最近调试环境，启动tomcat遇到如下问题：
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. 一月 25, 2018 11:58:37 上午 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. 一月 25, 2018 11:58:37 上午 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. 一月 25, 2018 11:58:37 上午 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. 一月 25, 2018 11:58:37 上午 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. 一月 25, 2018 11:58:37 上午 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. 一月 25, 2018 11:58:37 上午 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.
查看catalina.out日志，前前后后都没有任何错误信息。
网上有说热部署造成的，有说jar包冲突造成的，也有说可以忽略的，全部试了一遍以后，并不能解决问题。
其实造成这个问题的原因有很多种，比如数据库连不上，中间件连接初始化失败等等。但是，都不会输出在catalina.out，而是输出到logs目录下的localhost.201x-xx-xx.log文件。如果遇到这种问题，可以查看该日志，可迅速定位问题原因。