I am currently learning more about implementing JDBC and using databases in a Spring Boot webapp, and I encountered the following Stack Trace written in the bottom of the post.<
I faced a similar issue when I upgraded the Java version in my server to 11 from 8.
The spring boot started supporting Java 11 from 2.1 and onwards. So make sure your project's dependencies are also updated accordingly. This is relevant for this answer as SpringBoot also influence MySQL connector, Hibernate core, and other dependencies.
The inability to connect to DB was resulting in some more NoClassDefFoundErrors. So make sure you solve this first before looking into other errors.
An example pom dependency for the SpringBoot starter
org.springframework.boot
spring-boot-starter-parent
2.1.12.RELEASE
Hope this helps someone.