关于mybatis:Mybatis程序入门案例

思路：搭建环境 —> 导入 Mybatis—> 编写代码 —> 测试

搭建数据库

create databases if not exists `mybatis`;

use `mybatis`;

create table if not exists `user`(`id` int(20) not null,
    `name` varchar(30) default null,
    `pwd` varchar(30) default null,
    primary key(`id`)
)engine=innodb default charset=utf8;

插入数据

insert into `user`(`id`,`name`,`pwd`) values
(1,'孙悟空','123456'),
(2,'猪八戒','111222'),
(3,'唐僧','789456');

新建我的项目
1. 新建一个一般的 maven 我的项目
2. 删除 src 目录
3. 导入 maven 依赖

<dependencies>
    <!--mysql 驱动 -->
    <dependency>
        <groupId>mysql</groupId>
        <artifactId>mysql-connector-java</artifactId>
        <version>5.1.46</version>
    </dependency>
    
    <!--mybatis-->
    <dependency>
        <groupId>org.mybatis</groupId>
        <artifactId>mybatis</artifactId>
        <version>3.5.2</version>
    </dependency>
    
    <!--junit-->
    <dependency>
        <groupId>junit</groupId>
        <artifactId>junit</artifactId>
        <version>4.12</version>
    </dependency>
</dependencies>
<!-- 在 build 中配置 resources，来避免咱们资源导出失败的问题 -->
<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>

编写 Mybaris 的外围配置文件

<?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 外围配置文件 -->
<configuration>
<environments default="development">
  <environment id="development">
    <transactionManager type="JDBC"/>
    <dataSource type="POOLED">
      <property name="driver" value="com.mysql.cj.jdbc.Driver"/>
      <property name="url" value="jdbc:mysql://localhost:3306/mybatis?useSSL=true&amp;useUnicode=true&amp;characterEncoding=utf-8&amp;serverTimezone=Asia/Shanghai"/>
      <property name="username" value="root"/>
      <property name="password" value="root"/>
    </dataSource>
  </environment>
</environments>
<mappers>
  <mapper resource="com/jialidun/dao/UserMapper/xml"/>
</mappers>
</configuration>

编写 mybatis 工具类

package com.jialidun.utils;

//sqlSessionFactory--->sqlSession
public class MybatisUtils{

  private static SqlSessionFactory sqlSessionFactory;
  static{
  try{
      // 应用 mybatis 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();
      }
  }
// 既然有了 SqlSessionFactory，顾名思义，咱们能够从中取得 SqlSession 的实例。//SqlSession 提供了在数据库执行 SQL 命令所需的所有办法。public static SqlSession getSqlSession(){return sqlSessionFactory.openSession();
  }
}

实体类

package com.jialidun.pojo;

@Data
public class User{
  private int id;
  private String name;
  private String pwd;
}

Dao 接口

package com.jialidun.dao;

public interface UserDao{List<User> getUserList();

}

接口实现类由原来的 UserDaoImpl 转变为一个 Mapper 配置文件
UserMapper.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">
<!--namespace= 绑定一个对应的 Dao/Mapper 接口 -->
<mapper namespace="com.jialidun.dao.UserDao">

 <!--select 查问语句 -->
<select id="getUserList" resultType="com.jialidun.pojo.User">
  select * from mybatis.user
</select>
</mapper>

留神点：
org.apache.ibatis.binding.BindingException:Type interface com.jialidun.dao.UserDao is not know to the MapperRegistry.

package com.jialidun.dao;

public class UserDaoTest{
  @Test
  public void test(){
      
      // 第一步：取得 SqlSession 对象
      SqlSession sqlSession = MybatisUtils.getSqlSession();
      
      try{UserDao userDao= sqlSession.getMapper(UserDao.class);
      List<User> userList = userDao.getUserList();
      
      // 形式二：//List<User> userList = sqlSession.selectList("com.jialidun.dao.UserDao.getUserList");
      for(User user:userList){System.out.println(user);
      }
      }catch(Exception e){e.printStackTrace();
      }finally{
          // 敞开 SqlSession
          sqlSession.close();}
  
      
  }
}

可能遇到的问题：
1. 配置文件没有注册
2. 绑定接口谬误
3. 办法名不对
4. 返回类型不对
5.Maven 导出资源问题

关于mybatis:Mybatis程序入门案例

1.1、搭建环境

1.2、创立一个模块

1.3、编写代码

1.4、测试