I have a spring boot app that I haven't touched in a very long time, probably more than a year. I updated its build system with the latest bits from the spring initializr so it's using boot version 2.6.6, and I fixed the compile errors that introduced. This all used to work the last time I tried it. I was using some 2.1.x version of boot at the time.

I'm getting some ClassNotFoundException errors for classes in my own code that REALLY should be included in the jar. But I'm also seeing this, and as far as I know, the logback-classic jar IS included:

Exception in thread "bkDbProcess" java.lang.NoClassDefFoundError: ch/qos/logback/classic/spi/ThrowableProxy

I've been looking for a solution to this. I see a lot of people reporting the problem, but I've only found one suggestion on a solution, and that didn't work for me: Explicitly adding logback-classic as a dependency in build.gradle.

The program outputs a whole bunch of log entries before it throws that exception, so I know that logback is working.

Because it is also throwing that exception for some of MY classes as well as that logback class, this seems like a general classloader problem, not something specific to logback.

What other information can I gather? Anyone know how to fix it?