MyBatis 3.0_[tp-24-25]_映射文件_参数处理_#与$取值区别_#{}更丰富的用法

/**================Mybatis参数值的获取:#和$符号的区别===============
* #{}:可以获得map中的值或者pojo对象属性的值;
* ${}:可以获得map中的值或者pojo对象属性的值;
* 区别:
* #{}: 是以预编译的形式,直接将参数设置到sql语句中;
* 使用PreparedStatement的sql封装方法 ,防止sql注入;
* ${}: 取出的值直接封装在sql语句中,不能防止sql注入,会有安全问题;
* 总结:
* 大多数情况下,我们取参数的值都应该去使用#{};
* 但是,原生jdbc不支持占位符的地方,我们就可以使用${}进行取值;
* 比如分表/排序/取到的参数值是表名...:按照年份分表拆分:
* select * from ${year}_salary where xxx;
* select * from tbl_employee order by ${f_name};
* ----------------------------------
* #{}:更丰富的用法:
* 规定参数的一些规则: javatype/jdbcType/mode(存储过程)/.......
* jdbcType通常需要在某种特定的条件下被设置,在我们的数据为null的时候,
* 有些数据库可能不能识别mybatis对null的默认处理;比如Oracle(报错)mysql(没有问题).
*
*
*/

public interface EmployeeMapper {
//多个参数处理,传入map
public Employee getEmpByMap(Map<String,Object> map);
}

<mapper namespace="com.dao.EmployeeMapper"><!--namespace: 名称空间;id: 唯一标识; resultType:返回值类型; -->
<!--public Employee getEmpByMap(Map<String,Object> map);-->
<select id="getEmpByMap" resultType="com.bean.Employee" databaseId="mysql">
select * from ${table_name}
where id = ${id} and last_name = #{lastName}
</select>

public class test_tp24 {
public SqlSessionFactory getSqlSessionFactory() throws IOException {
String resource = "mybatis-config.xml";
InputStream inputStream=Resources.getResourceAsStream(resource);
return new SqlSessionFactoryBuilder().build(inputStream);
}
@Test
public void test05() throws Exception{
//默认是不自动提交数据的,需要我们自己手动提交
SqlSession openSession = getSqlSessionFactory().openSession();
try {
EmployeeMapper mapper = openSession.getMapper(EmployeeMapper.class); HashMap<String, Object> map = new HashMap<>();
map.put("lastName", "葫芦娃");
map.put("id", 4);
map.put("table_name", "tbl_employee");
Employee empByMap = mapper.getEmpByMap(map);
System.out.println(empByMap);
//最后手动提交
openSession.commit();
}finally {
openSession.close();
}
}
}

DEBUG 11-29 15:22:20,111 ==> Preparing: select * from tbl_employee where id = 4 and last_name = ? (BaseJdbcLogger.java:145)
DEBUG 11-29 15:22:20,132 ==> Parameters: 葫芦娃(String) (BaseJdbcLogger.java:145)
DEBUG 11-29 15:22:20,142 <== Total: 1 (BaseJdbcLogger.java:145) Employee{id=4, lastname='葫芦娃', email='葫芦娃@163.com', gender='0'}