第一个Mybatis程序

旧城等待， 2023-01-23 08:53 4阅读 0赞

最近再跟着B站狂神学习Mybits，跟着做了一个程序，记录下学习过程。

## 1、搭建环境 ##

1.1 创建数据库

CREATE DATABASE `mybatis`;
    
    USE `mybatis`;
    
    DROP TABLE IF EXISTS `user`;
    
    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;
    
    INSERT INTO `user`(`id`,`name`,`pwd`) VALUES
    (1,'狂神','123456'),
    (2,'张三','123456'),
    (3,'李四','123456')

1.2 新建maven项目，并导入maven项目

<?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.kuang</groupId>
        <artifactId>Mybatis-Study</artifactId>
        <version>1.0-SNAPSHOT</version>
    
        
        <dependencies>
            
            <dependency>
                <groupId>mysql</groupId>
                <artifactId>mysql-connector-java</artifactId>
                <version>8.0.22</version>
            </dependency>
            
            
            <dependency>
                <groupId>org.mybatis</groupId>
                <artifactId>mybatis</artifactId>
                <version>3.5.2</version>
            </dependency>
            
            <dependency>
                <groupId>junit</groupId>
                <artifactId>junit</artifactId>
                <version>4.12</version>
            </dependency>
        </dependencies>
    </project>

## 2、在resources文件下创建一个.xml文件用来编写mybatis的核心配置文件(连接数据据库) ##

<?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>
        <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=UTC&useSSL=false&useUnicode=true&characterEncoding=utf8"/>
                    <property name="username" value="root"/>
                    <property name="password" value="123456"/>
                </dataSource>
            </environment>
        </environments>
    </configuration>

编写mybatis工具类

package com.kuang.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 -->sqlSession
    public class MybatisUtils { 
    
        private static SqlSessionFactory sqlSessionFactory;
    
        static { 
            try { 
                //第一步：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，我们就可以从中获得sqlSession的实例了。
        //sqlSession完全包含了面向数据库执行SQL命令的所有方法
        //创建一个能执行sql的对象
        public static SqlSession getSqlSession(){ 
            return sqlSessionFactory.openSession();
        }
    }

3、编写代码

*  实体类

package com.kuang.pojo;
    
    //实体类
    public class User { 
        private int id;
        private String name;
        private  String ped;
    
        public User() { 
        }
    
        public User(int id, String name, String ped) { 
            this.id = id;
            this.name = name;
            this.ped = ped;
        }
    
        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 getPed() { 
            return ped;
        }
    
        public void setPed(String ped) { 
            this.ped = ped;
        }
    
        @Override
        public String toString() { 
            return "User{" +
                    "id=" + id +
                    ", name='" + name + '\'' +
                    ", ped='" + ped + '\'' +
                    '}';
        }
    }

*  Dao接口（操作实体类的接口）

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" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
    
    
    <mapper namespace="com.kuang.dao.UserDao">
    
        
        <select id="getUserList" resultType="com.kuang.pojo.User">
            select *from mybatis.user
        </select>
    </mapper>

## 4、测试 ##

junit测试：

package com.kuang.dao;
    
    import com.kuang.pojo.User;
    import com.kuang.utils.MybatisUtils;
    import org.apache.ibatis.session.SqlSession;
    import org.junit.Test;
    
    import java.util.List;
    
    public class UserDaoTest { 
    
        @Test
        public void test(){ 
            //第一步：获得sqlSession对象
            SqlSession sqlSession = MybatisUtils.getSqlSession();
    
            //方式一：geMapper
            UserDao userDao = sqlSession.getMapper(UserDao.class);
            List<User> userList = userDao.getUserList();
    
            for (User user : userList) { 
                System.out.println(user);
            }
    
            //关闭SqlSession
            sqlSession.close();
        }
    }

补充：再跟着视频做测试的时候，发现使用@Text需要安装 JUnitGenerator V2.0插件，然后出现插件安装不上的问题，如果有遇到同样问题的小伙伴可以看看[IDEA使用@Test注解报错][IDEA_Test]

注意：  
错误提示(绑定接口错误)

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

解决方法  
在mybatis的核心文件中进行注册

<mappers>
            <mapper resource="com/kuang/dao/UserMapper.xml"/>
        </mappers>

错误提示(找不到resources里的xml文件)  
就是导出资源问题：[在build中配置resources ， 来防止我们资源导出失败的问题][build_resources _]

java.lang.ExceptionInInitializerError
    	
    Caused by: org.apache.ibatis.exceptions.PersistenceException: 
    ### Error building SqlSession.
    ### The error may exist in com/kuang/dao/UserMapper.xml
    ### Cause: org.apache.ibatis.builder.BuilderException: Error parsing SQL Mapper Configuration. Cause: java.io.IOException: Could not find resource com/kuang/dao/UserMapper.xml

解决方法

<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>

[IDEA_Test]: https://blog.csdn.net/weixin_44096353/article/details/118713230?spm=1001.2014.3001.5501
[build_resources _]: https://blog.csdn.net/weixin_44096353/article/details/118631278?spm=1001.2014.3001.5501