Mybatis--(3)工具类和动态代理

package com.ltlrl.utils;

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 java.io.InputStream;

public class MyBatisUtils {
    //定义 SqlSessionFactory
    private static SqlSessionFactory factory = null;
    static {
        //使用 静态块 创建一次 SqlSessionFactory
        try{
            String config = "mybatis.xml";
            //读取配置文件
            InputStream in = Resources.getResourceAsStream(config);
            //创建 SqlSessionFactory 对象
            factory = new SqlSessionFactoryBuilder().build(in);
        }catch (Exception e){
            factory = null;
            e.printStackTrace();
        }
    }
    
    public static SqlSession getSqlSession(){
        SqlSession session = null;
        if( factory != null){
            session = factory.openSession();
        }
        return session;
    }
}

@Test
public void testUtils() throws IOException {
    SqlSession session = MyBatisUtil.getSqlSession();
    List studentList = session.selectList("com.ltlrl.dao.StudentDao.selectStudents");
    studentList.forEach( student -> System.out.println(student));
    session.close();
}

在mybatis中事务默认不是自动提交的，需要我们来手动进行提交

sqlSession.commit();//提交事务

将openSession方法的参数设为true就能实现自动提交

session = factory.openSession(true);

因为真正对数据库进行操作的工作其实是由框架通过mapper中的SQL完成的，所以MyBatis框架就抛开了 Dao 的实现类，直接定位到映射文件mapper中的相应SQL语句，对DB进行操作。这种对Dao的实现方式称为Mapper的动态代理方式。Mapper动态代理方式无需我们实现Dao接口。接口是由MyBatis结合映射文件自动生成的动态代理实现的。

只需调用 SqlSession的getMapper()方法，即可获取指定接口的实现类对象。

该方法的参数为指定Dao接口类的class值。

qlSession sqlSession = MyBatisUtils.getSqlSession();
StudentDao dao =sqlSession.getMapper(StudentDao.class);

    public void SelectStudents(){
        SqlSession sqlSession = MyBatisUtils.getSqlSession();
        StudentDao dao =sqlSession.getMapper(StudentDao.class);
        //调用dao的方法，执行数据库的操作
        Liststudents =dao.selectStudents();
        for(Student stu:students){
            System.out.println("学生="+stu);
        }
    }
    public void InsertStudent(){
        SqlSession sqlSession =MyBatisUtils.getSqlSession();
        StudentDao dao =sqlSession.getMapper(StudentDao.class);
        Student student =new Student();
        student.setId(1007);
        student.setName("李飞");
        student.setEmail("lifei@qq.com");
        student.setAge(27);
        int nums =dao.insertStudent(student);
        sqlSession.commit();
        System.out.println("添加对象的数量："+nums);
    }
    public void testUpdate(){
        SqlSession sqlSession = MyBatisUtils.getSqlSession();
        StudentDao dao =sqlSession.getMapper(StudentDao.class);
        Student student = new Student();
        student.setId(1006);
        student.setAge(28);
        int nums = dao.updateStudent(student);
        sqlSession.commit();
        System.out.println("修改数据的数量:"+nums);
    }
    public void testDelete(){
        SqlSession sqlSession = MyBatisUtils.getSqlSession();
        StudentDao dao =sqlSession.getMapper(StudentDao.class);
        int nums = dao.deleteStudent(1006);
        sqlSession.commit();
        System.out.println("删除数据的数量:"+nums);
    }