在实体和数据库字段一致 时直接使用resultType时可以的。

当字段不一致时，可以使用别名。使之一致。

以下讲解使用resultMap情况。

实体Order.java

 1 package pojo;
 2 
 3 import java.util.Date;
 4 
 5 public class Order {
 6     private Integer id;
 7 
 8     private Integer userId;
 9 
10     private String number;
11 
12     private Date createtime;
13 
14     private String note;
15 
16     public Integer getId() {
17         return id;
18     }
19 
20     public void setId(Integer id) {
21         this.id = id;
22     }
23 
24     public Integer getUserId() {
25         return userId;
26     }
27 
28     public void setUserId(Integer userId) {
29         this.userId = userId;
30     }
31 
32     public String getNumber() {
33         return number;
34     }
35 
36     public void setNumber(String number) {
37         this.number = number == null ? null : number.trim();
38     }
39 
40     public Date getCreatetime() {
41         return createtime;
42     }
43 
44     public void setCreatetime(Date createtime) {
45         this.createtime = createtime;
46     }
47 
48     public String getNote() {
49         return note;
50     }
51 
52     public void setNote(String note) {
53         this.note = note == null ? null : note.trim();
54     }
55 
56     @Override
57     public String toString() {
58         return "Order [id=" + id + ", userId=" + userId + ", number=" + number + ", createtime=" + createtime
59                 + ", note=" + note + "]";
60     }
61 
62 }

数据库字段：

两者user_id不一致。映射文件

OrderMapper.xml

<?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">
<!-- namespace命名空间，隔离sql文件 -->
<!-- #{}占位符相当于jdbc的？ -->
<!-- ${value} 字符串拼接 -->
<!-- 动态代理开发原则
1、namespace必须是接口的全路径
2、接口的方法必须与sql的id一致
3、接口的入参与parameterType类型一致
4、接口的返回值必须与resultType类型一致
 -->
<mapper namespace="mapper.OrderMapper">
    
    <!-- 定义resultMap -->
    <resultMap type="order" id="order_List_map">
        <id property="id" column="id"/>
        <result property="userId" column="user_id"/>
        <result property="number" column="number"/>
        <result property="createtime" column="createtime"/>
        <result property="note" column="note"/>
        
    </resultMap>
    
<!-- 引用resultMap -->
    <select id="getOrderList"  resultMap="order_List_map">
     select id,
     user_id,
     number,
     createtime,
     note 
     from order1
    </select>    
</mapper>

接口OrderMapper.java

package mapper;

import java.util.List;

import pojo.Order;

public interface OrderMapper {
    List<Order> getOrderList();
}    

测试（注：

SqlSessionFactoryUtil工具类获得SqlSessionFactory

）

    @Test
    public void getOrderList() {
        SqlSession openSession = SqlSessionFactoryUtil.getSqlSessionFactory().openSession();
        //获得接口实现类
        OrderMapper mapper = openSession.getMapper(OrderMapper.class);
        List<Order> orderList = mapper.getOrderList();
        for (Order order : orderList) {
            System.out.println(order);
        }
        openSession.close();
    }