Redis穿透问题解决方案

缓存穿透

　缓存穿透是指用户查询数据，在数据库没有，自然在缓存中也不会有。这样就导致用户查询的时候，在缓存中找不到，每次都要去数据库再查询一遍，然后返回空。这样请求就绕过缓存直接查数据库，这也是经常提的缓存命中率问题。

解决的办法就是：如果查询数据库也为空，直接设置一个默认值存放到缓存，这样第二次到缓冲中获取就有值了，而不会继续访问数据库，这种办法最简单粗暴。

把空结果，也给缓存起来，这样下次同样的请求就可以直接返回空了，即可以避免当查询的值为空时引起的缓存穿透。同时也可以单独设置个缓存区域存储空值，对要查询的key进行预先校验，然后再放行给后面的正常缓存处理逻辑。

查询查不到的数据，在缓存中没有，而直接走了数据库！反反复复的去这么做就崩溃了哦

Redis穿透：

4没有，redis中没有，然后去DB查询，会导致雪崩效应。称之为穿透效应。

穿透产生的原因：客户端随机生成不同的key，在redis缓存中没有该数据，数据库也没有该数据。这样的话可能导致一直发生jdbc连接

解决方案：

1、通过网关判断客户端传入对应key的规则，不符合数据库查询规则，直接返回空

2、如果使用的key数据库查询不到的话，直接在redis中存一份null结果。

在存入id为4的数据库的时候，直接清除对应redis为4的缓存（此时是空哈）

废话不多说，上代码：

pom：

<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.toov5.architect</groupId>
  <artifactId>architect</artifactId>
  <version>0.0.1-SNAPSHOT</version>
  <parent>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-parent</artifactId>
		<version>2.0.0.RELEASE</version>
	</parent>
	<dependencies>
		<!-- SpringBoot 对lombok 支持 -->
		<dependency>
			<groupId>org.projectlombok</groupId>
			<artifactId>lombok</artifactId>
		</dependency>
		<!-- SpringBoot web 核心组件 -->
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-web</artifactId>
		</dependency>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-tomcat</artifactId>
		</dependency>
		<!-- SpringBoot 外部tomcat支持 -->
		<dependency>
			<groupId>org.apache.tomcat.embed</groupId>
			<artifactId>tomcat-embed-jasper</artifactId>
		</dependency>
		<!-- springboot-log4j -->
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-log4j</artifactId>
			<version>1.3.8.RELEASE</version>
		</dependency>
		<!-- springboot-aop 技术 -->
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-aop</artifactId>
		</dependency>
		<!-- https://mvnrepository.com/artifact/commons-lang/commons-lang -->
		<dependency>
			<groupId>commons-lang</groupId>
			<artifactId>commons-lang</artifactId>
			<version>2.6</version>
		</dependency>
		<!-- https://mvnrepository.com/artifact/org.apache.httpcomponents/httpclient -->
		<dependency>
			<groupId>org.apache.httpcomponents</groupId>
			<artifactId>httpclient</artifactId>
		</dependency>
		<!-- https://mvnrepository.com/artifact/com.alibaba/fastjson -->
		<dependency>
			<groupId>com.alibaba</groupId>
			<artifactId>fastjson</artifactId>
			<version>1.2.47</version>
		</dependency>
		<dependency>
			<groupId>javax.servlet</groupId>
			<artifactId>jstl</artifactId>
		</dependency>
		<dependency>
			<groupId>taglibs</groupId>
			<artifactId>standard</artifactId>
			<version>1.1.2</version>
		</dependency>
		<!--开启 cache 缓存 -->
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-cache</artifactId>
		</dependency>
		<!-- ehcache缓存 -->
		<dependency>
			<groupId>net.sf.ehcache</groupId>
			<artifactId>ehcache</artifactId>
			<version>2.9.1</version><!--$NO-MVN-MAN-VER$ -->
		</dependency>
		<dependency>
			<groupId>org.mybatis.spring.boot</groupId>
			<artifactId>mybatis-spring-boot-starter</artifactId>
			<version>1.1.1</version>
		</dependency>
		<!-- mysql 依赖 -->
		<dependency>
			<groupId>mysql</groupId>
			<artifactId>mysql-connector-java</artifactId>
		</dependency>
		<!-- redis 依赖 -->
		<dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-redis</artifactId>
        </dependency>
	</dependencies>
  
</project>

　service:

package com.toov5.service;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.cache.ehcache.EhCacheCacheManager;
import org.springframework.stereotype.Component;

import net.sf.ehcache.Cache;
import net.sf.ehcache.Element;


@Component
public class EhCacheUtils {

    // @Autowired
    // private CacheManager cacheManager;
    @Autowired
    private EhCacheCacheManager ehCacheCacheManager;

    // 添加本地缓存 (相同的key 会直接覆盖)
    public void put(String cacheName, String key, Object value) {
        Cache cache = ehCacheCacheManager.getCacheManager().getCache(cacheName);
        Element element = new Element(key, value);
        cache.put(element);
    }

    // 获取本地缓存
    public Object get(String cacheName, String key) {
        Cache cache = ehCacheCacheManager.getCacheManager().getCache(cacheName);
        Element element = cache.get(key);
        return element == null ? null : element.getObjectValue();
    }

    public void remove(String cacheName, String key) {
        Cache cache = ehCacheCacheManager.getCacheManager().getCache(cacheName);
        cache.remove(key);
    }

}

package com.toov5.service;

import java.util.Set;
import java.util.concurrent.TimeUnit;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.data.redis.core.StringRedisTemplate;
import org.springframework.stereotype.Component;

@Component
public class RedisService {

    @Autowired
    private StringRedisTemplate stringRedisTemplate;
    //这样该方法支持多种数据类型 
    public void set(String key , Object object, Long time){
        //开启事务权限
        stringRedisTemplate.setEnableTransactionSupport(true);
        try {
            //开启事务
            stringRedisTemplate.multi();
            
            String argString =(String)object;  //强转下
            stringRedisTemplate.opsForValue().set(key, argString);
            
            //成功就提交
            stringRedisTemplate.exec();
        } catch (Exception e) {
            //失败了就回滚
            stringRedisTemplate.discard();
            
        }
        if (object instanceof String ) {  //判断下是String类型不
            String argString =(String)object;  //强转下
            //存放String类型的
            stringRedisTemplate.opsForValue().set(key, argString);
        }
        //如果存放Set类型
        if (object instanceof Set) {
            Set<String> valueSet =(Set<String>)object;
            for(String string:valueSet){
                stringRedisTemplate.opsForSet().add(key, string);  //此处点击下源码看下 第二个参数可以放好多
            }
        }
        //设置有效期
        if (time != null) {
            stringRedisTemplate.expire(key, time, TimeUnit.SECONDS);
        }
        
    }
    //做个封装
    public void setString(String key, Object object){
        String argString =(String)object;  //强转下
        //存放String类型的
        stringRedisTemplate.opsForValue().set(key, argString);
    }
    public void setSet(String key, Object object){
        Set<String> valueSet =(Set<String>)object;
        for(String string:valueSet){
            stringRedisTemplate.opsForSet().add(key, string);  //此处点击下源码看下 第二个参数可以放好多
        }
    }
    
    public String getString(String key){
     return    stringRedisTemplate.opsForValue().get(key);
    }
    
    
}

package com.toov5.service;

import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import org.springframework.web.bind.annotation.RequestMapping;

import com.toov5.entity.Users;
import com.toov5.mapper.UserMapper;

import io.netty.util.internal.StringUtil;

@Service
public class SnowslideService {
    @Autowired
    private UserMapper userMapper; 
    @Autowired
    private RedisService redisService;
    
    private Lock lock = new ReentrantLock();
    
    public String getUser01(Long id){
    //定义key， key以当前的类名+方法名+id+参数值
    String key = this.getClass().getName() + "-" + Thread.currentThread().getStackTrace()[1].getMethodName()
                        + "-id:" + id;    
          //1查询redis
    String username = redisService.getString(key);
    if (!StringUtil.isNullOrEmpty(username)) {
        return username;
    }
    String resultUsaerName = null;
    try {
        //开启锁
        lock.lock();
        Users user = userMapper.getUser(id);
        if (username == null) {
            return null;
        }
        resultUsaerName =user.getName();
        redisService.setString(key, resultUsaerName);
    } catch (Exception e) {
        // TODO: handle exception
    }finally {
        //释放锁
        lock.unlock();
    }
          //3直接返回
    return resultUsaerName;
    }
    
    
    
//穿透解决方案    
    public String getUser02(Long id){
    //定义key， key以当前的类名+方法名+id+参数值
    String key = this.getClass().getName() + "-" + Thread.currentThread().getStackTrace()[1].getMethodName()
                        + "-id:" + id;    
          //1查询redis
    System.out.println("查询redis缓存"+"key"+key+".resultUserName");
    String username = redisService.getString(key);
    if (!StringUtil.isNullOrEmpty(username)) {
        return username;
    }
    String resultUsaerName = null;
    //如果数据库中，没有对应的数据信息的时候
       System.out.println("查询数据库：id"+id);
        Users user = userMapper.getUser(id);
        if (user == null) {
            resultUsaerName="${null}";  //做个标记  客户端识别到后 提示下吧
            
        }else {
            resultUsaerName=user.getName();
        }
        System.out.println("写入redis缓存"+"key"+key+".resultUserName"+resultUsaerName);
        redisService.setString(key, resultUsaerName);

          //3直接返回
    return resultUsaerName;
    }
    
    
}

package com.toov5.service;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;

import com.alibaba.fastjson.JSONObject;
import com.toov5.entity.Users;
import com.toov5.mapper.UserMapper;


import io.netty.util.internal.StringUtil;

@Component
public class UserService {
    @Autowired
    private EhCacheUtils ehCacheUtils;
    @Autowired
    private RedisService redisService;
    @Autowired
    private UserMapper userMapper;
    //定义个全局的cache名字
    private String cachename ="userCache";
    
    public Users getUser(Long id){
        //先查询一级缓存  key以当前的类名+方法名+id+参数值
        String key = this.getClass().getName() + "-" + Thread.currentThread().getStackTrace()[1].getMethodName()
                + "-id:" + id;
        //查询一级缓存数据有对应值的存在 如果有 返回
        Users user = (Users)ehCacheUtils.get(cachename, key);
        if (user != null) {
            System.out.println("key"+key+",直接从一级缓存获取数据"+user.toString());
            return user;
        }
        //一级缓存没有对应的值存在,接着查询二级缓存    
        // redis存对象的方式  json格式 然后反序列号
        String userJson = redisService.getString(key);
        //如果rdis缓存中有这个对应的值，修改一级缓存    最下面的会有的 相同会覆盖的    
        if (!StringUtil.isNullOrEmpty(userJson)) {  //有 转成json
            JSONObject jsonObject = new JSONObject();//用的fastjson
            Users resultUser = jsonObject.parseObject(userJson,Users.class);
            ehCacheUtils.put(cachename, key, resultUser);
            return resultUser;
        }
        //都没有 查询DB 
        Users user1 = userMapper.getUser(id);
        if (user1 == null) {
            return null;
        }
        //保证两级缓存有效期相同！？   一级缓存时间-二级缓存执行的时间
        //一级缓存时间 等于 二级缓存剩下的时间   
        //存放到二级缓存 redis中
        redisService.setString(key, new JSONObject().toJSONString(user1));
        //存放到一级缓存 Ehchache
        ehCacheUtils.put(cachename, key, user1);
        return user1;
    }
    
    
    
}

mapper

package com.toov5.mapper;

import java.util.List;

import org.apache.ibatis.annotations.Param;
import org.apache.ibatis.annotations.Select;
import org.springframework.cache.annotation.CacheConfig;
import org.springframework.cache.annotation.Cacheable;

import com.toov5.entity.Users;
//引入的jar包后就有了这个注解了 非常好用 （配置缓存的基本信息）
@CacheConfig(cacheNames={"userCache"})  //缓存的名字  整个类的
public interface UserMapper {
    @Select("SELECT ID ,NAME,AGE FROM users where id=#{id}")
    @Cacheable //让这个方法实现缓存 查询完毕后 存入到缓存中  不是每个方法都需要缓存呀！save()就不用了吧
    Users getUser(@Param("id") Long id);
}

entity

package com.toov5.entity;

import java.io.Serializable;

import lombok.Data;

@Data
public class Users implements Serializable{
  private String name;
  private Integer age;
}

controller

package com.toov5.controller;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

import com.toov5.service.SnowslideService;

@RestController
public class UserRedisController {
   @Autowired
   private SnowslideService snowslideService;
   
   @RequestMapping("/getUser02")
   public String getUser02(Long id){
       return snowslideService.getUser02(id); 
   }
   
}

package com.toov5.controller;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

import com.toov5.entity.Users;
import com.toov5.service.UserService;

@RestController
public class IndexController {
    @Autowired
    private UserService userService;
    
    @RequestMapping("/userId")
    public Users getUserId(Long id){
        return userService.getUser(id);  
    }
    
   
}

启动类

package com.toov5.app;

import org.mybatis.spring.annotation.MapperScan;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cache.annotation.EnableCaching;

@EnableCaching //开启缓存
@MapperScan(basePackages={"com.toov5.mapper"})
@SpringBootApplication(scanBasePackages={"com.toov5.*"})
public class app {
   public static void main(String[] args) {
    SpringApplication.run(app.class, args);
}
    
}

yml

###端口号配置
server:
  port: 8080
###数据库配置 
spring:
  datasource:
    url: jdbc:mysql://localhost:3306/test
    username: root
    password: root
    driver-class-name: com.mysql.jdbc.Driver
    test-while-idle: true
    test-on-borrow: true
    validation-query: SELECT 1 FROM DUAL
    time-between-eviction-runs-millis: 300000
    min-evictable-idle-time-millis: 1800000
# 缓存配置读取
  cache:
    type: ehcache
    ehcache:
      config: classpath:app1_ehcache.xml
  redis:
    database: 0 
    jedis:
      pool:
        max-active: 8
        max-wait: -1
        max-idle: 8
        min-idle: 0
    timeout: 10000
    cluster:
      nodes:
        - 192.168.91.5:9001
        - 192.168.91.5:9002
        - 192.168.91.5:9003
        - 192.168.91.5:9004
        - 192.168.91.5:9005
        - 192.168.91.5:9006

<?xml version="1.0" encoding="UTF-8"?>
<ehcache xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:noNamespaceSchemaLocation="http://ehcache.org/ehcache.xsd">

	<diskStore path="java.io.tmpdir/ehcache-rmi-4000" />


	<!-- 默认缓存 -->
	<defaultCache maxElementsInMemory="1000" eternal="true"
		timeToIdleSeconds="120" timeToLiveSeconds="120" overflowToDisk="true"
		diskSpoolBufferSizeMB="30" maxElementsOnDisk="10000000"
		diskPersistent="true" diskExpiryThreadIntervalSeconds="120"
		memoryStoreEvictionPolicy="LRU">
	</defaultCache>
  
	<!-- demo缓存 --><!-- name="userCache" 对应我们在 @CacheConfig(cacheNames={"userCache"}) ！！！！！ -->
	<!--Ehcache底层也是用Map集合实现的 -->
	<cache name="userCache" maxElementsInMemory="1000" eternal="false"
		timeToIdleSeconds="120" timeToLiveSeconds="120" overflowToDisk="true"
		diskSpoolBufferSizeMB="30" maxElementsOnDisk="10000000"
		diskPersistent="false" diskExpiryThreadIntervalSeconds="120"
		memoryStoreEvictionPolicy="LRU">  <!-- LRU缓存策略 -->
		<cacheEventListenerFactory
			class="net.sf.ehcache.distribution.RMICacheReplicatorFactory" />
		<!-- 用于在初始化缓存，以及自动设置 -->
		<bootstrapCacheLoaderFactory
			class="net.sf.ehcache.distribution.RMIBootstrapCacheLoaderFactory" />
	</cache>
</ehcache>

　再加一个拦截