Cookie & session learning

Catalog

Cookie

Session 

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Cookie

【 Concept 】

Client session technology , Save data to client .

【 Quick start 】

1. establish Cookie object , Data binding .   new Cookie(String name, String value) 

2. send out Cookie object .   response.addCookie(Cookie cookie) 

3. obtain Cookie, Get the data .   Cookie[]  request.getCookies() 

//1. establish cookie object 
        Cookie c = new Cookie("msg","hello");
        //2. send out Cookie
        response.addCookie(c);

//3. obtain Cookie
        Cookie[] cs = request.getCookies();
        // get data , Traverse Cookies
        if (cs != null) {
            for (Cookie c : cs) {
                String name = c.getName();
                String value = c.getValue();
                System.out.println(name+","+value);
            }
        }

【 Realization principle 】

Based on the response header set-cookie And the request header cookie Realization .

【cookie The details of the 】

1. You can send more than one at a time cookie：（ You can create multiple Cookie object , Use response Call several times addCookie Method to send cookie that will do ）

// Send multiple... At a time cookie

        //1. establish cookie object 
        Cookie c1 = new Cookie("msg","hello");
        Cookie c2 = new Cookie("happy","smile");
        //2. send out Cookie
        response.addCookie(c1);
        response.addCookie(c2);

2. cookie Save time in browser ：1） By default , When the browser is closed ,Cookie The data is destroyed    2） Persistent storage

//cookie How long to save in the browser ？

        //1. establish cookie object 
        Cookie c1 = new Cookie("msg","setMaxAge");

        // Set up cookie Storage time of 
        //c1.setMaxAge(30); // take cookie Persist to hard disk ,30 Automatically delete... In seconds cookie file 
        //c1.setMaxAge(-1); // The default value is , Delete data when one party closes 
        c1.setMaxAge(0); // Delete cookie Information 

        //2. send out Cookie
        response.addCookie(c1);

3. cookie Can you save Chinese ：

• stay tomcat 8 Before cookie Can't store Chinese data directly in （ Need to transcode Chinese data --- It is generally used URL code (%E3)）
• stay tomcat 8 after ,cookie Support Chinese data . Special characters are still not supported , It is recommended to use URL Encoding storage ,URL Decoding and parsing

4.cookie Sharing issues ：

//1. establish cookie object 
        Cookie c1 = new Cookie("msg"," Hello ");

        // Set up path, Let all projects deployed under the current server share Cookie Information 
        c1.setPath("/");

        //2. send out Cookie
        response.addCookie(c1);

5. Cookie The characteristics and functions of ：

• cookie Store data in the client browser
• Browser for single cookie There is a limit to the size of (4kb) as well as For the total under the same domain name cookie There is also a limit to the number (20 individual )

effect ：

• cookie Generally used to store a small amount of less sensitive data
• Without logging in , Complete the identification of the client by the server

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Session 

【 Concept 】

Server side session technology , Sharing data among multiple requests in a session , Save the data in the object on the server side .HttpSession.

【 Quick start 】 

1. obtain HttpSession object ：

• HttpSession session = request.getSession();

2. Use HttpSession object ：

• Object getAttribute(String name)  
• void setAttribute(String name, Object value)
• void removeAttribute(String name)  

// obtain session
        HttpSession session = request.getSession();
        // Store the data 
        session.setAttribute("msg","hello,session~");

// obtain session
        HttpSession session = request.getSession();
        // get data 
        Object msg = session.getAttribute("msg");
        System.out.println(msg);

【 principle 】

 Session The realization of depends on Cookie Of .

【 details 】 

1. When the client is shut down , The server does not shut down , Get twice session Is it the same ？（ No ）

notes ： If you need the same , You can create Cookie, The key is JSESSIONID, Set the maximum lifetime , Give Way cookie Persistent save

• Cookie c = new Cookie("JSESSIONID",session.getId());
• ​c.setMaxAge(60*60);
• ​response.addCookie(c);

// Use session Shared data 
        // obtain session
        HttpSession session = request.getSession();
        System.out.println(session);

        // After the client is expected to shut down ,session It can be the same 
        Cookie c = new Cookie("JSESSIONID",session.getId());
        c.setMaxAge(60*60);
        response.addCookie(c);

2. The client does not shut down , After the server is shut down , Acquired twice session Is it the same ？（ Not the same , But make sure the data is not lost .tomcat Automatically complete the following work ）

• session Passivation of ： Before the server is shut down properly , take session Serialize objects to hard disk
• session Activation of ： After the server starts , take session The file is converted to... In memory session Object can

3. session When it was destroyed ？1） Server down ​    2）session Object call invalidate()    3）session Default expiration time 30 minute ）

【session Characteristics 】

session Data used to store multiple requests for a session , There is a server side .

session Can store any type , Data of any size .

【session And Cookie The difference between 】

1. session Store data on the server side ,Cookie On the client side .
2. session There is no data size limit ,Cookie Yes .
3. session Data security ,Cookie Relative to insecurity .