Servlet Cookie processing

Cookie is a text file stored on the client computer and retains a variety oftracking information. Java Servlet clearly supports HTTP Cookie.

Identifying the returned user consists of three steps:

The server script sends a set of Cookie to the browser. For example: name, age or identification number, etc.
Browsers store this information on the local computer for future use.
The next time the browser sends any request to the Web server, the browser sends this Cookie information to the server, which the server uses to identify the user.

This chapter shows you how to set or reset Cookie, how to access them, and how to delete them.

Servlet Cookie processing requires encoding and decoding of Chinese as follows:

String   str   =   java.net.URLEncoder.encode("Chinese"，"UTF-8");            //code
String   str   =   java.net.URLDecoder.decode("Encoded string","UTF-8");   // code

Servlet Cookie method

Serial number	Method & description
1	`public void setDomain(String pattern)` this method sets the domain to which cookie applies, such as runoob.com.
2	`public String getDomain()` this method gets the domain to which cookie applies, such as runoob.com.
3	`public void setMaxAge(int expiry)` this method sets the time in seconds when the cookie expires. If this is not set, cookie will only persist in the current session session.
4	`public int getMaxAge()` this method returns the maximum lifetime of the cookie in seconds, and by default,-1 means that the cookie will continue until the browser is closed.
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 sets 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 the cookie applies. If you do not specify a path, all URL in the same directory as the current page (including subdirectories) will return cookie.
9	`public String getPath()` this method gets the path to which cookie is applicable.
10	`public void setSecure(boolean flag)` this method sets a Boolean value indicating whether cookie should be sent only on encrypted (that is, SSL) connections.
11	`public void setComment(String purpose)` set the comments for cookie. Thiscomment is useful when the browser renders the cookie to the user.
12	`public String getComment()` gets the comment of cookie, and returns null if cookie has no comment.

The following is a list of useful methods that can be used to manipulate Cookie in Servlet.

Set up Cookie through Servlet

Setting up Cookie through Servlet involves three steps:

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

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

Remember that neither the name nor the value should contain spaces or any ofthe following characters:

[ ] ( ) = , " / ? @ : ;

(2)set the maximum life cycle: you can use the setMaxAge method to specify cookie the time (in seconds) that can be kept valid. The following will set a maximum validity period of 24 hours cookie .

cookie.setMaxAge(60*60*24);

(3)send Cookie to HTTP response header: you can use the response.addCookie to add the Cookie in the HTTP response header, as follows:

response.addCookie(cookie);

Example

Let’s modify our form data instance to set the Cookie for the first and lastname.

package com.runoob.test;

import java.io.IOException;
import java.io.PrintWriter;
import java.net.URLEncoder;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Servlet implementation class HelloServlet
 */
@WebServlet("/HelloForm")
public class HelloForm extends HttpServlet {
    private static final long serialVersionUID = 1L;

    /**
     * @see HttpServlet#HttpServlet()
     */
    public HelloForm() {
        super();
        // TODO Auto-generated constructor stub
    }

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException
    {
        // Create cookies for first and last names
        Cookie name = new Cookie("name",
                URLEncoder.encode(request.getParameter("name"), "UTF-8")); // Chinese transcoding
        Cookie url = new Cookie("url",
                      request.getParameter("url"));

        // Set the expiration date for two cookies to 24 hours later
        name.setMaxAge(60*60*24);
        url.setMaxAge(60*60*24);

        // Add two cookies to the response header
        response.addCookie( name );
        response.addCookie( url );

        // Set response content type
        response.setContentType("text/html;charset=UTF-8");

        PrintWriter out = response.getWriter();
        String title = "Set Cookie Instance";
        String docType = "<!DOCTYPE html>\n";
        out.println(docType +
                "<html>\n" +
                "<head><title>" + title + "</title></head>\n" +
                "<body bgcolor=\"#f0f0f0\">\n" +
                "<h1 align=\"center\">" + title + "</h1>\n" +
                "<ul>\n" +
                "  <li><b>site name：</b>："
                + request.getParameter("name") + "\n</li>" +
                "  <li><b>site URL：</b>："
                + request.getParameter("url") + "\n</li>" +
                "</ul>\n" +
                "</body></html>");
        }

    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        doGet(request, response);
    }

}

Compile the Servlet above HelloForm and in the web.xml create the appropriate entry in the file:

<?xml version="1.0" encoding="UTF-8"?>
<web-app>
  <servlet>
    <!-- Class name -->
    <servlet-name>HelloForm</servlet-name>
    <!-- The package it is in -->
    <servlet-class>com.runoob.test.HelloForm</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>HelloForm</servlet-name>
    <!-- Visited website -->
    <url-pattern>/TomcatTest/HelloForm</url-pattern>
  </servlet-mapping>
</web-app>

Finally, try the following HTML page to call Servlet.