第一个Mybatis程序-蒲公英云

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>
    <!--父工程-->
    <groupId>com.kuang</groupId>
    <artifactId>Mybatis-Study</artifactId>
    <version>1.0-SNAPSHOT</version>
    <!--导入依赖-->
    <dependencies>
        <!--mysql驱动-->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.22</version>
        </dependency>
        <!--Mybatis-->
        <!-- https://mvnrepository.com/artifact/org.mybatis/mybatis -->
        <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>
        </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">
<!--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.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">

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

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

<!--每一个Mapper.xml都需要在Mybatis核心配置文件中注册！-->
    <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

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

<!--在build中配置resources，来防止资源导出失败问题-->
    <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>