org.apache.commons.dbcp.SQLNestedException: Cannot create PoolableConnectionFactory (Data source rejected establishment of connection, message from server: "Too many connections")
This indicates that something is leaking connections. I.e. something keeps acquiring (opening) connections without ever closing them and/or returning to connection pool. Restarting the DB so that it can hard-close all opened connections should temporarily fix the issue. Fixing something so that it is properly closing the connection after use should permanently fix the issue.
Although the posted JDBC code is not following the optimal idiom, it doesn't look like to be the cause of leaking connections. Probably the DB is already running for hours/days and you've during earlier tests acquired too many connections without closing them so that the DB is running out of them.
