This is an issue I've tried to pursue multiple times in the past, and each time
I've given up and used an awkward solution that won't work in the current
situation I'm seeing this. I thought perhaps I had asked it here before, but I
don't see it in the archives.
We have a couple hundred Java SpringBoot services, most of them using
SpringBoot 3.2.5. Internally, it is using Tomcat through the
"tomcat-embed-core" artifact, version 10.1.30.
Every once in a while, I run into a problem where the service startup fails
with some variation of this:
WebServerException: Unable to start embedded Tomcat
The stacktrace provided in this case has no stack entries in application code.
It provides no clue of what actually went wrong. Whenever I run into this, if I
can run the service on my desktop, I set breakpoints in the StandardContext
class wherever it sets "ok" to false. That always leads to the solution. It
almost always points to a conflict with dependencies, but knowing that fact
doesn't help me until I know what the conflict is.
I really shouldn't have to do this. I can clearly see in the StandardContext
class that it tries to log the exception message (usually a "MultiException" or
something like that). Ideally, I should just be able to configure the logging
for tomcat-embed-core to make it print the exception details. Several times I
have struggled to make this work, and I've never been able to get it working.
Tomcat uses java.util.logging, but it seems to have some variations that
seemingly make it more difficult to configure. I've tried variations with a
"logging.properties" file, but it never seems to make any difference. I've seen
some posts that try to address this, but I've never found a complete solution
for getting this working in a SpringBoot application.
In the latest instance, I'm seeing this happen in an environment I can't run
the debugger in, so I have no way to diagnose this.
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