CREATE DATABASE mybatis;
USE mybatis;
CREATE TABLE users(id INT PRIMARY KEY AUTO_INCREMENT,NAME VARCHAR(20),age INT);
INSERT INTO users(NAME,age) VALUES('codeRose',24);
INSERT INTO users(NAME,age) VALUES('codeRose',24);

<?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>
 <environments default="development">
 <environment id="development">
<transactionManager type="JDBC" />
 <!-- 配置数据库连接信息 -->
 <dataSource type="POOLED">
<property name="driver" value="com.mysql.jdbc.Driver" />
<property name="url" value="jdbc:mysql://localhost:3306/mybatis" />
<property name="username" value="root" />
<property name="password" value="" />
</dataSource>
</environment>
</environments>
</configuration>

package codeRose.dao;
public class User {
  //实体类的属性与表中字段一一对应
  private int id;
  private String name;
  private int age;
  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 int getAge() {
    return age;
  }
  public void setAge(int age) {
    this.age = age;
  }
  @Override
  public String toString() {
    return "User [id=" + id + ", name=" + name + ", age=" + age + "]";
  }
}

<?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">
<!-- 为这个mapper指定一个唯一的namespace，namespace的值为包名+sql映射文件名，这样就能保证namespace值唯一 -->
<mapper namespace="codeRose.mapping.userMapper">
  <!-- 在select标签中编写查询的SQL语句， 设置select标签的id属性为getUser，id属性值必须是唯一的，不能够重复 使用parameterType属性指明查询时使用的参数类型，resultType属性指明查询返回的结果集类型 
    resultType="me.gacl.domain.User"就表示将查询结果封装成一个User类的对象返回 User类就是users表所对应的实体类 -->
  <!-- 根据id查询得到一个user对象 -->
  <select id="getUser" parameterType="int" resultType="codeRose.dao.User">
    select * from users where id=#{id}
  </select>
</mapper>

<?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>
 <environments default="development">
 <environment id="development">
<transactionManager type="JDBC" />
 <!-- 配置数据库连接信息 -->
 <dataSource type="POOLED">
<property name="driver" value="com.mysql.jdbc.Driver" />
<property name="url" value="jdbc:mysql://localhost:3306/mybatis" />
<property name="username" value="root" />
<property name="password" value="" />
</dataSource>
</environment>
</environments>
<!-- 注册sql映射文件 -->
<mappers>
<!-- 包名/文件名 -->
<mapper resource="codeRose/mapping/userMapper.xml"/>
</mappers>
</configuration>

package codeRose.test;
import java.io.InputStream;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import codeRose.dao.User;
public class Test {
  public static void main(String[] args) {
    // myBatis的配置文件
    String resource="conf.xml";
    //使用类加载器加载mybatis的配置文件（它也加载关联的映射文件）
    InputStream is=Test.class.getClassLoader().getResourceAsStream(resource);
    //构建sqlSession的工厂
    SqlSessionFactory sessionFactory=new SqlSessionFactoryBuilder().build(is);
    //使用Mybatis提供的Resources类加载MyBatis的配置文件
    //Reader reader=Resources.getResourceAsReader(resource);
    //构建sqlSession的工厂
    //SqlSessionFactory sessionFactory=new SqlSessionFactoryBuilder().build(reader);
    //创建能执行映射文件中sql的sqlSession
    SqlSession session=sessionFactory.openSession();
    /*
     * 映射sql的标识字符串，
     * codeRose.mapping.userMapper是userMapper.xml文件中mapper标签的namespace属性的值，
     * getUser是select标签的id属性值，通过select标签的id属性值就可以找到要执行的SQL
     */
    String statement="codeRose.mapping.userMapper.getUser";
    //执行查询返回一个唯一user对线的sql
    User user=session.selectOne(statement,1);
    System.out.println("查询所得的数据库信息为："+user);
  }
}