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/*.xmlconfiguration: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.baomidou</groupId><artifactId>mybatis-plus-boot-starter</artifactId><version>3.5.4.1</version>
</dependency><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-data-redis</artifactId>
</dependency><dependency><groupId>org.redisson</groupId><artifactId>redisson-spring-boot-starter</artifactId><version>3.24.3</version>
</dependency><dependency><groupId>cn.hutool</groupId><artifactId>hutool-all</artifactId><version>5.8.22</version>
</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@Primarypublic 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redisTemplateRedisTemplate<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;}@Beanpublic 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;// redisTemplateprivate final RedisTemplate redisTemplate;// 缓存Idprivate 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redisTemplatethis.redisTemplate = SpringUtil.getBean(RedisTemplate.class);//创建读写锁this.redissonReadWriteLock = SpringUtil.getBean(RedissonClient.class).getReadWriteLock("mybatis-cache-lock:"+this.id);}@Overridepublic 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);}@Overridepublic 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;}@Overridepublic 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;}@Overridepublic void clear() {log.debug("[Mybatis 二级缓存]清空缓存,id={}",getCachePrefix());Set keys = redisTemplate.keys(getCachePrefix()+":*");redisTemplate.delete(keys);}@Overridepublic int getSize() {Long size = (Long) redisTemplate.execute((RedisCallback<Long>) RedisServerCommands::dbSize);return size.intValue();}@Overridepublic ReadWriteLock getReadWriteLock() {return this.redissonReadWriteLock;}@Overridepublic 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> {
}