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Servlets
Outline• Introduction to web terminologies
– WWW ,URL, HTML and HTTP• Servlet & Its Advantages• Life Cycle of Servlet• Steps for Creating Servlet( in Apache Tomcat)
– Directory Structure – web.xml
• Servlet Request and Servlet Response• Servlet handling from data (Sample Programs on Servlet)• RequestDispatcher• State Management
– Cookies– HttpSession
WWW (World Wide Web)• The Web is a distributed information system based on
hypertext.• Most Web documents are hypertext documents
formatted via the HyperText Markup Language (HTML)• HTML documents contain
– text along with font specifications, and other formatting instructions
– hypertext links to other documents, which can be associated with regions of the text.
– forms, enabling users to enter data which can then be sent back to the Web server
URL (Unified Resources Locators)
• URL example: http://www.mit.asia/mca– The first part indicates how the document is to be
accessed• “http” indicates that the document is to be accessed
using the Hyper Text Transfer Protocol.– The second part gives the unique name of a
machine on the Internet.– The rest of the URL identifies the document within
the machine.
HTML & HTTP• HTML provides formatting, hypertext link, and image
display features– including tables, stylesheets (to alter default formatting), etc.
• HTML also provides input features• Select from a set of options
– Pop-up menus, radio buttons, check lists• Enter values
– Text boxes
• HyperText Transfer Protocol (HTTP) used for communication with the Web server
HTML Sample Code<html><body> <table border>
<tr> <th>ID</th> <th>Name</th> <th>Department</th> </tr><tr> <td>00128</td> <td>Zhang</td> <td>Comp. Sci.</td> </tr>
</table> <form action=“FirstPage" method=get>
Search for: <select name="persontype"> <option value="student" selected>Student </option> <option value="instructor"> Instructor </option> </select> <br>Name: <input type=text size=20 name="name"><input type=submit value="submit">
</form></body> </html>
Display of Sample HTML Source
Servlet• Servlet is a technology that is used to create web
application • Web component that is deployed on server side
to create dynamic web pages• Servlet is an API that provides many Interfaces
and classes including documentation• Servlet is an Interface that must be implemented
for creating any servlet• Servlet is a class that extend the functionalities
of server and responds to the incoming requests
Java Web Application Request Handling
Servlet
Advantages of Servlet Performance
The performance of servlets is superior to CGI because there is no process creation for each client request.
Each request is handled by the servlet container process. After a servlet has completed processing a request, it stays resident in
memory, waiting for another request. Portability
Like other Java technologies, servlet applications are portable. Rapid development cycle
As a Java technology, servlets have access to the rich Java library that will help speed up the development process.
Robustness Servlets are managed by the Java Virtual Machine. Don't need to worry about memory leak or garbage collection, which
helps you write robust applications. Widespread acceptance
Java is a widely accepted technology.
Life Cycle of Servlet
Initializationinit()
Serviceservice()
doGet()doPost()
doDelete()doHead()doTrace()
doOptions()
Destructiondestroy()
Concurrent Threadsof Execution
Life Cycle Methods• init() : – Servlet loads and initializes the servlet
• service():– Servlet handles one or more client Request and
Responses to the client• destroy():– Servlet is deactivated or server is terminated– Memory allocated for the servlet and its object are
garbage collected
Note: All above methods are inherited from GenericServlet class
Directory StructureROOT
Save .java program
Web.xml
Servlet Request• Servlet API provides two important interfaces– javax.servlet.ServletRequest– javax.servlet.http.HttpServletRequest
ServletRequest<<interface>>
HttpServletRequest<<interface>>
extends
getParameter()getAttribute()
getSession()getMethod()
Servlet Response• Servlet API provides two important interfaces– javax.servlet.ServletResponse– javax.servlet.http.HttpServletResponse
ServletResponse<<interface>>
HttpServletResponse<<interface>>
extends
PrintWriter getWriter()setContentType( String type)
void addCookie(Cookie c )int getStatus()
Sample Servlet Exampleimport java.io.*;import javax.servlet.*;
public class ServletExample extends GenericServlet{
public void service(ServletRequest request,ServletResponse response) throws ServletException,IOException{response.setContentType("text/html"); // server responds in HTML format
PrintWriter out=response.getWriter();out.println("<html>");out.println("<body>");out.println("Hello World...");out.println("</body>");out.println("</html>");}
}
Request Dispatcher• It is an interface• Object of this interface can dispatch the
request to any resources(such as HTML,JSP, Servlet) on server
Methods Description
void forward(ServletRequest request,ServletResponse response)
Forwards a request from a servlet to another resource (HTML,JSP, Servlet) on the server
void include(ServletRequest request,ServletResponse response)
Includes the content of a resource (HTML,JSP, Servlet) in the response
Request Dispatcher
1) forward() method:RequestDispatcher rd=
request.getRequestDispatcher("Employee.jsp"); rd.forward(request, response);
2) include() method :RequestDispatcher rd=
request.getRequestDispatcher("HomePage.html"); rd.include(request, response);
Session Management
• Http is a Stateless protocol. Each request and response is independent
• Session Management is a mechanism used by WEB CONTAINER to store session information for the particular user.
Session Management
Session ManagementTechniques used by Servlet application for session management :– Cookies– HttpSession
Cookies(javax.servlet.http.Cookie class)• Small piece of information that are sent from web
server to the client• Stored on client’s computer
Cookies
• Advantages:– Simplest technique of maintaining the state– Maintained at client side
• Disadvantages:– It will not work if cookie is disabled from browser– Only textual information can be set in cookie
object
ExampleFirstServlet.javaprotected void doGet(HttpServletRequest request,HttpServletResponse response) throws ServletException,
IOException { Cookie ck = null; ck = new Cookie("uname", "MCA"); //setting value response.addCookie(ck); RequestDispatcher rd =
request.getRequestDispatcher(“SecondServlet"); rd.forward(request, response);}
ExampleSecondServlet.javaprotected void doGet(HttpServletRequest request,HttpServletResponse response) throws ServletException, IOException {
Cookie cookvar = null;response.setContentType("text/html");PrintWriter out = response.getWriter();Cookie[] cks = request.getCookies(); //accepting cookie valueif (cks != null) {for (int i = 0; i < cks.length; i++) {cookvar = cks[i];out.print("Value:" + cookvar.getValue() );out.print( "Name:" + cookvar.getName());}
}out.close();
}
HttpSession
• HttpSession object is used to store entire session with specific client
• We can store , retrive and remove attribute from HttpSession object
• Any servlet can have access to HttpServlet object through the getSession() method of HttpServletRequest object
1) On Client’s first request, the Web container generates a unique session ID and gives it back to the client with response
2) The Client sends back the session ID with each request3) The Web Container uses this ID ,finds the matching session with the ID
and associates the session with the request
FirstServlet.javaimport java.io.*;import javax.servlet.*;import javax.servlet.http.*;
public class FirstServlet extends HttpServlet {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);HttpSession session=request.getSession();session.setAttribute("uname",n);out.print("<a href=‘SecondServlet'>visit</a>");out.close();
}catch(Exception e){System.out.println(e);}}
}
SecondServlet.javaimport java.io.*;import javax.servlet.*;import javax.servlet.http.*;
public class SecondServlet extends HttpServlet {public void doGet(HttpServletRequest request, HttpServletResponse response){
try{response.setContentType("text/html");PrintWriter out = response.getWriter();
HttpSession session=request.getSession(false);String n=(String)session.getAttribute("uname");out.print("Hello "+n);out.close();
}catch(Exception e){System.out.println(e);}}
}
Assignment
1. Explain session management in detail .Also, explain how HttpSession works?
2. Write a servlet program to insert Employee details like : empid,employee_name,address,date_of_birth in Employee table using JDBC.
