Introduction of Servlets in java prog.

7/31/2019 Introduction of Servlets in java prog.

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Serv le tsServ le ts


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Exit

Bill

------

------

A Day In A Typical Restaurant

This system runs smoothly runs with a few customer

Then the money

is paid The customer asksfor the bill

A Waiter Accept the orderand then serves food

The customer

leaves the

restaurant

A customer entersthe restaurant


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An example - McDonalds a Chain of Restaurants

Order

A customer enters

the restaurant

Collects the

items and leavesPays the bill

He places the order

He goes to the

counter...

Back end Chef

Food Counter


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A Ty p ical Rest au r an t

Client

Places order Passes it

Sends back the

processed order

ServesWaiter Chef

The restaurant may need to be expanded

Increased cost

Greater Investment This can be a solution butincase customers want to

place orders from a remotelocation, then the web can

come to rescue


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The W eb Based So lu t ion - New way of doing business - E-commerce

Web Serverreceives request

(Waiter)

Places order HTTP request

Servlets act

as Chefs

Client Browser

Checks the

restaurant

database

Items are Present

Requests for Items

Dish

Ready

Information sent back to

client as an HTTP response


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Serv le ts -de f ined

Java se rv le t i s a se rve r side app l i ca t ion w r i t t en inj av a lan g u ag e.

I t dyn am ica l l y genera t ed HTML pages.

Java v i r t ua l m ach ine and pack age j avax .serv let i sneeded to r un j ava serv let .


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Advan t ages o f Se rv let s

Loaded in the same

process space as the

web server

Faster than common

scripting languages

More secure and almost

crash proof,no bufferoverflow

Inexpensive

Completely protocol

independent

Advantages


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Ser v let s I n t r o du ct i on

A serv le t i s a Java c lass used t o ex t end t he capab i l i t i es o fse rve r s th a t hos t app l i ca t i on s accessed v ia a r equest -r e sp o n se p r o g r a m m i n g m o d el

Other

Applications


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Serv l e t s a re no t t i ed t o a speci f i c cl i en t - serv e r p ro t oco l bu tt h e y ar e m o st co m m o n l y u se d w i t h H TTP

Typ ica l uses fo r HTTP Serv le t s inc lude :

Read exp l i ci t d a ta sen t by c l i en t ( f o rm da ta )

Read im p l i ci t da ta sen t by c l i en t ( request headers )

Genera t e the resu l t s

Send t he exp l i c i t da t a back t o cl ien t ( HTML)

Send t he im p l i ci t da ta t o c l ien t ( s ta tus codes and response

headers ) Manag ing s ta t e i n fo rm a t i on on t op o f t he s ta te less H TTP

Ser v let s I n t r o du ct i on


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A se r v l et e n g in e p r o v i d es t h e r u n t i m e en v i r o n m e n t i n w h i ch aserv le t ex ecu t es

The se rv l e t eng ine m anages t he l i f e- cycl e of serv l e t s f romw h e n t h e y ar e f i r s t cr e at e d t h r o u g h t o t h e ir i m m i n i en tdes t ruc t i on

The serv le t eng in e execu t es w i th in a Java Vi r t ua l Mach in e

Serv l e t eng ines com e i n t w o f l avou rs : Stand -a l one and Add -on

A standa lone se rv l e t eng ine i s a f u l l y f u nc t i on i ng w eb

se rve r w i t h suppo r t f o r serv l et s. Fo r exam p le -

W ebSpher e , Java Web Serve r and I p lane t

An add-on se rv le t eng ine i s a p lug - i n t ha t can be addedt o a w e b se r v er t o g i v e i t t h e se r v l et s u p p o r t i t w a s

pr obab ly never designed t o have . Fo r exam p le -

Se rv l e tExec and Tom ca t

Ser v le t En g in e


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Adv an t ages o f u sing Java Serv let s

Ef f i cien t : t h r eads ins tead o f OS pr ocesses, one ser v le t copy ,pers is tence

Conv en ien t : l o t s o f h igh l eve l u t i l i t i es

Pow er fu l : t a l k i n g to se rve r , sha r ing da t a , poo l i ng , pe rs is tence

Por t ab l e: r u n on v i r t ua l ly a l l opera t i ng syst em s and se rve rsSecu r e : no bu f f e r ove r f l ow s

I nexpens iv e : i nexpens i ve p l ug - i ns i f se rv l e t suppo r t no tbund l ed


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Basic Serv le t a r ch i t ect u r e

Ser v le t L i fe cyc le HTTP Ser v let


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Ser v le t Li f e Cy cle


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Servlet

GenericServlet

HttpServlet

GenericServlet


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i n i t ( ) M ar k s t h e b eg i n n i n g o f a se r v l et s l i f e

Cal led on ly w hen t he se rv le t i s f i r s t l oaded

Ta k e s o n e p ar a m e t er , Se r v l et Co n f i g w h i ch h a s t h e se r v l et s st a r t u pcon f i gu r a t i on and i n i t i a l izat i on pa ram e te rs

D oes no t re tu rn any v a lueserv ice ( )

Execu ted af t e r t he serv le t s i n i t ( ) m e thod i s execu t ed success fu l ly

Ta k es t w o p ar a m e t e r s - H t t p Se r v le t Req u est a n dHt tpServ le tResponse

D oes no t re tu rn any v a lue

Gener i cSe rv le t s serv i ce( ) m e thod i s abst r act

HTTPServ le t : Ther e are 2 serv ice m eth ods in t h is c lass . Pub l icserv i ce ( ) m e thod d i spat ches t h e reques t t o t he p ro t ected serv i ce ( )m e t h o d w h i ch i n t u r n s en d s t h e r e qu e st t o t h e d o Ge t ( ) o r d o Po st ( )m e thods de f i ned i n t h e class

d e s t r o y ( ) M ar k s t h e e n d o f a se r v l et s l i f e

Cal led on ly w hen t he se rv le t i s un loadeded

D oes no t re tu rn any v a lue


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HTTP Ser v le t

The genera l ru les t o be fo l l ow ed w h i l e w r i t i ng a HTTP Serv le t : Ex t end Ht tp Se rv l e t cl ass, w h i ch im p lem en ts t he Se rv l e t

i n te r f ace

M u st c al l su p e r .i n i t ( co n f i g ) i n t h e se r v l et s i n i t ( ) m e t h o d , i n

o r d e r t o s t o r e co n f i g u r a t i o n i n f o r m a t i o n p r o v i d ed b y t h eserv le t con t a ine r , to be accessib le i n t he serv le t fo r l a te ruse . Th i s super ca l l saves t he Serv le t Con f i g ob j ect , w h ich

w ou l d no t be ava i lab le o th e rw i se .

Ov er r i de doGe t ( ) - t o hand le GET request s . Ove r r i de

doPos t ( ) m e th od t o hand le POST requ est s .

W i t h i n t h e d o Ge t / Po st m e t h o d , u s er ' s r e q u est i srep res en t ed by an H t t pSe rv l e tRequest ob j ect and responset o t he user i s rep r esen t ed by an H t t pServ le t Respon se

ob j ec t . Th e r e sp o n se ca n b e w r i t t e n t o t h e u se r t h r o u g h Pr i n t W r i t e r

o b j e ct o b t a i n ed f r o m t h e Ht t p Se r v l et Re sp o n se o b j e ct .


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HTTP Ser v le t

doGe t ( ) Ca ll ed by t he se rve r ( v i a t he serv i ce m e thod ) t o a l l ow a

serv le t han dle a GET r equ est Pa r am e t e r s a r e p asse d t o t h e d o Ge t ( ) m e t h o d t h r o u g h t h e

URL

There i s a l im i t a t i on o f da ta ( say 255 cha ract e rs) t h a t can besen t t h rou gh GET m e thod

doPos t ( )

Ca ll ed by t he se rve r ( v i a t he serv i ce m e thod ) t o a l l ow aser v le t t o h and le a POST r eques t .

The r equest body con ta i ns t h e pa ram e te rs and va l ues

POST m e thod doesn t h ave l im i t a t i on on t he am oun t o f da tab e in g s en t t h r o u g h .

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i m p o r t j a v a .i o .* ; i m p o r t j a v a.n e t .* ; i m p o r t j a v a x .s er v l et . * ; i m p o r t j a v a x .se r v le t .h t t p . * ;

p u b l i c cl ass N ew Se r v l et e x t e n d s H t t p Se r v l et { p ro t ected vo id p r ocessRequest ( H t t pSe rv le tRequest request ,

H t t pSe rv le tResponse response ) t h r ow s Serv le t Excep t ion , I OExcep t ion

{ r e sp o n se .se t Co n t e n t Ty p e ( " t e x t / h t m l ;ch a r se t = UTF- 8 " ) ; Pr i n t W r i t er o u t = r e sp on se.g et W r i t e r ( ) ; t r y { } f in al l y { o ut .cl ose( ) ; } }

p ro t ected vo id doGe t ( H t t pSe rv le tRequest request ,H t t pSe rv le tResponse response )

t h r o w s Se r v l et Ex c ep t i o n , I OEx c ep t i o n { pr ocessReques t ( requ est , response) ; t r y { o u t .p r i n t l n ( " < H TM L> < H EA D> < TI TLE> H el lo Cl ien t ! < / TI TLE> " +

" < / H EAD> < BODY> H el lo M y Fi r st j a v aCl ien t !< / BODY> < / HTML> " ) ;

ou t . c l ose ( ) ; } f in al ly { ou t .cl ose ( ) ; } }


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pr o t ect ed vo id doPos t ( H t t pServ le t Reques trequest , H t t pSe rv l e tResponse response )

t h r o w s Se r v l et Ex c ep t i o n , I OEx c ep t i o n { pr ocessReques t ( requ est , response) ; }

p u b l i c St r i n g g e t Se r v l et I n f o ( ) { r e t u r n " Sh o r t d e scr i p t i o n " ; } }


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Sign i f i can t En t i t i es i n Serv let s t echn o logy

Request Response Servletcontext Session & Session Tracking


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Request

Request ob j ect encapsu la tes al l i n f o rm a t i on f r om th e cl i en t request Request pa ram e te rs a re st r i ngs sen t by t he c li en t t o a se rv le t con ta ine r

as pa r t o f a reques t

Wh en th e request i s a Ht t pSe rv le tRequest , t h e a t t r i bu t es a re popu la tedf r o m t h e U RI q u e r y s t r i n g o r p o ssi b l y p o st e d f o r m d a t a

Param e te rs a re sto r ed by t he serv le t con t a iner as a set o f nam eva lue

pa i r s The fo l low ing m e thods o f t he Se rv le tRequest i n te r f ace are ava il ab le t o

access pa ram ete rs : ge tParamete r

ge tPa rame te rNames

ge tParamete rVa lues

A serv le t can access th e headers o f an HTTP requ est th rou gh t hef o l lo w i n g m e t h o d s of t h e H t t p Se r v l et Re q u est i n t e r f a ce : getHeader

ge tHeaders

ge tHeaderNames

Request ob j ect can have a t t r i bu t es associa ted w i t h i t . A t t r i bu t es m aybe se t by a se rv le t t o com m un icate i n fo rm a t i on t o ano t he r serv le t

At t r i bu t es a re accessed w i t h t h e m e thods o f t he Se rv le tRequesti n te r f ace: g e t A t t r i b u t e

g e t A t t r i b u t e N a m e s

s e t A t t r i b u t e

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RequestRequestSample.html

< h t m l > < h e a d >

< META HTTP-EQUI V= " Cont en t -Type" CONTENT= " tex t / h t m l ; " >

< t i t l e > D at a En t r y Pa ge < / t i t l e >

< / h ead >



< f o r m m e t h o d = " p o st " a c t io n = " Fo r m H a n d le r Se r v le t " >

< t a b l e ce ll p ad d i n g= " 0 " ce ll sp a ci n g = " 0 " b o r d e r = " 0 " >

< t r >

< t d > Pl ea se en t e r y ou r n a m e :< / t d >

< t d > < / t d > < / t r >

< t r >

< t d > 

g r ad u at e < / t d >

< / t r >

< t r >

< t d > p o st - g r ad u at e < / t d >

< / t r >

< t r > < t d > 

doct rat e < / t d>

< / t r >

< t r > < t d > < / t d > < t d > < in pu t t y pe= " s ub m it " v alu e= " Su bm i t " >< / t d>

< / t r >

< / t ab le>

< / f o r m > < / body > < / h t m l>


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eques t :FormHand le rServ le t .java

import javax.servlet.*;import javax.servlet.http.*;

import java.io.*;

public class RequestSample extends HttpServlet {

public void doGet(HttpServletRequest objRequest,

HttpServletResponse objResponse)

throws IOException, ServletException {

doPost(objRequest, objResponse);

}


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public void doPost(HttpServletRequest Request,

HttpServletResponse Response)

throws IOException, ServletException {

objResponse.setContentType("text/html");

PrintWriter out = Response.getWriter(); String enteredValue;

// gets all the selected options from the client browser

String[] selectedOptions =request.getParameterValues("options");

// gets the enteredValue fields value enteredValue = request.getParameter("enteredValue");

PrintWriter printWriter;

try

{ // get a printwriter from the HttpServletResponse objectsref.

printWriter = response.getWriter();

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// return on the HttpServletResponse objects ref. requested values printWriter.println("

"); printWriter.print("You entered: "); printWriter.print(enteredValue); printWriter.print("
"); printWriter.println("
"); printWriter.print("The following options were selected:");

printWriter.println("
");

if (selectedOptions != null) { for (int i=0;i< selectedOptions.length;i++) {

printWriter.print(selectedOptions[i]); printWriter.println("
"); } } else { printWriter.println("None");

} printWriter.println("
"); } catch (IOException e) { e.printStackTrace();
} } }


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Response

Respon se ob j ect encapsu la t es a l l i n fo r m at ion t o be re tu rn edf r o m t h e se r v er t o t h e cl ie n t

I n f o r m a t i o n is t r a n sm i t t e d f r o m t h e se r v er t o t h e cl ie n t e i t h e rby HTTP headers o r t he m essage body o f t he r equest i n HTTPpro toco l

A serv le t can se t h eaders o f an HTTP response v ia the f o l l ow ingm e t h o d s o f t h e H t t p Se r v l et Re sp o n se i n t e r f a ce :

setHeader

addHeader

se t He ad e r m e t h o d se t s a h ea d er w i t h a g i v en n a m e an d v a l u e. I fa p rev iou s header ex is ts , i t i s rep laced by t he new header

a d d He ad e r m et h o d a d d s a h e ad e r v a lu e t o t h e se t o f h e a de r sw i t h a g i ven nam e . I f t he re a re no headers a l ready associa tedw i t h t h e g i v en n a m e , t h i s m e t h o d w i l l cr e at e a n ew se t


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Response H t t pSe rv le tResponse supp l i es a num ber o f m e thods f o r speci f y i ng

co m m o n h e ad e r s

se t Co n t en t Ty p e m et h o d

Sets th e Con t en t -Type header t ha t speci f i es th e MI ME t ype o f t hed o cu m e n t t h a t s er v l e t i s g oi n g t o o u t p u t

D ef a u l t MI M E t y p e f o r se r v l et s i s t e x t / p l ai n , b u t t h e y u su a l l ye x p li ci t l y sp eci f y t e x t / h t m l

Example: response.setContentType("text/html")

MI ME ( Mu l t i -Pu rp ose I n t e rne t Ma i l Ex t ensions ) w as o r i g i na l l yd e v el o p ed t o a l l o w I n t e r n e t e m a il t o c o n t a in s o m e t h i n g o t h e rth an j u s t sim p le ASCI I cha racte rs

W hen a se rve r sends a f i l e to a c l ien t app l i cat ion , i t speci f i es theMI ME t y pe i n t h e header and t h e b row ser ei t he r d i sp lays i t w i t hi t s bu i l t i n p laye rs or p lug - i ns

a d d Co o k i e m e t h o d s et s a co o k i e g et W r i t e r / g et Ou t p u t St r e am - Ret r i ev es an o u t p u t s t r eam t o s en d

da ta t o t he cl i en t

To se n d ch a r a ct e r d a t a , u s e t h e Pr i n t W r i t e r r e t u r n e d b y t h er e sp o n se 's g et W r i t e r m et h o d

To send b ina ry da ta in a MI ME body r esponse , use theSe r v l et O u t p u t St r ea m r e t u r n e d b y g et O u t p u t St r e am


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Response

SampleResponseSample.java

import java.io.*;

import javax.servlet.*;

import javax.servlet.http.*;

public class ResponseSample extends HttpServlet {

public void doGet (HttpServletRequest req, HttpServletResponse res)

throws ServletException, IOException

{

ServletOutputStream out = res.getOutputStream();res.setContentType("text/html");

out.println(" ResponseSample Output

");

out.println(" ResponseSample Output ");

out.println("

This is output from ResponseSample.");

out.println("");

out.close();

}

}


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Exerc ise

1 . W r i t e a ser v l et w i t h d o Get a n d d oPo st m et h o d s t o p r o cess t h ef o l l ow i n g h t m l f o r m el em en t s :

" Em a il - Tex t Fi el d

" N am e Tex t Fie ld

Sex - Ch eck b o x"Company -Tex tF i e l d

" St r e et - Tex t Fi el d

" Ci t y - Tex t Fie l d

" St at e - Dr op d ow n" Zip co de - Tex t Fie ld

" Cou n t r y - Tex t Fie ld

" Ph on e - Tex t Fie ld

d o Ge t m e t h o d h a n d l es t h e in i t i a l in v o ca t i o n o f t h e se r v l et . I tr e sp o n d s w i t h a f o r m , t h a t w i l l u se t h e " POST" m e t h o d t o su b m i t

da ta .

d o Po st m e t h o d r e sp o n d s t o t h e " POST" q u e r y f r o m t h e or i g i n al

f o r m s u p p l i ed b y t h e d o Ge t ( ) m e t h o d

Introduction of Servlets in java prog.

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