2022.5.13 第一个Mybatis程序

2、第一个Mybatis程序

思路:搭建环境-->导入Mybatis-->编写代码-->测试!

2.1、搭建环境

搭建数据库

 CREATE DATABASE `mybatis`
 USE `mybatis`
 ​
 CREATE TABLE `user`(
  `id` INT(20) NOT NULL,
  `name` VARCHAR(30) NOT NULL,
  `pwd` VARCHAR(30) NOT NULL,
  PRIMARY KEY(`id`)
 )ENGINE=INNODB DEFAULT CHARSET=utf8;
 ​
 INSERT
 INTO `user`(`id`,`name`,`pwd`) 
 VALUES(1,'小明','123456'),(2,'小红','123456'),(3,'小蓝','123457')

新建普通maven项目

1、新建一个普通的maven项目

2、删除src目录

3、导入maven依赖

 <?xml version="1.0" encoding="UTF-8"?>
 <project xmlns="http://maven.apache.org/POM/4.0.0"
          xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
          xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
     <modelVersion>4.0.0</modelVersion>
 ​
     <groupId>com.xing</groupId>
     <artifactId>Mybatis-Study</artifactId>
     <version>1.0-SNAPSHOT</version>
 ​
     <properties>
         <maven.compiler.source>8</maven.compiler.source>
         <maven.compiler.target>8</maven.compiler.target>
     </properties>
 ​
     <dependencies>
         <!-- https://mvnrepository.com/artifact/mysql/mysql-connector-java -->
         <dependency>
             <groupId>mysql</groupId>
             <artifactId>mysql-connector-java</artifactId>
             <version>8.0.27</version>
         </dependency>
 ​
         <!-- https://mvnrepository.com/artifact/org.mybatis/mybatis -->
         <dependency>
             <groupId>org.mybatis</groupId>
             <artifactId>mybatis</artifactId>
             <version>3.5.7</version>
         </dependency>
 ​
         <!-- https://mvnrepository.com/artifact/junit/junit -->
         <dependency>
             <groupId>junit</groupId>
             <artifactId>junit</artifactId>
             <version>4.12</version>
         </dependency>
 ​
     </dependencies>
 ​
 </project>

2.2、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>
 ​
     <environments default="development">
         <environment id="development">
             <transactionManager type="JDBC"/>
             <dataSource type="POOLED">
                 <property name="driver" value="com.mysql.jdbc.Driver"/>
                 <!--                                                    mybatis自己创建的数据库-->
                 <property name="url" value="jdbc:mysql://localhost:3306/mybatis?useSSL=true&amp;useUnicode=true&amp;characterEncoding=UTF-8"/>
 <!--                自己的用户名与密码-->
                 <property name="username" value="root"/>
                 <property name="password" value="123456"/>
             </dataSource>
         </environment>
     </environments>
 ​
 </configuration>

• 编写mybatis工具类

 package com.xing.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;
 ​
 //工具类 SqlSessionFactory-> SqlSession
 public class MybatisUtils {
     //提升作用域 
     private static SqlSessionFactory sqlSessionFactory;
     //加载配置文件
     static{
         try {
             //获取SqlSessionFactory对象
             String resource = "mybatis-config.xml";
             InputStream inputStream = Resources.getResourceAsStream(resource);//转变成流
             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();
 //        SqlSession sqlSession = sqlSessionFactory.openSession();
 //        return sqlSession;
     }
 ​
 ​
 }

2.3、编写代码

• 实体类

 package com.xing.pojo;
 ​
 //实体类
 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

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

接口实现类由原来的UserDaolmpl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.xing.dao.UserDao">
 <!--    id对应接口中的方法名 resultType返回的结果集类型(写集合中的范型类型)-->
     <select id="getUserList" resultType="com.xing.pojo.User">
         select * from mybatis.user;
     </select>
 </mapper>

2.4、测试

package com.xing.dao;
 ​
 import com.xing.pojo.User;
 import com.xing.utils.MybatisUtils;
 import org.apache.ibatis.session.SqlSession;
 import org.junit.Test;
 ​
 import java.util.List;
 ​
 public class UserDaoTest {
     @Test
     public void test() {
         SqlSession sqlSession = MybatisUtils.getSqlSession();
         //方式一：执行  得到接口对象调用其中方法  接口的class对象
         UserDao userDao = sqlSession.getMapper(UserDao.class);
         List<User> userList = userDao.getUserList();
 ​
         for (User user : userList) {
             System.out.println(user);
         }
 ​
         //关闭SqlSession
         sqlSession.close();
     }
 }

运行报错

注意：

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

修改mybatis的核心配置文件，添加mappers资源路径

 <?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.jdbc.Driver"/>
                 <!--                                                    mybatis自己创建的数据库-->
                 <property name="url" value="jdbc:mysql://localhost:3306/mybatis?useSSL=true&amp;useUnicode=true&amp;characterEncoding=UTF-8"/>
 <!--                自己的用户名与密码-->
                 <property name="username" value="root"/>
                 <property name="password" value="123456"/>
             </dataSource>
         </environment>
     </environments>
 ​
     <!--每一个Mapper.XML都需要在Mybatis核心配置文件中注册!-->
     <mappers>
         <mapper resource="com/xing/dao/UserMapper.xml"></mapper>
     </mappers>
 </configuration>

在运行报错

 

 

由于maven约定大于配置，生成的target文件中没有导出UserMapper.xml

 

 

 

 

在pom文件中添加

 <!--buiLd中配置resources，来防止我们资源导出失败的问题，例java目录中只能导出java文件-->
 <build>
     <resources>
         <resource>
             <directory>src/main/resources</directory>
             <includes>
                 <include>**/*.properties</include>
                 <include>**/*.xml</include>
             </includes>
             <filtering>false</filtering>
         </resource>
         <resource>
             <directory>src/main/java</directory>
             <includes>
                 <include>**/*.properties</include>
                 <include>**/*.xml</include>
             </includes>
             <filtering>false</filtering>
         </resource>
     </resources>
 </build>

 

 

你们可以能会遇到的问题:

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