Correct way to keep pooled connections alive (or time them out and get fresh ones) during longer inactivity for MySQL, Grails 2 app

I have a grails app that has flurries of high activity, but then often periods of inactivity that can last several hours to over night. I notice that the first users in the morning get the following type of exception, and I believe this is due to the connections in the pool going stale and MYSql database closing them.

WebApp (Tomcat-jdbc) Pooled DB connection throwing abandon exception

I have been browsing SO for some time, and chewing my hat in the process, but cannot find an exact match to my problem.
For short, I am getting superb stack trace (org.apache.tomcat.jdbc.pool.ConnectionPool abandon) after 60 seconds of inactivity, which is a normal behavior for a couple of server side threads.
I am using Tomcat JDBC Connection Pooling (org.apache.tomcat.jdbc.pool.DataSource) directly
Stack Trace:

Optimal number of connections in connection pool

Currently we are using 4 cpu windows box with 8gb RAM with MySQL 5.x installed on same box. We are using Weblogic application server for our application. We are targeting for 200 concurrent users for our application (Obviously not for same module/screen). So what is optimal number of connections should we configured in connection pool (min and max number) (We are using weblogic AS’ connection pooling mechanism) ?