Javaweb Session Management: (1) cookies

Session Technology

Serial Number	name	Data Storage location
1	Cookie Technology	Session data is saved in the browser client.
2	Session Technology	Session data is saved on the server side.

1. Cookie Technology

1.1. Features

Cookie Technology: Session data is saved in the browser client.

1.2. The core of Cookie technology

Cookie class: Used to store session data.

Cookie Core API

Serial Number	category	API
1	Constructing Cookie Objects	Cookie (string name, String value)
2	Set cookies	void SetPath (String uri): Sets the valid access path for the cookie void setmaxage (int expiry): Set the effective time of the cookie void SetValue (String newvalue): Sets the value of the cookie
3	Send cookies to browser-side save	void Response.addcookie (Cookie cookie): Sending a cookie
4	Server receives cookies	Cookie[] Request.getcookies (): Receive cookies

1.3. Cookie principle

1) The server creates a cookie object that stores session data in a cookie object.

Cookie cookie = new Cookie ("username", "Lsieun");

2) The server sends cookie information to the browser

Response.addcookie (cookie);

Example: Set-cookie:username=lsieun (hides the response header that sent a set-cookie name)

650) this.width=650; "src=" Http://s3.51cto.com/wyfs02/M00/80/E9/wKiom1dET13SkYAjAAAhwbM8yHY063.png "title=" Response_header_set_cookie.png "alt=" Wkiom1det13skyajaaahwbm8yhy063.png "/>

3) The browser gets the cookie sent by the server and then saves it on the browser side.

4) The browser will take cookie information the next time it accesses the server

Example: Cookie:username=lsieun (hide with a request header called Cookie name)

650) this.width=650; "src=" Http://s4.51cto.com/wyfs02/M00/80/E8/wKioL1dEUGnwsVLFAABo6ekUy70072.png "title=" Request_header_cookie.png "alt=" Wkiol1deugnwsvlfaabo6ekuy70072.png "/>

5) The server receives the cookie information that the browser brings

cookie[] cookies = request.getcookies ();//Receive cookies sent by the browser if (cookie = null) {for (cookie c:cookies) {String cookiename = C.getname (); String cookievalue = C.getvalue (), int cookieage = C.getmaxage (); Out.write (CookieName + ":" + Cookievalue + ", Age:" + C ookieage);}}

Complete code: Demo01.java

Package Com.rk.http.a_cookie;import Java.io.ioexception;import Javax.servlet.servletexception;import Javax.servlet.http.cookie;import Javax.servlet.http.httpservlet;import javax.servlet.http.HttpServletRequest; Import javax.servlet.http.httpservletresponse;/** * Send cookies to Browser * @author Lsieun * */public class Demo01 extends Httpserv let{@Overrideprotected void doget (HttpServletRequest request, httpservletresponse response) throws Servletexception, Ioexception{cookie cookie = new Cookie ("username", "Lsieun");//Create Cookie Object Response.addcookie (cookie);// Send cookie data to browser System.out.println ("Cookie Saved!!!");}}

Complete code: Receivecookie.java

package com.rk.http.a_cookie;import java.io.ioexception;import java.io.printwriter;import  javax.servlet.servletexception;import javax.servlet.http.cookie;import  javax.servlet.http.httpservlet;import javax.servlet.http.httpservletrequest;import  javax.servlet.http.httpservletresponse;/** *  receive cookie *  @author from the browser  lsieun *  */public class receivecookie extends httpservlet{@Overrideprotected  void  Doget (Httpservletrequest request, httpservletresponse response)  throws  Servletexception, ioexception{response.setcharacterencoding ("Utf-8"); Response.setcontenttype ("text/html; Charset=utf-8 "); Printwriter out = response.getwriter (); Cookie[] cookies = request.getcookies ();//Receive cookie information sent by browser if (cookies != null)// Note: Determine if null,  otherwise null pointer {out.write ("
package com.rk.http.a_cookie;import java.io.ioexception;import java.io.printwriter;import  javax.servlet.servletexception;import javax.servlet.http.httpservlet;import  Javax.servlet.http.httpservletrequest;import javax.servlet.http.httpservletresponse;public class  HeaderCookie extends HttpServlet{private int count = 0; @Overrideprotected  void doget (Httpservletrequest request, httpservletresponse response)  throws  servletexception, ioexception{response.setcharacterencoding ("Utf-8"); Response.setcontenttype ("text/ Html;charset=utf-8 "); Printwriter out = response.getwriter ();//1. Use GetHeader () to obtain browser cookie information String strcookie  = request.getheader ("cookie"); Out.write ("Cookie information obtained from the browser is:"  + strCookie +  "< Br/> ");int num = 0;synchronized  (Headercookie.class) {count++;num = count;} 2. Use SetHeader () to set cookie information REsponse.setheader ("Set-cookie",  "username" +num+ "=lsieun" +num);}} 



1.4. Details of cookies
1) void SetPath (java.lang.String uri): Sets the valid access path for the cookie.
Valid path refers to where the valid path of a cookie is saved, and the browser takes cookie information when it accesses the server under a valid path, otherwise it does not have cookie information.
2) void Setmaxage (int expiry): Sets the effective time of the cookie.
Positive integer: Indicates that the cookie data is saved in the browser's cache directory (on the hard disk) and the value indicates the time of the save.
Negative integer: Indicates that the cookie data is saved in the browser's memory. Browser Close cookie is lost!!
0: Delete cookie data with the same name
3) The cookie data type can only be stored in non-Chinese string types.
Multiple cookies can be saved, but browsers generally allow only 300 cookies, with a maximum of 20 cookies per site and a limit of 4KB per cookie size.

Sample Code Demo02.java
package com.rk.http.a_cookie;import java.io.ioexception;import javax.servlet.servletexception; import javax.servlet.http.cookie;import javax.servlet.http.httpservlet;import  Javax.servlet.http.httpservletrequest;import javax.servlet.http.httpservletresponse;public class  demo02 extends httpservlet{@Overrideprotected  void doget (httpservletrequest  Request, httpservletresponse response)  throws ServletException, IOException{/**  * 1. Creating a Cookie Object  */cookie cookie1 = new cookie ("username", "Lsieun"); Cookie cookie2 = new cookie ("Password", "123456"); Cookie cookie3 = new cookie ("Email", "[email protected]"); Cookie cookie4 = new cookie ("Hobby", "swiming");/** * 2. Set a valid path for the Cookie. Default: The valid path is under the current Web application.  */cookie1.setpath ("/");//valid path is the root directory of the site Cookie2.setpath (Request.getcontextpath ());//And the following three effects are the same COOKIE3.SETPATh ("/myweb");//cookie4 uses the default value/** * 3. Sets the effective time  *  positive integer of the cookie: indicates that the cookie data is saved in the browser's cache directory (on the hard disk), and the value indicates the time of the save.  *  Negative integer: Indicates that the cookie data is saved in the browser's memory. Browser Close cookie is lost!!  *  0: Delete cookie data with the same name  */cookie1.setmaxage (20);//20 seconds, starting from the last non-invocation of the cookie Cookie2.setmaxage (-1); The cookie is saved in the browser memory (session cookie) cookie3.setmaxage (0);//delete cookie data with the same name//COOKIE4 use the default value/** * 4. Sending cookie data to the browser  */response.addcookie (COOKIE1); Response.addcookie (cookie2); Response.addcookie (COOKIE3); Response.addcookie (COOKIE4);}}


1.5. Case-Shows the last time the user visited
package com.rk.http.a_cookie;import java.io.ioexception;import java.io.printwriter;import  java.text.simpledateformat;import java.util.date;import javax.servlet.servletexception;import  javax.servlet.http.cookie;import javax.servlet.http.httpservlet;import  Javax.servlet.http.httpservletrequest;import javax.servlet.http.httpservletresponse;public class  historycookie extends httpservlet{@Overrideprotected  void doget (httpservletrequest  request, httpservletresponse response)  throws servletexception, ioexception{ Response.setcharacterencoding ("Utf-8"); Response.setcontenttype ("Text/html;charset=utf-8"); Printwriter out = response.getwriter ();/** *  get current time  */SimpleDateFormat  Format = new simpledateformat ("Yyyy-mm-dd hh:mm:ss"); String curtime = format.format (New date ()); Cookie[] cookies = request.getcoOkies (); String lastlogontime = null;if (Cookies != null) {for (cookie c : cookies {if (C.getname () equals ("Lasttime")) {Lastlogontime = c.getvalue ();//1. Display the last access time to the browser out.write ("Welcome back, The last time you visited was: " + lastLogonTime + ", the current time is: " + curtime);//2. Update Cookiec.setvalue ( Curtime); C.setmaxage (1*30*24*60*60);//3. Send the updated cookie to the browser Response.addcookie (c); return;//there is no break. This is because after the break, it jumps out of the current loop, executes the subsequent code, and return exits the current method directly. }}}//first visit (no cookie  or   cookies, but no cookie named Lasttime) if (cookies == null | |  lastlogontime==null) {//1. Displays the current time to the browser out.write ("You are the first to visit this site, the current time is:"  + curTime +  "<br/ >//2. Create a Cookie Object Cookie cookie = new cookie ("Lasttime", Curtime); Cookie.setmaxage (1*30* 24*60*60)//3. Send the cookie to the browser to save the Response.addcookie (cookie);} Else{}}}



Javaweb Session Management: (1) cookies