This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
java.sql.SQLException: Closed Connection
You went to get a connection from the connection pool, but you got an exception. So check out these things: is there code which is taking connections but not returning them to the pool? Was the database server restarted, or did the database manager kill some sessions which corresponded to connections in the pool? Do you just not have enough connections in the pool to support the number of users you have now?