mysql - What causes java.sql.SQLException: Cannot work with a closed Connection? -

i have long set of queries i'm running in hibernate, error everytime try run them (using mysql) :

javax.persistence.persistenceexception: org.hibernate.exception.genericjdbcexception: not execute query ... caused by: org.hibernate.exception.genericjdbcexception: not execute query ... caused by: java.sql.sqlexception: cannot work closed connection ...   [jdbctransaction] not toggle autocommit com.mysql.jdbc.exceptions.jdbc4.mysqlnontransientconnectionexception: no operations allowed after connection closed. caused by: java.sql.sqlexception: cannot work closed connection 

is there parameter change prevent happening? thank in advance.