Yes, I understand that a type is required before you can have a format, and the format date-time actually needs type string.
As workaround I manually wrote type=number, format=date-time into the query parameter in the specification and adopted our code generator to generate from that config a util.Date as Java type.
But as this is not standard conform: Do you have a suggestion how I could configure a parameter as type=number without having format=date-time and nevertheless know in my consuming generator that for this parameter util.Date is expected to be generated?
Your workaround is likely the best option for you right now since there aren’t really any valid options for configuring a parameter like this.
Heads up: The workaround itself won’t be valid JSON Schema because the ‘date-time’ format is supposed to be a RFC3339 formatted timestamp, which is based on the JSON Schema specification itself. You can still leave it as is though for documentation purposes, but you will want to keep this in mind if you run it through other validation or linting tooling.