MyBatis Plus整合Redis实现分布式二级缓存

MyBatis缓存描述

MyBatis提供了两种级别的缓存， 分别时一级缓存和二级缓存。一级缓存是SqlSession级别的缓存，只在SqlSession对象内部存储缓存数据，如果SqlSession对象不一样就无法命中缓存，二级缓存是mapper级别的缓存，只要使用的Mapper类一样就能够共享缓存。

在查询数据时，Mybatis会优先查询二级缓存，如果二级缓存没有则查询一级缓存，都没有才会进行数据库查询。

Mybatis的一级缓存默认是开启的，而二级缓存需要在mapper.xml配置文件内或通过@CacheNamespace注解手动开启。

需要注意的是，在于Spring进行整合时，必须开启事务一级缓存会生效，因为不开启缓存的话每次查询都会重新创建一个SqlSession对象，因此无法共享缓存。

通过@CacheNamespace开启某个Mapper的二级缓存。

@Mapper
@CacheNamespace 
public interface EmployeeMapper extends BaseMapper<Employee> {
}

开启所有的二级缓存：

mybatis-plus:
    mapper-locations: classpath:mybatis/mapper/*.xml
    configuration:
      cache-enabled: true

MybatisPlus整合Redis实现分布式二级缓存

Mybatis内置的二级缓存在分布式环境下存在分布式问题，无法使用，但是我们可以整合Redis来实现分布式的二级缓存。

1.引入依赖

<dependency>
    <groupId>com.baomidougroupId>
    <artifactId>mybatis-plus-boot-starterartifactId>
    <version>3.5.4.1version>
dependency>

<dependency>
    <groupId>org.springframework.bootgroupId>
    <artifactId>spring-boot-starter-data-redisartifactId>
dependency>

<dependency>
    <groupId>org.redissongroupId>
    <artifactId>redisson-spring-boot-starterartifactId>
    <version>3.24.3version>
dependency>

<dependency>
    <groupId>cn.hutoolgroupId>
    <artifactId>hutool-allartifactId>
    <version>5.8.22version>
dependency>

2.配置RedisTemplate

import com.fasterxml.jackson.annotation.JsonAutoDetect;
import com.fasterxml.jackson.annotation.PropertyAccessor;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.jsontype.impl.LaissezFaireSubTypeValidator;
import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
import org.springframework.cache.CacheManager;
import org.springframework.cache.annotation.EnableCaching;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Primary;
import org.springframework.data.redis.cache.RedisCacheConfiguration;
import org.springframework.data.redis.cache.RedisCacheManager;
import org.springframework.data.redis.cache.RedisCacheWriter;
import org.springframework.data.redis.connection.RedisConnectionFactory;
import org.springframework.data.redis.core.RedisTemplate;
import org.springframework.data.redis.serializer.GenericJackson2JsonRedisSerializer;
import org.springframework.data.redis.serializer.RedisSerializationContext;
import org.springframework.data.redis.serializer.RedisSerializer;
import org.springframework.data.redis.serializer.StringRedisSerializer;

import java.time.Duration;

@Configuration
@EnableCaching
public class RedisConfiguration {
    private static final StringRedisSerializer STRING_SERIALIZER = new StringRedisSerializer();
    private static final GenericJackson2JsonRedisSerializer JACKSON__SERIALIZER = new GenericJackson2JsonRedisSerializer();


    @Bean
    @Primary
    public CacheManager redisCacheManager(RedisConnectionFactory redisConnectionFactory) {
        //设置缓存过期时间
        RedisCacheConfiguration redisCacheCfg = RedisCacheConfiguration.defaultCacheConfig()
                .entryTtl(Duration.ofHours(1))
                .serializeKeysWith(RedisSerializationContext.SerializationPair.fromSerializer(STRING_SERIALIZER))
                .serializeValuesWith(RedisSerializationContext.SerializationPair.fromSerializer(JACKSON__SERIALIZER));
        return RedisCacheManager.builder(RedisCacheWriter.nonLockingRedisCacheWriter(redisConnectionFactory))
                .cacheDefaults(redisCacheCfg)
                .build();
    }

    @Bean
    @Primary
    @ConditionalOnMissingBean(name = "redisTemplate")
    public RedisTemplate<String, Object> redisTemplate(RedisConnectionFactory factory) {
        // 配置redisTemplate
        RedisTemplate<String, Object> redisTemplate = new RedisTemplate<>();
        redisTemplate.setConnectionFactory(factory);
        // key序列化
        redisTemplate.setKeySerializer(STRING_SERIALIZER);
        // value序列化
        redisTemplate.setValueSerializer(JACKSON__SERIALIZER);
        // Hash key序列化
        redisTemplate.setHashKeySerializer(STRING_SERIALIZER);
        // Hash value序列化
        redisTemplate.setHashValueSerializer(JACKSON__SERIALIZER);
        // 设置支持事务
        redisTemplate.setEnableTransactionSupport(true);

        redisTemplate.afterPropertiesSet();
        return redisTemplate;
    }

    @Bean
    public RedisSerializer<Object> redisSerializer() {
        //创建JSON序列化器
        ObjectMapper objectMapper = new ObjectMapper();
        objectMapper.setVisibility(PropertyAccessor.ALL, JsonAutoDetect.Visibility.ANY);
        //必须设置，否则无法将JSON转化为对象，会转化成Map类型
        objectMapper.activateDefaultTyping(LaissezFaireSubTypeValidator.instance, ObjectMapper.DefaultTyping.NON_FINAL);
        return new GenericJackson2JsonRedisSerializer(objectMapper);
    }
}

3.自定义缓存类

import cn.hutool.extra.spring.SpringUtil;
import cn.hutool.json.JSONUtil;
import lombok.extern.slf4j.Slf4j;
import org.apache.ibatis.cache.Cache;
import org.redisson.api.RReadWriteLock;
import org.redisson.api.RedissonClient;
import org.springframework.data.redis.connection.RedisServerCommands;
import org.springframework.data.redis.core.RedisCallback;
import org.springframework.data.redis.core.RedisTemplate;

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


@Slf4j
public class MybatisRedisCache implements Cache {

    // redisson 读写锁
    private final RReadWriteLock redissonReadWriteLock;
    // redisTemplate
    private final RedisTemplate redisTemplate;
    // 缓存Id
    private final String id;
    //过期时间 10分钟
    private final long expirationTime = 1000*60*10;

    public MybatisRedisCache(String id) {
        this.id = id;
        //获取redisTemplate
        this.redisTemplate = SpringUtil.getBean(RedisTemplate.class);
        //创建读写锁
        this.redissonReadWriteLock = SpringUtil.getBean(RedissonClient.class).getReadWriteLock("mybatis-cache-lock:"+this.id);
    }


    @Override
    public void putObject(Object key, Object value) {
        //使用redis的Hash类型进行存储
        redisTemplate.opsForValue().set(getCacheKey(key),value,expirationTime, TimeUnit.MILLISECONDS);
    }

    @Override
    public Object getObject(Object key) {
        try {
            //根据key从redis中获取数据
            Object cacheData = redisTemplate.opsForValue().get(getCacheKey(key));

            log.debug("[Mybatis 二级缓存]查询缓存,cacheKey={},data={}",getCacheKey(key), JSONUtil.toJsonStr(cacheData));

            return cacheData;
        } catch (Exception e) {
            log.error("缓存出错",e);
        }
        return null;
    }

    @Override
    public Object removeObject(Object key) {
        if (key != null) {
            log.debug("[Mybatis 二级缓存]删除缓存,cacheKey={}",getCacheKey(key));
            redisTemplate.delete(key.toString());
        }
        return null;
    }

    @Override
    public void clear() {
        log.debug("[Mybatis 二级缓存]清空缓存,id={}",getCachePrefix());
        Set keys = redisTemplate.keys(getCachePrefix()+":*");
        redisTemplate.delete(keys);
    }

    @Override
    public int getSize() {
        Long size = (Long) redisTemplate.execute((RedisCallback<Long>) RedisServerCommands::dbSize);
        return size.intValue();
    }

    @Override
    public ReadWriteLock getReadWriteLock() {
        return this.redissonReadWriteLock;
    }

    @Override
    public String getId() {
        return this.id;
    }

    public String getCachePrefix(){
        return "mybatis-cache:%s".formatted(this.id);
    }
    private String getCacheKey(Object key){
        return getCachePrefix()+":"+key;
    }

}

4.Mapper接口上开启二级缓存

//开启二级缓存并指定缓存类
@CacheNamespace(implementation = MybatisRedisCache.class,eviction = MybatisRedisCache.class)
@Mapper
public interface EmployeeMapper extends BaseMapper<Employee> {
}