2、 第一個Mybatis程式

思路：搭建環境->匯入mybatis->編寫程式碼->測試

2.1 搭建環境

• 搭建資料庫：

CREATE SCHEMA `mybatis` DEFAULT CHARACTER SET utf8;
CREATE TABLE `mybatis`.`user` (
  `id` INT NOT NULL AUTO_INCREMENT,
  `name` VARCHAR(45) NOT NULL,
  `pwd` VARCHAR(45) NOT NULL,
  PRIMARY KEY (`id`))
DEFAULT CHARACTER SET = utf8;
INSERT INTO `mybatis`.`user` (`id`, `name`, `pwd`) VALUES ('1', '狂神', '123456');
INSERT INTO `mybatis`.`user` (`id`, `name`, `pwd`) VALUES ('2', '張三', '123456');
INSERT INTO `mybatis`.`user` (`id`, `name`, `pwd`) VALUES ('3', '李四', '123456');
 

• 新建普通的Maven專案

• 刪除src

• 加入Maven依賴(mybatis,juint,mysql)

2.2 搭建環境

參考官方文件[https://mybatis.org/mybatis-3/zh/index.html

• 編寫mybatis核心配置檔案(xml)

  <?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">
  <!--核心配置檔案-->
  <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?useUnicode=true&amp;characterEncoding=utf8&amp;useSSL=true"/>
                  <property name="username" value="root"/>
                  <property name="password" value="12345678"/>
              </dataSource>
          </environment>
      </environments>
  <!--    每一個mapper.xml都需要在該核心配置檔案中註冊-->
      <mappers>
          <mapper resource="com/bao/dao/UserMapper.xml"/>
      </mappers>
  </configuration>
   
  

• 編寫獲取sqlsession的工具類

  package com.bao.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.InputStream;
  
  public class MybatisUtils {
      public static SqlSessionFactory sqlSessionFactor;
      // 從 XML 中構建 SqlSessionFactory
      static {
          try {
              String resource = "mybatis-config.xml";
              InputStream inputStream = Resources.getResourceAsStream(resource);
              sqlSessionFactor = new SqlSessionFactoryBuilder().build(inputStream);
          }catch (Exception e){
              e.printStackTrace();
          }
      }
      // 獲取SqlSession
      //SqlSession中包含面向資料庫執行SQL命令的所有方法
      public static SqlSession getSqlSession(){
          return sqlSessionFactor.openSession();
      }
  }
   
  

2.3 編寫程式碼

• 實體類

• Dao介面

  package com.bao.dao;
  
  import com.bao.pojo.User;
  
  import java.util.List;
  
  public interface UserDao {
      List<User> getUserList();
  }
  

• Dao介面實現類

  <?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">
  <!--使用namespace=繫結一個對應的介面-->
  <mapper namespace="com.bao.dao.UserDao">
      <select id="getUserList" resultType="com.bao.pojo.User">
      select * from mybatis.user
      </select>
  </mapper>
  

• 測試

import java.util.List;

public class UserDaoTest {
    @Test
    public void test(){
        // 獲取sqlSession物件
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        // 執行 Sql語句
        UserDao mapper = sqlSession.getMapper(UserDao.class);
        List<User> userList = mapper.getUserList();
        for (User user : userList) {
            System.out.println(user);
        }
        sqlSession.close();
    }
}

可能遇到的問題

1. 配置檔案沒註冊
2. 繫結介面錯誤
3. 方法名不對
4. 返回型別不對
5. Maven匯出資源問題，可在pom中新增以下配置資訊來結局

   <!--在build中配置resources，來防止我們資源匯出失敗的問題-->
       <build>
           <resources>
               <resource>
                   <directory>src/main/resources</directory>
                   <includes>
                       <include>**/*.properties</include>
                       <include>**/*.xml</include>
                   </includes>
                   <filtering>true</filtering>
               </resource>
               <resource>
                   <directory>src/main/java</directory>
                   <includes>
                       <include>**/*.properties</include>
                       <include>**/*.xml</include>
                   </includes>
                   <filtering>true</filtering>
               </resource>
           </resources>
       </build>