logger.go
func (dl *DefaultLogger) Error(message string, params ...interface{}) {
	dl.logger.Errorf(fmt.Sprintf("%s %s", caller(), message), params...)
}
func (dl *DefaultLogger) Error(message string, params ...interface{}) {
	dl.logger.Errorf(fmt.Sprintf("%s %s", caller(), message), params...)
}
// Error formats a given message according to given params to log with level Error.