2012-04-23 13:41:02,120 WARN (com.mchange.v2.c3p0.management.ActiveManagementCoordinator:56) - A C3P0Registry mbean is already registered. This probably means that an application using c3p0 was undeployed, but not all PooledDataSources were closed prior to undeployment. This may lead to resource leaks over time. Please take care to close all PooledDataSources.
如果是单独一个使用c3p0的项目放在tomcat下，打出的日志是：2012-04-23 13:48:47,289 INFO (com.mchange.v2.c3p0.C3P0Registry:204) - Initializing c3p0-0.9.1.2 [built 21-May-2007 15:04:56; debug? true; trace: 10]
We had this problem when we were trying to deploy multiple applications within same tomcat. So it was a case of multiple class loaders within same VM.
How did we solve this ?
We moved the jar files from WEB-INF of each folder to the tomcat/lib directly.
This solved the problem.
We were also seeing some out of memory problems which are not happening right now.
Refer to C3P pool documentation