Introduction to Servlet technology

Cookies are text files stored in client computer which is used for tracking information. Java Servlets supports HTTP cookies.

Below are used for checking returning users:

• Server script send a set of cookies to browser. For example name etc.
• Browser stores below information in local machine for future reference.
• When browser sends any request to web server next time then it sends cookies information to server for identifying the user.

Servlet Cookies Methods

Below are the methods which is used to manipulate cookies: 

Setting Cookies with Servlet

Setting cookies with servlet involves following steps:

Creating Cookie object:

The Cookie constructor contain a cookie name and a cookie value which are strings.

Cookie cookie = new Cookie("key","value");

Setting the maximum age:

The setMaxAge  specify how long (in seconds) cookie should be valid.

cookie.setMaxAge(60*60*24);

Sending Cookie into HTTP response headers:

The response.addCookie to add cookies in HTTP response header:

response.addCookie(cookie);

Below is the example of use of cookie in servlets:

import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;

public class CookieExample extends HttpServlet {

    public void doGet(HttpServletRequest request, HttpServletResponse response)
    throws IOException, ServletException
    {
        response.setContentType("text/html");
        PrintWriter out = response.getWriter();

        // print out cookies

        Cookie[] cookies = request.getCookies();
        for (int i = 0; i < cookies.length; i++) {
            Cookie c = cookies[i];
            String name = c.getName();
            String value = c.getValue();
            out.println(name + " = " + value);
        }

        // set a cookie

        Cookie c = new Cookie("myCookie", "myCookieValue");
        response.addCookie(c);

       // delete a cookie

        for (int i = 0; i < cookies.length; i++){
            cookie = cookies[i];
            if((cookie.getName( )).compareTo("myCookie") == 0 ){
                 cookie.setMaxAge(0);
                 response.addCookie(cookie);
                 out.print("Deleted cookie : " + 
                              cookie.getName( ) + "<br/>");
            }
            out.print("Name : " + cookie.getName( ) + ",  ");
            out.print("Value: " + cookie.getValue( )+" <br/>");
         }
 } 
}