MyBatis初步学习

Posted 2020-09-20 睡猪遇上狼

1、准备工作

jar包:

　　mybatis-3.4.4.jar，下载地址：https://github.com/mybatis/ignite-cache/releases

　　mysql-connector-java-5.1.40-bin.jar，下载地址：https://dev.mysql.com/downloads/connector/j/

项目目录结构：

数据库建标语句

/*如果已经存在此数据库，先删除*/
drop database if exists sqltest  ;
/*创建并设置编码为UTF-8*/
create database sqltest default character set utf8 ;
/*选择数据库*/
use sqltest ;

/*删除已有的学生表*/
drop table if exists tb_student ;

/*创建学生表*/
CREATE TABLE `tb_student` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `stuId` varchar(45) DEFAULT NULL,
  `name` varchar(45) DEFAULT NULL,
  `clsId` varchar(45) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

/*插入学生的数据*/
insert into tb_student (stuId,name,clsId) value (\'1001\',\'张三\',\'201\') ;
insert into tb_student (stuId,name,clsId) value (\'1002\',\'李四\',\'201\') ;
insert into tb_student (stuId,name,clsId) value (\'1003\',\'王五\',\'201\') ;
insert into tb_student (stuId,name,clsId) value (\'1004\',\'赵六\',\'202\') ;
insert into tb_student (stuId,name,clsId) value (\'1005\',\'巩发财\',\'202\') ;
insert into tb_student (stuId,name,clsId) value (\'1006\',\'柏拉图\',\'202\') ;
insert into tb_student (stuId,name,clsId) value (\'1007\',\'钱老虎\',\'203\') ;
insert into tb_student (stuId,name,clsId) value (\'1008\',\'杨伟\',\'203\') ;
insert into tb_student (stuId,name,clsId) value (\'1009\',\'陈海\',\'203\') ;

 

二、代码编写

实体类Student：

package org.yoki.edu.main.vo;

public class Student {

    private Integer id;
    private String stuId;
    private String name;
    private String clsId;

    /*省略setter、getter方法*/

}

 

MyBatis的配置文件：

<?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>

    <!-- typeAliases必须写在environments和mappers前面，不然报错，这是dtd格式限制的 -->
    <typeAliases>
        <!-- 用于在实体类的映射文件进行使用student，而不用每次使用类的全名 -->
        <typeAlias type="org.yoki.edu.main.vo.Student" alias="student" />
    </typeAliases>
    
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC" />
            <!-- 数据库链接信息，注：分号改为&amp;转义符，防止报错 -->
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.jdbc.Driver" />
                <property name="url" value="jdbc:mysql://localhost:3306/sqltest?useUnicode=true&amp;characterEncoding=UTF-8&amp;useSSL=false" />
                <property name="username" value="root" />
                <property name="password" value="root" />
            </dataSource>
        </environment>
    </environments>
    
    <mappers>
        <!-- 实体类的映射文件 -->
        <mapper resource="org/yoki/edu/main/vo/StudentMapper.xml" />
    </mappers>
    
</configuration>

 

实体类Student配置文件：

<?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">
<!-- namespace随意内容 -->
<mapper namespace="this.is.student.mapper.namespace">

    <!-- 方法一 -->
    <!-- type属性对应与在MyBatis配置文件中typeAliases标签下定义的引用 -->
    <resultMap id="studentMapper" type="student">
    <!-- 属性名称<>列名 -->
        <id property="id" column="id" />
        <result property="stuId" column="stuId" />
        <result property="name" column="name" />
        <result property="clsId" column="clsId" />
    </resultMap>
    
    <!-- resultMap属性值对应 -->
    <select id="selectById" resultMap="studentMapper">
        select * from tb_student where id = #{id}
    </select>
    
    <!-- 方法二 -->
    <!-- resultType可以使用类的全名，也可以使用MyBatis配置文件中typeAliases标签下定义的引用 -->
<!--     <select id="selectById" resultType="org.yoki.edu.main.vo.Student"> -->
<!--         select * from tb_student where id = #{id} -->
<!--     </select> -->
    
</mapper>

SessionUtils（用于初始化SqlSessionFactory和提供获取SqlSession的接口）：

package org.yoki.edu.utils;

import java.io.IOException;
import java.io.InputStream;

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

public class SessionUtils {
    
    private static SqlSessionFactory fa = null ;
    
    static{
        /*静态代码块，在类加载后执行*/
        String resource = "org/yoki/edu/utils/mybatis-config.xml" ;
        InputStream input;
        try {
            /*获取配置文件的输入流*/
            input = Resources.getResourceAsStream(resource);
            /*根据输入流生成SqlSessionFactory*/
            fa = new SqlSessionFactoryBuilder().build(input) ;
            int j = 0 ;
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    
    public SqlSession getSqlSession(){
        if(null == fa)
            return null;
        SqlSession session = fa.openSession() ;
        return session ;
    }

}

StudentDao（这里偷懒没有使用接口）：

package org.yoki.edu.main.dao;

import org.apache.ibatis.session.SqlSession;
import org.yoki.edu.main.vo.Student;
import org.yoki.edu.utils.SessionUtils;

public class StudentDao {
    
    private SessionUtils utils = new SessionUtils() ;
    
    public Student getById(Integer id){
        SqlSession session = utils.getSqlSession() ;
        /*selectOne的第一个参数对应映射文件的namespace + \'.\' + （select、update、insert、delete）id*/
        Student st = session.selectOne("this.is.student.mapper.namespace" + ".selectById", id) ;
        return st ;
    }

}

 测试类：

package org.yoki.edu.main;

import org.yoki.edu.main.dao.StudentDao;
import org.yoki.edu.main.vo.Student;

public class MainRun {

    public static void main(String[] args) {
        StudentDao dao = new StudentDao() ;
        Student st = dao.getById(2) ;
        System.out.println(st);
    }
    
}

结果：