3.Mybatis基本配置（查询操作）

configuration.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>
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"></transactionManager>
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/newtest?useSSL=false&amp;characterEncoding=UTF-8"/>
                <property name="username" value="root"/>
                <property name="password" value="cy414ljh212,,,"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <mapper resource="mapper/StudentMapper.xml"></mapper>
    </mappers>
</configuration>

StudentMapper.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="dao.StudentDao">

    <select id="selectOne" resultType="domain.Student">
        select * from newstudent where id = 1;
    </select>

    <select id="selectAll" resultType="domain.Student">
        select * from newstudent;
    </select>

    <select id="selectCount" resultType="int">
        select count(*) as ct from newstudent;
    </select>

    <select id="selectNameById" resultType="String">
        select name from newstudent where id =3;
    </select>

    <select id="selectCountBySex" resultType="HashMap">
        select sex,count(*) as ct from newstudent group by sex;
    </select>
</mapper>

StudentDao

package dao;

import domain.Student;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;

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

public class StudentDao {

    //设计一个方法，根据编sex分组，统计每组人数
    public List<Map<String,Object>> selectCountBySex(){
        SqlSessionFactoryBuilder builder=new SqlSessionFactoryBuilder();
        InputStream inputStream=Thread.currentThread().getContextClassLoader().getResourceAsStream("configuration.xml");
        SqlSessionFactory factory= builder.build(inputStream);
        SqlSession sqlSession=factory.openSession(true);
        return sqlSession.selectList("selectCountBySex");
    }

    //设计一个方法，根据编号查询对应人名
    public String selectNameById(){
        SqlSessionFactoryBuilder builder=new SqlSessionFactoryBuilder();
        InputStream inputStream=Thread.currentThread().getContextClassLoader().getResourceAsStream("configuration.xml");
        SqlSessionFactory factory= builder.build(inputStream);
        SqlSession sqlSession=factory.openSession(true);
        return sqlSession.selectOne("selectNameById");
    }

    //设计一个方法，查询表格中记录的个数
    public int selectCount(){
        SqlSessionFactoryBuilder builder=new SqlSessionFactoryBuilder();
        InputStream inputStream=Thread.currentThread().getContextClassLoader().getResourceAsStream("configuration.xml");
        SqlSessionFactory factory= builder.build(inputStream);
        SqlSession sqlSession=factory.openSession(true);
        return sqlSession.selectOne("selectCount");
    }

    //设计一个方法，查询表格中全部记录
    public List<Student> selectAll(){
        SqlSessionFactoryBuilder builder=new SqlSessionFactoryBuilder();
        InputStream inputStream=Thread.currentThread().getContextClassLoader().getResourceAsStream("configuration.xml");
        SqlSessionFactory factory= builder.build(inputStream);
        SqlSession sqlSession=factory.openSession(true);
        return sqlSession.selectList("selectAll");//SQL语句的id、SQL上问号信息、告知每一行记录存储的类型
    }

    //设计一个方法，查询单条记录 读操作，携带返回值
    public Student selectOne(){//此处模拟用用固定记录来进行演示
        /*
        原先的框架底层：
        JDBC+SQL，告知SQL--告知SQL上问号信息（非必须有）---告知容器（一行记录）类型
        加载驱动--获取连接--状态参数（conn.preparedStatement(sql)）--
        将SQL和问号信息拼接完整--执行操作--将查询结果取出后装入新容器（数组、集合、domain对象）--关闭结果集--
        关闭操作--返回新的容器
         */

        //找寻SqlSession对象
        SqlSessionFactoryBuilder builder=new SqlSessionFactoryBuilder();
        InputStream inputStream=Thread.currentThread().getContextClassLoader().getResourceAsStream("configuration.xml");
        //第二种获取输入流的方式，有几点需要注意
        //InputStream inputStream1= Resources.getResourceAsStream("configuration.xml");
        //1.Resources这个类是Mybatis框架提供的，依赖度很高
        //2.方法名与我们之前用到的ClassLoader加载方法一致，且框架提供的这个方法必须处理异常
        SqlSessionFactory factory=builder.build(inputStream);
        SqlSession sqlSession=factory.openSession(true);
        //让SqlSession对象帮我们做事
        return sqlSession.selectOne("selectOne");//1.SQL语句的id、SQL语句上的问号信息（暂无）、查询结果装入什么容器
    }

}