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)