Design pattern for creating object from file?

Question

Hi,

I am creating a software project in which most business objects are stored in files (in a legacy format). The objects will only be instantiated from an inputstream.

I do this today with making the constructor private and instantiating in a static function as follows:

public class BusinessObject {

    private BusinessObject() {}

    public static BusinessObject fromStream(Stream stream) {
        // Do initialization here
    }
}

I would like my code to use established design patterns, since other people will be modifying it.

Is this a known pattern, or is there a design pattern that I can use instead of the above?

Thanks,

Martin

Answer 1

Sounds like you're looking for either deserialization or one of the construction patterns like factory

Answer 2

It looks you're making a Factory.

It might depend on what you're doing in the "initialization" phase, but you might be able to just make a constructor that takes in the Stream. If you're already disallowing the null constructor and only allowing them to be created from a Stream, it seems like the same only simpler. The only reason I can see this not working is if there are multiple subclasses of BusinessObject.

Answer 3

That's a very good way to do it. You're using the Factory pattern.

Ideally, you could use serialization/deserialization in your implementation to persist the object, but that may not be an option for you if the legacy format is required.