[Java知识库]mybatis二级缓存（侧重于springboot整合mybatis）

1.引入依赖

        <!--mybatis-->
        <dependency>
            <groupId>org.mybatis.spring.boot</groupId>
            <artifactId>mybatis-spring-boot-starter</artifactId>
            <version>2.1.3</version>
        </dependency>

<!--        mysql-->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
        </dependency>
<!--        druid-->
        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>druid</artifactId>
            <version>1.1.24</version>
        </dependency>

2.编写配置文件

（这里需要修改成自己的 数据库 账号 密码）

server.port=8080

spring.datasource.type=com.alibaba.druid.pool.DruidDataSource
spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver
spring.datasource.url=jdbc:mysql://localhost:3306/users?useUnicode=true&useJDBCCompliantTimezoneShift=true&useLegacyDatetimeCode=false&serverTimezone=Asia/Shanghai&useSSL=true&characterEncoding=UTF-8
spring.datasource.username=root
spring.datasource.password=123456

mybatis.mapper-locations=classpath:com/redis/mapper/*.xml
mybatis.type-aliases-package=com.redis.pojo

logging.level.com.redis.dao=debug

3.创建数据库并连接

?4.编写实体类

（根据数据库表）

package com.redis.pojo;
import lombok.Data;

import java.io.Serializable;
import java.util.Date;
@Data
public class User implements Serializable {
??? private String id;
??? private String name;
??? private Integer age;
??? private Date bir;
}

5.编写mapper（dao）接口

（别忘了注解）

package com.redis.dao;

import com.redis.pojo.User;
import org.apache.ibatis.annotations.Mapper;

import java.util.List;
@Mapper
public interface UserDao {
??? List<User> findAll();
}

6.编写映射xml文件

（名字要与mapper接口一样）

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">

<mapper namespace="com.redis.dao.UserDao">
    <select id="findAll" resultType="User">
        select id,name,age,bir from t_user
    </select>
</mapper>

7.编写业务接口

package com.redis.service;

import com.redis.pojo.User;

import java.util.List;

public interface UserService {
??? List<User> findAll();
}

8.实现类

package com.redis.service;


import com.redis.dao.UserDao;
import com.redis.pojo.User;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import org.springframework.transaction.annotation.Transactional;

import java.util.List;

@Service
@Transactional
public class UserServiceImpl implements UserService {
    @Autowired
    private UserDao userDao;
    @Override
    public List<User> findAll() {
        return userDao.findAll();
    }
}

9.进行测试

package com.redis.tsts;

import com.redis.service.UserService;
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;

@SpringBootTest
public class mybatis {
    @Autowired
    private UserService userService;

    @Test
    public void test1(){
        userService.findAll().forEach(System.out::println);

        System.out.println("=========================================");

        userService.findAll().forEach(System.out::println);
    }
}

这里我们可以看到?? 两次相同的查询? 查询了两次数据库

?10.使用二级缓存

?

?由此可见 两次相同的查询? 查询了数据库一次? 查询了缓存一次