A class being scanned from multiple locations can lead to problems, but it’s not obvious that this is what’s causing your problem.
Could you share a bit more of the logs? Is there a stack trace or any other errors?
If you want to try solving the scanned from multiple locations issue, you could try running with a newer Guava version. At least guava-30.1-jre does not seem to contain those classes anymore, although I’m not sure what else changed in that version.
You either have a dependency on Guava defined in your pom.xml, or then there is a transitive dependency on it. In this case you can find out where it comes from with mvn dependency:tree -Dincludes=com.google.guava.
Apparently Jetty might display that error if the address is already in use, i.e. something else is running on that port.
You can try running it with the -X flag to show debug output (e.g. mvn jetty:run -X).
The address is already in use. I ran the mvn jetty:run -X and got the following errors:
Caused by: java.net.BindException: Address already in use: bind
FAILED ServerConnector@1777ef25{HTTP/1.1,[http/1.1]
}{0.0.0.0:8080}: java.io.IOException: Failed to bind to 0.0.0.0/0.0.0.0:8080
FAILED MavenServerConnector@68a7ea1e{FAILED}: java.io.IOException: Failed to bind to 0.0.0.0/0.0.0.0:8080
FAILED Server@7b5d68fc{FAILED}[9.4.15.v20190215]
: java.io.IOException: Failed to bind to 0.0.0.0/0.0.0.0:8080
I recently port-forwarded to port 8080, could that be the cause of the issue? I get the error after a fresh restart of my computer too.
Once you have the process ID, you should be able to find it in the Task Manager on Windows or Activity Monitor on Mac. On Windows, you might have to click More details and then right click on a column and select PID to get the process ID to show.