Session management by Cookies

A cookie is one of the most common ways to track a user on internet and maintain a user's session. Cookie is a text file using which you can store the information in user's browser and access it when you need it. This makes cookie one of the techniques to maintain a user's session and to differentiate a user from the others. You can even specify the duration for which this Cookie file is going exist before it gets deleted by the browser.

Java Servlet Technology allows us to perform user's session management using its Cookie class.

Constructor of Cookie class

Constructor	Description
void *Cookie(String* name, String value)**	Constructs a Cookie with a name and a value.

How to add a cookie

We can add cookie in the client's system by calling the addCookie() method of HttpServletResponse interface by using the response object.

Method	Description
void *addCookie(String* name, String value)**	Adds a cookie within the client's browser.

Some useful methods of Cookie class.

The methods in the table below are part of javax.servlet.http.Cookie class, hence these methods are available to the object of Cookie class.

Methods	Description
void *setDomain(String* name)**	Sets the domain name which will be associated with the Cookie.
String getDomain()	Returns the domain name associated with the Cookie.
void *setMaxAge(int* expiry)**	Sets the maximum time(in seconds) till the Cookie lasts.
int getMaxAge()	Returns the maximum time(in seconds) till the Cookie lasts.
void *setComment(String* message)**	Sets a message/comment describing the Cookie.
String getComment()	Returns the message describing the Cookie.
void *setValue(String* value)**	Sets the value of the Cookie that is already created.
String getValue()	Returns the value of the Cookie.

Creating a webpage which calls the Servlet

We are creating a webpage which asks the user to enter the name and city and press the submit button, which when clicked calls the Servlet with the <url-pattern> SaveCookie, specified in the deployment descriptor file(web.xml), passing this Servlet the parameters named username and cityname, using default get method.

Form1.htm

<html>

<head>
<title> Cookies Demo </title>
</head>


<body>
<b>Please enter your details :</b>

<br/>
<br/>

<form action = "SaveCookie" >
Name : <input  type = "text" name = "username"/>
City : <input type = "text"   name = "cityname" />
<input  type = "submit" name = "submit"/>
</form>

</body>
</html>

Creating, setting the Cookie using Servlet

In this Servlet, we are going to -

create a cookie using the Cookie.
Set a cookie, by calling a method addCookie() of HttpServletResponse's response object.
Asking a user to click hyperlinks to read or delete the cookie, which was just set. Clicking on any of these hyperlinks will call the specific Servlet to read or delete the set cookie.

MyServlet1.java

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

public class MyServlet1 extends HttpServlet
{

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

String name = request.getParameter("username");
String city = request.getParameter("cityname");


//Creating a Cookie object to maintain a session
Cookie cookie = new Cookie(name, city);


//Setting the cookie in the client browser
response.addCookie(cookie);

out.println("<br/>");

out.println(" Do you want to read the Cookie?");
out.println(" If yes, please visit <a href ='ReadCookie'/> Read the Cookie</a> ");

out.println("<br/>");

out.println("Do you want to delete the Cookie? if yes, please visit the  <a href ='DeleteCookie'/> Delete the Cookie</a>");

}
}

reads the cookie

MyServlet1.java

MyServlet2.java

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

public class MyServlet2 extends HttpServlet
{

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

out.println("<h2>Reading Cookies</h2>");

Cookie[] array= request.getCookies();
for(int i=0; i<array.length; i++)
{
out.println("<br/>");
out.println("Name of the cookie : " + array[i].getName() + "<br/>");
out.println("Value in cookie : " + array[i].getValue());
}

}
}

deletes the cookie

MyServlet1.java

DeleteCookie.jsp

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

public class MyServlet3 extends HttpServlet
{

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

out.println("<h2>Deleting Cookies</h2>");

Cookie[] array= request.getCookies(); 
for(int i=0; i<array.length; i++)
{
out.println("<br/>");
out.println("Name of the cookie : " + array[i].getName() + "<br/>");
out.println("Value in cookie : " + array[i].getValue());

//Deleting the cookie
array[i].setMaxAge(0);
response.addCookie(array[i]); //After this, although cookie will be not be visible from browser's memory
			      //but Cookie data will still be visible until you refresh this page.
}

}
}

Directory Structure of Servlet files

Project Folder - We have created a project folder named CookiesEx within the webapps folder of Tomcat installation folder. This folder contains the Servlet class(.java) file and WEB-INF folder.

WEB-INF - Within your project folder, you create another folder named WEB-INF and this folder should contain the deployment descriptor file(web.xml) of your Java Servlet program.

classes - Within the WEB-INF folder you should create a folder named classes. This folder should contain the compiled(.class) form of your Java Servlet class.

Creating the Deployment Descriptor file

XML

web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee
                      http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
  version="4.0"
  metadata-complete="true">

  <display-name>Welcome tomcat</display-name>
  <description>
     Welcome tomcat
  </description>

  
<servlet>
 	<servlet-name>FirstServlet</servlet-name>
	<servlet-class>MyServlet1</servlet-class>
</servlet>



<servlet-mapping>
	<servlet-name>FirstServlet</servlet-name>
	<url-pattern>/SaveCookie</url-pattern>
</servlet-mapping>




<servlet>
 	<servlet-name>SecondServlet</servlet-name>
	<servlet-class>MyServlet2</servlet-class>
</servlet>



<servlet-mapping>
	<servlet-name>SecondServlet</servlet-name>
	<url-pattern>/ReadCookie</url-pattern>
</servlet-mapping>





<servlet>
 	<servlet-name>ThirdServlet</servlet-name>
	<servlet-class>MyServlet3</servlet-class>
</servlet>



<servlet-mapping>
	<servlet-name>ThirdServlet</servlet-name>
	<url-pattern>/DeleteCookie</url-pattern>
</servlet-mapping>





</web-app>

deployment descriptor

<servlet>

<servlet-name>

<servlet-class>

<servlet-name> tag is used to specify a unique name for our Servlet class.

<servlet-class> tag is used to specify the full qualified name of the Servlet class .

Note

<servlet-name>

<servlet>

<servlet-name>

<servlet-mapping>

<url-pattern>

URL

We have named this URL Serv1. to access the first servlet, MyServlet1.java
We have named this URL ReadCookie. to access the first servlet, MyServlet2.java
We have named this URL DeleteCookie. to access the first servlet, MyServlet3.java

Setting the classpath

classpath

servlet-api.jar

lib

Tomcat installation folder

C: Drive

lib

servlet-api.jar

C:\apache-tomcat-9.0.2\lib

You could set the classpath by entering this command at the Command Prompt, but this only temporarily sets the classpath to the path of servlet-api.jar file. If you restart your system, you will have to set the classpath again.
```
set classpath=C:\apache-tomcat-9.0.2\lib\servlet-api.jar
```
In order to set the classpath permanently, you need to set your classpath system variables. A simple tutorial on how to permanently set the classpath system variables, you may read How to permanently set the classpath system variable

Compiling the Servlet class

javac -d WEB-INF/classes MyServlet1.java

javac -d WEB-INF/classes MyServlet2.java

javac -d WEB-INF/classes MyServlet3.java

Executing the Servlet

We are creating a webpage which asks the user to enter his/her name and city and press the submit button.
On entering the details and clicking the submit button calls the Servlet with the <url-pattern> SaveCookie, specified in the deployment descriptor file(web.xml), passing this Servlet the parameter named username and cityname, using the default get method.

Next, on clicking Read the Cookie link calls the Second Servlet which reads the cookie and displays the value present in this Cookie.

Deleting a Cookie using JSP

First, by calling the setMaxAge() method of Cookie class and passing it a zero(0) in its parameters, which sets the cookie age to zero seconds.
Next, by calling addCookie() method of response object deletes the cookie from the browser's memory, as shown below.

MyServlet3.java

MyServlet1.java

Let's go back to the same example and say - after saving the cookie, what would have happened, had we clicked the DeleteCookie hyperlink.
Next, on clicking Delete the Cookie link calls the MyServlet3 Servlet with the <url-pattern> DeleteCookie as specified in web.xml. This Servlet deletes the cookie but the value in this cookie is displayed the first time this page loads.

Next, on refreshing the page, the values associated with the cookie are not displayed because this cookie is deleted from the browser's memory.

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