meljun cortes introduction to servlets

8/11/2019 MELJUN CORTES Introduction to Servlets

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TOPIC TITLE: Servlet

SPECIFIC OBJECTIVES:

At the end of the topic session, the students are expected to:

Cognitive :

1. Discuss Common Gateway Interface.2. Explain what a serlet is.!. Compare serlet from Common Gateway Interface "CGI#$. Discuss the %erelt A&I.'. Create a simple serlet.

Affective:

1. &articipate in a (roup actiities2. )e attentie to the teacher*s lectures and demonstrations!. &articipate on class and (roup discussions

Psychomotor:1. Create and deploy serlet.

MATERIALS/EQUIPMENTS:

1. +&2. -opic %lide

TOPIC PREPARATION:

1. eiew of %erlet.

TOPIC PRESENTATION:

-he topic will reole around Servlet. Discussions will include CommonGateway Interface, serlet, context root, we/ application directorystructure and deployment descriptor. .

-his will /e the su((ested flow of discussion for Servlet.

1. Explain what Common Gateway Interface is.2. Discuss the operation o( CGI pro(rams.!. Discuss the adanta(es and disadanta(es o( CGI.$. Explain what serlet is.'. Discuss the adanta(es of serlet.0. Descri/e the life cycle of a serlet.. Discuss the applications that can /e /uilt usin( serlet.. Explain what context root is.3. Explain the we/ application directory structure.14. Discuss the deployment descriptor.

Common Gateway Interface of 8

Common Gatea! Inter"a#e



In the early deelopment of -56, desi(ners created a mechanism topermit a user to ino7e a pro(ram on the 8e/ serer. -his was calledthe Cmmon Gateway Interface "CGI#. 8hen a 8e/ site includes CGI

processin(, this is called a 8e/ application.

In order to ino7e the CGI pro(ram, the /rowser sends data to the CGIpro(ram on the 8e/ serer. -he CGI specification defines how thedata is pac7a(ed and sent in the --& re9uest to the serer. -he datais usually typed in into the 8e/ /rowser in an -56 form.

-he 6 determines which CGI pro(ram to execute. -his could /e ascript or an executa/le file. -he CGI pro(ram then parses the data inthe re9uest, process the data and (enerates a response. -his responseis sent /ac7 to the 8e/ /rowser.

$Common Gatea! Inter"a#e% Pa&e ' o" ()

CGI Programs on the WebServer Pages 2! of 8

CGI Pro&ram* on t+e ,e- Server

)elow are the operations of CGI pro(rams.1. )rowser initiates re9uest2. 8e/ serer receies the re9uest.!. ;or each re9uest, we/ serer spawns a new operatin( system

process to execute the CGI<&erl &ro(ram.

-he fi(ure a/oe shows the flow of operations in executin( a CGIpro(ram. At first, the /rowser initiates the re9uest. -he 8e/ serer then responds to that re9uest and it spawns a new opratin( system"+%# process to execute the CGI pro(ram.

At runtime, a CGI pro(ram is launched /y the 8e/ serer as a separateopearatin( system "+%# shell. -he shell includes an +% enironmentand process to execute the code of the CGI pro(ram.

,e-Bro*er

,e-Server

Perl/CGI

Create

New process

Bro*er'

,e-Server

Perl'

Bro*er.

Bro*erN

Perl.

PerlN



-he fi(ure a/oe shows that for each re9uest, a separate +% process is/ein( spawned.

oweer, each new CGI re9uest launches a new operatin( system shellon the serer. -he runtime performance of multiple CGI re9uest isshown a/oe.

$CGI Pro&ram* on t+e ,e- Server% Pa&e* .0 o" ()

A"vantages of CGI ProgramsPage # of 8

A1vanta&e* o" CGI Pro&ram*

;lexi/le = &ro(rams can /e written in a ariety of lan(ua(es.

%ta/le = A /u((y CGI pro(ram will not crash the 8e/ serer.

&ro(rams are easy to reference = &ro(rams are easy for a 8e/

desi(ner to reference. 8hen the script is written, the desi(ner canreference it in one line in a 8e/ pa(e.

>o concurrency conflict = )ecause CGI pro(rams execute in their

own +% shell, these pro(rams do not hae concurrency conflictswith other --& re9uests executin( the same CGI pro(ram.

All serice proiders support CGI pro(rams

$A1vanta&e* o" CGI Pro&ram*% Pa&e 2 o" ()

$isa"vantages of CGIProgramsPage % of 8

34*a1vanta&e* o" CGI Pro&ram*

%low

-he response time of CGI pro(rams is ery hi(h /ecause CGIpro(rams execute in their own +% shell. -he creation of an +%shell is a heaywei(ht actiity for the +%.

>ot scala/le

CGI is not scala/le. If the num/er of people accessin( the 8e/application increases from '4 to '444, for example, CGI cannot /e

adapted to handle the load. -here is a limit on the num/er of separate operatin( system processes a computer can run.

>ot secured or o/?ect@oriented

-he lan(ua(es for CGI are not always secure or o/?ect@oriented.

%criptin( lan(ua(es are often platform dependent

-he CGI script has to (enerate an -56 response so the CGI codeis min(led with -56. -his is not (ood separation of presentationand /usiness lo(ic.

)ecause of these disadanta(es, deelopers need other CGIsolutions. %erlets is the aa technolo(y solution used to process



CGI data.

$34*a1vanta&e* o" CGI Pro&ram*% Pa&e 5 o" ()

ServletsPage & of 8

Servlet*

A aa serlet is a aa technolo(y pro(ram similar to CGI pro(ram thatruns on the serer. -he types of tas7s that you can run with serlets aresimilar to those you can run with CGI.

A serlet is used to sere serer@side resources to the client. )eforeserlets and its peer technolo(ies such as CGI and Actie %erer &a(eswere introduced, a we/ serer was a/le to sere only static we/ pa(esto the client.

Servlet Ar#+4te#t6re

-he fi(ure a/oe shows the %erlet architecture. nli7e CGI ro(rams,serlets run within a component container architecture. -his container is called the 8e/ container also 7nown as the serlet en(ine. -he 8e/container is a aa irtual machine that supplies an implementation of the serlet application pro(rammin( interface "A&I#. %erlet instancesare components that are mana(ed /y the 8e/ container to respond to--& re9uests.

$Servlet*% Pa&e 7 o" ()

A"vantages of Servlet Page ' of 8

A1vanta&e* o" Servlet

&owerful

%erlets can tal7 directly to the we/ serers.

5ultiple serlets can share data:

&articularly important for maintainin( data/ase connections.

Includes powerful techni9ues for trac7in( user sessions.

&orta/le

CLIENT

WEB

SERVER

Web

Container

SERVLET

DATABASE

Request

Response



Bou can therefore write your serlets on 8indows, then deploy them

on >I. Bou can also run any of your serlets on any aa@ena/led we/

serer, with no code chan(es.

%ecure

-raditional CGI pro(rams hae a num/er of 7nown security

ulnera/ilities. ence, you usually need to include a separate &erl<CGI module to

supply the necessary security protection. aa has a num/er of /uilt@in security layers.

ence, serlets are considered more secure than traditional CGI

pro(rams.

Inexpensie

Bou can download free serlet 7its for deelopment use.

Bou can therefore (et started for free

>onetheless, production stren(th serlet we/ serers can (et 9uite

expensie.

$A1vanta&e* o" Servlet% Pa&e 8 o" ()

(ife of a Servlet Page 8) of 8

L4"e o" a Servlet

e(ardless of the application, serlets usually carry out the followin(

routine:

1. ead any data sent /y the user 2. 6oo7 up any --& information!. Generate the esults$. ;ormat the esults'. %et the Appropriate --& headers0. %end the document /ac7 to the client

Servlet Pro&ram Ro6t4ne

$L4"e o" a Servlet% Pa&e (9 o" ()

,e-Bro*e

r

,e-Server

3ata

-a*e 3

6Java

Servlet

,e-Bro*e

r

,e-Server

3ata

-a*e

4,5Java

Servlet

,e-Bro*er

,e-Server

3ata-a

*e

1,2

Java

Servlet



What can yo* b*il" withServlets+Page 1, of 22

,+at #an !o6 -64l1 4t+ Servlet*

Search -ngines

Personaliation Systems -Commerce A//lications

Sho//ing Carts

Pro"*ct Catalogs

Intranet A//lications

Gro*/ware A//lications: b*lletin boar"s0 file sharing0 etc.

$,+at #an !o6 -64l1 4t+ Servlet*% Pa&e '; o" ';)

Contet oot Page 11 of 22

Conte<t Root

Eery we/ application has a uni9ue context root

-he context root forms a part of the re9uest 6

-he container maps a re9uest to the correspondin( application

/ased on the context root

Example, consider an application called 6o(inApplication, the

6 will /e

htt/:33www.myA//s.com3login3(oginServlet

-he context root is also called as the 8e/ application context name. Itis part of the 6 you use to access a 8e/ application. It is the first

leel of hierarchy in the path structure of the 6. -he (eneral syntaxof a serlet 8e/ application 6 is:

http://host:port/context/path/file

where context is the 8e/ application context name.

Examples:

≠ http:<<www.sti.edu.ph<enrolment<admin.html≠ http:<<www./as7et/all.or(<lea(ues<re(istration.html

$Conte<t Root% Pa&e '; o" ';)

Web A//lication $irectoryStr*ct*rePage 12 of 22

,e- A==l4#at4on 34re#tor! Str6#t6re

http://www.myapps.com/login/LoginServlet

http://www.myapps.com/login/LoginServlet



-he directory structure for we/ applications is (ien in the fi(ure a/oe.

e-A==l4#at4on = holds the contents of the 8e/ Application Archie"8AR # file that will /e deployed to the serer It contains all the we/resources, includin( -56 files, %&s and (raphics needed for theapplication.

e-A==l4#at4on/t+eme = contains cascadin( style sheets and other style@related o/?ects.

e-A==l4#at4on/4ma&e* = contains ima(es used /y the application

e-A==l4#at4on/,EBINF = contains the supportin( we/ resources for a we/ application, includin( the we/.xml deployment descriptor file, theclasses and li/.

e-A==l4#at4on/,EBINF/#la**e* = it the aa compiler outputdirectory. It contains all the class files pertainin( to the we/ application.-he application class loader loads the classes from this directory.

e-A==l4#at4on/,EBINF/l4- = contains the .?ar files that the we/application references. Any classes contained in these .?ar files will /eaaila/le for the we/ application.

$,e- A==l4#at4on 34re#tor! Str6#t6re% Pa&e '. o" ';)



$e/loyment $escri/tor Page 1! of 22

3e=lo!ment 3e*#r4=tor

Deployment descriptor is a file containin( deployment

information

-he we/ container reads it durin( the deployment of the

we/ application onto the we/ serer

2EE compliant we/ containers use an 56 file called

e-><ml as the deployment descriptor

-he deployment descriptor is a file containin( deployment information.2EE compliant we/ containers use an 56 file called the we/.xml asthe deployment descriptor. -he Document -ype Definition "D-D# for thewe/.xml file is specified /y the aa %erlet specification. It is an 56file which contains names of arious serlets in the we/ application, the

6 mappin(s for each serlet, security information and other deployment information.

$3e=lo!ment 3e*#r4=tor% Pa&e '0 o" ';)

Servlet Class 4ierarchy Page 1# of 22

Servlet Cla** ?4erar#+!

All the serlets inherits from the class --&%erlet. -he --&%erletin turn inherits from the Generic%erlet class and the Generic%erletclass implements the %erlet interface.

-he %erlet interface specifies the methods that the container willino7e on the serlet. -he interface forms a contract /etween the we/container and the serlet. All the serlets therefore hae to directlyimplement the %erlet interface. -he interface defines the init"#,serice"#, and destroy"# methods used /y the container for mana(in(the life cycle of the serlet.

-he Generic%erlet class is an a/stract class that proides a /asic

implementation of the %erlet interface. %erlets inheritin( from thisclass can use the implementation it has proided for all the methods of

ServletServlet

HTTPServletHTTPServlet

Generic ServletGeneric Servlet



the serlet interface except the serice"# method.

-he ttp%erlet class proides --&@specific implementation of the

%erlet interface. -he ttp%erlet class oerrides the serice"# methodit inherits from the Generic%erlet. -he ttp%erlet class is an a/stractclass and all classes inheritin( from this class should proide either thedoGet"# or do&ost"# methods. Dependin( on the --& methodssupported /y the application, the pro(rammer should proideimplementation for the correspondin( doxx"# method in the serlet.

$Servlet Cla** ?4erar#+!% Pa&e '2 o" ';)

Creating Servlet Page 1%18 of 22

Creat4n& Servlet

6isted /elow are the steps in creatin( a serlet.

1. Import the %erlet A&I:

import ?aax.serlet.Fimport ?aax.serlet.http.F

-o create serlets, you must remem/er to always use these two importstatements. All your serlets must extend --&%erlet.

2. --&%erlet represents the /ase class for creatin( %erlets withinthe %erlet A&I. -herefore, you must extend the--&%erlet class.

!. +nce you hae extended --&%erlet, you must oerride one or

/oth:o doGet"#: to capture --& Get e9uests

o do&ost"#: to capture --& &ost e9uests

-he doGet"# and do&ost"# methods each ta7e two parameters: --&%erlete9uest: encapsulates all information

re(ardin( the /rowser re9uest such as form data, clienthost name, --& re9uest headers.

--&%erletesponse: encapsulates all information

re(ardin( the serlet response such as --& eturnstatus, out(oin( coo7ies, -56 response.

If you want the same serlet to handle /oth GE- and &+%-,you can hae doGet call do&ost or ice ersa. se GE-re9uest if the amount of form data is small and you want toallow the re9uest to /e /oo7mar7ed. se &+%- re9uest if youwant to modify the serer "data/ase#, the amount of form datais lar(e and the contents of the form data should not /e isi/lein the re9uest 6.

$. Gettin( an +utput%tream

-he --&esponse o/?ect has a (et8riter"# method that allows

you to print out data. -his method returns a ?aa.io.&rint8ritero/?ect for writin( data out to the 8e/ )rowser.

&rint8riter out response.(et8riter"#F



+nce you hae an +utput%tream o/?ect, you ?ust call the println"#method to output to the /rowser. Anythin( you print will display

directly within the we/ /rowser.

out.println" HInalid ID >um/er @ Diision /y ero ErrorJnH #F

Example:

import java.io.*;

import javax.servlet.*;

import javax.servlet.http.*;

public class ServletTemplate extends HttpServlet {

public void doGet(HttpServletRequest request,

HttpServletResponse response) throws ServletException, !Exception {

rint!riter out " response.#et!riter();

"

"

-he example a/oe shows a simple serlet. It does nothin( /ut it showsthe /asic re9uirement for a serlet to /e executed properly such as theimport statement for the serlet, the doGet implementation and the useof the (et8riter"# method.

$Creat4n& Servlet% Pa&e '5'( o" '0)

Case St*"y Page 1)22 of 22

Ca*e St61y

Bour school administrator has as7ed your (roup to come up with apro(ram to implement the new username al(orithm for all students oncampus. e will proide the first name, last name, and an ei(ht@di(it idnum/er that will /e used in the creation of the user name.

-he proposed user name will /e the first three characters of the lastname followed /y the last three characters of the first name. +nce thetext portion is completed, the user name will contain a four@di(it num/er.-he four@di(it num/er is the last six di(its of the id num/er diided /ythe first two di(its. In the eent the first name or last name is less than

! characters, use all aaila/le characters and do not add any extraspace.

-he first two num/ers to the id num/er should /e chec7ed for diide /yKero errors and any diision should use inte(er diision "truncate thedecimal point#. -he first name and last name will not exceed 2''characters. -he pro(ram should continue to input data until a L@1M isproided.

%ample Inputoe%mith4!$44!2

%ample +utput:



%mioe$'

%olution:

import javax.servlet.http.*;

import javax.servlet.*;

import java.io.*;

public class #ser$ame exten%s

javax.servlet.http.&ttpServlet {

public voi% %o'et(&ttpServlet)euest re,

&ttpServlet)esponse resp+

throws !Exception, ServletException {

Strin tTemp - , t!utput - ;

lon lower - 0, l#pper1 - 0;

Strin t2irst$ame - re.et3arameter(fname+;

Strin tast$ame - re.et3arameter(lname+;

lon l4$umber -

nteer.parsent(re.et3arameter(i%++;

3rint5riter out-resp.et5riter(+;

tTemp - tast$ame.substrin(0,6+;

t!utput - tTemp;

if ( t2irst$ame.lenth(+ 7- 6 +

tTemp -t2irst$ame.substrin(t2irst$ame.lenth(+8

6,t2irst$ame.lenth(+ +;

else

tTemp - t2irst$ame;

//mo%ulus

lower - l4$umber 9 000000;

//inteer %ivision

l#pper1 - l4$umber / 000000;

out.println(html7+;

out.println(bo%<7+;

out.println(h7+;

if ( l#pper1 -- 0 +{

out.println( nvali% 4 $umber 8

4ivision b< =ero Error>n +;

"

else{

out.println(#sername: ?t!utput?tTemp?((

lower / l#pper1 + 9 0000++;

"

out.println(/h7+;

out.println(/bo%<7+;

out.println(/html7+;

"

public voi% %o3ost(&ttpServlet)euest re,

&ttpServlet)esponse resp+



throws !Exception, ServletException {

%o'et(re, resp+;

"

" // en% of class #ser$ame

-o (enerate -56, you need to add two steps:

-ell the /rowser that you are sendin( /ac7 -56.

5odify the println"# statements to return alid -56.

html7

hea%7/hea%7

bo%<7

&7#ser $ame 'enerator/&7

form action-user metho%-post7

2irst $ame:

input t<pe-text name-fname 7

ast $ame:input t<pe-text name-lname 7

#ser 4:

input t<pe-passwor% name-i% 7

input t<pe-submit value-3rocess7

/form7

/bo%<7

/html7

$Ca*e St61!% Pa&e '9.. o" ';)

EVALUATION/GENERALI@ATION

1. Explain what serlet is.2. Identify and discuss the adanta(es of serlet oer CGI.

REFERENCES

o %ams -each Bourself aaN 2 in 21 Days, ;ourth

Edition /y o(ers Cadenhead, 6aura 6emay

o ust aaN 2 %I- EDI-I+>

/y &E-E an der 6I>DE>

o -he aa -utorial @ An excellent collection of on@linefrom %> 5icrosystems"http:<<?aa.sun.com<docs</oo7s<tutorial<#

o aa 2 'th Ed. -he Complete eference

/y er/ert %childt

meljun cortes introduction to servlets

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