SpringBoot系列之使用Redis做Mybatis二级缓存

开发环境

• JDK 1.8
• SpringBoot2.2.1
• MybatisPlus3.4.3.4
• Maven 3.2+
• Mysql5.7.36
• 开发工具

• IntelliJ IDEA
• smartGit

使用阿里的脚手架，链接：​​https://start.aliyun.com​​

选择mybatis plus framework

然后项目基础架构搭建好之后，加上redis配置

<dependency>
   <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-data-redis</artifactId>
</dependency>

加上redis配置：

spring:
  redis:
    host: 127.0.0.1
    port: 6379
    password:
    database: 0

MyBatisPlus开启缓存支持

实现​​​Cache​​​接口，因为这个类不是Spring管理的，所以通过​​SpringContextHolder​​从ioc容器里获取redisTemplate类

package com.example.mybatisplus.common.cache;


import com.example.mybatisplus.common.ioc.SpringContextHolder;
import lombok.extern.slf4j.Slf4j;
import org.apache.ibatis.cache.Cache;
import org.springframework.data.redis.core.RedisTemplate;
import org.springframework.util.StringUtils;

import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;

@Slf4j
public class MyBatisRedisCache implements Cache {

    private static RedisTemplate<String , Object> redisTemplate;

    private final ReadWriteLock readWriteLock = new ReentrantReadWriteLock(true);

    private String id;


    public MyBatisRedisCache(String id) {
        if (StringUtils.isEmpty(id)) {
            throw new IllegalArgumentException("cache instances require an id.");
        }
        this.id = id;
        if (redisTemplate == null) {
            redisTemplate = SpringContextHolder.getBean("redisTemplate");
        }
    }

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

    @Override
    public void putObject(Object key, Object value) {
        if (!StringUtils.isEmpty(value)) {
            redisTemplate.opsForHash().put(id, key.toString() , value);
            log.info("mybatis缓存,{}:[{}]" , key , value );
        }
    }

    @Override
    public Object getObject(Object key) {
        if (!StringUtils.isEmpty(key)) {
            Object object = redisTemplate.opsForHash().get(id , key.toString());
            log.info("mybatis缓存读取,{}:[{}]", key , object);
            return object;
        }
        return null;
    }

    @Override
    public Object removeObject(Object key) {
        if (!StringUtils.isEmpty(key)) {
            redisTemplate.delete(key.toString());
        }
        return null;
    }

    @Override
    public void clear() {
        redisTemplate.delete(id.toString());
    }

    @Override
    public int getSize() {
        return redisTemplate.opsForHash().size(id.toString()).intValue();
    }

    @Override
    public ReadWriteLock getReadWriteLock() {
        return readWriteLock;
    }


}

修改​​CacheNamespace​​​指定缓存类，​​implementation​​​ 属性：默认是​​PerpetualCache​​​类，即​​hashMap​​实现

package com.example.mybatisplus.mapper;

import com.baomidou.dynamic.datasource.annotation.DS;
import com.baomidou.mybatisplus.core.mapper.BaseMapper;
import com.example.mybatisplus.common.cache.MyBatisRedisCache;
import com.example.mybatisplus.model.User;
import org.apache.ibatis.annotations.CacheNamespace;

@DS(value = "shop")
@CacheNamespace(implementation = MyBatisRedisCache.class ,eviction = MyBatisRedisCache.class)
public interface UserMapper extends BaseMapper<User>{

}

SpringContextHolder 类

package com.example.mybatisplus.common.ioc;


import org.springframework.beans.BeansException;
import org.springframework.beans.factory.DisposableBean;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;
import org.springframework.context.annotation.Lazy;
import org.springframework.stereotype.Service;
import org.springframework.util.Assert;

@Service
@Lazy(false)
public class SpringContextHolder implements ApplicationContextAware, DisposableBean {

    private static ApplicationContext applicationContext = null;

    @Override
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
        SpringContextHolder.applicationContext = applicationContext;
    }

    public static ApplicationContext getApplicationContext() {
        assertContextInjected();
        return applicationContext;
    }

    public static <T> T getBean(String name) {
        assertContextInjected();
        return (T) applicationContext.getBean(name);
    }

    public static <T> T getBean(Class<T> requiredType) {
        assertContextInjected();
        return applicationContext.getBean(requiredType);
    }

    public static void clearHolder() {
        applicationContext = null;
    }

    @Override
    public void destroy() throws Exception {
        SpringContextHolder.clearHolder();
    }

    private static void assertContextInjected() {
        Assert.state(applicationContext != null,"applicaitonContext属性未注入");
    }
}

测试，缓存里没数据，读取数据库

缓存有数据，不读取数据库

本博客代码例子可以在GitHub找到​​下载链接​​