Interview difficulties: difficulties in implementing distributed session, this is enough!

source ：blog.csdn.net/Gaowumao/

article/details/124309548

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• How to solve the distributed problem Session The problem? ？

  • One 、 Solution list

  • Two 、Java Code implementation to solve distributed problems Session

The usual projects are in an application system , And all the operations are on one Tomcat Server , It doesn't trigger Session share The problem of , So it won't affect our system , But when we deploy multiple microservices , Match again Nginx When load balancing , If you don't deal with distributed Session problem , When we access different functions in the system, there will be frequent user login operations

Graphical analysis of causes ：

Premise ： User login function and commodity order module in the figure 、 The spike buying module belongs to a separate micro service module When users want to successfully log in to the other two modules in the diagram , because Nginx Use the default load balancing policy （ polling  ）, At this time, the request will be distributed to the back-end application one by one in chronological order , That is to say, the user is Tomcat1 After login successfully on , The user's information is placed in Tomcat1 Of Session in , After a while , The user wants to perform the function operation of second kill activity , The request was again Nginx Distributed to Tomcat2, And then Tomcat2 Upper Session There is no user information in , So there is a situation that allows users to log in again , In distributed services , Different functional modules are bound to be divided into their own microservices , Suppose you need to log in again to access a function , The user experience is bound to decline significantly ！

How to solve the distributed problem Session The problem? ？

One 、 Solution list

1. Session Copy

advantage ：

• No need to change the code , It just needs to be modified Tomcat To configure

shortcoming ：

• Session Synchronous transmission occupies intranet broadband

• More than one Tomcat The synchronization performance degrades exponentially

• Session Take up memory , Cannot effectively expand horizontally

2. Front end storage

advantage ：

• No server memory

shortcoming ：

• There are security risks

• Data size affected cookie Limit

• Occupy Internet broadband

3. Session viscous

advantage ：

• No need to change the code

• The server can expand horizontally

shortcoming ：

• Add new machines , Will return Hash, Cause re login

• After the app restarts , Need to login again

4. Back end centralized storage

advantage ：

• Security

• Easy to expand horizontally

advantage ：

• Increase complexity

• You need to change the code

Two 、Java Code implementation to solve distributed problems Session

1. SpringSession - Redis Solve distributed Session

Add dependency

<!--Redis-->
<dependency>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-data-redis</artifactId>
</dependency>
<!--commons-pools2  Object pool dependency -->
<dependency>
  <groupId>org.apache.commons</groupId>
  <artifactId>commons-pool2</artifactId>
</dependency>
<!--spring session  rely on -->
<dependency>
  <groupId>org.springframework.session</groupId>
  <artifactId>spring-session-data-redis</artifactId>
</dependency>

add to Redis To configure

## Redis To configure 
spring:
  redis:
     Server address 
    host: localhost
     port 
    port: 6379
     database 
    database: 0
     Timeout time 
    connect-timeout: 10000ms
    lettuce:
      pool:
         maximum connection 
        max-active: 8
         Maximum connection blocking wait time   Default  -1
        max-wait: 10000ms
         Maximum free time   Default 8
        max-idle: 200
         Minimum free connection   Default 8
        min-idle: 5

Business logic implementation

/**
     *  Login function 
     * @param loginVo
     * @return
     */
    @Override
    public RespBean doLogin(LoginVo loginVo, HttpServletRequest request, HttpServletResponse response) {
   
     

        String username = loginVo.getUserName();
        String password = loginVo.getPassword();

        User user = userMapper.selectByUserName(username);
        if (user == null){
   
     
            throw new GlobalException(RespBeanEnum.LOGIN_ERROR);
        }
        // Determine if the password is correct 
        if (!MDUtils.formPassToDBPass(password,user.getSalt()).equals(user.getPassword())){
   
     
            throw new GlobalException(RespBeanEnum.LOGIN_ERROR);
        }
        // Use UUID Generate a string instead of Cookie
        String ticket = UUIDUtil.uuid();
        request.getSession().setAttribute(ticket,user);
        CookieUtil.setCookie(request,response,"userTicket",ticket);
        return RespBean.success();
    }

View control layer

/**
     *  Jump to product list 
     * @param session
     * @param model
     * @return
     */
    @RequestMapping("/toList")
    public String toList(HttpSession session, Model model,@CookieValue("userTicket")String ticket){
   
     
        if (StringUtils.isEmpty(ticket)){
   
     
            return "login";
        }
        User user = (User) session.getAttribute(ticket);
        if (user == null){
   
     
            return "login";
        }
        model.addAttribute("user",user);
        return "goodsList";
    }

Log on to the test

open Redis Management software discovery Session Information has been added to Redis It's in

2. Redis Solve distributed Session

Import dependence

<!--Redis-->
<dependency>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-data-redis</artifactId>
</dependency>
<!--commons-pools2  Object pool dependency -->
<dependency>
  <groupId>org.apache.commons</groupId>
  <artifactId>commons-pool2</artifactId>
</dependency>

Business logic layer

@Override
    public RespBean doLogin(LoginVo loginVo, HttpServletRequest request, HttpServletResponse response) {
   
     

        String username = loginVo.getUserName();
        String password = loginVo.getPassword();

        User user = userMapper.selectByUserName(username);
        if (user == null){
   
     
            throw new GlobalException(RespBeanEnum.LOGIN_ERROR);
        }
        // Determine if the password is correct 
        if (!MDUtils.formPassToDBPass(password,user.getSalt()).equals(user.getPassword())){
   
     
            throw new GlobalException(RespBeanEnum.LOGIN_ERROR);
        }
        // success Cookie
        String ticket = UUIDUtil.uuid();
        // Store user information in redis in 
        redisTemplate.opsForValue().set("userTicket",ticket);
        redisTemplate.opsForValue().set("user:"+ticket,user);
        //request.getSession().setAttribute(ticket,user);
        CookieUtil.setCookie(request,response,"userTicket",ticket);
        return RespBean.success();
    }

    /**
     *  according to cookie obtain cookie
     * @param ticket
     * @return
     */
    @Override
    public User getUserByByCookie(String ticket,HttpServletRequest request,HttpServletResponse response) {
   
     
        if (StringUtils.isEmpty(ticket)){
   
     
            return null;
        }
        User user = (User) redisTemplate.opsForValue().get("user:" + ticket);
        if (user == null){
   
     
            CookieUtil.setCookie(request,response,"userTicket",ticket);
        }
        return user;
    }

View control layer

/**
     *  Jump to product list 
     * @param session
     * @param model
     * @return
     */
    @RequestMapping("/toList")
    public String toList(HttpSession session, Model model,HttpServletRequest request,HttpServletResponse response){
   
     
        String ticket = (String) redisTemplate.opsForValue().get("userTicket");
        if (StringUtils.isEmpty(ticket)){
   
     
            return "login";
        }
        //User user = (User) session.getAttribute(ticket);
        User user = userService.getUserByByCookie(ticket, request, response);
        if (user == null){
   
     
            return "login";
        }
        model.addAttribute("user",user);
        return "goodsList";
    }

Test success

see Redis Management tools

End

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