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．