1. Problem
Error querying database. Cause: java.sql.SQLException: Error setting driver on UnpooledDataSource…
All red when the test is running! ! !
2. Investigation ideas
1. 配置编写错误
2. 配置文件引用错误或依赖坐标引入及版本问题
3. Report an error
3.1 Driver?
It was said that there was a problem with my driver. After checking the data, it was said that it might be an error in the SQL version. I checked the actual situation and checked it out.
It’s really hard to find a needle in a haystack. Driver is written as drive, which is embarrassing.
3.2 SQL query ID unique identification?
There is an error, findById is wrongly written as findId! ! ! Ah it's true
3.3 Success
I thought it was really a small mistake and I thought I could really run away. . . . . Or did I think...
4. The biggest problem!
To separate com.mysql.jdbc.Driver
4.1 mybatis-config.xml configuration items
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Cofig 3.0//EN"
"//http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
<!--引入外部的db.properties数据库配置文件-->
<properties resource="db.properties"></properties>
<!--环境配置-->
<!--加载类路径下的属性文件-->
<!--environments是用来配置mybatis环境的-->
<environments default="development">
<environment id="development" >
<transactionManager type="JDBC"/>
<!--数据库连接(数据库连接池)相关配置，db.properties 文件中的内容-->
<dataSource type="POOLED">
<!-- <property name="driver" value="com.mysql.cj.jdbc.Driver"/> 出现报错的写法-->
<property name="driver" value="com.mysql.cj.jdbc.Driver"/>
<property name="url" value="${mysql.url}"/>
<property name="username" value="${mysql.username}"/>
<property name="password" value="${mysql.password}"/>
</dataSource>
</environment>
</environments>
<!-- 配置xxxMapper文件的路径配置，该文件主要存放SQL语句-->
<mappers>
<mapper resource="mapper/UserMapper.xml"/>
</mappers>
</configuration>
5. Successful takeoff
public class UserTest {
@Test
public void userFindByIdTest() {
//1. 获取核心配置文件mybatis-config.xml
String resources = "mybatis-config.xml";
//2. 创建流
Reader reader = null;
try {
//读取mybatis-config.xml配置文件内容到reader对象中
reader = Resources.getResourceAsReader(resources);
}catch (IOException e){
e.printStackTrace();
System.out.println("输入流段错误！");
}
//3. 初始化mybatis数据库，创建 SqlSessionFactory
SqlSessionFactory sqlMapper = new SqlSessionFactoryBuilder().build(reader);
//4. 创建SqlSession 实例
SqlSession sqlSession = sqlMapper.openSession();
//5. 传入参数查询，返回结果
User user = sqlSession.selectOne("findById",1);
//6. 输出结果
System.out.println(user.getUname());
//7. 关闭流sqlSession
sqlSession.close();
}
}
6. Share some configurations for using mybatis for the first time.
** The following is in random order, you will know whoever configures it first! **
6.1 pom.xml
<!--引入相关的坐标-->
<dependencies>
<!-- mybatis的jar包-->
<dependency>
<groupId>org.mybatis</groupId>
<artifactId>MyBatis</artifactId>
<version>3.5.11</version>
</dependency>
<!--mysql数据库jar坐标配置-->
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-jdbc-java</artifactId>
<version>8.0.28</version>
<scope>runtime</scope>
</dependency>
<!-- junit 单元测试jar包坐标依赖-->
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>4.13.2</version>
<scope>test</scope>
</dependency>
</dependencies>
6.2 Database db.properties configuration items
Note, db.properties, db is the file name, you can write it casually, but the suffix must be xxx.properties! properties!properties!
mysql.driver = com.mysql.cj.jdbc.Driver;
mysql.url = jdbc:mysql://localhost:3306/mybatis?serverTimezone=UTC&characterEncoding=utf8&Unicode=true&useSSL=false
mysql.username=root
mysql.password=root
6.3 mapper configuration items
xxxMapper is mainly used to store the mapping between SQL statements and java objects. It is best to create a mapper folder specifically to store xxxMapper files.
<?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标签： 配置各种类声明
namespace： 名称空间， 由于映射文件可能有多个，
为了防止 crud 语句的唯一标识被重复，需要设置空间名称
mapper 为映射的根节点，namespace指定Dao接口的完整类名，mybatis会依据这个接口，动态创建一个实现类
去实现这个接口，二这个实现类是一个Mapper 对象
-->
<mapper namespace="com.javaEElcb.pojo.User">
<!--
select: 查询的statement （声明），用来编写查询语句
id： 语句的唯一标识
resultType： 配置返回结果的类型
parameterType： 传递的参数类型，可以省略
- - - - - - - - - - - - - - - - - - - - - - - -
id = "接口中的方法名" parameterType= "传入的参数类型"
resultType = "返回实体类对象，使用 包.类名"
-->
<select id="findById" parameterType = "int"
resultType = "com.javaEElcb.pojo.User">
select * from users where uid=#{id}
</select>
</mapper>
6.4 mybatis-config.xml configuration
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Cofig 3.0//EN"
"//http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
<!--引入外部的db.properties数据库配置文件-->
<properties resource="db.properties"></properties>
<!--环境配置-->
<environments default="development">
<environment id="development" >
<transactionManager type="JDBC"/>
<!--数据库连接相关配置，db.properties 文件中的内容-->
<dataSource type="POOLED">
<property name="driver" value="com.mysql.cj.jdbc.Driver"/>
<property name="url" value="${mysql.url}"/>
<property name="username" value="${mysql.username}"/>
<property name="password" value="${mysql.password}"/>
</dataSource>
</environment>
</environments>
<!-- 配置xxxMapper文件的路径配置，该文件主要存放SQL语句-->
<mappers>
<mapper resource="mapper/UserMapper.xml"/>
</mappers>
</configuration>
attached
有一段时间了，回看了一下代码.........数据库连接中的db配置文件多了一个不该出现的**<font color="red">分号</font>**！！！ 删了就可以在mybatis-config中使用<font color="red">${mysql.driver}</font>了。。
/*mysql.driver = com.mysql.cj.jdbc.Driver;*/
//mysql.driver = com.mysql.cj.jdbc.Driver
mysql.url = jdbc:mysql://localhost:3306/mybatis?serverTimezone=UTC&characterEncoding=utf8&Unicode=true&useSSL=false
mysql.username=root
mysql.password=root