When reading the MySQL source code, download the source code, write a simple demo, run and report errors

java.sql.SQLException: Error setting driver on UnpooledDataSource. Cause: java.lang.ClassNotFoundException: Cannot find class: com.mysql.jdbc.Driver
at org.apache.ibatis.exceptions.ExceptionFactory.wrapException(ExceptionFactory.java:30)
at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:153)
at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:145)
at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:140)
at org.apache.ibatis.session.defaults.DefaultSqlSession.selectOne(DefaultSqlSession.java:76)
at org.apache.ibatis.demo.MybatisMain.main(MybatisMain.java:36)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at com.intellij.rt.execution.application.AppMain.main(AppMain.java:147)

After checking online, most of them are the same as mysql-connector-java-x.x.x-bin.jar, but no matter what version of package I introduce, the problem still exists.

After step-by-step debugging, it is found that the place where the com.mysql.jdbc.driver class is loaded is the following method of org.apache.ibatis.io.classloaderwapper

Class<?> classForName(String name, ClassLoader[] classLoader) throws ClassNotFoundException {
  for (ClassLoader cl : classLoader) {
    if (null != cl) {
      try {
        return Class.forName(name, true, cl);
      } catch (ClassNotFoundException e) {
        // we'll ignore this until all classloaders fail to locate the class
      }
    }
  }
  throw new ClassNotFoundException("Cannot find class: " + name);
}

But why can’t I load it?

So test it in the main method

public class MybatisMain {
  public static void main(String[] args) throws IOException
  {
    try {
      Class.forName("com.mysql.jdbc.Driver", true, Thread.currentThread().getContextClassLoader());
    } catch (ClassNotFoundException e) {
      e.printStackTrace();
    }
  }
}

As a result, it still can’t be loaded.

Conclusion:

Look at the POM file

<dependency>
  <groupId>mysql</groupId>
  <artifactId>mysql-connector-java</artifactId>
  <version>8.0.24</version>
  <scope>test</scope>
</dependency>

Notice the <scope>test</scope> in the pom file, the problem lies here, comment out this line, the problem is solved.