I have webapp using Spring 5.1.10, running on Jetty 9.4.20. Through out the app JCL is used for logging. Jetty is configured by enabling jcl-slf4j (to capture webapp and Spring messages) and logging-logback module and editing corresponding resources/logback.xml. In that configuration file, there is defined a logger that have two MDC's in pattern: %mdc{instance:-internal} and %mdc{user:-default}. MCD key instance is set by a Filter and user by RequestInterceptor. Basically they work, as when logging statements is called by some controller, correct values for instance and user end up in log file.
The problem is that there is controller, that deals with legacy part of the system. It looks up a class file, loads this class using custom class loader, does some setup (setting some properties) then executes a method, that actually does the job. The problem is that all loaded classes that emit log messages have both MDC keys as default values (internal and default respectively) despite both values being set to correct values.
I have added log statements to filter and request interceptor and it looks like they occupy the same thread as the class being loaded. Also I have added a test log statement to controller, which is emitted after custom class is loaded, but before its method execution. The result is that despite all entities being executed within the same thread MCD works in controllers, filters and interceptors and doesn't work with loaded classes. That leads me to believe, that class loading somehow is involved.
The question is: How I can get MDC to work within classes loaded by custom class loader?
