JSP - Cookies Handling

Cookies are text files stored on the client computer and they are kept for various information tracking purpose. JSP transparently supports HTTP cookies using underlying servlet technology. There are three steps involved in identifying returning users:

• Server script sends a set of cookies to the browser. For example name, age, or identification number etc.
• Browser stores this information on local machine for future use.
• When next time browser sends any request to web server then it sends those cookies information to the server and server uses that information to identify the user or may be for some other purpose as well.

This chapter will teach you how to set or reset cookies, how to access them and how to delete them using JSP programs.

The Anatomy of a Cookie:

Cookies are usually set in an HTTP header (although JavaScript can also set a cookie directly on a browser). A JSP that sets a cookie might send headers that look something like this:


As you can see, the Set-Cookie header contains a name value pair, a GMT date, a path and a domain. The name and value will be URL encoded. The 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 resend the cookie to the server. The browser's headers might look something like this:


A JSP script will then have access to the cookies through the request method request.getCookies()which returns an array of Cookie objects.

Servlet Cookies Methods:

Following is the list of useful methods associated with Cookie object which you can use while manipulating cookies in JSP:

S.N.	Method & Description
1	public void setDomain(String pattern) This method sets the domain to which cookie applies, for example tutorialspoint.com.
2	public String getDomain() This method gets the domain to which cookie applies, for example tutorialspoint.com.
3	public void setMaxAge(int expiry) This method sets how much time (in seconds) should elapse before the cookie expires. If you don't set this, the cookie will last only for the current session.
4	public int getMaxAge() This method returns the maximum age of the cookie, specified in seconds, By default, -1 indicating the cookie will persist until browser shutdown.
5	public String getName() This method returns the name of the cookie. The name cannot be changed after creation.
6	public void setValue(String newValue) This method gets the value associated with the cookie.
7	public String getValue() This method gets the value associated with the cookie.
8	public void setPath(String uri) This method 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.
9	public String getPath() This method gets the path to which this cookie applies.
10	public void setSecure(boolean flag) This method sets the boolean value indicating whether the cookie should only be sent over encrypted (i.e. SSL) connections.
11	public void setComment(String purpose) This method specifies a comment that describes a cookie's purpose. The comment is useful if the browser presents the cookie to the user.
12	public String getComment() This method returns the comment describing the purpose of this cookie, or null if the cookie has no comment.

Setting Cookies with JSP:

Setting cookies with JSP involves three steps:


(1) Creating a Cookie object:
You call the Cookie constructor with a cookie name and a cookie value, both of which are strings.


Keep in mind, neither the name nor the value should contain white space or any of the following characters:


(2) Setting the maximum age: You use setMaxAge to specify how long (in seconds) the cookie should be valid. Following would set up a cookie for 24 hours.


(3) Sending the Cookie into the HTTP response headers: You use response.addCookie to add cookies in the HTTP response header as follows:


Example:

Let us modify our Form Example to set the cookies for first and last name.


Let us put above code in main.jsp file and use it in the following HTML page:


Keep above HTML content in a file hello.jsp and put hello.jsp and main.jsp in / webapps/ROOT directory. When you would access http://localhost:8080/hello.jsp, here is the actual output of the above form.

First Name:
Last Name:

Try to enter First Name and Last Name and then click submit button. This would display first name and last name on your screen and same time it would set two cookies firstName and lastName which would be passed back to the server when next time you would press Submit button.

Next section would explain you how you would access these cookies back in your web application.

Reading Cookies with JSP:

To read cookies, you need to create an array of javax.servlet.http.Cookie objects by calling thegetCookies( ) method of HttpServletRequest. Then cycle through the array, and use getName() and getValue() methods to access each cookie and associated value.

Example:

Let us read cookies which we have set in previous example:

<html>
<head>
<title>Reading Cookies</title>
</head>
<body>
<center>
<h1>Reading Cookies</h1>
</center>
<%
Cookie cookie = null;
Cookie[] cookies = null;
// Get an array of Cookies associated with this domain
cookies = request.getCookies();
if( cookies != null ){
out.println("<h2> Found Cookies Name and Value</h2>");
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>");
}
%>
</body>
</html>

Now let us put above code in main.jsp file and try to access it. If you would have set first_name cookie as "John" and last_name cookie as "Player" then running http://localhost:8080/main.jsp would display the following result:

Found Cookies Name and Value

Name : first_name, Value: John
Name : last_name, Value: Player

Delete Cookies with JSP:

To delete cookies is very simple. If you want to delete a cookie then you simply need to follow up following three steps:

• Read an already existing cookie and store it in Cookie object.
• Set cookie age as zero using setMaxAge() method to delete an existing cookie.
• Add this cookie back into response header.

Example:

Following example would delete and existing cookie named "first_name" and when you would run main.jsp JSP next time it would return null value for first_name.

<html>
<head>
<title>Reading Cookies</title>
</head>
<body>
<center>
<h1>Reading Cookies</h1>
</center>
<%
Cookie cookie = null;
Cookie[] cookies = null;
// Get an array of Cookies associated with this domain
cookies = request.getCookies();
if( cookies != null ){
out.println("<h2> Found Cookies Name and Value</h2>");
for (int i = 0; i < cookies.length; i++){
cookie = cookies[i];
if((cookie.getName( )).compareTo("first_name") == 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/>");
}
}else{
out.println(
"<h2>No cookies founds</h2>");
}
%>
</body>
</html>

Now let us put above code in main.jsp file and try to access it. It would display the following result:

Cookies Name and Value

Deleted cookie : first_name
Name : first_name, Value: John
Name : last_name, Value: Player

Now try to run http://localhost:8080/main.jsp once again and it should display only one cookie as follows:

Found Cookies Name and Value

Name : last_name, Value: Player

You can delete your cookies in Internet Explorer manually. Start at the Tools menu and select Internet Options.

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