Setting Oracle 11g Session Timeout

After rebooting the server, the oracle connection from the Tomcat server times out every night. Prior to the reboot, the connection didn't timeout. Now, in the morning, the application throws a JDBC connection error while accessing the DB. Restarting Tomcat corrects the issue. I'm assuming that's due to the connections being re-established. I think, this is due to the Oracle DB timing out the session. How can the session timeout be disabled in Oracle 11g?
Thanks!
Steve

Config.groovy with dev and test omitted.

dataSource {
  pooled = true
}

hibernate {
   cache.use_second_level_cache = true
   cache.use_query_cache = true
   cache.provider_class = 'net.sf.ehcache.hibernate.EhCacheProvider'
}

// environment specific settings
environments {
production {
  dataSource {
    driverClassName = "oracle.jdbc.driver.OracleDriver"
    username = "XXXXX"
    password = "XXXXXX"
    dialect = "org.hibernate.dialect.Oracle10gDialect"
    dbCreate = "update" // one of 'create', 'create-drop','update'
    url = "jdbc:oracle:thin:@XXXXXX:1521:xxxx"
  }
}  }