mybatis学习四 mybatis的三种查询方式

Posted 2021-01-05 阿瞒123

      <select id="selAll" resultType="com.caopeng.pojo.Flower">
          select * from flower
      </select>
      
      <select id="selCount" resultType="int">
          select count(*) from flower
      </select>
      
      <select id="selMap" resultType="com.caopeng.pojo.Flower">
          select * from flower
      </select>    

package com.caopeng.demo;

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

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 com.caopeng.pojo.Flower;


public class Demo {
    public static void main(String[] args) throws IOException {
        //加载配置文件
        InputStream in = Resources.getResourceAsStream("mybatis.xml");
        //使用工厂设计模式   【注意】以后sqlSessionFactory都会被spring 管理，不需要我们自己创建
        SqlSessionFactory sqlSessionFactory=new SqlSessionFactoryBuilder().build(in);
        
        //获取sqlSession
        SqlSession sqlSession=sqlSessionFactory.openSession();
        
        //查询结果返回一个resultType的值作为泛型值的List
        List<Flower> flowrList = sqlSession.selectList("com.caopeng.mapper.FlowerMapper.selAll");
        for (Flower flower : flowrList) {
            System.out.println(flower);
        }
        //查询结果返回一个Obejct
        int count=sqlSession.selectOne("com.caopeng.mapper.FlowerMapper.selCount");
        System.out.println(count);
        
        //查询结果返回一个Map,其中key值是selectMap的最后一个参数，value为resultType的指定的返回的对象
        Map<Object,Object> map= sqlSession.selectMap("com.caopeng.mapper.FlowerMapper.selMap", "name");
        System.out.println(map);
        sqlSession.close();
    }
}