IT2255 Web Essentials - Unit V Servlets and Database Connectivity

Servlets: Java Servlet Architecture – Servlet Life cycle – Form GET and POST actions – Sessions – Cookies – Database connectivity – JDBC

1. IT2253 Web Essentials
Unit V –Servlets and Database Connectivity
Kaviya.P
Kamaraj College of Engineering & Technology

2. Unit IV –Servlets and Database Connectivity
Servlets:JavaServletArchitecture–ServletLifecycle
–FormGETandPOSTactions–Sessions–Cookies–
Databaseconnectivity–JDBC–Creationofsimple
interactiveapplications–Simpledatabaseapplications

3. Servlets –Introduction
•Servlettechnologyisusedtocreateawebapplication(residesatserversideand
generatesadynamicwebpage).
•ServletsaretheJavaprogramsthatrunontheJava-enabledwebserveror
applicationserver.
•Theyareusedtohandletherequestobtainedfromthewebserver,processthe
request,producetheresponse,thensendaresponsebacktothewebserver.
•Properties:
•Servletsworkontheserver-side.
•Servletsarecapableofhandlingcomplexrequestsobtainedfromthe
webserver.

4. Java Servlet Architecture
ExecutionofServletsbasicallyinvolvessixbasicsteps:
1.Theclientssendtherequesttothewebserver.
2.Thewebserverreceivestherequest.
3.Thewebserverpassestherequesttothecorrespondingservlet.
4.Theservletprocessestherequestandgeneratestheresponseintheformof
output.
5.Theservletsendstheresponsebacktothewebserver.
6.Thewebserversendstheresponsebacktotheclientandtheclientbrowser
displaysitonthescreen.

5. Java Servlet Architecture

6. Java Servlet Architecture
•Client:ItsendsHTTPrequestsovertothewebserverandagainprocessing
theresponseitgetsbackfromtheserver.
•WebServer:Primaryjobofawebserveristoprocesstherequestsand
responsesthatausersendsovertimeandmaintainhowawebuserwould
beabletoaccessthefilesthathasbeenhostedovertheserver.Theserveris
asoftwarewhichmanagesaccesstoacentralizedresourceorserviceina
network..Therearepreciselytwotypesofwebservers:
–Staticwebserver
–Dynamicwebserver

7. Java Servlet Architecture
•WebContainer:Acomponentinservletarchitecturewhichisresponsible
forcommunicatingwiththeservlets.Twoprimetasksofawebcontainer
are:
–Managingtheservletlifecycle
–URLmapping
Webcontainersitsattheserver-sidemanagingandhandlingalltherequests
thatarecomingineitherfromtheservletsorfromsomeJSPpagesor
potentiallyanyotherfilesystem.

8. Java Servlet Architecture
Types of Servlets:
•Generic Servlets
•HTTP Servlets
To create a Servlet:
1.Implementing Servlet Interface
2.Extending Generic Servlet
3.Extending HTTP Servlet

9. Java Servlet Architecture
CGI(CommonGatewayInterface)
•CGItechnologyenablesthewebservertocallanexternalprogramandpassHTTPrequest
informationtotheexternalprogramtoprocesstherequest.
•Foreachrequest,itstartsanewprocess.
Disadvantages
•Ifthenumberofclientsincreases,ittakesmoretimeforsendingtheresponse.
•Foreachrequest,itstartsaprocess,andthewebserverislimitedtostartprocesses.
•Itusesplatformdependentlanguagee.g.C,C++,perl.

10. Java Servlet Architecture
AdvantagesofServlet
•ThewebcontainercreatesthreadsforhandlingthemultiplerequeststotheServlet.
•ThreadshavemanybenefitsovertheProcessessuchastheyshareacommon
memoryarea,lightweight,costofcommunicationbetweenthethreadsarelow.
•Advantages:Betterperformance,Portability,Robust,Secure.

11. Java Servlet Architecture
Website:staticvs
dynamic
Acollectionofrelatedwebpagesthatmaycontaintext,images,
audioandvideo.
HTTPThedatacommunicationprotocolusedtoestablish
communicationbetweenclientandserver.
HTTPRequestsTherequestsendbythecomputertoawebserverthatcontains
allsortsofpotentiallyinterestinginformation.
GetvsPostItgivesthedifferencebetweenGETandPOSTrequest.
ContainerUsedinjavafordynamicallygeneratingthewebpagesonthe
serverside.
Server:Webvs
Application
Usedtomanagethenetworkresourcesandforrunningthe
programorsoftwarethatprovidesservices.
ContentTypeHTTPheaderthatprovidesthedescriptionaboutwhatareyou
sendingtothebrowser.

12. Servlet Life Cycle
•TheentirelifecycleofaServletismanagedbytheServletcontainerwhichuses
thejavax.servlet.
•StagesoftheServletLifeCycle:
•LoadingaServlet:LoadingandinitializingtheServletbytheServletcontainer
•InitializingtheServlet:AftertheServletisinstantiatedsuccessfully,the
ServletcontainerinitializestheinstantiatedServletobject.Thecontainer
initializestheServletobjectbyinvokingtheServlet.init(ServletConfig)method
•Requesthandling:ItcreatestheServletRequestandServletResponseobjects.
•DestroyingtheServlet:WhenaServletcontainerdecidestodestroytheServlet

13. Servlet Life Cycle

14. Servlet Life Cycle
ServletLifeCycleMethods
•init():TheServlet.init()methodiscalledbytheServletcontainerto
indicatethatthisServletinstanceisinstantiatedsuccessfullyandisaboutto
putintoservice.
•service():ItisinvokedtoinformtheServletabouttheclientrequests.
•destroy():ItrunsonlyonceduringthelifetimeofaServletandsignalsthe
endoftheServletinstance.

15. Servlet Life Cycle
ServletLifeCycleMethods

16. Form GET and POST Actions
GETMethod
•TheGETmethodsendstheencodeduserinformationappendedtothepagerequest.
•Thepageandtheencodedinformationareseparatedbythe?(questionmark)
symbol.
•TheGETmethodisthedefaultmethodtopassinformationfrombrowsertoweb
server.
•TheGETmethodhassizelimitation:only1024characterscanbeusedinarequest
string.
•ServlethandlesthistypeofrequestsusingdoGet()method.
•Example
http://www.test.com/hello?key1 = value1&key2 = value2

17. Form GET and POST Actions
POSTMethod
•MorereliablemethodofpassinginformationtoabackendprogramisthePOST
method.
•ThispackagestheinformationinexactlythesamewayasGETmethod,butinstead
ofsendingitasatextstringaftera?(questionmark)intheURLitsendsitasa
separatemessage.
•ServlethandlesthistypeofrequestsusingdoPost()method.

18. Form GET and POST Actions
ReadingFormDataUsingServlet
•getParameter()−Callrequest.getParameter()methodtogetthevalueofaform
parameter.
•getParameterValues()−Callthismethodiftheparameterappearsmorethanonce
andreturnsmultiplevalues,forexamplecheckbox.
•getParameterNames()−Callthismethodifyouwantacompletelistofall
parametersinthecurrentrequest.

19. Sessions
•SessionTrackingisawaytomaintainstate(data)ofanuser.Itisalso
knownassessionmanagementinservlet.
•Httpprotocolisastatelesssoitisneededtomaintainstateusingsession
trackingtechniques.
•Eachtimeuserrequeststotheserver,servertreatstherequestasthenew
request.
•Soweneedtomaintainthestateofanusertorecognizetoparticularuser.
•HTTPisstatelessthatmeanseachrequestisconsideredasthenewrequest.

20. Sessions

21. Sessions
SessionTrackingTechniques:TherearefourtechniquesusedinSession
tracking:
1.Cookies
2.HiddenFormField
3.URLRewriting
4.HttpSession

22. Cookies
•Acookieisasmallpieceofinformationthatispersistedbetweenthe
multipleclientrequests.
•Acookiehasaname,asinglevalue,andoptionalattributessuchasa
comment,pathanddomainqualifiers,amaximumage,andaversion
number.
TypesofCookie
•Non-persistentcookie:Itisvalidforsinglesessiononly.Itisremoved
eachtimewhenuserclosesthebrowser.
•Persistentcookie:Itisvalidformultiplesession.Itisnotremovedeach
timewhenuserclosesthebrowser.Itisremovedonlyifuserlogoutor
signout.

23. Cookies
AdvantageofCookies
1.Simplesttechniqueofmaintainingthestate.
2.Cookiesaremaintainedatclientside.
DisadvantageofCookies
1.Itwillnotworkifcookieisdisabledfromthebrowser.
2.OnlytextualinformationcanbesetinCookieobject.

24. Cookies
Cookieclass
•javax.servlet.http.Cookieclassprovidesthefunctionalityofusing
cookies.Itprovidesalotofusefulmethodsforcookies.
ConstructorofCookieclass
ConstructorDescription
Cookie()constructsacookie.
Cookie(Stringname,Stringvalue)constructsacookiewitha
specifiednameandvalue.

25. Cookies
MethodsofCookieclass
MethodDescription
publicvoidsetMaxAge(int
expiry)
Setsthemaximumageofthecookiein
seconds.
publicStringgetName()Returnsthenameofthecookie.The
namecannotbechangedaftercreation.
publicStringgetValue()Returnsthevalueofthecookie.
publicvoidsetName(Stringname)changesthenameofthecookie.
publicvoidsetValue(Stringvalue)changesthevalueofthecookie.

26. Database Connectivity -JDBC
•JDBCstandsforJavaDatabaseConnectivity.
•JDBCisaJavaAPItoconnectandexecutethequerywiththedatabase.

27. Database Connectivity -JDBC
•Thejava.sqlpackagecontainsclassesandinterfacesforJDBCAPI.
•AlistofpopularinterfacesofJDBCAPIaregivenbelow:
•Driverinterface
•Connectioninterface
•Statementinterface
•PreparedStatementinterface
•CallableStatementinterface
•ResultSetinterface
•ResultSetMetaDatainterface
•DatabaseMetaDatainterface
•RowSetinterface

28. Database Connectivity -JDBC
•AlistofpopularclassesofJDBCAPIaregivenbelow:
•DriverManagerclass
•Blobclass
•Clobclass
•Typesclass
•OnecanuseJDBCAPItohandledatabaseusingJavaprogramandcan
performthefollowingactivities:
1.Connecttothedatabase
2.Executequeriesandupdatestatementstothedatabase
3.Retrievetheresultreceivedfromthedatabase.

29. Database Connectivity -JDBC

30. Database Connectivity -JDBC
StepsinJDBC
•RegistertheDriverclass
Class.forName("oracle.jdbc.driver.OracleDriver");
•Createconnection
Connectioncon=DriverManager.getConnection("jdbc:oracle:thin:@localhost:
1521:xe","system","password");
•Createstatement
Statementstmt=con.createStatement();

31. Database Connectivity -JDBC
StepsinJDBC
•Executequeries
ResultSetrs=stmt.executeQuery("select*fromemp");
while(rs.next()){
System.out.println(rs.getInt(1)+""+rs.getString(2));
}
•Closeconnection
con.close();