Session tracking technology

A method of maintaining browser state , The server needs to identify whether multiple requests come from the same browser , To share data between multiple requests in the same session

Cookie:

Client session technology : Save data to client , Every request in the future will carry Cookie Data access

Cookie Basic use

send out Cookie：

1. establish Cookie object , Set up the data

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

2. send out Cookie To client ： Use response object

response.addCookie(cookie)

obtain Cookie

1. obtain Cookie Array

Cookie[] cookies = request.getCookies();

2. Traversal array

for (Cookie c :cookies
) {
    String name = c.getName();
    if ("username".equals(name)) {
//3. obtain Cookie data 
        String value = c.getValue();
        System.out.println(name+":"+value);
    }
}

Cookie principle

Cookie The implementation is based on HTTP Agreed

Response head :set-cookie

Request header :cookie

Cookie Details of the use of ：

Cookie Life time of ：

By default ,Cookie Stored in browser memory , When the browser closes , Memory free , be Cookie Be destroyed

setMaxAge(int seconds): Set up Cookie Life time of

1. Positive numbers ： take Cookie Write to the computer hard disk where the browser is located , Persistent storage . Automatically delete by time

2. negative ： The default value is ,Cookie In the current browser memory , When the browser closes , be Cookie Be destroyed

3. zero ： Delete corresponding Cookie

@WebServlet("/asServlet")
public class asServlet extends HttpServlet {
​
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
​
        // send out Cookie
        //1. establish Cookuie object 
        Cookie cookie=new Cookie("username","zhangsan");
​
        // Set the time to live  7 God 
        cookie.setMaxAge(60*60*24*7);
​
​
        //2. send out Cookie
        response.addCookie(cookie);
    }
​
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doGet(request, response);
    }
}

Cookie Store Chinese :

//URL code 
 String value=" Zhang San ";
value= URLEncoder.encode(value,"UTF-8");
 Cookie cookie=new Cookie("username",value);

String value = c.getValue();
//URL decode 
value= URLDecoder.decode(value);
System.out.println(name+":"+value);

Session

Server session tracking technology ： Save the data to the server

Session Is based on Cookie Realized

Use ：

session.setAttribute// Storage

session.getAttribute// obtain

session.removeAttribute// Delete

//1. obtain Session object 
HttpSession session = request.getSession();
//2. Storage Session object 
session.setAttribute("username","zhangsan");

//1. obtain Session object 
HttpSession session = request.getSession();
// get data 
Object username = session.getAttribute("username");
System.out.println("username:"+username);

Session Details of the use of ：

Session passivation , activation ：

After the server restarts ,Session The data in also exists

passivation ： After the server shuts down normally ,Tomcat Will automatically Session Write to the file on the hard disk

activation ： After starting the server again , Load data from file to Session in

Session The destruction ：

1. stay web.xml Middle configuration

Default 30 Minute destruction

<session-config>
    <session-timeout>100</session-timeout>
</session-config>

2. Destroy yourself

session.invalidate();

summary ：

Cookie and Session It is to complete the data sharing between multiple requests in a session

difference ：

Storage location ：Cookie Is to store data to the client ,Session Is to store data to the server

Security ：Cookie unsafe ,Session Security

data size ：Cookie Maximum 3KB,Session No size limit

Storage time ：Cookie Long term storage ,Session Default 30 minute

Server performance ：Cookie Does not occupy server resources ,Session Occupancy resources