java serv lets

7/31/2019 Java Serv Lets

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JavaJava ServletsServlets

Key points to be rememberedKey points to be remembered ServletsServlets areare server side Java Applicationsserver side Java Applications

that can be loaded dynamicallythat can be loaded dynamically

Java Applets are used to create Client sideJava Applets are used to create Client side

ApplicationsApplications


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PrehistoryPrehistory In general, web server has to handle largeIn general, web server has to handle large

amount of requests concurrently & thus it isamount of requests concurrently & thus it is

not able to handle all transactions that keepnot able to handle all transactions that keep

coming incoming in

For this purpose, some applications haveFor this purpose, some applications have

been designed to extend the functionality ofbeen designed to extend the functionality ofweb serversweb servers


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PrehistoryPrehistory Example:Example: Server Side ApplicationsServer Side Applications

CGICGI

ServletsServlets ASPASP


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PrehistoryPrehistory

Server

Call for CGI A

Call for CGI B

Call for CGI A

Process for CGI A

Process for CGI B

Process for CGI A

CGI Based Server


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PrehistoryPrehistory In traditional CGI,In traditional CGI, For each request web serverFor each request web server

calls for separate process for CGI scriptcalls for separate process for CGI scripthandling.handling.

At this instant, server passes all the data thatAt this instant, server passes all the data thatthe CGI program need to generate thethe CGI program need to generate theresponse with the help of environmentresponse with the help of environment

variablevariable

Limits the number of requestsLimits the number of requests takes moretakes moretime for executiontime for execution & extra resources& extra resources


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PrehistoryPrehistory To overcome this issue,To overcome this issue, FastCGIFastCGI is developedis developed

which creates the single persistent object forwhich creates the single persistent object for

each CGI programeach CGI program


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Server

Call for CGI A

Call for CGI B

Call for CGI A

Process for CGI A

Process for CGI B

Process for CGI A

FAST CGI Based Server


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PrehistoryPrehistory FastCGIFastCGI also creates overhead when aalso creates overhead when a

security crash occurssecurity crash occurs


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PrehistoryPrehistory JavaJava ServletsServlets are Java Programs that can beare Java Programs that can be

loaded dynamically & executed on theloaded dynamically & executed on thememory of servermemory of server

ServletServlet extends the functionality of serverextends the functionality of server andandruns inside the JVMruns inside the JVM

CGI andCGI and FastCGIFastCGI run multiple processes torun multiple processes tohandle different requests where ashandle different requests where as JavaJavaServletServlet handles each request usinghandles each request usingMultithreadingMultithreading CapabilityCapability


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Call for Servlet A

Call for Servlet B

Call for Servlet A

Servlet A

Servlet B

Servlet Based Server

ServerJVM


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MertitsMertits ServletServlet becomes more efficient & scalablebecomes more efficient & scalable

Portable across all OS and web serversPortable across all OS and web servers


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ServletsServlets APIAPI It isIt is not a part of JDKnot a part of JDK

Have toHave to install JSDKinstall JSDK (Java(Java ServletServletDevelopment Kit)Development Kit)

Need 2 packagesNeed 2 packages

Javax.servletJavax.servlet (used to create protocol(used to create protocol

independentindependent servletservlet))

Javax.servlet.httpJavax.servlet.http (used to create HTTP(used to create HTTP

servletservlet))


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ServletsServlets APIAPI AllAll servletservlet must implementmust implement ServletServlet InterfaceInterface

Javax.servletJavax.servlet must extendmust extendJavax.servlet.GenericServletJavax.servlet.GenericServlet

Javax.servlet.httpJavax.servlet.http must extendmust extend

Javax.servlet.http.HttpServletJavax.servlet.http.HttpServlet wherewhereHttpServletHttpServlet is the subclass ofis the subclass of GenericServletGenericServlet


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ServletsServlets APIAPI AA servletservlet worksworks based onbased on RequestRequest--ResponseResponse

CycleCycle

A request is sent to theA request is sent to the ServletServlet by the clientby the client

thethe servletservlet process the request & generatesprocess the request & generates

the response and sends the response back tothe response and sends the response back to

the clientthe client


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ServletsServlets APIAPI With reference to the technical idea, AWith reference to the technical idea, A servletservlet

can be created in 2 wayscan be created in 2 ways

GenericServletGenericServlet handles the requesthandles the request--responseresponsecycle based oncycle based on service()service() methodmethod

This methodThis method accept 2 parametersaccept 2 parameters

ServletRequestServletRequest is a object specifies theis a object specifies theclient requestclient request

ServletResponseServletResponse is a object that specifiesis a object that specifies

the response of thethe response of the servletservlet to that requestto that request


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ServletsServlets APIAPI HttpServletHttpServlet handles the requesthandles the request--responseresponse

cycle based on eithercycle based on either doGetdoGet()() oror doPostdoPost()() oror

doServicedoService()() methodmethod

doGetdoGet() corresponds to GET method of HTTP() corresponds to GET method of HTTP

protocolprotocol

doPostdoPost() corresponds to POST method of() corresponds to POST method of

HTTP protocolHTTP protocol


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ServletsServlets APIAPI doServicedoService() method is a default method which() method is a default method which

in turn callsin turn calls doOptionsdoOptions() method &() method & doTracedoTrace()()

that causes a response with a messagethat causes a response with a message

containing all of the headers sent in the tracecontaining all of the headers sent in the tracerequestrequest


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ServletsServlets APIAPI HttpServletHttpServlet handles the requesthandles the request--responseresponse

cycle based on eithercycle based on either doGetdoGet()() oror doPostdoPost()()

methodmethod

This methodThis method accept 2 parametersaccept 2 parameters

HttpServletRequestHttpServletRequest is a object specifiesis a object specifies

the client requestthe client request HttpServletResponseHttpServletResponse is a object thatis a object that

specifies the response of thespecifies the response of the servletservlet to thatto that

requestrequest


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ServletServlet Life CycleLife Cycle AA servletservlet is a Server based Java Applicationis a Server based Java Application

program that runs within a Web server.program that runs within a Web server.

It can receive requests from clients and returnIt can receive requests from clients and returnresponses.responses.

The wholeThe whole life cycle of alife cycle of a servletservlet breaks up intobreaks up into3 phases3 phases::

InitializationInitialization

ServiceService

DestructionDestruction


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ServletServlet

Life CycleLife Cycle

InitializationInitialization A servlet is first loaded and initialized

usually when it is requested by thecorresponding clients.

Loading of servlet will be taken care byServlet Container

After creating the instances, the servletcontainer calls the init() method and passesthe servlet initialization parameters to theinit() method.


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ServletServlet

Life CycleLife Cycle

InitializationInitialization The init() must be called by the servlet

container before the servlet can service anyrequest.

The initialization parameters persist untillthe servlet is destroyed.

The init() method is called only oncethroughout the life cycle of the servlet.


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ServletServlet Life CycleLife Cycle

ServiceService After initialization, the servlets serve clients

on request, implementing the applicationlogic of the web application they belong to.

i.e., After successfully completing theinitialization process, the servlet will beavailable for service.

Servlet creates seperate threads for eachrequest. The servlet container calls theservice() method for servicing any request.


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ServiceService The service() method determines the kind of

request and calls the appropriate method(doGet() or doPost()) for handling therequest and sends response to the clientusing the methods of the response object


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DestructionDestruction If the servlet is no longer needed for

servicing any request, the servlet containercalls the destroy() method .

Like the init() method this method is alsocalled only once throughout the life cycle ofthe servlet.

Calling the destroy() method indicates to theservlet container not to sent the any requestfor service and the servlet releases all the

resources associated with it.


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DestructionDestruction At this instant, Java Virtual Machine claims

for the memory associated with theresources for garbage collection

java serv lets

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