Session & cookie details

conversation

conversation : When the browser opens , Access to the server Indicates the beginning of the session
Session in progress : Communication between browser and server ( One communication Multiple communications )
End of session : When the browser closes , End of session
Session problems : Data generated in the session Need to save
A session is a process of interaction between a browser and a server , Data must be generated in the session , Valid data and invalid data , Valid data may need to be saved , Memory of the saved location , Hard disk . We can exist on the browser side perhaps Server side

Conversational Technology

Conversational Technology :
​ effect : Save the data
​ Browser side technology : cookie
​ Server side technology : session

cookie

Session level cookie

OneServlet

public class OneServlet extends HttpServlet {
    
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    

    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    
        System.out.println("OneServlet");

        //1. There is data to save   establish cookie
        Cookie cookie = new Cookie("ds" , "meimei");
        //2. take cookie Respond to the browser 
        response.addCookie( cookie  );
    }
}

TwoServlet

public class TwoServlet extends HttpServlet {
    
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    

    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    
        System.out.println("TwoServlet");
        // Get the information delivered by the browser cookie
        Cookie[] cookies = request.getCookies();
        // Traversing an array 
        // All... Contained in this request  Cookie  Array of , If the request does not  cookie, Then return to  null
        if(cookies != null ){
    
            // Traverse cookie
            //Idea-a04ab689 @@ b23c0a93-4c5e-4a7e-9125-9dbc273d9498
            // This is idea Version problem   Some versions produce a cookie
            for (Cookie cookie : cookies) {
    
                //name  Express cookie The name of  value Express cookie Value 
                System.out.println( cookie.getName() +" @@ "+cookie.getValue() );
            }
        }else{
    
            System.out.println(" No, cookie data ");
        }
    }
}

Summary :

The default browser closes cookie disappear , Conversation level cookie , End of session cookie It doesn't work
Cookie cookie = new Cookie(name , value); establish cookie
response.addCookie( cookie ); Respond to cookie
Cookie[] cookies = request.getCookies(); get cookie
cookie Is saved in the browser , Different browsers Cannot share cookie

Persistence level cookie

cookie.setMaxAge( Time ); Set up cookie Maximum survival time Unit second
cookie.setPath( ) Set the path

cookie Details

/** * cookie Small details of : * 1.cookie  No Chinese support  , tomcat8 I've dealt with  tomcat 7  Not dealt with  ( No Chinese support ) * 2.cookie  follow 423 The rules of ( The old saying goes ) * 4 Express 4kb: cookie The length of should not be too long   Maximum 4kb( Precise ) * 2 Express 20 individual :  A website supports the largest cookie Number 20 individual  ( Imprecise ) * 3 Express 300 individual :  The whole browser   All the websites add up cookie 300 individual ( Imprecise ) * @param request * @param response * @throws ServletException * @throws IOException */
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    
        System.out.println("OneAPIServlet");

        //1. There is data to save   establish cookie
        Cookie cookie = new Cookie("ds" , " ha-ha ");

        // Set up cookie Properties of 
        // Set up cookie Maximum effective lifetime   Company : second 
        cookie.setMaxAge( 0 );

        /** *  Set up path route  * path The meaning is : * 1. Indicates that the request is sent to the server again  cookie Basis for automatic carrying   Must satisfy  path  Or path All subdirectories are OK  * path : localhost/day05 * localhost:8080/day05/a/b/c  resources   It'll carry it automatically cookie  subdirectories  * localhost:8080/day05/a  resources   It'll carry it automatically cookie  Same path  * localhost:8080/day05/a/a.html  resources   It'll carry it automatically cookie  subdirectories  * localhost:8080/day06/a  resources   Will not automatically carry cookie  Does not conform to the path  * www.baidu.com:8080/day06/a  resources   Will not automatically carry cookie  Does not conform to the path  * 2.path  and  name  decision cookie Is it the only  * cookie You can have the same name locally   As long as it is placed path The path is different  *  Summary : Be careful , When setting the path later   General advice  cookie.setPath("/");  Try not to carry the project name  *  A company   Ten projects   Ten projects cookie Suggestions are shared  *  Set to  localhost/  Subsequent projects  localhost/day05 localhost/day06  You can visit this cookie * *  problem 1: If it covers cookie? * name + path  Must follow the previous cookie Corresponding  *  problem 2: How to delete cookie? * (name + path)  Cover  +  Time ( Lapse immediately )  No direct deletion cookie Of api */
        cookie.setPath("/");

        //2. take cookie Respond to the browser 
        response.addCookie( cookie  );
    }

Record the last visit time

/** *  Output the last access time of the user  ,  Record the user's current login time  * @param request * @param response * @throws ServletException * @throws IOException */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    
    	// Prevent confusion code 
     	request.setCharacterEncoding("utf-8");
        response.setContentType("text/html;charset=utf-8");
        //1. Determine whether the user is visiting for the first time or for the second time N visit 
        // get cookie
        Cookie[] cookies = request.getCookies();

        boolean flag = false;  // The default is false

        String cookieValue = null;// Define a cookie Value 
        if(cookies != null ){
    // The first visit or the N visit   It doesn't mean the first time   Nor does it mean that N Time   Not sure 
            // There are other cookie  for example  ds  But it's not lastTime
            for (Cookie cookie : cookies) {
    
                if( "lastTime".equals(cookie.getName()) ){
    // If you can get into if It means   There is last time   It means the first one N visit 
                    cookieValue = cookie.getValue();
                    flag=true;
                }//else{// First visit ?  hypothesis  ds dzd username lastTime nickname
                //}
            }
        }//else{// First visit   No, cookie signify   No,  lastTime  First visit 
        //}

        if(flag == true ){
     // The first N visit 
            //3. The first N visit   Output your last access time as ....
            // Get the last visit time 
            // The result is the result before coding   Must also decode 
            String decode = URLDecoder.decode(cookieValue, "utf-8");
            System.out.println(" Your last visit was :"+ decode +" @@" +cookieValue );

            // Overwrite the local time again   Cover cookie On the condition that  : path + name  As like as two peas 
            String date = new Date().toLocaleString();// Creation time 
            String encode = URLEncoder.encode(date, "utf-8");//  code 
            Cookie cookie = new Cookie("lastTime" , encode);
            cookie.setMaxAge(60*60); // Set the effective time 
            cookie.setPath("/");// Set the path 
            response.addCookie( cookie );

        }else{
     //  First visit 
            //2. First visit   Output is your first visit 
            // Report errors :java.lang.IllegalArgumentException: An invalid character [32] was present in the Cookie value
            //cookie Not all special symbols are supported   code  :  Change the original characters into other symbols   To restore symbols   Decode it 
            String date = new Date().toLocaleString();
            // code : use URL code  (jdk Bring your own tools )
            // Parameters 1: A string that needs to be encoded   Parameters 2:  Later decoded code table 
            String encode = URLEncoder.encode(date, "utf-8");

            System.out.println(" This is the first time you access the time before compilation :" +date + " @@  Time after compilation :" +encode );
            Cookie cookie = new Cookie("lastTime" , encode);
            cookie.setMaxAge(60*60); // Set the effective time 
            cookie.setPath("/");// Set the path 
            response.addCookie( cookie );
        }
    }