mybatis

1.搭建数据库

CREATE DATABASE `mybatis`;

USE `mybatis`;

DROP TABLE IF EXISTS `user`;

CREATE TABLE `user` (
`id` int(20) NOT NULL,
`name` varchar(30) DEFAULT NULL,
`pwd` varchar(30) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

insert  into `user`(`id`,`name`,`pwd`) values (1,'王琦','123456'),(2,'张三','abcdef'),(3,'李四','987654');

2.创建项目

2.1 创建 maven 项目
2.2 导入依赖

    <dependencies>
        <!--导入mysql驱动-->
        <dependency>
           <groupId>mysql</groupId>
           <artifactId>mysql-connector-java</artifactId>
           <version>5.1.47</version>
        </dependency>

        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-mxj-db-files</artifactId>
            <version>5.0.12</version>
        </dependency>
        <!--mybatis的依赖-->
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.5.11</version>
        </dependency>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
            <scope>test</scope>
        </dependency>
    </dependencies>

2.3 创建模块

官网：https://mybatis.net.cn/getting-started.html

• mybatis 核心配置文件：创建 mybatis-config.xml 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>
    <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://localhost:3306/mybatis?useSSL=true&amp;useUnicode=true&amp;characterEncoding=utf8"/>
                <property name="username" value="root"/>
                <property name="password" value="1234"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <mapper resource="org/mybatis/example/BlogMapper.xml"/>
    </mappers>
</configuration>

在<mappers> </mappers>注册是是对应的UserMapper:

<mapper resource="com/dao/UserMapper.xml"/>

2.4 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。

从 XML 文件中构建 SqlSessionFactory 的实例非常简单，建议使用类路径下的资源文件进行配置。 但也可以使用任意的输入流（InputStream）实例，比如用文件路径字符串或 file:// URL 构造的输入流。MyBatis 包含一个名叫 Resources 的工具类，它包含一些实用方法，使得从类路径或其它位置加载资源文件更加容易：

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

在我们的代码中如下：

public class MybatisUtils {

    private static SqlSessionFactory sqlSessionFactory;
    static {

        try {
            // 获取  sqlSessionFactory 对象，以下步骤固定
            String resource = "mybatis-config.xml";
            InputStream inputStream = null;
            inputStream = Resources.getResourceAsStream(resource);
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        } catch (IOException e) {
            e.printStackTrace();
        }

    }

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

2.5 pom.xml 导入配置

在 pox.xml 导入：（否则找不到配置的 Mapper.xml 文件夹）

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

2.6 创建实体类

public class User {
   
   private int id;  //id
   private String name;   //姓名
   private String pwd;   //密码
   
   //构造,有参,无参
   //set、get
   //toString()
   
}

2.7 编写Mapper接口类

import com.kuang.pojo.User;
import java.util.List;

public interface UserMapper {
   List<User> selectUser();
}

2.8 编写Mapper.xml配置文件

<?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="com.kuang.dao.UserMapper">
 <select id="selectUser" resultType="com.kuang.pojo.User">
  select * from user
 </select>
</mapper>

2.9 Test

public class UserDaoTest {

    @Test
    public void test(){
        //1. 获得 sqlsession
        SqlSession sqlSession = MybatisUtils.getSqlSession();

        //2. 执行Sql
        // 方式1：getMapper
        UserDao userDao = sqlSession.getMapper(UserDao.class);
        List<User> userList = userDao.getUserList();

        for (User user : userList) {
            System.out.println(user);
        }

        // 关闭SqlSession
        sqlSession.close();
    }
}

2.10 注意

• 首先定义总的配置文件mybatis-config.xml:里面定义数据库连接之类的信息
• 在Dao 层，接口中对应的 一个Mapper。对应着配置文件（例如UserMapper.xml）:在配置文件中写Sql语言。告别传统的写Sql语言的方式。