解决：the JDBC Driver has been forcibly unregistered

　　启动Tomcat时报错

1 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.
2 一月 25, 2018 11:58:37 上午 org.apache.catalina.loader.WebappClassLoader clearReferencesJdbc
3 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.
4 一月 25, 2018 11:58:37 上午 org.apache.catalina.loader.WebappClassLoader clearReferencesThreads
5 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.
6 一月 25, 2018 11:58:37 上午 org.apache.catalina.loader.WebappClassLoader clearReferencesThreads
7 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.
8 一月 25, 2018 11:58:37 上午 org.apache.catalina.loader.WebappClassLoader clearReferencesThreads
9 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.
10 一月 25, 2018 11:58:37 上午 org.apache.catalina.loader.WebappClassLoader clearReferencesThreads
11 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.
12 一月 25, 2018 11:58:37 上午 org.apache.catalina.loader.WebappClassLoader clearReferencesThreads
13 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。

以上转载自：https://www.iteye.com/blog/rhodian-2409008

我出现的问题是，增量更新服务器class文件时，直接替换会出现class文件自动删减末尾的情况，报错：Caused by: java.lang.ClassFormatError: Extra bytes at the end of class file。只有替换class文件会出现，新增不会，目前原因不明；

同样的问题还发现，利用xftp直接编辑线上的文件，也会出现同样的情况（删减末尾）。

慎用这种粗暴的方式，用linux命令。

补充：像过滤器，拦截器，以及没有被捕捉的异常报出的问题都会记录在localhost.xxxx-xx-xx.log文件中。【了解tomcat日志文件的区别】