第二章 第一个Mybatis程序

第二章 第一个Mybatis程序

思路：

搭建环境--->导入Mybatis--->编写代码----->测试

1.搭建环境

2.创建项目

1. 新建一个普通Maven项目

2. 导入Maven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>3.5.4</version>
       </dependency>
       <!--junit-->
       <dependency>
           <groupId>junit</groupId>
           <artifactId>junit</artifactId>
           <version>4.13</version>
           <scope>test</scope>
       </dependency>
   ​
   </dependencies>

    

3. 创建模块

   • 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">
             <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?serverTimezone=Asia/Shanghai&amp;useUnicode=true&amp;characterEncoding=UTF-8"/>
                     <property name="username" value="root"/>
                     <property name="password" value="123456"/>
                 </dataSource>
             </environment>
         </environments>
     ​
     </configuration>

      

      

• 编写mybatis工具类

  package com.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;
  ​
  //sqlSessionFactory   -->sqlSessioin
  public class MybatisUtils {
  ​
      private static SqlSessionFactory sqlSessionFactory;
  ​
      static {
          try {
              //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。
      public static SqlSession getSqlSession(){
         return sqlSessionFactory.openSession();
      }
  }

   

  • 编写代码

    1. 实现类

       package com.pojo;
       ​
       public class User {
           private int id;
           private String name;
           private String pwd;
       ​
       ​
           @Override
           public String toString() {
               return "User{" +
                       "id=" + id +
                       ", name='" + name + '\'' +
                       ", 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;
           }
       }

        

       2. DAO接口

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

           

       3. 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绑定一个对应的Dao/Mapper接口-->
          <mapper namespace="com.dao.UserDao">
             <select id="getUserList" resultType="com.pojo.User">
                 select * from mybatis.user
             </select>
          </mapper>

           

• 测试

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

  public void test(){
      //第一步：获得SqlSession对象
      SqlSession sqlSession = MybatisUtils.getSqlSession();
      //方式一：执行SQL
      UserDao userDao = sqlSession.getMapper(UserDao.class);
      List<User> userList = userDao.getUserList();
      for (User user : userList) {
          System.out.println(user);
      }
      //关闭SqlSession
      sqlSession.close();
  }

   

   

可能遇见的问题：

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导出资源类型