The document provides an overview of servlets and related technologies. It discusses that servlets are Java programs that run on a web or application server, process client requests, and produce dynamic web pages. Servlets act as a middle layer between requests from browsers/clients and databases on the server. The document also covers common gateway interface (CGI), GET and POST methods, query strings, advantages of servlets over CGI, the servlet API, servlet lifecycle, session tracking techniques including cookies, and examples of using cookies to track sessions.

1. Advanced Java Programming
Topic: Servlet
By
Ravi Kant Sahu
Asst. Professor, LPU

2. Introduction

Servlets are java programs that run on a Web or Application
server.

Servlets are used to process client requests or produce dynamic
Web pages.

Servlet are designed to work within a request/response
processing model.

It act as a middle layer between a request coming from a Web
browser or other HTTP client and databases on the HTTP server.
Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)

3. Web Pages
Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)

4. Static Web Contents

Web pages are stored as files in Web Server.

A user types a URL for the web-page from a Web browser.

The browser contacts the Web server and requests the file or web-page.

The server finds the file and returns it to the browser.

The browser then displays the file to the user.
Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)

5. Dynamic Web Contents

To view up-to-date information on the Web.

HTML pages for displaying recent information must be generated
dynamically.

Dynamic Web pages are generated by Web servers.

The Web server needs to run certain programs to process user
requests in order to produce a customized response.
Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)

6. Common Gateway Interface (CGI)

CGI was proposed to generate dynamic Web content.

CGI provides a standard framework for Web servers to interact
with external programs, known as CGI programs.

The Web server receives a request from a Web browser and passes
it to the CGI program.

The CGI program processes the request and generates a response
at runtime.

CGI programs are written in C, C++ or Perl (widely used).
Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)

7. Common Gateway Interface
Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)

8. GET and POST Methods

The two most common HTTP requests, also known as methods,
are GET and POST.

The Web browser issues a request using a URL or an HTML
form to trigger the Web server to execute a CGI program.

When issuing a CGI request directly from a URL, the GET
method is used. This URL is known as a query string.

Example:
http://www.webserverhost.com/cgi-bin/
getBalance.cgi?accountId=scott+smith&password=tiger
Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)

9. GET and POST Methods


The GET and POST methods both send requests to the Web server.
The POST method always triggers the execution of the
corresponding CGI program.

The GET method may not cause the CGI program to be executed,
if the previous same request is cached in the Web browser.

Use the GET method to speed up performance and use a POST
method if the request will actually update the database.

POST method is more secure than the GET method.
Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)

10. Query String

http://www.webserverhost.com/cgi-bin/
getBalance.cgi?accountId=scott+smith&password=tiger

The ? symbol separates the program from the parameters.

The parameter name and value are associated using the =
symbol.

Parameter pairs are separated using the & symbol.

The + symbol denotes a space character.
Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)

11. CGI Vs Servlets



Speed: CGI is very slow when handling a large number of requests
simultaneously, because the Web
server spawns a process for executing each CGI program. Each
process has its own runtime environment that contains and runs the
CGI program.
Server Crash: If many CGI programs are executed simultaneously,
System resource would be quickly exhausted, potentially causing the
server to crash.
Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)

12. ServletS
Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)

13. Servlet Advantages

Performance is significantly better.

Servlets execute within the address space of a Web server.

Servlets are platform-independent.

Java security manager on the server enforces a set of restrictions
to protect the resources on a server machine.

The full functionality of the Java class libraries is available to a
servlet.
Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)

14. Servlet Container

All servlets run inside a servlet container, also referred to as a
servlet server or a servlet engine.

A servlet container is a single process that runs in a Java Virtual
Machine.

The JVM creates a thread to handle each servlet.

Example:


Tomcat (developed by Apache, www.apache.org)
GlassFish(developed by Sun, glassfish.dev.java.net).
Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)

15. The Servlet API
Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)

16. The Servlet Interface

public void init() throws ServletException;

public void service(ServletRequest request, ServletResponse
Response) throws ServletException, IOException;

public void destroy();
Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)

17. Servlet Life Cycle

The init method is called when the servlet is first created.

The service method is invoked each time the server receives a
request for the servlet.

The destroy method is invoked after a timeout period has passed
or as the Web server is terminated.
Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)

18. Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)

19. ServletConfig interface

The ServletConfig interface allows a servlet to obtain
configuration data.

String getInitParameter(String name)

Enumeration getInitParameterNames()

ServletContext getServletContext()

String getServletName()
Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)

20. GenericServlet Class

GenericServlet is an abstract class that defines a generic,
protocol independent servlet.

It implements javax.servlet.Servlet and
javax.servlet.ServletConfig.

All the methods in Servlet and ServletConfig are implemented
in GenericServlet except service().
Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)

21. HttpServlet Class
It is an abstract class that extends GenericServlet and
implements the service method.
Methods to process HTTP request:
 doGet()
 doPost()
 doDelete()
 doPut()
 doOptions()
 doTrace()
protected void doXxx(HttpServletRequest req,
HttpServletResponse res) throws ServletException,
java.io.IOException

Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)

22. ServletRequest Interface

String getParameter(String name)

String[] getParameterValues(String name)

String getRemoteAddr()

String getRemoteHost()
Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)

23. HttpServletRequest Interface


String getHeader(String name)
String getMethod()

String getQueryString()

javax.servlet.http.Cookies[] getCookies()

HttpSession getSession(boolean create)
Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)

24. ServletResponse Interface

java.io.PrintWriter getWriter()

void setContentType(type: String)
Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)

25. HttpServletResponse Interface

void addCookie(Cookie cookie)
Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)

26. Types of Servlet
Generic servlets
 Extend javax.servlet.GenericServlet.
 Are protocol independent. They contain no inherent HTTP
support or any other transport protocol.
HTTP servlets
 Extend javax.servlet.HttpServlet.
 Have built-in HTTP protocol support and are more useful in a
Sun Java System Web Server environment.
Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)

27. Servlet Context Interface

An object of ServletContext is created by the web-container at
the time of deploying the project.

This object is used to get configuration-information from
web.xml file.

There is only one ServletContext object for any web-application.

If any information is to be shared with many servlets, its better
to provide it in the web.xml file using <context-param> element.
Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)

29. HTML FORMs
Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)

30. HTML Forms

HTML forms enable us to submit data to the Web server.

It can contain text fields, text area, check boxes, combo boxes,
lists, radio buttons, and buttons.
Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)

31. HTML tags to create HTML Form

<form> ... </form> tag is used to define the body of a form.

The attributes for the <form> tag are action and method.

The action attribute specifies the server program to be executed
on the Web server when the form is submitted.

The method attribute is either get or post.

<label> ... </label> is used to define a label.
Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)

32. HTML tags to create HTML Form


<input> defines an input field.
Attributes for <input> are type, name, value, checked, size, and
maxlength.

The type attribute specifies the input type. Possible types are text
for a one-line text field, radio for a radio button, and checkbox
for a check box.

The name attribute gives a formal name for the attribute which is
used by the servlet program to retrieve its associated value.

The names of the radio buttons in a group must be identical.
Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)

33. HTML tags to create HTML Form

The value attribute specifies a default value for a text field and
text area.

The checked attribute indicates whether a radio button or a
checkbox is initially checked.

The size attribute specifies the size of a text field, and the
maxlength attribute specifies the maximum length of a text field.
Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)

34. HTML tags to create HTML Form

<select> ... </select> defines a combo box or a list.

The attributes for this tag are name, size, and multiple.

The size attribute specifies the number of rows visible in the list.

The multiple attribute specifies that multiple values can be
selected from a list.

Set size to 1 and do not use a multiple for a combo box.
Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)

35. HTML tags to create HTML Form






<option> ... </option> defines a selection list within a <select>
... </select> tag.
This tag may be used with the value attribute to specify a value
for the selected option (e.g., <option value = "CS"> Computer
Science).
If no value is specified, the selected option is the value.
<textarea> ... </textarea> defines a text area.
The attributes are name, rows, and cols.
The rows and cols attributes specify the number of rows and
columns in a text area.
Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)

36. Obtaining Parameter Values from
HTML Forms
Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)

37. Retrieving Parameter Values



Each GUI component in the form has a name attribute.
The servlet uses the name attribute in the following method to
obtain the parameter value as a string.
String getParameter(attributeName)
In case of a list with multiple values, use the following method to
return the parameter values in an array of strings:
String[] getParameterValues(attributeName)
NOTE: If an attribute doesn’t exist, the getParameter method returns null.

If an empty value of the parameter is passed to the servlet, the
getParameter method returns a string with an empty value.
Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)

38. Retrieving Parameter Values

We can specify the value attribute in a text field, text area, combo
box, list, check box, or radio button in an HTML form.

For text field and text area, the value attribute specifies a default
value to be displayed in the text field and text area.

The user can type in new values to replace it.
Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)

39. Retrieving Parameter Values

For combo box, list, check box, and radio button, the value
attribute specifies the parameter value to be returned from the
getParameter and getParameterValues methods.

If the value attribute is not specified for a combo box or a list, it
returns the selected string from the combo box or the list.

If the value attribute is not specified for a radio button or a check
box, it returns string on for a checked radio button or a checked
check box, and returns null for an unchecked check box.
Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)

40. Session Tracking
Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)

41. Session Tracking

A session can be defined as a series of related interactions
between a single client and the Web server over a period of time.

Tracking data among requests in a session is known as session
tracking.
Techniques for session tracking
 Session Tracking Using Hidden Values
 Session Tracking Using Cookies
 Session Tracking Using the Servlet API
Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)

42. Session Tracking Using Cookies

Cookies are small text files that store sets of name/value pairs on
the disk in the client’s computer.

Cookies are sent from the server through the instructions in the
header of the HTTP response.

The javax.servlet.http.Cookie is used to create and manipulate
cookies
Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)

43. Cookies
Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)

44. Session Tracking Using Cookies

Cookie(String name, String value)

String getName()
String getValue()
Void setValue(String newValue)
int getMaxAge()
void setMaxAge(int expiration)
boolean getSecure()
void setSecure(boolean flag)
String getComment()
Void setComment(String purpose)








Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)

45. Using Cookies

Cookie stores a name/value pair and other information about the
cookie.

To send a cookie to the browser, use the addCookie() method in
the HttpServletResponse class.
response.addCookie(cookie);

To obtain cookies from a browser, use getCookie() method.
request.getCookies();

where request/response is an instance of HttpServletRequest/
HttpServletResponse.
Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)

46. Example using Cookies
Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)

47. Session Tracking using Cookies(Servlet1)
public void doPost(HttpServletRequest request, HttpServletResponse respon
se){ try{
response.setContentType("text/html");
PrintWriter out = response.getWriter();
String n=request.getParameter("userName");
out.print("Welcome "+n);
Cookie ck=new Cookie("uname",n); //creating cookie object
response.addCookie(ck); //adding cookie in the response
//creating submit button
out.print("<form action='servlet2'>");
out.print("<input type='submit' value='go'>");
out.print("</form>");
out.close(); } catch(Exception e){}}
Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)

48. Session Tracking using Cookies (Servlet 2)
public void doPost(HttpServletRequest request, HttpServletRespon
se response)
{ try{
response.setContentType("text/html");
PrintWriter out = response.getWriter();
Cookie ck[]=request.getCookies();
out.print("Hello "+ck[0].getValue());
out.close();
}
catch(Exception e){System.out.println(e);}
}
Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)

49. Session Tracking Using Hidden Values

We can track a session by passing data from the servlet to the
client as hidden values in a dynamically generated HTML form
by including a field like this one:
<input type= "hidden” name= “sessionid" value=“12345">

The next request will submit the data back to the servlet.

The servlet retrieves this hidden value just like any other
parameter value, using the getParameter method.
Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)

50. Hidden Form Fields
Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)

51. Servlet 1
public void doGet(HttpServletRequest request, HttpServletResponse response)
{
try{
response.setContentType("text/html");
PrintWriter out = response.getWriter();
String n=request.getParameter("userName");
out.print("Welcome "+n);
//creating form that have invisible textfield
out.print("<form action='servlet2'>");
out.print("<input type='hidden' name="uname" value='"+n+"'>");
out.print("<input type='submit' value='go'>");
out.print("</form>");
out.close();
}
catch(Exception e){System.out.println(e);}
}
Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)

52. Servlet 2
public void doGet(HttpServletRequest request, HttpServletRespon
se response)
try{
response.setContentType("text/html");
PrintWriter out = response.getWriter();
//Getting the value from the hidden field
String n=request.getParameter("uname");
out.print("Hello "+n);
out.close();
}
catch(Exception e){System.out.println(e);}
}
Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)

53. Session Tracking using HTTP Session

The Container creates a session id for each user.

The container uses this id to identify the particular user.

An object of HttpSession can be used to perform two tasks:
1. Bind objects
2. View and manipulate information about a session, such as the
session identifier, creation time, and last accessed time.
Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)

54. Session Tracking using HTTP Session
Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)

55. Creating Session Object

The HttpServletRequest interface provides two methods to get
the object of HttpSession:
public HttpSession getSession()
Returns the current session associated with this request, or if the
request does not have a session, creates one.
public HttpSession getSession(boolean create)
Returns the current HttpSession associated with this request or,
if there is no current session and create is true, returns a new
session.
Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)

56. Methods of HTTP Session Interface

public String getId():Returns a string containing the unique
identifier value.

public long getCreationTime():Returns the time when this
session was created, measured in milliseconds since midnight
January 1, 1970 GMT.

public long getLastAccessedTime():Returns the last time the
client sent a request associated with this session, as the number
of milliseconds since midnight January 1, 1970 GMT.

public void invalidate():Invalidates this session then unbinds any
objects bound to it.
Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)

57. Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)