Servlet

CGICGI
Common Gateway InterfaceCommon Gateway Interface

Common Gateway Interface (CGI)
• As Fire walls are maintained in internet we can’t
access the resources of one network through the
other network systems, Fire wall allows only Http
Protocol.
• CGI is the standard way of communication
between Client and Application on the Server.
• It is an interface which allows to communicate
with an application on the server.
CGICGI

• CGI allows to generate Dynamic content in
response to the request from client.
• Programmes available on server side are called as
CGI scripts. These are loaded whenever it receives
client request.
• Scripting Language for CGI script must be in a
position to read and write from standard input &
output Streams.
• CGI is introduced with PERL(Practical Extraction
and Reporting Language) which is developed to
overcome the problems of c-language.
CGICGI

• CGI is commonly implemented by C, C++, PERL and
Java etc.
• With C and C++, CGI scripts are generated as
executable files and stores in CGI BIN directory
with executable permissions.
• C and C++ based CGI scripts will have problems like
Security problems, Platform Dependent, and lack
of proper support to Strings.
• PERL implementation of CGI scripts has overcome
the above problems.
CGICGI

• PERL is mainly used to generate Reports after
reading the data. Hence it has extended the
support of Strings.
• PERL is secured Language because of lack of
pointers.
• PERL is interpreter based language, where syntax
is mixture of shell script and C-Lang. As it is
interpreter the programme can be ported to any
platform without changes.
• As it is Interpreter based, the performance may
come down.
CGICGI

Drawbacks of CGI
1. CGI is slow since for every client request a new
process starts. If number of clients increases, less
memory is available which tends to bring down
the performance.
It becomes slower if the application is written in
interpreter based language.
It becomes unsafe if they are written in compiler
based languages.
CGICGI

Drawbacks of CGI
2. Fast CGI is better in performance when compare
to CGI since it uses concept of persistent process
( single process provides response to the many
clients if they request for same script).
This concept is implemented using Java but java
has lack of env variable reading support.
Accessing such variables may make a java
programme dependent on platform.
CGICGI

Drawbacks of CGI
3. Server Side Extension (API)
IIS  ISAPI
NServer  NSAPI
These have drawbacks as specific to web server
as script is based on API provided by the vendor
of web server.
They are not portable as specific to one web
server only.
CGICGI

SERVLETSERVLET
Servlets are Java platform technology of choice for
extending and enhancing Web servers .
•component-based
•server- independent
•platform-independent
•protocol-independent
•fast and efficient
•most secured

• Servlets are used for building Web-based
applications, without the performance
limitations of CGI programs.
• Servlets have access to the entire family of Java
APIs, including the JDBC API to access enterprise
databases.
• Servlets can also access a library of HTTP-specific
calls and receive all the benefits of the mature
Java language, including portability,
performance, reusability, etc.
SERVLETSERVLET

WEB SERVER
JVM
SERVLET
CLEINT
Request
Response
Servlet Name +
parameters
DATA
BASE
Servlet context
SERVLETSERVLET

•JVM loads the servlet on the request from client if
servlet is not loaded.
•Heavily used servlets has to be loaded on starting of
web server to avoid loading and creating instance on
every client request.
•On every client request a service method is called by
creating it as separate thread in JVM, i.e. every client
request has a thread created.
•Unloading of servlet depends on vender specification
i.e., unloads after response or if no response for a
specific amount of time etc.
SERVLETSERVLET

INSTANCECLASS
INIT
SERVICE
DESTROY
DOGETDOPOST
Life Cycle of SERVLETLife Cycle of SERVLET

Servlet is an API which is provided as servlet.jar
Servlet is an interface of package javax.servlet
javax.servlet.Servlet
javax.servlet.GenericServlet
javax.servlet.http.HttpServletFor HTTP protocol
SERVLETSERVLET

Methods to provide service
public void service(ServletRequest req ,
ServletResponse res) throws IOException,
ServletException
public void doGet(HttpServletRequest req ,
HttpServletResponse res) throws IOException,
ServletException
public void doPost(HttpServletRequest req ,
ServletException
SERVLETSERVLET

import javax.servlet.*;
public class NewServlet extends GenericServlet
{
public void init(ServletConfig conf)
{initialisation code; }
public void service(ServletRequest req,
ServletResponse res) throws IOException,
ServletException {service
code;}
public void destroy() { destroy code; }
}
SERVLETSERVLET

import javax.servlet.*;
import javax.servlet.http.*;
public class NewServlet extends HttpServlet
{
public void init(ServletConfig conf)
{initialisation code;}
public void service(HttpServletRequest req,
ServletException {service code;}
public void destroy(){ destroy code;}
}
SERVLETSERVLET

HTTP Technology allows to request in two ways
GET : requested from address bar and information
parameters are given as Query String which is part of
URL and separated by ‘?’ GETURL?QueryString
POST : requested from form and large amount of
information can be send to input streams.
• POST is most preferred send large amount of data as
data gets truncated in GET request.
SERVLETSERVLET

public class NewServlet extends HttpServlet
{ public void init(ServletConfig conf) {init code;}
public void doGet(HttpServletRequest req,
ServletException {Get Service
code;}
public void doPost(HttpServletRequest req,
ServletException {Post
Service code;}
public void destroy() {destroy code;}
}
SERVLETSERVLET

res.setContentType( “MIME TYPE”);
To set the header format of response
ServletOutputStream sos=res.getOutputStream();
To create OutputStream to send response
sos.println( “html tags/data” );
Method used to send the data with OutputStream
SERVLETSERVLET

MIME TypesMIME Types
text/plain
text/html
text/java
image/gif
image/jpg
image/bmp
audio/midi
audio/wav
audio/all

1.Create a Servlet and save that as
ServletName.java file.
2.Compile that from the place of creation.
3.Create a Deployment Descriptor with web.xml
file, which includes servlet name and servlet
mapping.
4.Deploy the class file and deployment descriptor
into web server with the specified process of
deployment of a web server.
SERVLETSERVLET

web.xmlweb.xml
<?xml version="1.0" encoding="ISO-8859-1"?>
<!DOCTYPE web-app
PUBLIC "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"
"http://java.sun.com/dtd/web-app_2_3.dtd">
<web-app>
<servlet>
<servlet-name>ServletName</servlet-name>
<servlet-class>ServletClassName</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>ServletName</servlet-name>
<url-pattern>/vfolder/ServletName</url-pattern>
</servlet-mapping>
</web-app>

•The hierarchy structure to deploy the servlet file in
tomcat web server.
SERVLET DeploymentSERVLET Deployment

•war file has to be created to deploy the web
application into web server.
•Creating “application.war” is possible by “jar”
command
SERVLET DeploymentSERVLET Deployment
prompt> jar –cvf <war_filename> <info_folder>
Example:
C:erp:> jar –cvf erp.jar .WEB-INF

Requesting from ClientRequesting from Client
Call The servlet by using the URL in client
application (HTML Form, Browser AddressBar,
Applet etc.) as…..
http://HostIpAddress:PortNo/app_name/url-
pattern
Example:
http://localhost:8080/erp/register
http://127.0.0.1:8080/erp/login

Call The servlet by using HTML Form
<form
action=“http://IpAddress:port/application/vFilena
me” method=“post”>
<button type=“submit”>
</form>

Call The servlet by using Applet/Midlet
String ues=URLEncoder.encode(“url”);
URL u=new URL(ues);
URLConnection con=u.openConnection();
BufferedReader br=new BufferedReader(new
InputStreamReader(con.getInputStream());
String s=br.readLine();
ta.setText(s); //ta is TextArea

Request ParametersRequest Parameters
Enumeration e = req.getParameterNames()
To get parameter names sent with the request
String name = (String) e.getNextElement()
To get name stored in Enumeration Object
String[] s = req.getPrameter(String)
To get the parameter value of given name
String[] s = req.getPrameterValues(String)
To get multiple parameter values of given name

String user = req.getPrameter(“user”)
String pwd = req.getPrameter(“password”)
Note:
This will become hardcode of parameter names and no.
of parameter.
servlet may not work in case of any changes in
parameter names/numbers in client request.
Better to get all the names of parameters sent in
request and then get the values of each parameter
name.

Enumeration e = req.getParamenterNames();
while (e.hasMoreElements())
{
String name = (String)e.nextElement();
String value = req.getParamenter(name);
out.println(name + " = " + value);
}

Servlet ContainerServlet Container
A servlet container comprises essentially the
component of a web server that hosts and interacts
with Java servlets.
Web components (Servlet, JSP) run in a Web container
which provides system services to Web components.
Web container specifies a runtime environment for
web components that includes security, life-cycle
management, deployment, and other services.

Session TrackingSession Tracking

HTTPHTTP
•Http is a stateless protocol. Every request is treated
as request from a new user, even though the same
client is requesting.
•Http is stateless since the purpose of this protocol is
just to distribute the information and not to retain
information about client.
•Each time a client retrieves a Web page, it opens a
separate connection to the Web server, and the server
does not automatically maintain contextual
information about a client.

•Session tracking is a mechanism that servlets use to
maintain state about a series of requests from the
same user (that is, requests originating from the same
browser) across some period of time.
•To maintain the information of client, Cookie is
invented by Netscape company.
•Cookie is a part of Http.

URL rewriting is used by appending a unique ID after
the URL to identify the user.
Hidden <form> fields can be used to store a unique ID
for the session.
Cookies are small files that the servlet can store on the
client computer, and retrieve later.
Http Session is an alternative to cookies. It keeps the
session data available until browsing ends.

URL Rewriting
• Every local URL requested by user can be modified
dynamically by the servlet to include extra info
(session tracking info).
• Extra info can hold information for the session, e.g.
Session id, User Name etc.
e.g. URL with an additional parameter added on by
your code:
– http://server/MyServlet?sessionid=123

URL Rewriting
Example: banking application. Bank employee’s branch-id
is passed from one servlet to another to save re-entry
// Get the current employee and branch ids
String bid = req.getParameter(branchid);
String eid = req.getParameter(empid);
out.println(“<FORM ACTION = ”bankservlet?
branchid=“+bid+”&empid=“+eid+"">");
out.println("</FORM>");

Hidden Fields
•“Hidden” fields are added to a form which will not be
displayed on the browser
<form action=“/moviefinder” method=“post”>
<input type=“hidden” name=“pin” value=“420”>
•From servlets, there is no difference in hidden fields
and visible fields, both are request parameters only.
•The servlet retrieves the hidden fields by using
req.getParameter(“pin”) or
req.getParameterValues(“pin”)

Hidden Fields
Example:
String[] items = req.getParameterValues("item");
out.println("<FORM ACTION="someServlet" METHOD=POST>");
if (items != null)
for (int i = 0; i < items.length; i++){ out.println("<INPUT
TYPE=HIDDEN NAME="item“ VALUE=""+items[i]+"">");
}
out.println("Would you like to<BR>");
out.println("<INPUT TYPE=SUBMIT VALUE="Add More Items">");
out.println("<INPUT TYPE=SUBMIT VALUE="Check Out">");
out.println("</FORM>");

Cookies are name, valued objects which are created at
server and stored on client side by the server.
Cookie contents the information of client itself.
The next time client sends the request, cookie is also
send as part of request.
Bye default Cookie is stored as text file in
c:windowstemp
CookieCookie

Cookie
Every cookie has only one name and value
Cookie will be associated with Max Age, Domain Name,
Path and Comment
Limitations:
•Max size of cookie can be 4KB
•Max no. of cookies per site can be 20
•Not more than 300 cookies total

Max Age:
Default is up to destroying the browser.
-ve means valid till current session.
0 means deleting cookie on client side.
We can set the age of cookie explicitly as
24x60x60 for 1 day
2x24x60x60 for 2 days etc.
CookieCookie

Domain: Every cookie will have domain apart from
maximum age. Default of cookie is the domain from
which cookie is sent to the client.
Path: Cookie having a path will not be send to server if
request URL doesn't contain the cookie path.
Comment: Some user agents have facility to worn the
clients before accepting cookies. This working is
through a dialog which can also show comment of the
cookie.
CookieCookie

Cookie is a class present in javax.servlet.http package.
Constructor:
Cookie(String name, String value)
res.addCookie(c);
Cookie[ ] c = req.getCookies();
CookieCookie

Methods:
String n=c.getName()
String v=c.getValue()
Int t=c.getMaxAge() c.setMaxAge(int)
String p=c.getPath() c.setPath(String)
String com=c.getComment(),
c.setComment(String)
CookieCookie

String n = req.getParameter(“pname");
String v = req.getParameter(“pvalue”);
Cookie nc = new Cookie(n, v);
res.addCookie(nc);
Cookie[] old_cs = req.getCookies();
for(Cookie oc:old_cs)
res.addCookie(oc);
CookieCookie

if(v.equals(“bill”)
{
Double tbill=0.0;
Cookie[ ] pcs = req.getCookies();
for(Cookie c:pcs)tbill+=Double.valueOf(c.getValue());
Cookie tb=new Cookie(“tbill”, tbill.toString());
res.addCookie(tb);
}
CookieCookie

Advantages:
•Cookies can easily store more data than hidden fields
•Data is stored on the client computer, not on server which
saves space on the server and will not have any effect on
server performance.
Disadvantages:
•Data is stored on the client computer, this means the data is
neither safe nor secure
•Cookies are good for keeping session data, not user data
•Cookies may be discarded or the user may contact the
server from another computer
•Users can tell their browser to turn cookies off
CookieCookie

SessionSession
A Session begins when a client establishes a connection
with http server.
For every client an object will be created at server side
which is called as HttpSession.
Session is a concept which internally works with
cookie. It is called as Server Side Cookie.
HttpSession stores the information of client on the
server which is identified by the server by using cookie,
which is created and set by the web server (Servlet
Engine).

Session will have the features of storing and retrieving
the information.
Cookie is validated till the session is valid.
It is valid until the client is connected to server.
Session may also disposed if the client is idle for more
than a specific time, which is dependent on server
vendor/ Administrator.
Session object implements the interface of
HttpSession.
SessionSession

SessionSession
HttpSession ses = req.getSession();
Creates a new HttpSession object, or retrieves a
previous one
Creates a unique session ID
Makes a new cookie object
Associates the cookie with the session ID
Puts the cookie in the response (under the Set-Cookie
header)

HttpSession ses = req.getSession();
Enumeration e = ses.getAttributeNames();
while (e.hasMoreElements())
{
String n = (String)e.nextElement();
String v = ses.getAttribute(name).toString();
out.println(n + " = " + v);
}
SessionSession

Methods:
hs.removeAttribute(name);
hs.invalidate();
Boolean b=hs.isNew();
String id=hs.getId();
long t=hs.getCreationTime();
long t=hs.getLastAccessedTime();
SessionSession

Servlet to Servlet CommunicationServlet to Servlet Communication
res.encodeRedirectURL(“URL?QueryString”));
Example:
res.encodeRedirectURL(“http://server:8080/servlet/color
”));
res.encodeRedirectURL(“http://server:8080/color.html”))
;

All The Best
…. I Career Craft

Servlet

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