Mybatis学习笔记(一)入门例子

开始学习另一个ORM 框架：Mybatis，与Hibernate类似，感觉比Hibernate轻量，比较小．

这节要完成入门例子．

１.建表mybatis_student

idnameage

２.实体类

package com.skymr.mybatis.model;public class Student {private int id;private String name;private int age;/** * 必须要有无参构造器，有参构造器可有可无（至少我测试时是这样） * 如果没有无参构造器，只有有参构造器，会报错 */public Student() {}public Student(String name, int age) {this.name = name;this.age = 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;}public String toString(){return "["+name+","+age+"]";}}

３.mybatis配置文件

jdbc.properties : jdbc配置信息

jdbc.driverClassName=com.mysql.jdbc.Driverjdbc.url=jdbc:mysql://127.0.0.1:3306/websitejdbc.username=rootjdbc.password=root

conf.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><!-- 引入jdbc配置信息 --><properties resource="jdbc.properties"></properties><typeAliases><!-- 别名配置，方便书写 --><typeAlias alias="Student" type="com.skymr.mybatis.model.Student"/></typeAliases><!-- 环境配置 -->    <environments default="development">    <!-- 开发环境，企业里面可能有多个环境 -->        <environment id="development">            <transactionManager type="JDBC" />            <!-- 配置数据库连接信息 -->             <dataSource type="POOLED">                 <property name="driver" value="${jdbc.driverClassName}" />                 <property name="url" value="${jdbc.url}" />                 <property name="username" value="${jdbc.username}" />                 <property name="password" value="${jdbc.password}" />             </dataSource>         </environment>     </environments>          <mappers>         <!-- 注册StudentMapper.xml文件， -->         <mapper resource="com/skymr/mybatis/mappers/StudentMapper.xml"/>     </mappers></configuration>

与Hibernate太像了啊．

４.映射文件与映射接口

映射接口

package com.skymr.mybatis.mappers;import com.skymr.mybatis.model.Student;public interface StudentMapper {public Student getStudent(int id);}

映射文件，类似Hibernate的xml配置的映射

<?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:Mapper映射 --><!-- 这个文件感觉就像StudentMapper接口的实现一样，只是从java文件变成了xml文件充当了Dao类的功能 --><mapper namespace="com.skymr.mybatis.mappers.StudentMapper"><select id="getStudent" parameterType="int" resultType="Student"><!-- mybatis要自己写sql语句 -->select * from mybatis_Student where id=#{id}</select></mapper> 

这个映射文件感觉就是映射接口的实现类

５.工具类，获取Session

package com.skymr.mybatis.util;import java.io.InputStream;import org.apache.ibatis.session.SqlSession;import org.apache.ibatis.session.SqlSessionFactory;import org.apache.ibatis.session.SqlSessionFactoryBuilder;/** * 工具类，单例 * @author skymr * */public class MybatisUtil {private static SqlSessionFactory factory;public static SqlSessionFactory getSessionFactory(){if (factory == null){InputStream is = MybatisUtil.class.getClassLoader().getResourceAsStream("conf.xml");factory = new SqlSessionFactoryBuilder().build(is);}return factory;}public static SqlSession openSession(){return getSessionFactory().openSession();}}

６.测试

package com.skymr.mybatis.service;import org.apache.ibatis.session.SqlSession;import com.skymr.mybatis.mappers.StudentMapper;import com.skymr.mybatis.util.MybatisUtil;public class StudentTest {public static void main(String[] args){//        String statement = "com.skymr.mybatis.mappers.StudentMapper.getStudent";//映射sql的标识字符串//        //执行查询返回一个唯一user对象的sql//        Student student = MybatisUtil.openSession().selectOne(statement, 1);//        System.out.println(student);SqlSession session = MybatisUtil.openSession();StudentMapper mapper = session.getMapper(StudentMapper.class);System.out.println(mapper.getStudent(1));session.close();}}

ps:

session需要关闭；

从session里取出映射接口的实例就可调用操作数据库的方法了，底层一定是根据映射配置文件实现了一个映射接口，这个跟hibernate不一样啊．

数据库里添加一行数据，id=1

测试成功．