mybatis查询结果封装javabean属性时属性名与数据库字段不同都能封装？？？？

问题现象：

• 通过mybatis查询数据库中的表记录，封装成javaBean, 本来属性名和字段名不相同的情况下，属性最后应该注入null的，结果能够正常注入。

javaBean:

public class Employee {
    private Integer id;
    private String empname;
    private Integer age;
    private Integer gender;
    private String email;
    private String loginName;


    @Override
    public String toString() {
        return "Employee{" +
                "id=" + id +
                ", empname='" + empname + '\'' +
                ", age=" + age +
                ", gender=" + gender +
                ", email='" + email + '\'' +
                ", loginName='" + loginName + '\'' +
                '}';
    }

    public Employee(Integer id, String empname, Integer age, Integer gender, String email, String loginName) {
        this.id = id;
        this.empname = empname;
        this.age = age;
        this.gender = gender;
        this.email = email;
        this.loginName = loginName;
    }

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getEmpname() {
        return empname;
    }

    public void setEmpname(String empname) {
        this.empname = empname;
    }

    public Integer getAge() {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }

    public Integer getGender() {
        return gender;
    }

    public void setGender(Integer gender) {
        this.gender = gender;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }
}

• 表信息：

CREATE TABLE `employee` (
  `id` int NOT NULL AUTO_INCREMENT,
  `empname` varchar(20) NOT NULL,
  `age` int DEFAULT NULL,
  `gender` int DEFAULT NULL,
  `email` varchar(20) DEFAULT NULL,
  `login_name` varchar(20) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8mb3

• mapper.xml中的sql语句：

<mapper namespace="com.tx.imapper.EmployeeMapper">
    <select id="getEmployeeById" resultType="com.tx.bean.Employee">
        select * from employee where id = #{id}
    </select>
</mapper>

• Test类

public class Test {
    public static SqlSessionFactory sqlSessionFactory;

    @Before
    public void init() throws IOException {
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
         sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
    }

    @org.junit.Test
    public void test(){
        SqlSession sqlSession = sqlSessionFactory.openSession();
        EmployeeMapper mapper = sqlSession.getMapper(EmployeeMapper.class);
        Employee emp = mapper.getEmployeeById(3);
        System.out.println(emp);	// Employee{id=1, empname='admin', age=40, gender=1, email='[email protected]', loginName='adminUser'}
        sqlSession.close();
    }

}

按照我的预估，loginName=null的，结果居然能够正常注入属性？ 本来想测试resultMap的，结果我瞬间麻了。

刚开始我以为mybatis最新版本将驼峰规则默认改成true了，但来我甚至将loginName的属性名改成其他完全不相干名称，都能照样注入属性。

问题所在：

后来才发现，我的javaBean缺少空参构造器。添上空参构造器后，才会正常显示null。 具体原因不清楚以后有时间再看mybatis源码吧。