Tomcat 7.0.40 has a issue running the standard connection pooler. Following the Apache tutorial can lead to a error
javax.naming.NamingException: Could not create resource factory instance [Root exception is java.lang.ClassNotFoundException: org.apache.tomcat.dbcp.dbcp.BasicDataSourceFactory]
The solution is to add a different factory reference to your resource definition.
Demo Datasource jdbc/resourceName javax.sql.DataSource Container
This should solve the issue with Tomcat selecting the inappropriate factory for connection pooling.