【spring笔记】Mybaties入门

1、官方文档

https://mybatis.org/mybatis-3/zh/getting-started.html

2、搭建一个Mybatis实例

2.1 首先看配置文件mybatis-config.xml

这里面包括获取数据库连接实例的数据源（DataSource）以及决定事务作用域和控制方式的事务管理器（TransactionManager）（这里只是一个简单的事例）

<?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>
  <environments default="development">
    <environment id="development">
      <transactionManager type="JDBC"/>
      <dataSource type="POOLED">
        <property name="driver" value="${driver}"/>
        <property name="url" value="${url}"/>
        <property name="username" value="${username}"/>
        <property name="password" value="${password}"/>
      </dataSource>
    </environment>
  </environments>
  <mappers>
    <mapper resource="org/mybatis/example/BlogMapper.xml"/>
  </mappers>
</configuration>

注意 XML 头部的声明，它用来验证 XML 文档的正确性。environment 元素体中包含了事务管理和连接池的配置。mappers 元素则包含了一组映射器（mapper），这些映射器的 XML 映射文件包含了 SQL 代码和映射定义信息。

2.2 SqlSessionFactory

每个基于 MyBatis 的应用都是以一个 SqlSessionFactory 的实例为核心的。SqlSessionFactory 的实例可以通过 SqlSessionFactoryBuilder 获得。而 SqlSessionFactoryBuilder 则可以从 XML 配置文件或一个预先配置的 Configuration 实例来构建出 SqlSessionFactory 实例。通过SqlSessionFactory 实例就可以完成增删改查操作，mybatis框架通过对mapper的映射配置，直接调用接口的方法就可以实现。

利用配置文件构造SqlSessionFactory

String resource = "org/mybatis/example/mybatis-config.xml";
InputStream inputStream = Resources.getResourceAsStream(resource);
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);

写成工具类如下:

package com.wcy.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.IOException;
import java.io.InputStream;


public class MybatisUtils {

    private static SqlSessionFactory sqlSessionFactory;

    static {
        try {
            //获取sqlSessionFactory对象
            String resource = "mybatis-config.xml";
            InputStream inputStream = Resources.getResourceAsStream(resource);
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public static SqlSession getSqlSession() {
        return sqlSessionFactory.openSession();
    }
}

2.3、 Mapper映射

StudentMapper接口

package com.wcy.mapper;

import com.wcy.pojo.Student;

import java.util.List;

public interface StudentMapper {
    List<Student> getStudentList();
}

StudentMapper.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<!--绑定对应的mapper-->
<mapper namespace="com.wcy.mapper.StudentMapper">
    <select id="getStudentList" resultType="com.wcy.pojo.Student">
        select * from test.student;
    </select>
</mapper>

2.4、 Test

import com.wcy.mapper.StudentMapper;
import com.wcy.pojo.Student;
import com.wcy.utils.MybatisUtils;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;

import java.util.List;

public class MyTest {
    @Test
    public void test() {
        //获取session对象
        SqlSession sqlSession = MybatisUtils.getSqlSession();

        //方式一：获取mapper
        StudentMapper studentMapper = sqlSession.getMapper(StudentMapper.class);
        List<Student> studentList = studentMapper.getStudentList();
        for (Student stu : studentList) {
            System.out.println(stu.toString());
        }
        //关闭session
        sqlSession.close();
    }
}

注意事项：由于maven项目默认配置文件是在resources里面的，所以如果配置文件放到java下面就需要设置静态过滤


pom.xml下添加

<build>
    <resources>
        <resource>
            <directory>src/main/java</directory>
            <includes>
                <include>**/*.properties</include>
                <include>**/*.xml</include>
            </includes>
            <filtering>true</filtering>
        </resource>
        <resource>
            <directory>src/main/resources</directory>
            <includes>
                <include>**/*.properties</include>
                <include>**/*.xml</include>
            </includes>
            <filtering>true</filtering>
        </resource>
    </resources>
</build>