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Cookies

Are text files stored on the client computer and they are kept for various information tracking purposes

JSP transparently supports HTTP cookies using underlying servlet technology

3 Steps involved in identifying and returning users

1. Server script sends a set of cookies to the browser

2. Browser stores this information on the local machine for future use

3. When the next time the browser sends any request to the web server then it sends those cookies information to the server and server uses that information to identify the user

Cookies are usually set in an HTTP header (although JS can also set a cookie directly on a browser)

A JSP that sets a cookie might send headers

HTTP/1.1 200 OK
Date: Fri,  18 Feb 2022 11:44:38 GMT
Server : Apache/1.3.9 (UNIX) PHP / 4.0b3
Set-Cookie: name = xyz; expires = Friday, 18-Feb-21 12:44:38 GMT;
Path = /; domain = spongebob53.github.io
Connection: close
Content-Type: text/html

Name and value will be URL encoded

Expires field is an instruction to the browser to forget the cookie after the given time and date

If the browser is configured to store cookies, it will then keep this information until the expiry date

If the user points the browser at any page that matches the path and domain of the cookie,

It will resent the cookie to the server

Servlet Cookies method

setDomain(String pattern) : Sets the domain to which the cookie applies

getDomain() : Gets the domain to which the cookie applies

setMaxAge(int expiry) : Sets how much time (in seconds) should elapse before cookies expires. If you don’t set this, the cookie will last only for the current session

getMaxAge() : Returns the maximum age of the cookie, specified in seconds, By default -1 indicating the cookie will persist until the browser shutdown

getName() : Returns the name of the cookie. The name can’t be changed after the creation

setValue(String newValue) : Sets the value associated with the cookie

getValue() : Gets the value associated with the cookie

setPath(String uri) : Sets the path to which this cookie applies. If you don’t specify a path, the cookie is returned for all URLs in the same directory as the current page as well as all subdirectories

getPath() : Gets the path to which this cookie applies

setSecure(boolean flag) : Sets the Boolean value indicating whether the cookie should only be sent over encrypted(i.e, SSL) connections

setComment(String purpose) : Specifies a comment that describes a cookie’s purpose. The comment is useful if the browser presents the cookie to the user

getComment() : Returns the comment describing the purpose of this cookie, or null if the cookies has no comment

Set Cookies

1. Creating a Cookie object

Cookie cookie = new Cookie(“key”, “value”);

1. Setting the maximum age

Cookie.setMaxAge(60*60*24);

1. Sending the Cookie into the HTTP response headers

response.addCookie(cookie);

Reading Cookies

<%
    Cookie cookie = null;
    Cookie[] cookies = null;
    // Get an array of Cookies associated with the this domain
    cookies = request.getCookies();
    if( cookies != null ) {
        for (int i = 0; i < cookies.length; i++) {
            cookie = cookies[i];
            out.print("Name : " + cookie.getName( ) + ",  ");
            out.print("Value: " + cookie.getValue( )+" <br/>");
        }
    } else {
        out.println("<h2>No cookies founds</h2>");
    }
%>

Delete Cookies

1. Read an already existing cookie and store it in Cookie object

2. Set cookie age as zero using the setMaxAge() to delete an existing cookie

3. Add this cookie back into the response header