The environment at that time:

When testing the UAT project, I suddenly found that the project could not be accessed normally. In fact, there are many times when the project is still in good condition in the last second and explodes in the next second. It’s very uncomfortable, especially when testing the joint debugging

So he opened the log with curiosity and found that the original report was wrong

java.lang.IllegalStateException: Illegal access: this web application instance has been stopped already.
 
Could not load [java.beans.PropertyChangeEvent]. The following stack trace is thrown for debugging 

purposes as well as to attempt to terminate the thread which caused the illegal access.

His general meaning is that the web application has stopped and can’t load something called XXXXXXXX.

Then kill the Tomcat process, and then get up
to solve the problem….

be careful:

if you restart tomcat, you cannot solve the problem.

to modify the server.xml , add a child element to the tag, find the tag, and set the attribute value of reloadable to reloadable = false.

It means hot deployment, which is convenient for developers