Advance Java Programming (CM5I) 6.Servlet

6.Servlet(Marks 14)
Miss.P.S.Dungarwal
Lecturer in CM Department.
SHHJB Polytechnic, Chandwad.
Advance Java Programming(22517)

Mr. Nilesh Vishwasrao Patil
Web and Web Application
 Web consists of billions of clients and server
connected through wires and wireless networks.
 The web clients make requests to web server. The web
server receives the request, finds the resources and return
the response to the client.
2Miss.P.S.Dungarwal

Web Application
 A web application is an application accessible from
the web.
 A Web application is a web site with dynamic
functionality on the server. Google, Facebook,
Twitter are examples of web applications.
 A web application is composed of web components
like Servlet, JSP, Filter etc. and other components such
as HTML.
 The web components typically execute in Web Server
and respond to HTTP request.
3Miss.P.S.Dungarwal

HTTP
 HTTP is a protocol that clients and servers use on
the web to communicate.
 It is similar to other internet protocols such as
SMTP (Simple Mail Transfer Protocol) and FTP
(File Transfer Protocol) but there is one
fundamental difference.
 HTTP is a stateless protocol.
 The client sends an HTTP request and the server
answers with an HTML page to the client, using HTTP.
4Miss.P.S.Dungarwal

Mr. Nilesh Vishwasrao Patil
HTTP methods
Method Name Description
OPTIONS Request for communication options that are available on the
request/response chain.
GET Request to retrieve information from server using a given URI.
HEAD Identical to GET except that it does not return a message-body,
only the headers and status line.
POST Request for server to accept the entity enclosed in the body of
HTTP method.
DELETE Request for the Server to delete the resource.
CONNECT Reserved for use with a proxy that can switch to being a tunnel.
PUT This is same as POST, but POST is used to create, PUT can be
used to create as well as update. It replaces all current
representations of the target resource with the uploaded content.
6Miss.P.S.Dungarwal

HTTP methods
GET Request POST Request
Data is sent in header to the
server
Data is sent in the request body
Get request can send only
limited amount of data
Large amount of data can be
sent.
Get request is not secured
because data is exposed in URL
Post request is secured
because data is not exposed in
URL.
Get request can be
bookmarked and is more
efficient.
Post request cannot be
bookmarked.
7Miss.P.S.Dungarwal

Servlet : Introduction
 Servlet technology is used to create web
application (resides at server side and generates
dynamic web page).
 Servlet is Java program which run on web server
and responding to request of clients (Web
browser).
 Servlet technology is robust and scalable because
of java language.
10Miss.P.S.Dungarwal

Servlet
 Web applications are helper applications that resides at web
server and build dynamic web pages.
 A dynamic page could be anything like a page that randomly
chooses picture to display or even a page that displays the
current time.

Servlet : Defined in many ways
 Servlet is a technology i.e. used to create web application.
 Servlet is an API that provides many interfaces and
classes including documentations.
 Servlet is an interface that must be implemented
for creating any servlet.
 Servlet is a class that extend the capabilities of the
servers and respond to the incoming request. It can
respond to any type of requests.
 Servlet is a web component that is deployed on the
server to create dynamic web page. 12Miss.P.S.Dungarwal

Servlet : Defined

Servlet
 A Java Servlet is a Java object that responds to
HTTP requests. It runs inside a Servlet container.

Servlet
 A Servlet is part of a Java web application.
 A Servlet container may run multiple web applications at the
same time, each having multiple servlets running inside.

Servlet
 A Java web application can contain other
components than servlets.
 It can also contain Java Server Pages (JSP), images,
text files, documents, Web Services etc.

HTTP Request and Response
 The browser sends an HTTP request to the Java web
server.
 The web server checks if the request is for a servlet. If it is,
the servlet container is passed the request.
 The servlet container will then find out which servlet the
request is for, and activate that servlet.
 The servlet is activated by calling the
Servlet.service()method.
 Once the servlet has been activated the servlet processes the
request, and generates a response. The response is then sent
back to the browser. 24Miss.P.S.Dungarwal

Servlet Containers
 Java servlet containers are usually running inside a Java web
server.
 Example: Tomcat, GlasssFish, Jboss etc.
 Container:
 It provides runtime environment for JavaEE (j2ee)
applications.
 It performs many operations that are given below:
 Life Cycle Management
 Multithreaded support
 Security etc.

Types of Servlet
 Generic Servlet:
 It is in javax.servlet.GenericServlet package
 It is protocol independent.
 HTTP Servlet
 It is in javax.servlet.HTTPServlet package
 Built-in HTTP protocol support.

Types of Servlet
Generic Servlet HTTP Servlet
Package: javax.servlet Package: javax.servlet.http
It is protocol independent
servlet
It is protocol dependent
specifically only HTTP protocol
request- response handle.
It uses service() method for
handling request-response.
It uses methods like doPost(),
doGet()

Servlet life cycle
 Each servlet instance is loaded once.
 Each execution happens in a separate thread
 Three methods:
 init() : call only once to initialize servlet.
 service() : Call for every request.
 destroy() : call only once
 Method service() is invoked every time a request
comes. It spawns off threads to perform doGet or
doPost based on the method invoked.

Servlet life cycle
1. Load Servlet Class.
2. Create Instance of Servlet.
3. Call the servlets init() method.
4. Call the servlets service() method.
5. Call the servlets destroy() method.
Note: Step 1,2,3 executed only once when servlet is initially
loaded.
Step 4 executed "N"-timeswhenever http requestcomes
Step 5 executed to destroy servlet means unload servlet class

Mr. N ilesh Vishwasrao Patil
Servlet life cycle

Servlet API
 Servlet API consists of two important packages
that encapsulates all the important classes and
interface, namely :
 javax.servlet
 javax.servlet.http

Servlet Interface: javax.servlet
Interfaces Description
Servlet Declare life cycle methods for servlet. To
implement this interface we have to extends
GenericServlet or HttpServlet classes.
ServletConfig Helps servlet to get initialization parameter
means startup information, basic
information about servlet.
ServletContext Allows servlet to log events and access
information about their environment
ServletRequest Used to read data from client
ServletResponse Used to sent data to client

Servlet Classes: javax.servlet
Classes Description
GenericServlet Used to create servlet (Protocol
independent)
ServletInputStream Provides an input stream for reading
requests from client.
ServletOutputStream This class supports an output stream
for writing responses to a client
ServletException For handling exception: Error Occurred
UnavailableException For handling exception: generate when
servlet not available

Servlet Interface: javax.servlet.http
Classes Description
HttpServlet Used to create http servlet (Protocol
dependent)
HttpServletRequest It enables servlets to read data from an
HTTP request
HttpServletResponse It enables servlets to write data to an
HTTP response
HttpSession It allows to read and write session data.
Cookie Cookie class allows state information to
be stored on a client machine

Servlet Interface: Methods

GenericServlet class
 It implements Servlet, ServletConfig and
Serializable interfaces.
 It provides the implementation of all the methods of
these interfaces except the service method (You
have to write code in your servlet class for this
method).
 GenericServlet class can handle any type of
request so it is protocol-independent.

ServletConfig interface
 Object of ServletConfig created by the web
container for each servlet.
 This object can be used to get configuration
information from web.xml file.
 Advantage: No need to edit the servlet file if
information is modified from the web.xml file.

 public String getInitParameter(String name):
Returns the parameter value for the specified
parameter name.
 Enumeration getInitParameterNames():
Returns all the initialized parameter names.
 public String getServletName():
Returns the name of the servlet.
 public ServletContext getServletContext():
Returns an object of ServletContext.

ServletContext interface
 An object of ServletContext is created by the
web container at time of deploying the project
(web application).
 This object can be used to get configuration
information from web.xml file.
 There is only one ServletContext object per web
application.

ServletContext interface
<context-param>
<param-name>dname </param-name>
<param-value> sun.jdbc.odbc.JdbcOdbcDriver
</param-value>
</context-param>

HttpServlet
 It extends GenericServlet class and
implements Servlet, ServletConfig and
Serializable interface.
 It provides http specific methods such as
doGet, doPost, doHead, doTrace etc.

HttpServlet
• The most important are six doxxx methods that get
called when a related HTTP request method is used.
• The six methods are doPost, doPut, doGet, doDelete,
doOptions and doTrace.
• For instance, the doGet method is invoked when the
servlet receives an HTTP request that was sent using
the GET method.
• Of the six doxxx methods, the doPost and the doGet
methods are the most frequently used.

Implementation
 A Java Servlet is just an ordinary Java class
which implements the interface
 javax.servlet.Servlet;
 The easiest way to implement this interface is
to extend either the
 class GenericServlet or HttpServlet.

Implementation
 When an HTTP request arrives at the web
server, targeted for your Servlet, the web
server calls your Servlet's service() method.
 The service() method then reads the request,
and generates a response which is sent back to
the client (e.g. a browser).

Implementation:HTTP
 The javax.servlet.http.HttpServlet class is a
slightly more advanced base class than
the GenericServlet
 The HttpServlet class reads the HTTP request,
and determines if the request is an HTTP GET,
POST, PUT, DELETE, HEAD etc. and calls one
the corresponding method.

Implementation: HTTP

HttpRequest: Interface
 This interface present in
javax.servlet.http.HttpRequest
 The purpose of the HttpRequest object is to
represent the HTTP request a browser sends to
your web application. 56Miss.P.S.Dungarwal

HttpRequest: Parameters
 Thus, anything the browser may send,
is accessible via the HttpRequest.
 We can read initialization parameters also
using HttpServletRequest object with
getInitParameter method.

HttpRequest: Parameters
 Also we can use following code if request parameters is
send through body part of the Http request.
 If the browser sends an HTTP GET request, the
parameters are included in the query string in the URL.
 If the browser sends an HTTP POST request, the
parameters are included in the body part of the HTTP
request. 58Miss.P.S.Dungarwal

HttpRequest: Header
 The request headers are name, value pairs sent by the browser
along with the HTTP request.
 The request headers contain information about e.g. what
browser software is being used, what file types the browser is
capable of receiving etc. In short, at lot of meta data around the
HTTP request.
 Above example reads the Content-Length header sent by the
browser.

HttpRequest: InputStream
 If the browser sends an HTTP POST request, request
parameters and other potential data is sent to the server
in the HTTP request body.
 If does not have sent data in parameters means may be
binary data, that time we will require InputStream for
accessing request body come from client.
 InputStream requestBodyInput =
request.getInputStream();
 NOTE: You will have to call this method before
calling any getParameter() method.

HttpRequest: Session
 It is possible to obtain the session object from the
HttpRequest object too.
 The session object can hold information about a given user,
between requests.
 So, if you set an object into the session object during one
request, it will be available for you to read during any
subsequent requests within the same session time scope.

HttpResponse: Interface
 This interface is present in java.servlet.http package.
 The purpose of the HttpResponse object is to represent the
HTTP response of web application sends back to the browser.

HttpResponse: Writing HTML
 To send HTML back to the browser, you have to obtain the
a PrintWriter from the HttpResponse object.

HttpResponse: Headers
 Headers must be set before any data is written to the response.
 Examples:
 Syntax:
response.setHeader("Header-Name", "Header Value");
 Set Content type:
response.setHeader("Content-Type", "text/html");
 Writing text
response.setHeader("Content-Type", "text/plain");
PrintWriter writer = response.getWriter();
writer.write("This is just plain text");
 Content-length
response.setHeader("Content-Length", "31642"); 64Miss.P.S.Dungarwal

HttpResponse: Writing Binary
Data
 We can also write binary data back to the browser instead of
text.
 For instance, we can send an image back, a PDF file or a Flash
file or something like that.
 First we have to set content type. And need to use following
code:
OutputStream outputStream = response.getOutputStream();
outputStream.write(...);

HttpResponse: Redirecting
 We can redirect the browser to a different URL from your
servlet.
 You cannot send any data back to the browser when
redirecting
response.sendRedirect("http://www.google.com");
Or Another servlet file call
response.sendRedirect(“HelloServlet");

HttpSession
 The HttpSession object represents a user session.
 A user session contains information about the user across
multiple HTTP requests.
 When a user enters your site for the first time, the user is given
a unique ID to identify his session by.
 This ID is typically stored in a cookie or in a request parameter.

HttpSession
 We can store values in the session object, and retrieve
them later. Do it in following way:
session.setAttribute("userName", "theUserName");
 This code sets an attribute named "userName", with
the value "theUserName".
 To read the value again:
String userName = (String) session.getAttribute("userName");
 Values stored in the session object are stored in the
memory of the servlet container.

HttpSession: Example
 Create one HTML file: index.html which send user name
and password to the servlet file.
 Create two servlet file, one will save user name into
session and that session information is send to another
servlet. This example shows the session tracking.

RequestDispatcher
 The RequestDispatcher class enables your servlet to "call"
another servlet from inside another servlet.
 We can obtain a RequestDispatcher from the
HttpServletRequest object.
 The above code obtains a RequestDispatcher targeted at whatever Servlet
(or JSP) that is mapped to the URL /anotherUrl.simple. 71Miss.P.S.Dungarwal

RequestDispatcher
 You can call the RequestDispatcher using either its include()
or forward() method.
 The forward() method intended for use in forwarding the request,
meaning after the response of the calling servlet has been committed. You
cannot merge response output using this method.
 The include() method merges the response written by the calling servlet,
and the activated servlet. This way you can achieve "server side includes"
using the include().

Servlet: Load on start up
 The <servlet> element has a sub-element called
<load-on-startup> which you can use to control when the servlet container
should load the servlet.
 If you do not specify a <load-on-startup> element, the servlet container will
typically load your servlet when the first request arrives for it.
 By setting a <load-on-startup> element, you can tell the servlet container to
load the servlet as soon as the servlet container starts.
 Remember, the servlets init() method is called when the servlet is loaded.
<load-on-startup>1</load-on-startup>

Cookie
 HTTP Cookies are little pieces of data that a web
application can store on the client machine of users
visiting the web application.
 Typically up to 4 kilo bytes(KB) of data can be store.
 We can write cookies using HttpServletResponse object:
 Example:
Cookie cookie = new Cookie("myCookie",
"myCookieValue"); response.addCookie(cookie);

Cookie
 By default, each request is considered as a new request.
 In cookies technique, we add cookie with response
from the servlet.
 So cookie is stored in the cache of the browser.
 After that if request is sent by the user, cookie is added
with request by default. Thus, we recognize the user as
the old user.

Cookie: Types
 Non-persistent cookie:
 It is valid for single session only. It is removed each time
when user closes the browser.
 Persistent cookie:
 It is valid for multiple session . It is not removed each time
when user closes the browser. It is removed only if user
logout or sign-out or clear cookies/cache memory of
browsers.

Cookie: Pros/Cons
 Advantages:
 Simplest technique of maintaining the state.
 Cookies are maintained at client side.
 Disadvantages
 It will not work if cookie is disabled from the browser.
 Only textual information can be set in Cookie object.

Cookie: Constructor
 javax.servlet.http.Cookie class provides the
functionality of using cookies. It provides a lot of
useful methods for cookies.
Constructor Description
Cookie() constructs a cookie.
Cookie(String name, String value) constructs a cookie with a specified
name and value.

Cookie: Methods
 Useful methods:
Method Description
public void setMaxAge(int expiry) Sets the maximum age of the cookie in
seconds.
public String getName() Returns the name of the cookie.
public String getValue() Returns the value of the cookie.
public void setName(String name) changes the name of the cookie.
public void setValue(String value) changes the value of the cookie.

Cookie: Methods
 Other methods:
 public void addCookie(Cookie ck):method of
HttpServletResponse interface is used to add cookie in
response object.
 public Cookie[] getCookies():method of
HttpServletRequest interface is used to return all the
cookies from the browser.

Cookie: How to create?
 Creating cookie object
Cookie ck=new Cookie("user",”Sandip");
 Adding cookie in the response
response.addCookie(ck);//

Cookie: For delete Cookies
 Deleting value of cookie
Cookie ck=new Cookie("user","");
 Changing the maximum age to 0 seconds
ck.setMaxAge(0);
 Adding cookie in the response
response.addCookie(ck);

Cookie: To get Cookies
Cookie ck[]=request.getCookies();
for(int i=0;i<ck.length;i++)
{
out.print("<br>"+ck[i].getName()+" "+ck[i].getValue());
//printing name and value of cookie
}

Cookie: Example

Cookie: Example
 Create one Html file which send user name to
first servlet.
 First servlet file set cookies of that user name and
call second servlet file.
 Second servlet file retrieve name of user from
cookies instead of from session.

MCQ
 Which is of the following are classes and which are
interfaces?
 1. Servlet
 2. ServletConfig
 3. ServletRequest
 4. ServletResponse
 5. HttpServlet
 6. GenericServlet
 7. Cookies
 8. Session 86Miss.P.S.Dungarwal

MCQ
 What is returntype of the getSession() method?
 1. Session
 2. int
 3. HttpSession
 4. boolean
 5. void

MCQ
 Javax.servlet packages does not have:
 1. HttpServlet
 3. ServletContext
 4. Servlet
 5. HttpServletRequest
 7. HttpServletResponse
 8. Cookies

MCQ
 Which is correct package for HttpServlet and
HttpServletResponse?
 1. javax.servlet.*;
 2. javax.servlet.http.*;
 3. javax.servlet.httpservlet.*;
 4. java.lang.*;

MCQ
 Which of the following method is invoked when Http
post request?
 1. doPost()
 2. doPostCall()
 3. doHttpPost()
 4. doPut()
 5. doTrace()
 6. doPostOptions()

Advance Java Programming (CM5I) 6.Servlet

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