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

id

name

age

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.Driver
jdbc.url=jdbc:mysql://127.0.0.1:3306/website
jdbc.username=root
jdbc.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．