "ESIDES CONTEXT EVENTS YOU CAN LISTEN FOR EVENTS RELATED TO CONTEXT ATTRIBUTES SERVLET REQUESTS AND ATTRIBUTES AND (440 SESSIONS AND SESSION ATTRIBUTES

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Chapter 5. Being a Web App

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Chapter 5. Being a Web App

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Chapter 5. Being a Web App

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Chapter 5. Being a Web App

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?PI\ M`IK\Ta Q[ IV I\\ZQJ]\M' 7E SAW HOW THE 3ERVLET#ONTEXT LISTENER CREATED A $OG OBJECT AFTER GETTING THE CONTEXT INIT PARAMETER AND WAS ABLE TO STICK SET THE $OG INTO THE 3ERVLET#ONTEXT AS AN ATTRIBUTE SO THAT OTHER PARTS OF THE APP COULD GET IT %ARLIER WITH THE BEER TUTORIAL WE SAW HOW THE SERVLET WAS ABLE TO STICK THE RESULTS OF THE CALL TO THE MODEL INTO THE 2EQUEST USUALLY (TTP3ERVLET2EQUEST OBJECT AS AN ATTRIBUTE SO THAT THE *30 VIEW COULD GET THE VALUE !N ATTRIBUTE IS AN OBJECT SET REFERRED TO AS BOUND INTO ONE OF THREE OTHER SERVLET !0) OBJECTSÂ&#x2C6;3ERVLET#ONTEXT (TTP3ERVLET2EQUEST OR 3ERVLET2EQUEST OR (TTP3ESSION 9OU CAN THINK OF IT AS SIMPLY A NAME VALUE PAIR WHERE THE NAME IS A 3TRING AND THE VALUE IS AN /BJECT IN A MAP INSTANCE VARIABLE )N REALITY WE DON T KNOW OR CARE HOW IT S ACTUALLY IMPLEMENTEDÂ&#x2C6;ALL WE REALLY CARE ABOUT IS THE SCOPE IN WHICH THE ATTRIBUTE EXISTS )N OTHER WORDS WHO CAN SEE IT AND HOW LONG DOES IT LIVE

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Chapter 5. Being a Web App

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Chapter 5. Being a Web App

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Chapter 5. Being a Web App

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Chapter 5. Being a Web App

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;aVKPZWVQbQVO \PM [MZ ^QKM UM\PWL Q[ I [XMK\IK]TIZTa *), QLMI /+ SO WE KNOW THAT SYNCHRONIZING THE SERVICE METHOD WILL KILL OUR CONCURRENCY BUT IT DOES GIVE YOU THE THREAD PROTECTION RIGHT 4AKE A LOOK AT THIS LEGAL CODE AND DECIDE WHETHER IT WOULD PREVENT THE PROBLEM +IM HAD WITH THE CONTEXT ATTRIBUTE BEING CHANGED BY ANOTHER SERVLET SXEOLF V\QFKURQL]HG YRLG GR*HW +WWS6HUYOHW5HTXHVW UHTXHVW +WWS6HUYOHW5HVSRQVH UHVSRQVH WKURZV ,2([FHSWLRQ 6HUYOHW([FHSWLRQ ^ UHVSRQVH VHW&RQWHQW7\SH ÂłWH[W KWPOÂ´ 3ULQW:ULWHU RXW UHVSRQVH JHW:ULWHU RXW SULQWOQ ÂłWHVW FRQWH[W DWWULEXWHV EU!Â´ JHW6HUYOHW&RQWH[W VHW$WWULEXWH ÂłIRRÂ´ Âł Â´ JHW6HUYOHW&RQWH[W VHW$WWULEXWH ÂłEDUÂ´ Âł Â´ RXW SULQWOQ JHW6HUYOHW&RQWH[W JHW$WWULEXWH ÂłIRRÂ´

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Chapter 5. Being a Web App

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If you synchronize the service method, you WILL stop the Container from starting any other methods for new requests coming into servlet A. So this WILL protect the context attributes from being accessed by more than one thread running a service method of Servlet A.

But you wonĂ&#x2022;t do anything to stop OTHER servlets! Regardless of whether the service methods in other servlets are synchronized or not... it still means other parts of the app have access to the context attributes.

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Chapter 5. Being a Web App

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AW] LWVÂź\ VMML I TWKS WV \PM [MZ ^TM\ aW] VMML \PM TWKS WV \PM KWV\M`\ 4HE TYPICAL WAY TO PROTECT THE CONTEXT ATTRIBUTE IS TO SYNCHRONIZE /. THE CONTEXT OBJECT ITSELF )F EVERYONE ACCESSING THE CONTEXT HAS TO l RST GET THE LOCK ON THE CONTEXT OBJECT THEN YOU RE GUARANTEED THAT ONLY ONE THREAD AT A TIME CAN BE GETTING OR SETTING THE CONTEXT ATTRIBUTE "UT THERE S STILL AN IF THERE )T ONLY WORKS IF ALL OF THE OTHER CODE THAT MANIPULATES THE SAME CONTEXT ATTRIBUTES !,3/ SYNCHRONIZES ON THE 3ERVLET#ONTEXT )F CODE DOESN T ASK FOR THE LOCK THEN THAT CODE IS STILL FREE TO HIT THE CONTEXT ATTRIBUTES "UT IF YOU RE DESIGNING THE WEB APP THEN YOU CAN DECIDE TO MAKE EVERYONE ASK FOR THE LOCK BEFORE ACCESSING THE ATTRIBUTES

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Chapter 5. Being a Web App

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Request B / Thread B %VEN THOUGH BOTH SERVLETS CAN ACCESS THE 3ESSION ATTRIBUTES IN SEPARATE THREADS EACH THREAD IS A SEPARATE REQUEST 3O IT LOOKS SAFE 5NLESS #AN YOU THINK OF A SCENARIO IN WHICH THERE COULD BE MORE THAN ONE REQUEST AT THE SAME TIME FROM THE SAME CLIENT

7HAT DO YOU THINK !RE SESSION ATTRIBUTES GUARANTEED THREAD SAFE

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Chapter 5. Being a Web App

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7E KNOW THAT CONTEXT ATTRIBUTES ARE INHERENTLY ./4 SAFE BECAUSE ALL PIECES OF THE APP CAN ACCESS CONTEXT ATTRIBUTES FROM ANY REQUEST WHICH MEANS ANY THREAD

6ERY GOOD .OW WHAT ABOUT 3ESSION ATTRIBUTES !RE THEY ARE SAFE

9OU HAVE MUCH TO LEARN GRASSHOPPER 9OU DO NOT KNOW THE TRUTH ABOUT SESSION ATTRIBUTES -EDITATE ON THIS BEFORE SPEAKING AGAIN

,ISTEN IN AS OUR TWO BLACK BELTS DISCUSS THE ISSUES AROUND PROTECTING THE STATE OF ATTRIBUTES FROM MULTITHREADING PROBLEMS

9ES MASTER !ND ) KNOW THAT SYNCHRONIZING THE SERVICE METHOD IS NOT A SOLUTION BECAUSE ALTHOUGH IT WILL STOP THAT SERVLET FROM SERVICING MORE THAN ONE REQUEST AT A TIME IT WILL ./4 STOP OTHER SERVLETS AND *30S IN THE SAME WEB APP FROM ACCESSING THE CONTEXT 9ES MASTER 4HEY ARE FOR ONLY ONE CLIENT AND THE LAWS OF PHYSICS PREVENT A CLIENT FROM MAKING MORE THAN ONE REQUEST AT A TIME

"UT MASTER ) HAVE MEDITATED AND STILL ) DO NOT KNOW HOW ONE CLIENT COULD HAVE MORE THAN ONE REQUEST

9OU MUST THINK OUTSIDE THE #ONTAINER #OLOR OUTSIDE THE LINES 2UN WITH SCISSORS 6ERY WISE ADVICE MASTER ) HAVE IT 4HE CLIENT COULD OPEN A NEW BROWSER WINDOW 3O THE #ONTAINER CAN STILL USE THE SAME SESSION FOR A CLIENT EVEN THOUGH IT S COMING FROM A DIFFERENT INSTANCE OF THE BROWSER 9ES 4HE #ONTAINER CAN SEE THE REQUEST FROM THE SECOND WINDOW AS COMING FROM THE SAME SESSION !ND HOW WOULD YOU PROTECT THESE SESSION ATTRIBUTES FROM THE HAVOC OF MULTIPLE THREADS

3O 3ESSION ATTRIBUTES ARE NOT THREAD SAFE AND THEY TOO MUST BE PROTECTED ) WILL MEDITATE ON THIS !H ) MUST SYNCHRONIZE THE PART OF MY CODE THAT ACCESSES THE SESSION ATTRIBUTES *UST THE WAY WE DID FOR THE CONTEXT ATTRIBUTES

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Chapter 5. Being a Web App

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/F COURSE IT IS 3URELY YOU VE DONE THIS YOURSELF WITHOUT A SECOND THOUGHTÂ&#x2C6;OPENED A SECOND WINDOW BECAUSE YOU WERE TIRED OF WAITING FOR THE OTHER ONE TO RESPOND OR BECAUSE YOU MINIMIZED ONE OR MISPLACED THE WINDOW WITHOUT REALIZING IT ETC 4HE POINT IS YOU CAN T TAKE THE CHANCE IF YOU NEED THREAD SAFETY FOR YOUR SESSION VARIABLES 9OU HAVE TO KNOW THAT IT S QUITE POSSIBLE FOR A SESSION SCOPED ATTRIBUTE TO BE USED BY MORE THAN ONE THREAD AT A TIME

)SN T IT A BAD IDEA TO SYNCHRONIZE CODE BECAUSE IT CAUSES A LOT OF OVERHEAD AND HURTS CONCURRENCY

9OU SHOULD !,7!93 THINK CAREFULLY BEFORE SYNCHRONIZING ANY CODE BECAUSE YOU RE RIGHTÂ&#x2C6;IT DOES ADD SOME EXPENSE IN CHECKING ACQUIRING AND RELEASING LOCKS )F YOU NEED PROTECTION THEN USE SYNCHRONIZATION BUT REMEMBER THE STANDARD RULE OF ALL FORMS OF LOCKINGÂ&#x2C6;KEEP THE LOCK FOR THE SHORTEST AMOUNT OF TIME TO ACCOMPLISH YOUR GOAL )N OTHER WORDS DON T SYNCHRONIZE THE CODE THAT DOESN T ACCESS THE PROTECTED STATE -AKE YOUR SYNCHRONIZED BLOCK AS SMALL AS POSSIBLE 'ET THE LOCK GET IN GET WHAT YOU NEED AND GET THE HECK OUT SO THE LOCK CAN RELEASE AND OTHER THREADS CAN RUN THAT CODE

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Chapter 5. Being a Web App

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<PM M^QT[ WN ; QVOTM<PZMIL5WLMT !LTHOUGH IT S NOT ON THE EXAM BECAUSE IT S EVIL YOU VE PROBABLY HEARD OF OR EVEN USED THE NOW DEPRECATED 3INGLE4HREAD-ODEL INTERFACE SO WE FEEL COMPELLED TO MENTION IT WHILE SIMULTANEOUSLY REINFORCING ITS EVILNESS 4HE 3INGLE4HREAD-ODEL SOUNDS GOOD TO NEWBIES AT l RST GLANCE AS A WAY TO SOLVE MULTI THREADING PROBLEMS 9OU SIMPLY HAVE YOUR SERVLET IMPLEMENT THE 3INGLE4HREAD-ODEL INTERFACE AND "//-Â&#x2C6;AS IF BY MAGIC YOUR SERVLET WILL NEVER HAVE MORE THAN ONE THREAD AT A TIME RUNNING )N OTHER WORDS YOU VE REDUCED YOUR SERVLET TO A SINGLE THREAD 'OODBYE MULTI THREADING PROBLEMS RIGHT .O OF COURSE NOT 9OU ALREADY KNOW WHY IMPLEMENTING 3INGLE4HREAD-ODEL IS NO DIFFERENT THAN SYNCHRONIZING THE SERVICE METHODÂ&#x2C6;ALL YOU VE DONE IS DEMOLISHED YOUR CONCURRENCY WITHOUT PROTECTING ATTRIBUTE STATE "ECAUSE AGAIN EVEN IF ALL YOUR SERVLETS IMPLEMENT 3INGLE4HREAD-ODEL YOU CAN STILL HAVE TWO SERVLETS EACH ONE DUTIFULLY RUNNING ONLY ONE CLIENT REQUEST THREAD AT A TIME IN THE SAME WEB APP ACCESSING CONTEXT ATTRIBUTES AT THE SAME TIME

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3INGLE4HREAD-ODEL OFFERS NOTHING BUT POOR PERFORMANCE IF YOUR APPLICATION HAS MORE THAN ONE COMPONENT 3INCE IT MISLED THOUSANDS OF NEW DEVELOPERS INTO THINKING THAT 3INGLE4HREAD-ODEL GAVE THEM THREAD SAFETY IT S BEEN DEPRECATED AND THE DEVELOPERS WHO USE IT NOW ARE SUBJECT TO RIDICULE AND HUMILIATION "UT NOW YOU KNOW AND YOU WOULD NEVER HAVE USED IT ANYWAY SINCE YOU ALREADY KNOW THAT RESTRICTING A SINGLE SERVLET TO A SINGLE THREAD PROTECTS YOU ONLY IF YOUR ENTIRE APPLICATION CONSISTS OF A SINGLE SERVLET 3O IF YOU CATCH ANYBODY USING 3INGLE4HREAD-ODEL REVOKE THEIR 3ERVLET LICENSE AND INSIST NO DEMAND THAT THEY BUY A COPY OF THIS BOOK

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Chapter 5. Being a Web App

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4HAT S RIGHT )F YOU HAVE MULTIPLE CLIENTS MAKING REQUESTS ON THAT SERVLET THAT MEANS MULTIPLE THREADS RUNNING THAT SERVLET CODE !ND ALL THREADS HAVE ACCESS TO THE SERVLET S INSTANCE VARIABLES SO INSTANCE VARI ABLES AREN T THREAD SAFE

"UT THEY 7/5,$ BE THREAD SAFE IF YOU IMPLE MENTED THE 3INGLE4HREAD-ODEL RIGHT

9ES BECAUSE YOU D NEVER HAVE MORE THAN ONE THREAD FOR THAT SERVLET SO THE INSTANCE VARIABLES WOULD BE THREAD SAFE "UT OF COURSE NOBODY WOULD EVER AL LOW YOU INTO THE SERVLETS CLUB EVER AGAIN

) WAS JUST TALKING HYPOTHETICALLY !S IN hIF SOMEONE 7%2% STUPID ENOUGH TO IMPLEMENT 3INGLE 4HREAD-ODEL v .OT THAT ) WOULD EVER DO IT "UT WHILE WE RE BEING HYPOTHETICAL IF ) HAVE A FRIEND WHO SAY SYNCHRONIZES THE SERVICE METHOD WOULDN T THAT !,3/ MAKE THE INSTANCE VARIABLES THREAD SAFE

9ES "UT YOUR FRIEND WOULD BE AN IDIOT 4HE EFFECT OF IMPLEMENTING 3INGLE4HREAD-ODEL IS VIRTUALLY THE SAME AS SYNCHRONIZING THE SERVICE METHOD "OTH CAN BRING A WEB APP TO ITS KNEES WITHOUT PROTECTING THE SESSION AND ATTRIBUTE STATE

"UT IF YOU RE NOT SUPPOSED TO USE 3INGLE 4HREAD-ODEL OR SYNCHRONIZE THE SERVICE METHOD THEN HOW $/ YOU MAKE INSTANCE VARIABLES THREAD SAFE

9OU DON T ,OOK AT A WELL WRITTEN SERVLET AND CHANCES ARE YOU WON T FIND ANY INSTANCE VARIABLES /R AT LEAST ANY THAT ARE NON FINAL !ND SINCE YOU RE A *AVA PROGRAMMER YOU KNOW THAT EVEN A FINAL VARIABLE CAN STILL BE MANIPULATED UNLESS IT S IMMUTABLE 3O JUST DON T USE INSTANCE VARIABLES IF YOU NEED THREAD SAFE STATE BECAUSE ALL THREADS FOR THAT SERVLET CAN STEP ON INSTANCE VARIABLES

4HEN WHAT 3(/5,$ YOU USE IF YOU NEED MUL TIPLE INSTANCES OF THE SERVLET TO SHARE SOMETHING

3TOP RIGHT THERE 9OU SAID hMULTIPLE INSTANCES OF THE SERVLETv 7E KNOW YOU DIDN T MEAN THAT BE CAUSE THERE IS ALWAYS ONLY /.% INSTANCE OF THE SERVLET /NE INSTANCE MANY THREADS )F YOU WANT ALL THE THREADS TO ACCESS A VALUE DECIDE WHICH ATTRIBUTE STATE MAKES THE MOST SENSE AND STORE THE VALUE IN AN ATTRIBUTE #HANCES ARE YOU CAN SOLVE YOUR PROBLEMS IN ONE OF TWO WAYS $ECLARE THE VARIABLE AS A LOCAL VARIABLE WITHIN THE SERVICE METHOD RATHER THAN AS AN INSTANCE VARIABLE /2 5SE AN ATTRIBUTE IN THE MOST APPROPRIATE SCOPE

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Chapter 5. Being a Web App

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Chapter 5. Being a Web App

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: MY]M[\,Q[XI\KPMZ ZM^MITML 2EQUEST$ISPATCHERS HAVE ONLY TWO METHODSÂ&#x2C6; FORWARD AND INCLUDE "OTH TAKE THE REQUEST AND RESPONSE OBJECTS WHICH THE COMPONENT YOU RE FORWARDING TO WILL NEED TO l NISH THE JOB /F THE TWO METHODS FORWARD IS BY FAR THE MOST POPULAR )T S VERY UNLIKELY YOU LL USE THE INCLUDE METHOD FROM A CONTROLLER SERVLET HOWEVER BEHIND THE SCENES THE INCLUDE METHOD IS BEING USED BY *30S IN THE JSP INCLUDE STANDARD ACTION WHICH WE LL REVIEW IN CHAPTER 9OU CAN GET A 2EQUEST$ISPATCHER IN TWO WAYS FROM THE REQUEST OR FROM THE CONTEXT 2EGARDLESS OF WHERE YOU GET IT YOU HAVE TO TELL IT THE WEB COMPONENT TO WHICH YOU RE FORWARDING THE REQUEST )N OTHER WORDS THE SERVLET OR *30 THAT LL TAKE OVER

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Any part of the web app including servlets, JSPs, ServletContextListeners, ServletContextAttributeListeners.

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Any servlet or JSP with The life of the session. A access to this particular session can be destroyed session. Remember, a session programmatically or can extends beyond a single client simply time-out. (WeÕll request to span multiple go into the details in requests by the same client, the Session Management which could go to different chapter.) servlets. Any part of the application that has direct access to the Request object. That mostly means only the Servlets and JSPs to which the request is forwarded using a RequestDispateher. Also Request-related listeners.

The life of the Request, which means until the ServletÕs service() method completes. In other words, for the life of the thread (stack) handling this request.

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Resources you want the entire application to share, including database connections, JNDI lookup names, email addresses., etc.

Data and resources related to this clientÕs session, not just a single request. Something that requires an ongoing conversation with the client. A shopping cart is a typical example.

Passing model info from the controller to the view... or any other data speciÞc to a single client request.

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Chapter 5. Being a Web App

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Chapter 5. Being a Web App

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Chapter 5. Being a Web App

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Chapter 5. Being a Web App

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7HICH TYPES OF OBJECTS CAN STORE ATTRIBUTES #HOOSE ALL THAT APPLY

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Chapter 5. Being a Web App

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7HICH STATEMENTS ACCURATELY DESCRIBE HOW MANY INSTANCES OF A SERVLET THE SERVLET CONTAINER INSTANTIATES FOR EACH WEB APPLICATION #HOOSE ALL THAT APPLY

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Chapter 5. Being a Web App

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-An IllegalStateException is caused when a response has already been Ă&#x201D;committedĂ&#x2022; to the client (the Ă&#x;ush method does that), and then you attempt a forward.

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-Option B is incorrect because ServletContext init parameters are only read at Container start-up time.

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-Option E is incorrect because there is only one ServletContext object per web application.

TO AN ENTIRE WEB APPLICATION

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Chapter 5. Being a Web App

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-Option B is the correct method. With it you can access the container populated javax.servlet.forward.Xxx and javax.servlet.include.Xxxx attributes.

-Options C and D refer to methods that donĂ&#x2022;t exist.

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-Options A and B are incorrect because these methods do not exist.

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Chapter 5. Being a Web App

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-Option A is incorrect because these is no ServletResponseListener interface.

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-Option E is

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such -Option B is incorrect becauseiately data is typically either immed scope. st returned or stored in reque

IMMEDIATELY TO A USER

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. 58 (Servlet v2.4 pg

ect because a query -Option A is incorr typically used . re mo is r ete am par operation immediately to perform an

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ServletContextListener would be used for this purpose.

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R % ! COPY OF AN INITIALIZATION PARAMETER RETRIEVED FROM A 6HUYOHW&RQWH[W OBJECT

-Option E is incorrect because servlet context parameters should stay with the ServletContext object.

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Chapter 5. Being a Web App

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` 7HAT LOGGING OUTPUT IS GENERATED

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-Tricky! The getValue method returns the OLD value of the attribute if the attribute was replaced.

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R ! GHVFULSWLRQ! R " OLVWHQHU QDPH! R # OLVWHQHU W\SH! R $ OLVWHQHU FODVV! -The <listener-class> sub-element is the ONLY required sub-element of R % VHUYOHW PDSSLQJ! the <listener> element.

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7HICH TYPES OF OBJECTS CAN STORE ATTRIBUTES #HOOSE ALL THAT APPLY

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-Options A, B, and C are s do invalid because these type not store attributes. -Option E is invalid because there is no such type.

(API) Note: The other two types related to servlets, that can store attributes are HttpSession and ServletContext.

s. 81-84)

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7HICH ARE TRUE #HOOSE ALL THAT APPLY

R ! 7HEN A WEB APPLICATION IS PREPARING TO SHUTDOWN THE ORDER OF LISTENER NOTIlCATION IS NOT GUARANTEED

R " 7HEN LISTENER FRIENDLY EVENTS OCCUR LISTENER INVOCATION ORDER IS NOT PREDICTABLE

-Options A and B are incorrect because the container uses the DD to determine the notiĂ&#x17E;cation order of registered listeners.

R # 4HE CONTAINER REGISTERS LISTENERS BASED ON DECLARATIONS IN THE DEPLOYMENT DESCRIPTOR

R $ /NLY THE CONTAINER CAN INVALIDATE A SESSION

-Option D is incorrect because a servlet can invalidate a session using the HttpSession.invalidate() method.

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65)

R ! ! 5HTXHVW'LVSDWFKHU CAN BE USED TO FORWARD A REQUEST TO ANOTHER SERVLET

R " 4HE ONLY METHOD IN THE 5HTXHVW'LVSDWFKHU INTERFACE IS IRUZDUG

R # 0ARAMETERS SPECIlED IN THE QUERY STRING USED TO CREATE A 5HTXHVW'LVSDWFKHU ARE NOT FORWARDED BY THE IRUZDUG METHOD

R $ 4HE SERVLET TO WHICH A REQUEST IS FORWARDED MAY ACCESS THE

-Option B is incorrect because the interface also contains an include method. -Option C is incorrect because such parameters are forwarded in this case.

ORIGINAL QUERY STRING BY CALLING JHW4XHU\6WULQJ ON THE 6HUYOHW5HTXHVW

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R ! )F THE SERVLET IMPLEMENTS MDYD[ VHUYOHW 6LQJOH7KUHDG0RGHO THE CONTAINER MAY CREATE ONE INSTANCE FOR EACH REQUEST

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R # 4HE ORDG RQ VWDUWXS! ZHE [PO ELEMENT CAN DETERMINE HOW -Option C is incorrect

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MANY INSTANCES ARE CREATED

R $ )F THE SERVLET DOES NOT IMPLEMENT 6LQJOH7KUHDG0RGHO THE CONTAINER WILL CREATE NO MORE THAN ONE INSTANCE PER *6-

rrect R ! 7RITE THE SERVLET CODE TO EXTEND 7KUHDG6DIH6HUYOHW -Option A and B areeSeinco rvlet does Saf ead Thr e aus bec R " (AVE THE SERVLET IMPLEMENT 6LQJOH7KUHDG0RGHO vlet API not exist in the SeradM odel is R # ,OG ALL SERVLET METHOD CALLS and the .SingleThre d in version 2.4 and ate rec dep R $ 5SE LOCAL VARIABLES EXCLUSIVELY AND IF YOU HAVE TO USE INSTANCE recommended.. VARIABLES SYNCHRONIZE ACCESS TO THEM

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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: stephengoss@gmx.net 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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!LL FOUR OF THE EXAM OBJECTIVES ON SESSION MANAGEMENT ARE COVERED COMPLETELY IN THIS CHAPTER ALTHOUGH SOME OF THESE TOPICS WERE TOUCHED ON IN THE PREVIOUS CHAPTER 4HIS CHAPTER IS YOUR ONE CHANCE TO LEARN AND MEMORIZE THESE TOPICS SO TAKE YOUR TIME

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0W_ KIV PM \ZIKS \PM KTQMV\Â¼[ IV[_MZ[' +IM S DESIGN WON T WORK UNLESS HE CAN KEEP TRACK OF EVERYTHING THE CLIENT HAS ALREADY SAID DURING THE CONVERSATION NOT JUST THE ANSWER IN THE CURRENT REQUEST (E NEEDS THE SERVLET TO GET THE REQUEST PARAMETERS REPRESENTING THE CLIENT S CHOICES AND SAVE IT SOMEWHERE %ACH TIME THE CLIENT ANSWERS A QUESTION THE ADVICE ENGINE USES ALL OF THAT CLIENT S PREVIOUS ANSWERS TO COME UP WITH EITHER ANOTHER QUESTION TO ASK OR A lNAL RECOMMENDATION 7HAT ARE SOME OPTIONS 8VH D VWDWHIXO VHVVLRQ HQWHUSULVH MDYDEHDQ 3URE HE COULD DO THAT (E COULD HAVE HIS SERVLET BECOME A CLIENT TO A STATEFUL SESSION BEAN AND EACH TIME A REQUEST COMES IN HE COULD LOCATE THAT CLIENT S STATEFUL BEAN 4HERE ARE A LOT OF LITTLE ISSUES TO WORK OUT BUT YES YOU CAN CERTAINLY USE A STATEFUL SESSION BEAN TO STORE CONVERSATIONAL STATE "UT THAT S WAY TOO MUCH OVERHEAD OVERKILL FOR THIS APP "ESIDES +IM S HOSTING PROVIDER DOESN T HAVE A FULL * %% SERVER WITH AN %*" #ONTAINER (E S GOT 4OMCAT A WEB #ONTAINER AND THAT S IT 8VH D GDWDEDVH

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<PM JM[\ XIZ\" \PM +WV\IQVMZ LWM[ ^QZ\]ITTa ITT \PM KWWSQM _WZS 9OU DO HAVE TO TELL THE #ONTAINER THAT YOU WANT TO CREATE OR USE A SESSION BUT THE #ONTAINER TAKES CARE OF GENERATING THE SESSION )$ CREATING A NEW #OOKIE OBJECT STUFlNG THE SESSION )$ INTO THE COOKIE AND SETTING THE COOKIE AS PART OF THE RESPONSE !ND ON SUBSEQUENT REQUESTS THE #ONTAINER GETS THE SESSION )$ FROM A COOKIE IN THE REQUEST MATCHES THE SESSION )$ WITH AN EXISTING SESSION AND ASSOCIATES THAT SESSION WITH THE CURRENT REQUEST

6HQGLQJ D VHVVLRQ FRRNLH LQ WKH 5(63216( +WWS6HVVLRQ VHVVLRQ UHTXHVW JHW6HVVLRQ 4HAT S IT 3OMEWHERE IN YOUR SERVICE METHOD YOU ASK FOR A SESSION AND EVERYTHING ELSE HAPPENS AUTOMATICALLY 9OU DON T MAKE THE NEW (TTP3ESSION OBJECT YOURSELF 9OU DON T GENERATE THE UNIQUE SESSION )$ 9OU DON T MAKE THE NEW #OOKIE OBJECT 9OU DON T ASSOCIATE THE SESSION )$ WITH THE COOKIE 9OU DON T SET THE #OOKIE INTO THE RESPONSE UNDER THE 3ET #OOKIE HEADER

est for a session, You ask the requer kicks everything and the Contain You donĂ&#x2022;t have to else into action.e! do anything els es more than just (This method do, but the FIRST on ssi se create a on the request, it time you invokeokitie to be sent with co a will cause thereĂ&#x2022;s still not the response. Nocliw,ent will ACCEPT e guarantee th t weĂ&#x2022;re getting ahead the cookie... bu of ourselves.)

!LL THE COOKIE WORK HAPPENS BEHIND THE SCENES

*HWWLQJ WKH VHVVLRQ ,' IURP WKH 5(48(67 +WWS6HVVLRQ VHVVLRQ UHTXHVW JHW6HVVLRQ ,OOK FAMILIAR 9ES IT S EXACTLY THE SAME METHOD USED TO GENERATE THE SESSION )$ AND COOKIE FOR THE RESPONSE )& THE REQUEST INCLUDES A SESSION )$ COOKIE lND THE SESSION MATCHING THAT )$ %,3% )& THERE S NO SESSION )$ COOKIE /2 THERE S NO CURRENT SESSION MATCHING THE SESSION )$

Whoa! The me od for GETTING a session ID cookth with an existingiese (and matching it as SENDING a ssion) is the same You never actuallsession ID cookie. ID yourself (althy SEE the session ough you can as the session to giv e it to you). k

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Chapter 6. Conversational state

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?PI\ QN 1 _IV\ \W SVW_ _PM\PMZ \PM [M[[QWV ITZMILa M`Q[\ML WZ _I[ R][\ KZMI\ML' 'OOD QUESTION 4HE NO ARG REQUEST METHOD GET3ESSION RETURNS A 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 WKURZV ,2([FHSWLRQ 6HUYOHW([FHSWLRQ ^ UHVSRQVH VHW&RQWHQW7\SH ÂłWH[W KWPOÂ´ 3ULQW:ULWHU RXW UHVSRQVH JHW:ULWHU RXW SULQWOQ ÂłWHVW VHVVLRQ DWWULEXWHV EU!Â´

s a session no matter getSession() returnnĂ&#x2022;t tell if itĂ&#x2022;s a new what.... but you caask the session. u yo ess unl session

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if the isNew() returns trueresponded yet t no s client ha with this session ID.

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9OU GET A SESSION BY CALLING REQUEST GET3ESSION BUT IS THAT THE ONLY WAY TO GET THE SESSION #AN T YOU GET IT FROM THE 3ERVLET#ONTEXT

9OU GET A SESSION FROM THE REQUEST OBJECT BECAUSEÂ&#x2C6; THINK ABOUT ITÂ&#x2C6;THE SESSION IS IDENTIFIED BY THE REQUEST 7HEN YOU CALL GET3ESSION ON THE #ONTAINER YOU RE SAYING h) WANT A SESSION FOR 4()3 CLIENT EITHER THE SESSION THAT 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 *30Â&#x2C6;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

SXEOLF YRLG VHVVLRQ&UHDWHG +WWS6HVVLRQ(YHQW HYHQW ^ +WWS6HVVLRQ VHVVLRQ HYHQW JHW6HVVLRQ HYHQW KDQGOLQJ FRGH `

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?PI\ QN 1 _IV\ 764A I XZM M`Q[\QVO [M[[QWV' 9OU MIGHT HAVE A SCENARIO IN WHICH A SERVLET WANTS TO USE ONLY A PREVIOUSLY CREATED SESSION )T MIGHT NOT MAKE SENSE FOR THE CHECKOUT SERVLET FOR EXAMPLE TO START A NEW SESSION 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 ^ UHVSRQVH VHW&RQWHQW7\SH ÂłWH[W KWPOÂ´ 3ULQW:ULWHU RXW UHVSRQVH JHW:ULWHU RXW SULQWOQ ÂłWHVW VHVVLRQV EU!Â´

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Now we can test for whether there was already a session (the no-arg getSession() would NEVER return null).

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s the method Passing Ă&#x2019;falseĂ&#x201C; meanting session, xis -e pre a s urn ret no session or null if there waiss client. th h wit ed at associ

we KNOW weĂ&#x2022;re making a new session.

)SN T THE CODE ABOVE JUST A STUPID INEFlCIENT WAY TO DO THE SAME THING AS THE OPPOSITE PAGE )N THE END YOU STILL CREATED A NEW SESSION

3O IT LOOKS LIKE GET3ESSION TRUE IS EXACTLY THE SAME AS GET3ESSION

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

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

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Chapter 6. Conversational state

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AW] KIV LW [M[[QWV[ M^MV QN \PM KTQMV\ LWM[VÂ¼\ IKKMX\ KWWSQM[ J]\ aW] PI^M \W LW I TQ\\TM UWZM _WZS 7E DON T AGREE THAT ANYBODY WITH HALF A BRAIN DISABLES COOKIES )N FACT MOST BROWSERS DO HAVE COOKIES ENABLED AND EVERYTHING S WONDERFUL "UT THERE S NO GUARANTEE )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 CLIENT BUT IT TAKES A LITTLE MORE EFFORT FROM YOU )F YOU USE THE SESSION CODE ON THE PREVIOUS PAGESÂ&#x2C6;CALLING GET3ESSION ON THE REQUESTÂ&#x2C6;THE #ONTAINER TRIES TO USE COOKIES )F COOKIES AREN T ENABLED IT MEANS THE CLIENT WILL NEVER JOIN THE SESSION )N OTHER WORDS THE SESSION S IS.EW METHOD WILL ALWAYS RETURN TRUE

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=:4 ZM_ZQ\QVO" [WUM\PQVO \W NITT JIKS WV )F THE CLIENT WON T TAKE COOKIES YOU CAN USE 52, REWRITING AS A BACK UP !SSUMING YOU DO YOUR PART CORRECTLY 52, REWRITING WILL ALWAYS WORKÂ&#x2C6;THE CLIENT WON T CARE THAT IT S HAPPENING AND WON T DO ANYTHING TO PREVENT IT 2EMEMBER THE GOAL IS FOR THE CLIENT AND #ONTAINER TO EXCHANGE SESSION )$ INFO 0ASSING 85/ COOKIES BACK AND FORTH IS THE SIMPLEST WAY TO EXCHANGE SESSION )$S BUT IF YOU CAN T PUT THE )$ IN A COOKIE WHERE CAN YOU PUT IT 52, REWRITING TAKES THE SESSION )$ THAT S IN THE COOKIE AND STICKS IT RIGHT ONTO THE END OF EVERY 52, THAT COMES IN TO THIS APP

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)MAGINE A WEB PAGE WHERE EVERY LINK HAS A LITTLE BIT OF EXTRA INFO THE SESSION )$ TACKED ONTO THE END OF THE 52, 7HEN THE USER CLICKS THAT hENHANCEDv LINK THE REQUEST GOES TO THE #ONTAINER WITH THAT EXTRA BIT ON THE END AND THE #ONTAINER SIMPLY STRIPS OFF THE EXTRA PART OF THE REQUEST 52, AND USES IT TO l ND THE MATCHING SESSION

We add the session ID to the end of all the URLs in the HTML we send back in the Response.

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The session ID comes back as Ă&#x2019;extraĂ&#x201C; info stuck to the end of the Request URL. (The semicolon separator is vendor-speciĂ&#x17E;c.)

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=:4 ZM_ZQ\QVO SQKS[ QV 764A QN KWWSQM[ NIQT IVL 764A QN aW] \MTT \PM ZM[XWV[M \W MVKWLM \PM =:4 )F COOKIES DON T WORK THE #ONTAINER FALLS BACK TO 52, REWRITING BUT ONLY IF YOU VE DONE THE EXTRA WORK OF ENCODING ALL THE 52,S YOU SEND IN THE RESPONSE )F YOU WANT THE #ONTAINER TO ALWAYS DEFAULT TO USING COOKIES lRST WITH 52, REWRITING ONLY AS A LAST RESORT YOU CAN RELAX 4HAT S EXACTLY HOW IT WORKS EXCEPT FOR THE lRST TIME BUT WE LL GET TO THAT IN A MOMENT "UT IF YOU DON T EXPLICITLY ENCODE YOUR 52,S AND THE CLIENT WON T ACCEPT COOKIES YOU DON T GET TO USE SESSIONS )F YOU DO ENCODE YOUR 52,S THE #ONTAINER WILL lRST ATTEMPT TO USE COOKIES FOR SESSION MANAGEMENT AND FALL BACK TO 52, REWRITING ONLY IF THE COOKIE APPROACH FAILS SXEOLF YRLG GR*HW +WWS6HUYOHW5HTXHVW UHTXHVW +WWS6HUYOHW5HVSRQVH UHVSRQVH WKURZV ,2([FHSWLRQ ^ UHVSRQVH VHW&RQWHQW7\SH Â³WH[W KWPOÂ´ 3ULQW:ULWHU RXW UHVSRQVH JHW:ULWHU n get a sessio +WWS6HVVLRQ VHVVLRQ UHTXHVW JHW6HVVLRQ RXW SULQWOQ Â³ KWPO! ERG\!Â´ RXW SULQWOQ Â³ D KUHI ?Â´Â´ UHVSRQVH HQFRGH85/ Â³ %HHU7HVW GRÂ´ Â³?Â´!FOLFN PH D!Â´ RXW SULQWOQ Â³ ERG\! KWPO!Â´ ` to this URL.

Add the extra session ID info

7AIT A MINUTE HOW $/%3 THE #ONTAINER KNOW THAT COOKIES AREN T WORKING !T WHAT POINT DOES THE #ONTAINER DECIDE TO USE 52, REWRITING

! REALLY DUMB #ONTAINER DOESN T CARE WHETHER COOK IES WORK OR NOTÂ&#x2C6;THE DUMB #ONTAINER WILL ALWAYS ATTEMPT TO SEND THE COOKIE !.$ DO 52, REWRITING EACH TIME EVEN IF COOKIES ARE WORKING "UT HERE S HOW A DECENT #ONTAINER HANDLES IT 7HEN THE #ONTAINER SEES A CALL TO GET3ESSION AND THE #ONTAINER DIDN T GET A SESSION )$ WITH THE CLIENT S REQUEST THE #ONTAINER NOW KNOWS THAT IT MUST ATTEMPT TO START A NEW SESSION WITH THE CLIENT !T THIS POINT THE #ONTAINER DOESN T KNOW IF COOKIES WILL WORK SO WITH THIS FIRST RESPONSE BACK TO THE CLIENT IT TRIES "/4( COOKIES AND 52, REWRITING

7HY CAN T IT TRY COOKIES lRST AND DO 52, REWRIT ING ON THE NEXT RESPONSE IF IT DOESN T GET BACK A COOKIE

2EMEMBER IF THE #ONTAINER DOESN T GET A SESSION )$ FROM THE CLIENT THE #ONTAINER WON T EVEN +./7 THAT THIS IS THE NEXT REQUEST FROM THAT CLIENT 4HE #ONTAINER WON T HAVE ANY WAY TO KNOW THAT IT TRIED COOKIES THE LAST TIME AND THEY DIDN T WORK 2EMEMBER THE /.,9 WAY THE #ONTAINER CAN RECOGNIZE THAT IT HAS SEEN THIS CLIENT BEFORE IS IF THE CLIENT SENDS A SESSION )$ 3O WHEN THE #ONTAINER SEES YOU CALL REQUEST GET3ESSION AND REALIZES IT NEEDS TO START A NEW SESSION WITH THIS CLIENT THE #ONTAINER SENDS THE RESPONSE WITH BOTH A h3ET #OOKIEv HEADER FOR THE SESSION )$ AND THE SESSION )$ APPENDED TO THE 52,S ASSUMING YOU USED RESPONSE ENCODE52, .OW IMAGINE THE NEXT REQUEST FROM THIS CLIENTÂ&#x2C6;IT WILL HAVE THE SESSION )$ APPENDED TO THE REQUEST 52, BUT IF THE CLIENT ACCEPTS COOKIES THE REQUEST WILL !,3/ HAVE A SESSION )$ COOKIE 7HEN THE SERVLET CALLS REQUEST GET3ESSION THE #ONTAINER READS THE SESSION )$ FROM THE REQUEST FINDS THE SESSION AND THINKS TO ITSELF h4HIS CLIENT ACCEPTS COOKIES SO ) CAN IGNORE THE RESPONSE ENCODE52, CALLS )N THE RESPONSE ) LL SEND A COOKIE SINCE ) KNOW THAT WORKS AND THERE S NO NEED FOR ANY 52, REWRITING SO ) WON T BOTHER v

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Chapter 6. Conversational state

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=:4 ZM_ZQ\QVO _WZS[ _Q\P [MVL:MLQZMK\ 9OU MIGHT HAVE A SCENARIO IN WHICH YOU WANT TO REDIRECT THE REQUEST TO A DIFFERENT 52, BUT YOU STILL WANT TO USE A SESSION 4HERE S A SPECIAL 52, ENCODING METHOD JUST FOR THAT UHVSRQVH HQFRGH5HGLUHFW85/ Â³ %HHU7HVW GRÂ´

7HAT ABOUT ALL MY STATIC (4-, PAGES THEY ARE FULL OF A HREF LINKS (OW DO ) DO 52, REWRITING ON THOSE STATIC PAGES

9OU CAN T 4HE ONLY WAY TO USE 52, REWRITING IS IF !,, THE PAGES THAT ARE PART OF A SESSION ARE DYNAMICALLY GENERATED 9OU CAN T HARD CODE SESSION )$ S OBVIOUSLY SINCE THE )$ DOESN T EXIST UNTIL RUNTIME 3O IF YOU DEPEND ON SESSIONS YOU NEED 52, REWRITING AS A FALL BACK STRATEGY !ND SINCE YOU NEED 52, REWRITING YOU HAVE TO DYNAMICALLY GENERATE THE 52,S IN THE RESPONSE (4-, !ND THAT MEANS YOU HAVE TO PROCESS THE (4-, AT RUNTIME 9ES THIS IS A PERFORMANCE ISSUE 3O YOU MUST THINK VERY CAREFULLY ABOUT THE PLACES WHERE SESSIONS MATTER TO YOUR APP AND WHETHER SESSIONS ARE CRITICAL TO HAVE OR MERELY GOOD TO HAVE

85/ UHZULWLQJ LV DXWRPDWLF EXW RQO\ LI \RX HQFRGH \RXU 85/V <28 KDYH WR UXQ DOO \RXU 85/V WKURXJK D PHWKRG RI WKH UHVSRQVH REMHFWÂ³HQFRGH85/ RU HQFRGH5HGLUHFW85/ Â³DQG WKH &RQWDLQHU GRHV HYHU\WKLQJ HOVH

9OU SAID THAT TO USE 52, REWRITING PAGES MUST BE DY NAMICALLY GENERATED SO DOES THIS MEAN ) CAN DO IT WITH *30S

9ES 9OU CAN DO 52, REWRITING IN A *30 AND THERE S EVEN A SIMPLE *34, TAG THAT MAKES IT EASY C 52, THAT YOU LL SEE WHEN YOU GET TO THE CHAPTER ON USING CUSTOM TAGS

4 $

)S 52, REWRITING HANDLED IN A VENDOR SPECIl C WAY

9ES 52, REWRITING IS HANDLED IN A VENDOR SPECIFIC WAY 4OM CAT USES A SEMICOLON h v TO APPEND THE EXTRA INFO TO THE 52, !NOTHER VENDOR MIGHT USE A COMMA OR SOMETHING ELSE !ND WHILE 4OMCAT ADDS hJSESSIONID v IN THE REWRITTEN 52, ANOTHER VENDOR MIGHT AP PEND ONLY THE SESSION )$ ITSELF 4HE POINT IS WHATEVER THE #ONTAINER USES AS THE SEPARATOR IS RECOGNIZED BY THE #ONTAINER WHEN A REQUEST COMES IN 3O WHEN THE #ONTAINER SEES THE SEPARATOR THAT IT USES IN OTHER WORDS THE SEPARATOR THAT IT ADDED DURING 52, REWRITING IT KNOWS THAT EVERYTHING AFTER THAT IS hEXTRA INFOv THAT THE #ONTAINER PUT THERE )N OTHER WORDS THE #ONTAINER KNOWS HOW TO RECOGNIZE AND PARSE THE EXTRA STUFF IT THE #ONTAINER APPENDED TO THE 52,

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, 5($//< GRQÂˇW ZDQW D EXQFK RI VWDOH VHVVLRQV VLWWLQJ DURXQG LQ P\ VHUYHU WDNLQJ XS YDOXDEOH VSDFH

/M\\QVO ZQL WN [M[[QWV[ 4HE CLIENT COMES IN STARTS A SESSION THEN CHANGES HER MIND AND LEAVES THE SITE /R THE CLIENT COMES IN STARTS A SESSION THEN HER BROWSER CRASHES /R THE CLIENT COMES IN STARTS A SESSION AND THEN COMPLETES THE SESSION BY MAKING A PURCHASE SHOPPING CART CHECK OUT /R HER COMPUTER CRASHES 7HATEVER 4HE POINT IS SESSION OBJECTS TAKE RESOURCES 9OU DON T WANT SESSIONS TO STICK AROUND LONGER THAN NECESSARY 2EMEMBER THE (440 PROTOCOL DOESN T HAVE ANY MECHANISM FOR THE SERVER TO KNOW THAT THE CLIENT IS GONE )N DISTRIBUTED APPLICATION TERMS FOR THOSE OF YOU FAMILIAR WITH THEMÂ&#x2C6; THERE S NO LEASING

"UT HOW DOES THE #ONTAINER OR YOU KNOW WHEN THE CLIENT WALKED AWAY (OW DOES THE #ONTAINER KNOW WHEN THE CLIENT S BROWSER CRASHED (OW DOES THE #ONTAINER KNOW WHEN IT S SAFE TO DESTROY A SESSION

(He wants to conse on his machine for rve space Ă&#x2019;The SimsĂ&#x201C; with th playing DateĂ&#x201C; expansion pae Ă&#x2019;Hot ck.)

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The getName() method returns the String name of the attribute that triggered the event. The getValue() method returns the object value of the attribute that triggered the event. Watch out! It returns the old value, not the new one. In other words, it returns the value the attribute had BEFORE the change that triggered the event!

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R ! ,INE ONLY R " ,INE ONLY R # ,INE ONLY R $ ,INE ONLY R % ,INE OR LINE R & ,INE OR LINE

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R ! ! SESSION WHOSE TIMEOUT PERIOD HAS BEEN SET TO WILL NEVER EXPIRE

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7HICH STATEMENTS ABOUT SESSION TRACKING ARE TRUE #HOOSE ALL THAT APPLY

R ! 52, REWRITING MAY BE USED BY A SERVER AS THE BASIS FOR SESSION TRACKING

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R # 7HEN USING COOKIES FOR SESSION TRACKING THERE IS NO RESTRICTION ON THE NAME OF THE SESSION TRACKING COOKIE

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R $ VHVVLRQ&UHDWHG AND VHVVLRQ'HVWUR\HG ARE ./4 THE ONLY METHODS DElNED BY THE +WWS6HVVLRQ/LVWHQHU INTERFACE

7HICH STATEMENTS ABOUT SESSION ATTRIBUTES ARE TRUE #HOOSE ALL THAT APPLY

R ! 4HE RETURN TYPE OF +WWS6HVVLRQ JHW$WWULEXWH 6WULQJ IS 2EMHFW

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R $ #ALLING VHW$WWULEXWH Â³NH\$Â´ Â³YDOXH%Â´ ON AN +WWS6HVVLRQ WHICH ALREADY HOLDS A VALUE FOR THE KEY NH\$ WILL CAUSE AN EXCEPTION TO BE THROWN

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Chapter 6. Conversational state

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R ! V UHPRYH$OO9DOXHV R " V UHPRYH$WWULEXWH Â³P\$WWU Â´ V UHPRYH$WWULEXWH Â³P\$WWU Â´

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R ! 7HEN A SESSION IS MOVED FROM ONE *6- TO ANOTHER ANY ATTRIBUTES STORED IN THE SESSION WILL BE LOST

R " 7HEN A SESSION IS MOVED FROM ONE *6- TO ANOTHER APPROPRIATELY REGISTERED +WWS6HVVLRQ%LQGLQJ/LVWHQHU OBJECTS WILL BE NOTIlED

R # 7HEN A SESSION IS MOVED FROM ONE *6- TO ANOTHER APPROPRIATELY REGISTERED +WWS6HVVLRQ$FWLYDWLRQ/LVWHQHU OBJECTS WILL BE NOTIlED

R $ 7HEN A SESSION IS MOVED FROM ONE *6- TO ANOTHER ATTRIBUTE VALUES THAT IMPLEMENT MDYD LR 6HULDOL]DEOH WILL BE TRANSFERRED TO THE NEW *6-

7HICH STATEMENTS ABOUT SESSION TIMEOUTS ARE TRUE #HOOSE ALL THAT APPLY

R ! 3ESSION TIMEOUT DECLARATIONS MADE IN THE $$ CAN SPECIFY TIME IN SECONDS

R " 3ESSION TIMEOUT DECLARATIONS MADE IN THE $$ CAN SPECIFY TIME IN MINUTES

R # 3ESSION TIMEOUT DECLARATIONS MADE PROGRAMMATICALLY CAN SPECIFY TIME ONLY IN SECONDS

R $ 3ESSION TIMEOUT DECLARATIONS MADE PROGRAMMATICALLY CAN SPECIFY TIME ONLY IN MINUTES

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Chapter 6. Conversational state

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Chapter 6. Conversational state

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'IVEN

SXEOLF FODVV 0\6HUYOHW H[WHQGV +WWS6HUYOHW ^ SXEOLF YRLG GR*HW +WWS6HUYOHW5HTXHVW UHT +WWS6HUYOHW5HVSRQVH UHV WKURZV ,2([FHSWLRQ 6HUYOHW([FHSWLRQ ^ UHTXHVW JHW6HVVLRQ VHW$WWULEXWH ÂłNH\Â´ ÂłYDOXHÂ´ UHTXHVW JHW+WWS6HVVLRQ VHW$WWULEXWH ÂłNH\Â´ ÂłYDOXHÂ´ +WWS6HVVLRQ UHTXHVW JHW6HVVLRQ

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R ! ,INE ONLY R " ,INE ONLY R # ,INE ONLY R $ ,INE ONLY lines 13 and R % ,INE OR LINE -Option E is correct because both cast to 15 make the correct method call. Thedoes reĂ&#x;ect R & ,INE OR LINE HttpSession is NOT necessary, but it

the correct type, so it is valid.

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R ! #OOKIES BUT ./4 52, REWRITING -Option B is correct because R " 52, REWRITING BUT ./4 COOKIES cookies CANNOT be used, but R # %ITHER COOKIES OR 52, REWRITING CAN BE USED URL rewriting does NOT depend . R $ .EITHER COOKIES NOR 52, REWRITING CAN BE USED on cookies being enabled R % #OOKIES AND 52, REWRITING MUST BE USED TOGETHER

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R ! ! SESSION WHOSE TIMEOUT PERIOD HAS BEEN SET TO WILL NEVER EXPIRE

R " ! SESSION WILL BECOME INVALID AS SOON AS THE USER CLOSES ALL BROWSER WINDOWS

use -Option B is incorrect beca there is no explicit termination signal in the HTTP protocol.

R # ! SESSION WILL BECOME INVALID AFTER A TIMEOUT PERIOD DElNED BY THE SERVLET CONTAINER

R $ ! SESSION MAY BE EXPLICITLY INVALIDATED BY CALLING +WWS6HVVLRQ LQYDOLGDWH6HVVLRQ

-Option D is incorrect because the method that should be used is called invalidate().

7HICH OF THE FOLLOWING ARE ./4 LISTENER EVENT TYPES IN THE * %% !0) #HOOSE ALL THAT APPLY

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R ! +WWS6HVVLRQ(YHQW R " 6HUYOHW5HTXHVW(YHQW R # +WWS6HVVLRQ%LQGLQJ(YHQW -HttpSessionBindingEvents are used for both HttpSessionBindingListeners AND R $ +WWS6HVVLRQ$WWULEXWH(YHQW HttpSessionAttributeListeners. R % 6HUYOHW&RQWH[W$WWULEXWH(YHQW

7HICH STATEMENTS ABOUT SESSION TRACKING ARE TRUE #HOOSE ALL THAT APPLY

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R ! 52, REWRITING MAY BE USED BY A SERVER AS THE BASIS FOR SESSION TRACKING

R " 33, HAS A BUILT IN MECHANISM THAT A SERVLET CONTAINER COULD USE TO OBTAIN DATA USED TO DElNE A SESSION

R # 7HEN USING COOKIES FOR SESSION TRACKING THERE IS NO RESTRICTION ON THE NAME OF THE SESSION TRACKING COOKIE

R $ 7HEN USING COOKIES FOR SESSION TRACKING THE NAME OF THE

-Option C is incorrect because the speciĂ&#x17E;cation dictates that the session tracking cookie must be JSESSIONID.

SESSION TRACKING COOKIE MUST BE -6(66,21,'

R % )F A USER HAS COOKIES DISABLED IN THEIR BROWSER THE CONTAINER MAY CHOOSE TO USE A MDYD[ VHUYOHW KWWS &RRNLHOHVV+WWS6HVVLRQ OBJECT TO TRACK THE USER S SESSION

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Chapter 6. Conversational state

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R ! 4HE METHOD SIGNATURE ON LINE IS ./4 CORRECT R " 4HE METHOD SIGNATURE ON LINE IS ./4 CORRECT R # 4HE IMPORT STATEMENT WILL ./4 IMPORT THE

276)

-Options A and B are correct because these methods should have an HttpSessionEvent parameter.

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Chapter 6. Conversational state

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Chapter 6. Conversational state

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Chapter 6. Conversational state

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Chapter 7. Being a JSP

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Chapter 7. Being a JSP Head First Servlets and JSP By Bert Bates, Kathy Sierra, Bryan Basham ISBN: 0596005407 Publisher:Prepared for Augusto Jaramillo Forcada, Safari ID: augustojf.cv@gmail.com O'Reilly Print Publication Date: 8/1/2004 User number: 729515 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 7. Being a JSP

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1V \PM MVL I 2;8 Q[ R][\ I [MZ ^TM\ 9OUR *30 EVENTUALLY BECOMES A FULL m EDGED SERVLET RUNNING IN YOUR WEB APP )T S A LOT LIKE ANY OTHER SERVLET EXCEPT THAT THE SERVLET CLASS IS WRITTEN FOR YOUÂ&#x2C6;BY THE #ONTAINER 4HE #ONTAINER TAKES WHAT YOU VE WRITTEN IN YOUR *30 TRANSLATES IT INTO A SERVLET CLASS SOURCE JAVA l LE THEN COMPILES THAT INTO A *AVA SERVLET CLASS !FTER THAT IT S JUST SERVLETS ALL THE WAY DOWN AND THE SERVLET RUNS IN EXACTLY THE SAME WAY IT WOULD IF YOU D WRITTEN AND COMPILED THE CODE YOURSELF )N OTHER WORDS THE #ONTAINER LOADS THE SERVLET CLASS INSTANTIATES AND INITIALIZES IT MAKES A SEPARATE THREAD FOR EACH REQUEST AND CALLS THE SERVLET S SERVICE METHOD

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Chapter 7. Being a JSP

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Chapter 7. Being a JSP

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Chapter 7. Being a JSP

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Chapter 7. Being a JSP

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Chapter 7. Being a JSP

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Chapter 7. Being a JSP

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Chapter 7. Being a JSP

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?PI\ :-)44A PIXXMV[ \W aW]Z 2;8 KWLM' 9OU WRITE A *30 BUT IT BECOMES A SERVLET 4HE ONLY WAY TO REALLY TELL WHAT S HAPPENING IS TO LOOK AT WHAT THE #ONTAINER DOES TO YOUR *30 CODE )N OTHER WORDS HOW DOES THE #ONTAINER TRANSLATE YOUR *30 INTO A SERVLET /NCE YOU KNOW WHERE DIFFERENT *30 ELEMENTS LAND IN THE SERVLET S CLASS lLE YOU LL lND IT MUCH EASIER TO KNOW HOW TO STRUCTURE YOUR *30 4HE SERVLET CODE ON THIS PAGE IS NOT THE REAL CODE GENERATED BY THE #ONTAINERÂ&#x2C6;WE SIMPLIlED IT DOWN TO THE ESSENTIAL PARTS 4HE #ONTAINER GENERATED SERVLET lLE IS WELL UGLIER 4HE REAL GENERATED SERVLET SOURCE CODE IS SLIGHTLY HARDER TO READ BUT WE WILL LOOK AT THE REAL THING IN A FEW PAGES &OR NOW THOUGH ALL WE CARE ABOUT IS WHERE IN THE SERVLET CLASS OUR *30 CODE ACTUALLY ENDS UP

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Chapter 7. Being a JSP

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Chapter 7. Being a JSP

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Chapter 7. Being a JSP

XVLQJ -63

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Chapter 7. Being a JSP

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Chapter 7. Being a JSP

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Chapter 7. Being a JSP

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Chapter 7. Being a JSP

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Chapter 7. Being a JSP

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Chapter 7. Being a JSP

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Chapter 7. Being a JSP

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Chapter 7. Being a JSP

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Chapter 7. Being a JSP

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Chapter 7. Being a JSP

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ct because all -Option C is incorre t. four lines include template tex -Option D is incorrect because line 12 does not include a JSP standard action.

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Chapter 7. Being a JSP

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Chapter 8. Script-free pages Head First Servlets and JSP By Bert Bates, Kathy Sierra, Bryan Basham ISBN: 0596005407 Publisher: O'Reilly Prepared for Stephen Goss, Safari ID: stephengoss@gmx.net 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 8. Script-free pages

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,MKWV[\Z]K\QVO $R[X"][M*MIV& IVL $R[X"OM\8ZWXMZ\a& !LL WE REALLY WANTED WAS THE FUNCTIONALITY OF JSP GET0ROPERTY BECAUSE WE WANTED ONLY TO DISPLAY THE VALUE OF THE PERSON S hNAMEv PROPERTY "UT HOW DOES THE #ONTAINER KNOW WHAT hPERSONv MEANS )F WE HAD ONLY THE JSP GET0ROPERTY TAG IN THE *30 IT S ALMOST LIKE USING AN UNDECLARED VARIABLEÂ&#x2C6;THE NAME hPERSONv 4HE #ONTAINER USUALLY HAS NO IDEA WHAT YOU RE TALKING ABOUT UNLESS YOU &)234 PUT A JSP USE"EAN INTO THE PAGE 4HE JSP USE"EAN IS A WAY OF DECLARING AND INITIALIZING THE ACTUAL BEAN OBJECT YOU RE USING IN JSP GET0ROPERTY

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7E KNOW HOW EASY IT IS TO PRINT AN ATTRIBUTE WHEN THE ATTRIBUTE ITSELF IRR 3HUVRQ IS A 3TRING 4HEN WE MADE AN ATTRIBUTE THAT WAS A NON 3TRING OBJECT A 0ERSON BEAN INSTANCE "UT WE DIDN T WANT TO PRINT THE ATTRIBUTE HW1DPH SXEOLF 6WULQJ J PERSON Â&#x2C6;WE WANTED TO PRINT A PROPERTY OF THE ATTRIBUTE IN OUR H 6WULQJ

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Chapter 8. Script-free pages

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Chapter 8. Script-free pages

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