前言
下面大部分内容来源于网上的相关帖子和官网，自己简单写了个demo体验了下，个人感觉mybatis的缓存并不是很合适
查询做缓存时，遇到更新操作就会刷新缓存，尤其是多表查询时，就会很难控制。对于那些需要缓存的热数据应该抽出来放到redis上做。
mybatis 一级缓存和二级缓存的概念
之所以称之为“二级缓存”，是相对于“一级缓存”而言的。既然有了一级缓存，那么为什么要提供二级缓存呢？我们知道，在一级缓存中，不同session进行相同SQL查询的时候，是查询两次数据库的。显然这是一种浪费，既然SQL查询相同，就没有必要再次查库了，直接利用缓存数据即可，这种思想就是MyBatis二级缓存的初衷。
另外，Spring和MyBatis整合时，每次查询之后都要进行关闭sqlsession，关闭之后数据被清空。所以MyBatis和Spring整合之后，一级缓存是没有意义的。如果开启二级缓存，关闭sqlsession后，会把该sqlsession一级缓存中的数据添加到mapper namespace的二级缓存中。这样，缓存在sqlsession关闭之后依然存在。
pom引入依赖
<dependencies>
<dependency>
<groupId>org.mybatis.spring.boot</groupId>
<artifactId>mybatis-spring-boot-starter</artifactId>
<version>2.2.2</version>
</dependency>
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<scope>runtime</scope>
</dependency>
<dependencies> application.properties 文件配置
spring.datasource.type=com.zaxxer.hikari.HikariDataSource
#Spring jdbc 数据源配置 需要mysql-connector-java驱动依赖
spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver
spring.datasource.url=jdbc:mysql://127.0.0.1:3306/gefrm?useUnicode=true&characterEncoding=utf-8&useSSL=false&useInformationSchema=true&serverTimezone=Asia/Shanghai&autoReconnect=true&failOverReadOnly=false
spring.datasource.username=root
spring.datasource.password=123456
#mybatis配置
mybatis.mapper-locations=classpath:mapper
SET NAMES utf8mb4;
SET
FOREIGN_KEY_CHECKS = 0;
-- ----------------------------
-- Table structure for bsc_dict_info_test
-- ----------------------------
DROP TABLE IF EXISTS `bsc_dict_info_test`;
CREATE TABLE `bsc_dict_info_test`
(
`dict_id` varchar(10) CHARACTER SET utf8 COLLATE utf8_general_ci NOT NULL DEFAULT ' ' COMMENT '字典标识',
`dict_name` varchar(256) CHARACTER SET utf8 COLLATE utf8_general_ci NOT NULL DEFAULT ' ' COMMENT '字典名称',
`dict_sitm_id` varchar(32) CHARACTER SET utf8 COLLATE utf8_general_ci NOT NULL DEFAULT ' ' COMMENT '字典子项标识',
`dict_sitm_name` varchar(256) CHARACTER SET utf8 COLLATE utf8_general_ci NOT NULL DEFAULT ' ' COMMENT '字典子项名称',
`suse_flag` char(1) CHARACTER SET utf8 COLLATE utf8_general_ci NOT NULL DEFAULT '0' COMMENT '启用标志',
`disp_orde` int(11) NOT NULL DEFAULT 0 COMMENT '展示顺序',
`memo` varchar(4000) CHARACTER SET utf8 COLLATE utf8_general_ci NOT NULL DEFAULT ' ' COMMENT '备注'
) ENGINE = InnoDB CHARACTER SET = utf8 COLLATE = utf8_general_ci ROW_FORMAT = Dynamic;
-- ----------------------------
-- Records of bsc_dict_info_test
-- ----------------------------
INSERT INTO `bsc_dict_info_test`
VALUES ('bbbbbtest', '担保人/被担保人与上市公司关联关系', '999', '无关联关系', '0', 190, '1');
INSERT INTO `bsc_dict_info_test`
VALUES ('aaaaatest', '担保人/被担保人与上市公司关联关系', '999', '无关联关系', '0', 190, '1');
INSERT INTO `bsc_dict_info_test`
VALUES ('bbbbbtest', '担保人/被担保人与上市公司关联关系', '999', '无关联关系', '0', 190, '1');
INSERT INTO `bsc_dict_info_test`
VALUES ('aaaaatest', '担保人/被担保人与上市公司关联关系', '999', '无关联关系', '0', 190, '1');
INSERT INTO `bsc_dict_info_test`
VALUES ('bbbbbtest', '担保人/被担保人与上市公司关联关系', '999', '无关联关系', '0', 190, '\'0\'');
SET
FOREIGN_KEY_CHECKS = 1;bean 类
package com.example.mybatis_cache.bean;
import lombok.Builder;
import lombok.Data;
import java.io.Serializable;
@Data
@Builder
public class BscDictInfoTestDO implements Serializable {
private String dictId;
private String dictName;
private String dictSitmId;
private String dictSitmName;
private String suseFlag;
private String dispOrde;
private String memo;
}mapper
package com.example.mybatis_cache.mapper;
import com.example.mybatis_cache.bean.BscDictInfoTestDO;
import org.apache.ibatis.annotations.Mapper;
import java.util.List;
@Mapper
public interface BscDictInfoTestMapper {
List<BscDictInfoTestDO> selectAll();
}service
package com.example.mybatis_cache.service;
public interface BscDictService {
void info(String name, int age);
}impl
package com.example.mybatis_cache.service.impl;
import com.example.mybatis_cache.bean.BscDictInfoTestDO;
import com.example.mybatis_cache.mapper.BscDictInfoTestMapper;
import com.example.mybatis_cache.service.BscDictService;
import lombok.extern.slf4j.Slf4j;
import org.springframework.stereotype.Component;
import javax.annotation.Resource;
import java.util.List;
@Slf4j
@Component
public class BscDictServiceImpl implements BscDictService {
@Resource
BscDictInfoTestMapper mapper;
@Override
public void info(String name, int age) {
log.warn("name:{}, age:{}", name, age);
List<BscDictInfoTestDO> list = mapper.selectAll();
list.forEach(item -> {
log.error("{}", item);
});
}
}测试类
package com.example.mybatis_cache.service.impl;
import com.example.mybatis_cache.service.BscDictService;
import com.mysql.cj.xdevapi.SessionFactory;
import lombok.extern.slf4j.Slf4j;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import static org.junit.jupiter.api.Assertions.*;
@Slf4j
@SpringBootTest
class BscDictServiceImplTest {
@Autowired
private BscDictService dictService;
@Test
void levelOneCacheTest() {
dictService.info("a", 1);
log.warn("======================== 分割线 ======================");
dictService.info("a", 2);
}
@Test
void testRawLevelOne() {
}
}测试结果
执行2次查询，只执行了一次，第二次命中的是缓存
踩坑
启动抛异常：
Error creating bean with name 'cacheAutoConfigurationValidator' defined in class path resource [org/springframework/boot/autoconfigure/cache/CacheAutoConfiguration.class]: Invocation of init method failed; nested exception is java.lang.IllegalArgumentException: No cache manager could be auto-configured, check your configuration (caching type is 'EHCACHE')
解决 添加依赖 spring-boot-starter-cache
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-cache</artifactId>
</dependency>
启动抛异常：
Error creating bean with name 'cacheManager' defined in class path resource [org/springframework/boot/autoconfigure/cache/EhCacheCacheConfiguration.class]: Unsatisfied dependency expressed through method 'cacheManager' parameter 1; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'ehCacheCacheManager' defined in class path resource [org/springframework/boot/autoconfigure/cache/EhCacheCacheConfiguration.class]: Bean instantiation via factory method failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [net.sf.ehcache.CacheManager]: Factory method 'ehCacheCacheManager' threw exception; nested exception is java.lang.IllegalArgumentException: Cache configuration does not exist 'ServletContext resource [/ehcache.xml]'
解决：注意classpath:不能少
spring.cache.ehcache.config=classpath:ehcache.xml
参考资料
MyBatis二级缓存介绍
mybatis官网中文
MyBatis 二级缓存全详解
Spring Cache和EhCache实现缓存管理
第四篇：SpringBoot中Cache缓存的使用
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