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

搭建数据库

-- 创建数据库
CREATE DATABASE `mybatis`;

USER `mybatis`;

-- 创建表
CREATE TABLE `user`(
	`id` int(20) NOT NULL PRIMARY KEY,
	`name` VARCHAR(30) DEFAULT NULL,
	`pwd` VARCHAR(30) DEFAULT NULL
)ENGINE=INNODB DEFAULT CHARSET=utf8

-- 插入表数据
INSERT INTO `user`(`id`,`name`,`pwd`) VALUES
(1,'小王','123456'),
(2,'张三','123456'),
(3,'李四','123456');

新建项目

1. 新建一个普通的maven项目

2. 删除src目录，将它设置为父工程

3. 导入maven依赖

   <!-- 导入依赖 -->
   <dependencies>
       <!-- MySql驱动 -->
       <dependency>
           <groupId>mysql</groupId>
           <artifactId>mysql-connector-java</artifactId>
           <version>5.1.47</version>
       </dependency>
       <!-- MyBatis驱动 -->
       <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>
           <scope>test</scope>
       </dependency>
   </dependencies>
   

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>
      <properties resource="jdbc.properties"/>
      <environments default="development">
          <environment id="development">
              <transactionManager type="JDBC"/>
              <dataSource type="POOLED">
                  <property name="driver" value="${jdbc.driver}"/>
                  <property name="url" value="${jdbc.url}"/>
                  <property name="username" value="${jdbc.username}"/>
                  <property name="password" value="${jdbc.password}"/>
              </dataSource>
          </environment>
      </environments>
      <mappers>
         <mapper resource="com/kuang/dao/userMapper.xml"/>
     	</mappers>
  </configuration>
  

• 编写MyBatis的工具类

  // sqlSessionFactory --> sqlSession
  public class MyBatisUtils {
      private static SqlSessionFactory sqlSessionFactory;
  
      static {
          try {
              // 使用MyBatis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();
      }
  }
  

3、编写代码

• 实体类

  // 实体类
  public class User {
      private Integer id;
      private String name;
      private String pwd;
     //构造,有参,无参
     //set/get
     //toString()
  }
  

• 编写Mapper接口

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

• 接口实现类由原来的Impl转化为一个mapper.xml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Mapper接口 -->
  <mapper namespace="com.jh.mapper.UserMapper">
      <!-- select 查询语句 -->
      <select id="getUserList" resultType="com.jh.domain.User">
          select * from user
      </select>
  </mapper>
  

4、测试代码

注意点：

org.apache.ibatis.binding.BindingException: Type interface com.jh.mapper.UserMapper is not known to the MapperRegistry.

MapperRegistry是什么？测试配置文件中注册mappers

• junit测试

  public class UserMapperTest {
      @Test
      public void test() {
          // 第一步：获得sqlSession对象
          SqlSession sqlSession = MyBatisUtils.getSqlSession();
          // 方式一：执行sql
          UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
          List<User> userList = userMapper.getUserList();
          // 方式二：(不推荐)
      //List<User> userList = sqlSession.selectList("com.jh.mapper.UserMapper.getUserList");
          for (User user : userList) {
              System.out.println(user);
          }
          sqlSession.close();
      }
  }
  

测试中可能会遇到的问题：

1. 配置文件没有注册
2. 绑定接口错误
3. 方法名不正确
4. 返回类型不正确
5. maven静态资源过滤问题

<resources>
   <resource>
       <directory>src/main/java</directory>
       <includes>
           <include>**/*.properties</include>
           <include>**/*.xml</include>
       </includes>
       <filtering>false</filtering>
   </resource>
   <resource>
       <directory>src/main/resources</directory>
       <includes>
           <include>**/*.properties</include>
           <include>**/*.xml</include>
       </includes>
       <filtering>false</filtering>
   </resource>
</resources>