resultMap结果集映射

resultMap结果集是用来定义sql查询的结果与java对象的映射关系。它主要解决2大问题：

1）可以解决POJO属性名和表结构的字段名不一致问题(甚至是 不是标准的驼峰命名法)

2）可以完成高级查询，例如：一对一，一对多，多对多

其中还有一个比较重要的属性：autoMapping自动映射  默认为true。

注意：1.如果true，并且列名称和字段名称一致，是可以完成映射。

2.如果为true，名称不一致，但是符合驼峰命名，但必须开启驼峰命名匹配。

下面简单介绍一个案列：

接口：UserMapper.java

package com.inter;

import java.util.List;

import org.apache.ibatis.annotations.Param;

import com.pojo.User;

public interface UserMapper {

//    查询数据
    public List<User> selectAll();

}

Mybatis配置文件：Mybatis-config.xml

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

  <configuration>
      <!-- 加载外部配置文件 -->
      <properties resource="jdbc.properties"></properties>
      
/*
      <settings>
      <!--开启驼峰命名法-->
         <setting name="mapUnderscoreToCamelCase" value="true"/>
     </settings>
*/   
 
      <!-- 起别名 -->
     <typeAliases>
       <typeAlias alias="User" type="com.pojo.User"/>
     </typeAliases>

   <environments default="development">
     <environment id="development">
       <transactionManager type="JDBC"/>
       <dataSource type="POOLED">
         <property name="driver" value="${jdbc.driver}"/>
         <property name="url" value="${jdbc.url}"/>
         <property name="username" value="${jdbc.username}"/>
         <property name="password" value="${jdbc.password}"/>
       </dataSource>
     </environment>
   </environments>

   <!-- 指定mapper的配置文件 -->
   <mappers>
     <mapper resource="UserMapper.xml"/>
   </mappers>

 </configuration>

映射文件：UserMapper.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">
 <mapper namespace="com.inter.UserMapper">

   <resultMap type="User" id="userResult" autoMapping="true">
           <id property="id" column="id"/>
   </resultMap>

   <!-- 查询所有的数据 -->
   <select id="selectAll" resultMap="userResult">
           select * from tb_user
   </select>

 </mapper>

实体类：User.java

package com.pojo;

public class User {
    private int id;
    private String name;
    private String age;
    private String sex;

    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public String getAge() {
        return age;
    }
    public void setAge(String age) {
        this.age = age;
    }
    public String getSex() {
        return sex;
    }
    public void setSex(String sex) {
        this.sex = sex;
    }
    @Override
    public String toString() {
        return "User [id=" + id + ", name=" + name + ", age=" + age + ", sex=" + sex + "]";
    }

}

测试类：

package com.test;

import static org.junit.Assert.*;

import java.io.InputStream;
import java.util.List;

import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.Before;
import org.junit.Test;

import com.inter.UserMapper;
import com.pojo.User;

public class TestMybatisoneTest {

     private UserMapper userMapper;

     InputStream inputStream;
     SqlSessionFactory sqlSessionFactory;
     SqlSession sqlSession;

    @Before
    public void setUp() throws Exception {

            String resource = "mybatis-config.xml";     

            inputStream = Resources.getResourceAsStream(resource);

            sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);

            sqlSession = sqlSessionFactory.openSession();

//            动态代理实现
            userMapper = sqlSession.getMapper(UserMapper.class);
    }

    @Test
    public void test4(){

        List<User> list = userMapper.selectAll();
        for (User user : list) {
            System.out.println(user+"   ");
        }
    }
}