MyBatis入门教程-优快云博客

本文链接：https://blog.youkuaiyun.com/it_tangke/article/details/120393176

2、第一个Mybits程序

思路：搭建环境–>导入Mybatis–>编写代码–>测试！

2.1、搭建环境

搭建数据库

CREATE TABLE `mybatis`.`user`  (
  `id` int NULL,
  `name` varchar(255) NULL,
  `pwd` varchar(255) CHARACTER SET utf8 COLLATE utf8_bin NULL
);

INSERT INTO `user`(`id`,`name`,`pwd`)VALUES
(1,'唐','123456')
(2,'罗','12345')
(3,'赵','1234')

新建项目

1.新建立一个普通的Maven项目

2.删除src目录（可以当一个父工程项目）

3.导入Maven依赖

 <!--导入依赖-->
    <dependencies>
        <!--mysql驱动-->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.19</version>
        </dependency>

        <!--mybatis-->
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.5.7</version>
        </dependency>

        <!--junit单元测试  -->

        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
        </dependency>
            </dependencies>
        <!--   在build中配置resources ， 来防止我们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>
            </resource>
            <resource>
                <directory>src/main/java</directory>
                <includes>
                    <include>**/*.properties</include>
                    <include>**/*.xml</include>
                </includes>
            </resource>

            <!-- Mapper.xml的位置是在java目录下，而非resource目录下。此处需加收进行扫描 -->
            <resource>
                <directory>src/main/java</directory>
                <includes>
                    <include>**/*.xml</include>
                    <include>**/*.properties</include>
                </includes>
            </resource>
            <resource>
                <directory>src/main/resources</directory>
            </resource>


        </resources>
    </build>

2.2创建一个模块

编写mybatis的核心配置文件

<?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核心配置文件-->
<configuration>

    <environments default="development">    <!--环境：environment；environments是能配置多套环境-->
        <environment id="development">
            <transactionManager type="JDBC"/>  <!--事务管理：transactionManager； 默认的是JDBC-->
            <dataSource type="POOLED">
                <!--原来的<property name="driver" value="${driver}"/> 得更改成-->
                <property name="driver" value="com.mysql.jdbc.Driver"/>
                
                <!--<property name="url" value="${url}"/>得更改成-->
                <property name="url" value="jdbc:mysql://localhost:3306/mybatis?useSSL=true&amp;useUnicode=true&amp;characterEncoding=UTF-8"/>
                
                <!--<property name="username" value="${username}"/>得更改成-->
                <property name="username" value="root"/>
                
                <!--<property name="password" value="${password}"/>得更改成-->
                <property name="password" value="3309064415"/>
                
             
            </dataSource>
        </environment>
    </environments>
  <!-- 每一个Mapper.xml 都需要在Mybatis核心配置文件中注册 -->
    <mappers>
        <mapper resource="com/tang/dao/UserMapper.xml"/>
    </mappers>
</configuration>

编写mybatis的工具类

/**
 * @author TangKe（唐柯）
 * @date 2021/9/17 - 12:11 下午
 */

//从 SqlSessionFactory 中获取 SqlSession
public class MyBatisUtils {


    private  static SqlSessionFactory sqlSessionFactory;//提升作用域。局部变量，变成全局变量

    static {
        try {
            //  使用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，我们可以从中获得 SqlSession 的实例。
    // SqlSession 提供了在数据库执行 SQL 命令所需的所有方法。你可以通过 SqlSession 实例来直接执行已映射的 SQL 语句。例如：

    public static SqlSession getSqlSession(){

      //SqlSession sqlSession = sqlSessionFactory.openSession();
      //return sqlSession;
        //优化代码

       return sqlSessionFactory.openSession();
    }

}

2.3、编写代码

实体类

/**
 * @author TangKe（唐柯）
 * @date 2021/9/17 - 4:18 下午
 */
public class User {
    
    private int id;
    private String name;
    private String pwd;

    public User() {
    }

    public User(int id, String name, String pwd) {
        this.id = id;
        this.name = name;
        this.pwd = pwd;
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getPwd() {
        return pwd;
    }

    public void setPwd(String pwd) {
        this.pwd = pwd;
    }
     @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", pwd='" + pwd + '\'' +
                '}';
    }
}

Dao类

/**
 * @author TangKe（唐柯）
 * @date 2021/9/17 - 4:20 下午
 */
public interface UserDao {

    List<User>getUserList();
}

接口实现类(由原来的Impl转化为一个Mapper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">


<!--namespace=绑定一个对应的Dao/Mapper接口-->
<mapper namespace="com.tang.dao.UserDao">   <!--namespace==>我们的Dao文件-->

    <!--select查询语句-->      <!--id==getUserList-->
      <!--记住这2个返回类型resultTyperesultMap-->
    <select id="getUserList" resultType="com.tang.pojo.User">


   select * from mybatis.user
  </select>
</mapper>

2.4、测试

junit测试

/**
 * @author TangKe（唐柯）
 * @date 2021/9/17 - 4:41 下午
 */
public class UserDaoTest {


    @Test
    public void test(){

        //第一步：获取SqlSession对象
        SqlSession sqlSession = MyBatisUtils.getSqlSession();

        //方式一: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();

    }
}

错误点一：没有注册UserMapper.xml

必须配置
       <!-- 每一个Mapper.xml 都需要在Mybatis核心配置文件中注册 -->
    <mappers>
        <mapper resource="com/tang/dao/UserMapper.xml"/>
    </mappers>

错误点二：Maven他们约定大于配置，我们之后可能遇到我们写的配置文件，无法被导出或者生效的问题，解决方法：

 <!--   在build中配置resources ， 来防止我们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>
          </resource>
          <resource>
              <directory>src/main/java</directory>
              <includes>
                  <include>**/*.properties</include>
                  <include>**/*.xml</include>
              </includes>
          </resource>
      </resources>
  </build>