mybatis入门

1. 建立maven项目

项目下需要java：Sources Root; resources: Resources Root

2. 添加mybatis的依赖

<!-- mysql -->
<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <version>8.0.16</version>
</dependency>
<!-- mybatis -->
<dependency>
    <groupId>org.mybatis</groupId>
    <artifactId>mybatis</artifactId>
    <version>3.5.1</version>
</dependency>

3. 定义配置文件

<?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>
    <properties resource="database.properties"></properties>
    <!--取别名 -->
    <typeAliases>
        <typeAlias type="pojo.Subject" alias="Subject"></typeAlias>
    </typeAliases>
    <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="mapper/SubjectMapper.xml"/>
    </mappers>
</configuration>

3.1 配置文件结构图

3.1.1 根节点

​ configuration:根节点

3.1.2 子节点

1、properties,配置文件，配置数据库信息

<!-- 同时存在，取properties文件中的 -->
<properties resource="database.properties">
    <property name="driver" value="com.mysql.cj.jdbc.Driver"/>
    <property name="url" value="jdbc:mysql://127.0.0.1:3306/myschool?serverTimezone=UTC&amp;useUnicode=true&amp;characterEncoding=UTF-8"/>
    <property name="username" value="root"/>
    <property name="password" value="root123"/>
</properties>

2、setting：修改mybatis在运行时的行为方式

3、typeAliases

<!--取别名 -->
<typeAliases>
    <typeAlias type="pojo.Subject" alias="Subject"></typeAlias>
</typeAliases>

4、typeHandlers:类型处理

5、objectFactory：对象工厂

6、plugins：插件

7、environments:环境

可以配置多组，当前用那一组，只需要将id对应的值设置在default设置，即可！

<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>

8、mappers：映射器

<mappers>
    <mapper resource="mapper/SubjectMapper.xml"/>
</mappers>

4. 定义实体类

5. 定义mapper文件

<?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="mapper.SubjectMapper"><!--namespace指向mapper接口 -->
    <select id="selectList" resultType="pojo.Subject">
        select subjectno,subjectname,classhour,gradeid from subject where 1 = 1
    </select>
</mapper>

可以在api中复制

6.定义测试，添加junit4测试

先要添加junit4插件, https://blog.youkuaiyun.com/hanchao5272/article/details/79197989

直接测试

@Test //实现测试
public void testSelect(){
    SqlSession sqlSession = null;
    try {
        InputStream is = Resources.getResourceAsStream( "mybatis-config.xml" );
        SqlSessionFactory factory = new SqlSessionFactoryBuilder().build( is );
        sqlSession = factory.openSession();
        List<Subject> list = sqlSession.selectList( "mapper.SubjectMapper.selectList" );
        for (Subject subject : list) {
            System.out.println(subject.getSubjectNo() + "," + subject.getSubjectName());
        }
        System.out.println(list.size());
    } catch (IOException e) {
        e.printStackTrace();
    }finally {
        sqlSession.close();
    }
}

定义工具类

工具类

package 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;
/**
 * mybatis工具类
 */
public class MyBatisUtil {
    private static SqlSessionFactory factory;
    static {
        try {
            InputStream is = Resources.getResourceAsStream( "mybatis-config.xml" );
           // InputStream is = Resources.getResourceAsStream( "mybatis-config2.xml" );
            factory = new SqlSessionFactoryBuilder().build( is );
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    public  static SqlSession createSqlSession(){
        return factory.openSession(false);
    }
    public static void closeSqlSession(SqlSession sqlSession){
        if(null != sqlSession){
            sqlSession.close();
        }
    }
}

测试类

@Test
public void testSelectByUtil(){
    SqlSession sqlSession = null;
    try {
        sqlSession = MyBatisUtil.createSqlSession();
        List<Subject> list = sqlSession.selectList( "mapper.SubjectMapper.selectList" );
        for (Subject subject : list) {
            System.out.println(subject.getSubjectNo() + "," + subject.getSubjectName());
        }
        System.out.println(list.size());
    } catch (Exception e) {
        e.printStackTrace();
    } finally {
        MyBatisUtil.closeSqlSession( sqlSession );
    }
}

定义mapper的java接口

接口

package mapper;
import pojo.Subject;
import java.util.List;
public interface SubjectMapper {
    List<Subject> selectList(); //方法名必须是在mapper存在的id
}

测试

@Test
public  void testSelectByMapper(){
    SqlSession sqlSession = null;
    List<Subject> list = new ArrayList<>();
    try {
        sqlSession = MyBatisUtil.createSqlSession();
        list = sqlSession.getMapper( SubjectMapper.class).selectList();
    } catch (Exception e) {
        e.printStackTrace();
    } finally {
        MyBatisUtil.closeSqlSession( sqlSession );
    }
    for (Subject subject : list) {
        System.out.println(subject.getSubjectNo() + "," + subject.getSubjectName());
    }
    System.out.println(list.size());
}

读取配置文件

mapper读取不到时

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

mybatis配置文件读取不到时

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