Recently, when debugging the environment and starting tomcat, I encountered the following problems:
严重: The web application [/service] registered the JDBC driver [com.alibaba.druid.proxy.DruidDriver] but failed to unregister it when the web application was stopped. To prevent a memory leak, the JDBC Driver has been forcibly unregistered. January 25, 2018 11:58:37 AM org.apache.catalina.loader.WebappClassLoader clearReferencesJdbc 严重: The web application [/service] registered the JDBC driver [com.mysql.jdbc.Driver] but failed to unregister it when the web application was stopped. To prevent a memory leak, the JDBC Driver has been forcibly unregistered. January 25, 2018 11:58:37 AM org.apache.catalina.loader.WebappClassLoader clearReferencesThreads 严重: The web application [/service] appears to have started a thread named [Abandoned connection cleanup thread] but has failed to stop it. This is very likely to create a memory leak. January 25, 2018 11:58:37 AM org.apache.catalina.loader.WebappClassLoader clearReferencesThreads 严重: The web application [/service] appears to have started a thread named [New I/O worker #1] but has failed to stop it. This is very likely to create a memory leak. January 25, 2018 11:58:37 AM org.apache.catalina.loader.WebappClassLoader clearReferencesThreads 严重: The web application [/service] appears to have started a thread named [New I/O worker #2] but has failed to stop it. This is very likely to create a memory leak. January 25, 2018 11:58:37 AM org.apache.catalina.loader.WebappClassLoader clearReferencesThreads 严重: The web application [/service] appears to have started a thread named [New I/O worker #3] but has failed to stop it. This is very likely to create a memory leak. January 25, 2018 11:58:37 AM org.apache.catalina.loader.WebappClassLoader clearReferencesThreads 严重: The web application [/service] appears to have started a thread named [New I/O worker #4] but has failed to stop it. This is very likely to create a memory leak.
Looking at the catalina.out log, there is no error message before or after.
On the Internet, some say that it is caused by hot deployment, some say that it is caused by jar package conflict, and some say that it can be ignored. After trying all of them, the problem cannot be solved.
In fact, there are many reasons for this problem, such as the database cannot be connected, the middleware connection fails to initialize, and so on. However, it will not output to catalina.out, but to the localhost.201x-xx-xx.log file in the logs directory. If you encounter such a problem, you can view the log to quickly locate the cause of the problem.