初学JavaWeb, 每次启动Tomcat有这样一个警告 :

20-Nov-2016 22:11:12.615 ?? [RMI TCP Connection(2)-127.0.0.1] org.apache.jasper.servlet.TldScanner.scanJars At least one JAR was scanned for TLDs yet contained no TLDs. Enable debug logging for this logger for a complete list of JARs that were scanned but no TLDs were found in them. Skipping unneeded JARs during scanning can improve startup time and JSP compilation time.

另外只要通过JDBC连接之后(我的版本是最新版:mysql-connector-java-5.1.40), 重新部署项目, 就有如下报错 :

20-Nov-2016 22:19:15.987 ?? [RMI TCP Connection(5)-127.0.0.1] org.apache.catalina.loader.WebappClassLoaderBase.clearReferencesJdbc The web application [ROOT] 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.
20-Nov-2016 22:19:15.988 ?? [RMI TCP Connection(5)-127.0.0.1] org.apache.catalina.loader.WebappClassLoaderBase.clearReferencesThreads The web application [ROOT] 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. Stack trace of thread:
 java.lang.Object.wait(Native Method)
 java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:143)
 com.mysql.jdbc.AbandonedConnectionCleanupThread.run(AbandonedConnectionCleanupThread.java:43)

网上搜索好多教程看都看不太懂, 而且也不说原因, 总之雨里雾里.