缓存穿透

什么叫做缓存穿透

缓存穿透只会发生在高并发的时候，就是当有10000个并发进行查询数据的时候，我们一般都会先去redis里面查询进行数据，但是如果redis里面没有这个数据的时候，那么这10000个并发里面就会有很大一部分并发会一下子都去mysql数据库里面进行查询了

解决缓存穿透

首先我模拟一下缓存穿透

比如下面的代码
Pom.xml代码

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.example</groupId>
    <artifactId>springboot</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>

    <name>springboot</name>
    <description>Demo project for Spring Boot</description>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.1.1.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <java.version>1.8</java.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-devtools</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>

        <dependency>
            <groupId>org.mybatis.spring.boot</groupId>
            <artifactId>mybatis-spring-boot-starter</artifactId>
            <version>1.1.1</version>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>


</project>

Application.properties

server.port=8081
#DB Configuration:
spring.datasource.driverClassName=com.mysql.jdbc.Driver
spring.datasource.url=jdbc:mysql://47.91.248.236:3306/hello?useUnicode=true&characterEncoding=utf8
spring.datasource.username=root
spring.datasource.password=root

#spring集成Mybatis环境
#pojo别名扫描包
mybatis.type-aliases-package=com.itheima.domain
#加载Mybatis映射文件
mybatis.mapper-locations=classpath:mapper/*Mapper.xml

MyController代码，下面的蓝色代码是模仿10000个并发线程

/**
 * sinture.com Inc.
 * Copyright (c) 2016-2018 All Rights Reserved.
 */
package com.itheima.controller;

import com.itheima.mapper.UserMapper;
import com.itheima.domain.User;
import com.itheima.service.UserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.ResponseBody;
import org.springframework.web.bind.annotation.RestController;

import java.util.HashMap;
import java.util.List;
import java.util.Map;

/**
 * @author xinzhu
 * @version Id: MyController.java, v 0.1 2018年12月05日 下午6:29 xinzhu Exp $
 */
@RestController
public class MyController {
    @Autowired
    private UserService userService;

    @RequestMapping("/hello/{id}")
    @ResponseBody
    public User queryUser(@PathVariable Integer id){
       // 蓝色代码注释开始
       new Thread(){
            @Override
            public void run() {
                for (int x = 0; x < 10000; x++) {
                    userService.queryUser(id);
                }
            }

        }.start();

        return userService.queryUser(id);
    }
}