i think i have gotton the reason by myself.
i have one class whose function is getting connection with oracle in which there is a
Connection object.i must creat another Connection object to receive the Connection
return value when i invoke the class.so there r 2 connection object.i have do to do with
these two Connection object when i need data from db.there must be some problem.
once more i think feibaook(飞豹) and other netpla's feedback.thanks!