简单易懂的Mybatis环境的搭建

思路：搭建环境 --> 导入MyBatis --> 编写代码 --> 测试

新建项目

1. 创建一个普通的maven项目

2. 导入maven依赖

   <!--导入依赖-->
   <dependencies>
       <!--mysqlq驱动-->
       <dependency>
           <groupId>mysql</groupId>
           <artifactId>mysql-connector-java</artifactId>
           <version>8.0.12</version>
       </dependency>
       <!--mybatis-->
       <dependency>
           <groupId>org.mybatis</groupId>
           <artifactId>mybatis</artifactId>
           <version>3.5.4</version>
       </dependency>
       <!--junit-->
       <dependency>
           <groupId>junit</groupId>
           <artifactId>junit</artifactId>
           <version>4.12</version>
           <scope>test</scope>
       </dependency>
   </dependencies>
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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">
        <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?userSSL=true&amp;useUnicode=true&amp;characterEncoding=UTF-8&amp;serverTimezone=UTC"/>
                <property name="username" value="root"/>
                <property name="password" value="root"/>
            </dataSource>
        </environment>
    </environments>
</configuration>
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编写mybatis工具类

//sqlSessionFactory --> sqlSession
public class MybatisUtils {

    static SqlSessionFactory sqlSessionFactory = null;

    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。
    public static SqlSession getSqlSession(){
        return sqlSessionFactory.openSession();
    }
}
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编写代码

• 实体类

• Dao接口

  public interface UserDao {
      public List<User> getUserList();
  }
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• 接口实现类 （由原来的UserDaoImpl转变为一个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=绑定一个指定的Dao/Mapper接口-->
  <mapper namespace="com.kuang.dao.UserDao">
      <select id="getUserList" resultType="com.kuang.pojo.User">
      select * from USER
    </select>
  </mapper>
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• 测试

  注意点：

  org.apache.ibatis.binding.BindingException: Type interface com.kuang.dao.UserDao is not known to the MapperRegistry.

  MapperRegistry是什么?

  核心配置文件中注册mappers

  • junit测试

        @Test
        public void test(){
    
            //1.获取SqlSession对象
            SqlSession sqlSession = MybatisUtils.getSqlSession();
            //2.执行SQL
            // 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();
        }
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可能会遇到的问题：

1. 配置文件没有注册
2. 绑定接口错误
3. 方法名不对
4. 返回类型不对
5. Maven导出资源问题

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