MyBatis基础学习笔记

零、什么是 MyBatis？

MyBatis 是一款优秀的持久层框架，它支持自定义 SQL、存储过程以及高级映射。MyBatis 免除了几乎所有的 JDBC 代码以及设置参数和获取结果集的工作。MyBatis 可以通过简单的 XML 或注解来配置和映射原始类型、接口和 Java POJO（Plain Old Java Objects，普通老式 Java 对象）为数据库中的记录。

一、搭建环境

二、导入 maven 依赖

<dependencies>
        <!--数据库相关依赖-->
        <!-- https://mvnrepository.com/artifact/mysql/mysql-connector-java -->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.47</version>
        </dependency>

        <!--MyBatis相关依赖-->
        <!-- https://mvnrepository.com/artifact/org.mybatis/mybatis -->
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.4.6</version>
        </dependency>

        <!--单元测试-->
        <!-- https://mvnrepository.com/artifact/junit/junit -->
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
            <scope>test</scope>
        </dependency>
    </dependencies>

三、工具类

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 {
            // 第一步： 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();
        }
    }

    // 第二步，通过 SqlSessionFactory 对象 获取 SqlSession 实例。
    public static SqlSession getSqlSession(){
        return sqlSessionFactory.openSession();
    }
}

四、核心配置 MyBatis-config.xml 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>
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://192.168.21.128:3306/fof?characterEncoding=UTF-8"/>
                <property name="username" value="root"/>
                <property name="password" value="root"/>
            </dataSource>
        </environment>
    </environments>

    <!--每一个 Mapper.xml 文件都需要在核心配置中注册-->
    <mappers>
        <mapper resource="com/ych/mapper/TestUserMapper.xml"/>
    </mappers>
</configuration>

五、mapper 接口类

import com.ych.model.TestUser;
import java.util.List;

public interface TestUserMapper {
    List<TestUser> getUsers();
}

六、mapper 类的实现 mapper.xml

<?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">
<mapper namespace="com.ych.mapper.TestUserMapper">
    <select id="getUsers" resultType="com.ych.model.TestUser">
        select * from fof.test_user
    </select>
</mapper>

七、测试

import com.ych.mapper.TestUserMapper;
import com.ych.model.TestUser;
import com.ych.utils.MyBatisUtils;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;

import java.util.List;

public class TestMyBatis {

    @Test
    public void MyBatis(){
        SqlSession sqlSession = MyBatisUtils.getSqlSession();
        TestUserMapper userMapper = sqlSession.getMapper(TestUserMapper.class);
        List<TestUser> userList = userMapper.getUsers();
        for (TestUser testUser : userList) {
            System.out.println(testUser);
        }
        // 关闭 sqlSession
        sqlSession.close();
    }
}

八、记录问题：

8.1:

## xml 文件没有注册到mapper中，解决方法：

8.2 : 在Build中配置resource，来防止资源导出失败的问题

    <!--在Build中配置resource，来防止资源导出失败的问题-->
    <build>
    <resources>
        <resource>
            <directory>src/main/resources</directory>
            <includes>
                <include>**/*.properties</include>
                <include>**/*.xml</include>
            </includes>
            <filtering>true</filtering>
        </resource>
        <resource>
            <directory>src/main/java</directory>
            <includes>
                <include>**/*.properties</include>
                <include>**/*.xml</include>
            </includes>
            <filtering>true</filtering>
        </resource>
    </resources>
</build>

注意问题：

1、mapper文件中的地址映射到实体类

2、核心配置的mapper.xml文件路径用 / 隔开，非逗号