初次学习mybatis，写了一个最简单的demo，然而运行报错：
java.sql.SQLException: Error setting driver on UnpooledDataSource. Cause: java.lang.ClassNotFoundException: Cannot find class: com.mysql.cj.jdbc.Driver

判断问题出在driver驱动上，根据网上常见解决办法依次排查（我的MySQL版本是8）：

step 1.检查maven依赖，好像没问题，很多人就是把mysql-connector-java版本从5升到8就好了：

<dependencies>
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.5.6</version>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.17</version>
        </dependency>
</dependencies>

step 2.检查mybatis配置文件：尝试在url "jdbc:mysql:///study?serverTimezone=UTC"中添加参数“&useSSL=false”,仍然报错。

<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:///study?serverTimezone=UTC"/>
                <property name="username" value="root"/>
                <property name="password" value="123"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <mapper resource="UserMapper.xml"/>
    </mappers>
</configuration>

step 3.偶然在maven仓库发现mysql-connector-java有更新版本，决定一试，把version 8.0.17换为8.0.23

替换后果然运行成功，看来问题还是在step 1，如果你也试了各种办法无解，可以再关注下是不是mysql-connector-java版本的问题。

<dependencies>
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.5.6</version>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.23</version>
        </dependency>
</dependencies>