Driver class 'com.mysql.cj.jdbc.Driver' not found.

This error message typically occurs when attempting to establish a connection to a MySQL database using JDBC, but the MySQL JDBC driver is not included in the classpath of the application or server.

To resolve this issue, you should download the MySQL JDBC driver from the official website and add it to the classpath. This can be done by either adding the JAR file to the project dependencies or by adding it to the server's classpath.

If you are using an IDE, such as Eclipse or IntelliJ IDEA, you can add the MySQL JDBC driver to your project by right-clicking on the project and selecting "Build Path" > "Configure Build Path" > "Libraries" > "Add External JARs" and selecting the downloaded JAR file.

If you are running a Java application from the command line, you can add the MySQL JDBC driver to the classpath using the "-cp" or "-classpath" option. For example:

java -cp mysql-connector-java-8.0.26.jar MyApplication

Alternatively, you can set the CLASSPATH environment variable to include the path to the MySQL JDBC driver.

It is important to ensure that the driver class name used in the JDBC connection URL matches the actual driver class name in the JAR file. For MySQL 8.0 or later, the driver class name is "com.mysql.cj.jdbc.Driver".