Cookies In Servlet

A cookie is a small piece of records that is continued among a couple of client requests.

A cookie has a identity, a single value, and non-obligatory attributes together with a comment, course and domain qualifiers, a most age, and a model number.

How Cookie works

By default, every request is taken into consideration as a new request. In cookies technique, we upload cookies with reaction from the servlet. So the cookie is saved withinside the cache of the browser. After that if the request is dispatched via way of means of the consumer, cookie is brought with request via way of means of default. Thus, we apprehend the consumer because the antique consumer.

Types Of Cookies:

Two types of Cookies are there in Servlets that are:

1.Non Persistent Cookies

2.Persistent Cookies

Non Persistent Cookies

It is legitimate for a single session only. It is eliminated every time the user closes the browser.

Persistent Cookies

It is legitimate for more than one session . It isn't eliminated every time the user closes the browser. It is eliminated most effectively if user logout or signout.

Benefits Of Cookies

• Simplest approach of keeping the state.
• Cookies are maintained at the purchaser side.

Disadvantage of Cookies

• It will now no longer paint if the cookie is disabled from the browser.
• Only textual facts may be set in the Cookie object.

Cookie Class

Javax.servlet.http.Cookie class presents the capability of the usage of cookies. It presents a whole lot of beneficial techniques for cookies.

Constructor of Cookie class

Useful Methods of Cookie Class:

Some commonly used methods of the Cookie class are Given Below:

Some Other methods required for using cookies

We need some ways provided by other interfaces for adding cookies or getting the value from the cookie. They are:

• public void addCookie(Cookie ck): ways of HttpServletResponse interface are made use to add cookies in response objects.
• public Cookie[] getCookies(): ways of HttpServletRequest interface are used to return all the cookies from the browser.

How to create a Cookie?

Simple code to create a cookie is here let’s see:

Cookie ck=new Cookie("user","sonoo jaiswal");//creating cookie object  
response.addCookie(ck);//adding cookie in the response  

How to delete a cookie?

It is mainly used to logout or sign out the user. Let’s see Simple code to create a cookie is here

Cookie ck=new Cookie("user","");//deleting value of cookie  
ck.setMaxAge(0);//changing the maximum age to 0 seconds  
response.addCookie(ck);//adding cookie in the response  

How to get cookies?

Easy code to get the cookies is here let’s see

Cookie ck[]=request.getCookies();  
for(int i=0;i<ck.length;i++){  
 out.print("<br>"+ck[i].getName()+" "+ck[i].getValue());//printing name and value of cookie  
} 

Simple Example of Servlet Cookies

In this example, we are storing the name of the user within the cookie object and accessing it in another servlet. As we all know well that session corresponds to the actual user. So if you access it from too many browsers with different values, you'll get various values.

Index.html

<form action="servlet1" method="post">  
Name:<input type="text" name="userName"/><br/>  
<input type="submit" value="go"/>  
</form>

FirstServlet.java

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

public class FirstServlet extends HttpServlet {  

  public void doPost(HttpServletRequest request, HttpServletResponse response){  
    try{   

    response.setContentType("text/html");  
    PrintWriter out = response.getWriter();  
          
    String n=request.getParameter("userName");  
    out.print("Welcome "+n);   

    Cookie ck=new Cookie("uname",n);//creating cookie object  
    response.addCookie(ck);//adding cookie in the response  
  
    //creating submit button  
    out.print("<form action='servlet2'>");  
    out.print("<input type='submit' value='go'>");  
    out.print("</form>");  
          
    out.close();   

        }catch(Exception e){System.out.println(e);}  
  }  
}  

SecondServlet.java

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

public class SecondServlet extends HttpServlet {   

public void doPost(HttpServletRequest request, HttpServletResponse response){  
    try{   

    response.setContentType("text/html");  
    PrintWriter out = response.getWriter();        

    Cookie ck[]=request.getCookies();  
    out.print("Hello "+ck[0].getValue()); 

    out.close();  
         }catch(Exception e){System.out.println(e);}  
    }        

}  

Web.xml

<web-app>  

<servlet>  
<servlet-name>s1</servlet-name>  
<servlet-class>FirstServlet</servlet-class>  
</servlet>  

<servlet-mapping>  
<servlet-name>s1</servlet-name>  
<url-pattern>/servlet1</url-pattern>  
</servlet-mapping>  

<servlet>  
<servlet-name>s2</servlet-name>  
<servlet-class>SecondServlet</servlet-class>  
</servlet>  
  
<servlet-mapping>  
<servlet-name>s2</servlet-name>  
<url-pattern>/servlet2</url-pattern>  
</servlet-mapping>   

</web-app>

Output