第一个MyBatis程序

第一个MyBatis程序

思路：环境搭建 --> 导入MyBatis --> 编写代码 --> 测试

1、搭建环境

搭建数据库：

CREATE DATABASE `mybatis`;
USE `mybatis`;

CREATE TABLE `user`(
	`id` INT NOT NULL,
	`name` VARCHAR(30) DEFAULT NULL,
	`pwd` VARCHAR(30),
	PRIMARY KEY(`id`)
)ENGINE=INNODB DEFAULT CHARSET=utf8;

INSERT INTO `user`(`id`,`name`,`pwd`) VALUES
(1,'狂神','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（当做一个父工程）

3. 导入maven依赖

   <!--导入依赖-->
       <dependencies>
       <!--mysql驱动-->
           <dependency>
               <groupId>mysql</groupId>
               <artifactId>mysql-connector-java</artifactId>
               <version>8.0.32</version>
           </dependency>
       <!--mybatis-->
           <dependency>
               <groupId>org.mybatis</groupId>
               <artifactId>mybatis</artifactId>
               <version>3.5.11</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"
          "https://mybatis.org/dtd/mybatis-3-config.dtd">
  <configuration>
      <environments default="development">
          <environment id="development">
              <transactionManager type="JDBC"/>
              <dataSource type="POOLED">
                  <property name="driver" value="com.mysql.jdbc.Driver"/>
                  <property name="url" value="jdbc:mysql://localhost:3306/mybatis?useSSL=false&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

  // sqlSessionFactory --> 获取sqlSession
  public class MybatisUtils {
      private static SqlSessionFactory sqlSessionFactory;
  
      static{
          try {
              // 使用MyBatis第一个：获取SQLSessionFactory对象
              String resource = "mybatis-config.xml";
              InputStream inputStream = Resources.getResourceAsStream(resource);
              sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
          } catch (Exception 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

  package com.kuang.pojo;
  
  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接口

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

• 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"
          "https://mybatis.org/dtd/mybatis-3-mapper.dtd">
  <!--namespace=绑定一个对应的Dao/Mapper接口-->
  <mapper namespace="com.kuang.dao.UserDao">
      <!--select查询语句-->
      <select id="getUserList" resultType="com.kuang.pojo.User">
          select * from mybatis.user;
      </select>
  </mapper>
  

  配置完Mapper文件后要返回MyBatis核心配置文件中注册

  <mappers>
          <mapper resource="UserDaoMapper.xml"/>
  </mappers>
  

  这段代码写在标签内，"UserDaoMapper.xml"写在resources文件夹内

4、测试

注意点：

报错1：
org.apache.ibatis.binding.BindingException: Type interface com.kuang.dao.UserDao is not known to the MapperRegistry.
在mybatis-config.xml文件中，一定要注册<mappers>中的文件，路径分隔符用“/”
报错2：
org.apache.ibatis.exceptions.PersistenceException: 
...
The error may exist in com/kuang/dao/UserMapper.xml

• Junit测试

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

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

防止资源到处失败的配置代码

<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>