mybatis中的#{}和${}的区别

#{}：底层使用PreparedStatement。

特点：先进行SQL语句的编译，然后给SQL语句中的占位符？传值。

${}:底层使用Statement.

特点：先进行SQL语句的拼接，然后在对SQL语句进行编译。

【注意】：优先使用#{}，这是原则，避免SQL注入的风险。

【什么时候用${}】：传入Mapper的语句不需要带? '? '? 的时候使用，如果需要SQL语句的关键字放到SQL语句中，只能使用${},因为#{}是以值的形式放到SQL语句当中的。

批量删除-CarMapper语句：

<?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.mapper.CarMapper">
    <delete id="deleteBatch">
        delete from t_car where id in(${ids})
    </delete>
</mapper>

测试程序：

 @Test
    public void testDeleteBatch(){
        SqlSession sqlSession = SqlSessionUtil.openSession();
        CarMapper mapper = sqlSession.getMapper(CarMapper.class);
        int i = mapper.deleteBatch("13,19,21");
        System.out.println(i);
    }

输出结果：3

模糊查询-CarMapper：

<?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.mapper.CarMapper">
    <select id="selectByBrandLike">
        select
           car_num as carNum,
           brand,
           guide_price as guidePrice,
           produce_time as produceTime,
           car_type as carType
        from
           t_car
        where
           <!--brand like '%${brand}%'-->                <!--第一种方式-->
           brand like concat('%',#{brand},'%')            <!--第二种方式-->
           brand like concat('%','${brand}','%')            <!--第三种方式-->
           "%"#{brand}"%"                                  <!--第四种方式-->
    </select>
<mapper>

测试样例：

 @Test
    public void testSelectByBrandLike(){
        SqlSession sqlSession = SqlSessionUtil.openSession();
        CarMapper mapper = sqlSession.getMapper(CarMapper.class);
        List<Car> cars = mapper.selectByBrandLike("东风");
        cars.forEach(car -> System.out.println(car));
    }