Cookie＆Session

Hello, everyone , I'm Xiao Sheng , Let me share with you my study Javaweb The notes

Web Develop conversation technology

What is conversation ？

Conversation can be simply understood as ： Users open a browser , Click on multiple hyperlinks , Access multiple servers web resources , Then close the browser , The whole process is called a conversation

Two techniques of conversation

Cookie

Concept ：Cookie The server saves the user's information on the client , Like login name , Browse history, etc , You can to cookie Way,

cookie Frame diagram

Cookie The role of

• Save the last login time and other information
• Save user name , password , You don't have to log in again for a certain time
• Personalization of the website , For example, customized website services , Content

Read Cookie data

1. Browser side creation email=1079936135qq.com The data of

   

2. Browser transfers to server Cookie data

   

3. The server read Cookie data

   protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
         
       Cookie[] cookies = request.getCookies();
       if(cookies != null && cookies.length != 0){
         
           for (Cookie coke : cookies) {
         
               // cookieName: email cookieValue1079936135
               // cookieName: Idea-6463f311 cookieValue6cb7445e-85d8-4a31-a12a-bcdbe5c375d9
               //  If you read the Chinese name 
               //  Can pass URLDecoder.decode(coke.getName(),"utf-8") decode 
               System.out.println("cookieName: " + coke.getName() + " cookieValue" + coke.getValue());
           }
       }
   }
   

establish Cookie example

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    
    System.out.println("cookie Called ");
    //  establish Cookie object 
    //  Solve the reason why Chinese cannot be stored , Need to carry out url code 
    String data = URLEncoder.encode(" Niansheng ","UTF-8");
    Cookie cookie = new Cookie("username",data);
    // take Cookie Send to browser and save 
    response.addCookie(cookie);
    response.setContentType("text/html;charset=utf-8");
    PrintWriter writer = response.getWriter();
    writer.write("<h1>Cookie Create success !</h1>");
    writer.flush();
    writer.close();
}

modify Cookie value

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    
    Cookie[] cookies = request.getCookies();
    String cookieName = "email";
    Cookie cookie = CookieUtils.nameToGetCookie(cookieName, cookies);
    CookieUtils.IterCookie(cookies);
    if(cookie == null){
    
        System.out.println(" There is no the Cookie");
    }else{
    
        cookie.setValue("[email protected]");
        CookieUtils.IterCookie(cookies);
        response.addCookie(cookie);
    }
}

//  Tool class 
public class CookieUtils {
    
    /** *  adopt CookieName To get the corresponding Cookie */
    public static Cookie nameToGetCookie(String cookieName,Cookie[] cookies){
    
        if(cookieName != null && !cookieName.equals("") && cookies != null && cookies.length != 0){
    
            for (Cookie cookie : cookies) {
    
                if(cookie.getName().equals(cookieName)){
    
                    return cookie;
                }
            }
        }
        return null;
    }

    /** *  Traverse Cookie, Show Cookie Of name-value */
    public static void IterCookie(Cookie[] cookies){
    
        System.out.println();
        if(cookies != null && cookies.length != 0){
    
            for (Cookie cookie : cookies) {
    
                System.out.println("cookieName: " + cookie.getName() + " cookieValue: " + cookie.getValue());
            }
        }
        System.out.println();
    }
}

cookie Life cycle

Common methods

//  Positive numbers , Represents an expiration after a specified number of seconds 
//  negative , Indicates that the browser is closed  Cookie  It will be deleted （ The default value is -1）
// 0, Delete immediately  Cookie ( Can be used to delete Cookie)
setMaxAge()

Code example

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    
    //  Create a new Cookie object 
    Cookie cookie = new Cookie("age","18");
    //  Set up Cookie Life cycle of  20s
    cookie.setMaxAge(20);
    //  Return to the browser to store 20s 
    response.addCookie(cookie);
}

cookie Effective path

Cookie Of path Attributes can effectively filter which Cookie Can be sent to the server , Which don't . path Attributes are effectively filtered through the requested address

//  Illustrate with examples  ( Default setPath:/ Project path  )
cookie1.setPath = / Project path  
cookie2.setPath = / Project path /aaa 
    
// url Request address : http://ip: port / Project path / resources  
cookie1  It will be sent to the server  
cookie2  It will not be sent to the server  
    
// url Request address : http://ip: port / Project path /aaa/ resources  
cookie1  It will be sent to the server  
cookie2  It will be sent to the server 

Cookie Notes and details

1. One Cookie Only one message can be identified , It contains at least one name that identifies the information （NAME） And settings （VALUE）

2. One WEB Sites can send multiple messages to a browser Cookie, A browser can also store multiple WEB The site provides Cookie

3. Cookie There is no limit to the total number of , But for each domain name Cookie Quantity and each Cookie There is a limit to the size of ( Different browsers have different restrictions ) , Cookie Not suitable for storing information with large amount of data

4. Pay attention to Chinese deposit cookie Need to encode and decode

   // url code 
   String data = URLEncoder.encode(" Chinese you want to deposit ","UTF-8");
   Cookie cookie = new Cookie("username",data);
   //url decode 
   URLDecoder.decode(cookie data ,"utf-8");
   

Session

Basic introduction

Concept ：Session It's server-side technology , The server creates an exclusive browser for each user at run time session object / aggregate , because session Exclusive for each user browser , So when users visit different pages of the server , From their own Of session Read from / Add data

session The default existence time of the object is 30min

<!-- ==================== Default Session Configuration ================= -->
<!-- You can set the default session timeout (in minutes) for all newly -->
<!-- created sessions by modifying the value below. -->
<!-- Tomcat in web.xml File can be configured with time , Default 30min -->
<session-config>
    <session-timeout>30</session-timeout>
</session-config>

Session The role of

• Put data into Session in , For users to access different pages , Achieve cross page access to data
• Save login user information
• Prevent users from illegally logging in to a page, and so on

session Storage structure diagram

name （key）	value （value）
String type	Object type

Common methods

// 1. Create and get  Session
//  The first 1 The next call is to create  Session  conversation ,  After that, the call is created and created.  Session  object  
HttpSession hs=request.getSession(); 
// 2. towards  session  Add attribute  
hs.setAttribute(String name,Object val); 
// 3. from  session  Get an attribute  
Object obj=hs.getAttribute(String name);
// 4. from  session  Delete a property : 
hs.removeAttribute(String name); 
// 5. Judge whether it has just been created  Session
hs.isNew(); 
// 6. Every Session There are 1 A unique identity Id value , adopt getId() obtain Session Conversation id value (JSESSIONID)

Schematic diagram

JSESSIONID

Used by the server to identify different sessions , Different sessions , The server will create different JSESSIONID

Frame diagram

Example of operation code

Set properties

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    
    response.setContentType("text/html;charset=utf-8");
    PrintWriter writer = response.getWriter();
    HttpSession session = request.getSession();
    session.setAttribute("id","1234956789");
    System.out.println(" Property setting complete ");
    writer.flush();
    writer.close();
}

read attribute

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    
    response.setContentType("text/html;charset=utf-8");
    PrintWriter writer = response.getWriter();
    HttpSession session = request.getSession();
    Object s = session.getAttribute("id");
    if(s != null){
    
        System.out.println((String)s);
    }else{
    
        System.out.println(" No attribute ");
    }
    writer.flush();
    writer.close();
}

session Life cycle

Session The life cycle of is ： client / The maximum interval between two browser requests is , Not the cumulative length of time . That is, when the client accesses its own session,session The life cycle of will start from 0 Start recalculating .( The interval between two requests in the same session )

Bottom : Tomcat Polling session status with a thread , If the idle time of a session exceeds the set maximum , Destroy the session

//  Set up  Session  Timeout for （ In seconds ）,  Exceeded the specified duration ,Session  Will be destroyed 
// 1. When the value is positive , Set up  Session  The timeout period of 
// 2. Negative numbers never time out 
// 3. If not called  setMaxInactiveInterval()  To specify the Session Life span of ,Tomcat  Will Session The default duration shall prevail ,Session  The default timeout is 30 minute , Can be in tomcat Of web.xml Set up ; Be careful Cookie Is the cumulative duration , When time comes, it will be destroyed 
public void setMaxInactiveInterval(int interval)
//  obtain  Session  Timeout for 
public int getMaxInactiveInterval()
//  Let the current  Session  The session is immediately invalid 
public void invalidate()

Classic case

Prevent illegal access to the management page

• login.html Submit the form to LoginCheckServlet.java
• If the validation is successful （ User name is not empty , The password for 666666,）, Then enter the management page ManageServelt.java, If the verification is not successful , Jump to error.html page
• If the user has direct access to ManageServet.java , Redirect to login.html

<!-- login.html -->
<!DOCTYPE html>
<html lang="en">
    <head>
        <meta charset="UTF-8">
        <title> The user login </title></head>
    <body><h1> The user login </h1>
    <form action="/session/loginCheck" method="post">
         user name ：<input type="text" name="username"/><br/><br/>
         The secret   code ：<input type="password" name="password"><br><br/>
        <input type="submit" value=" Sign in ">
    </form>
    </body>
</html>

<!-- error.html -->
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
    <h1> Login failed </h1>
    <a href="login.html" style="text-decoration: none"> Click back to log in again </a>
</body>
</html>

// LoginCheckServlet.java
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    
    String username = request.getParameter("username");
    String password = request.getParameter("password");
    if(username != null && password != null){
    
        if(!"".equals(username) && "666666".equals(password)){
    
            HttpSession session = request.getSession();
            session.setAttribute("username",username);
            request.getRequestDispatcher("/manageServlet").forward(request,response);
        }else{
    
            request.getRequestDispatcher("/error.html").forward(request,response);
        }
    }else{
    
        response.sendRedirect("/login.html");
    }
}

// ManageServlet.java
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    
    HttpSession session = request.getSession();
    Object username = session.getAttribute("username");
    if(username != null){
    
        response.setContentType("text/html;charset=utf-8");
        PrintWriter writer = response.getWriter();
        writer.println("<h1> User management page </h1>");
        writer.println(" Welcome , Administrators : " + (String)username);
        writer.flush();
        writer.close();
    }else{
    
        response.sendRedirect("/session/login.html");
    }
}