Support for multiple constructors

[kenston]

Is it possible to add support for deserializing to a class with multiple constructors where Genson will loop through the possible constructors and choose which one is appropriate based on the matching between JSON properties and constructor arguments?

[EugenCepoi]

At some point Genson was doing it but it led to ambiguous situations where you don't know what constructor to pick. Then I decided on purpose to use only one constructor and don't switch at runtime.

Do you have some strong use case/argument for this feature? Perhaps we can find some alternative.

On Aug 6, 2016, at 2:10 AM, Ken Choi [email protected] wrote:

Is it possible to add support for deserializing to a class with multiple constructors where Genson will loop through the possible constructors and choose which one is appropriate based on the arguments?

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[kenston]

I'm using Genson to configure the creation of Java objects similar to how beans are created using Spring XML configuration. There are cases where classes have multiple constructors but with different argument names and types. Maybe we can have an option at GensonBuilder to allow us to decide whether to offer that functionality or not.

[EugenCepoi]

Are the properties also settable using a setXx method? If so you can just pick one constructor and mark it with JsonCreator annotation. Genson then will use only this constructor and the setters for the other fields. You can also allow deser to private properties, which should work also in the case of final properties. Let me know if any of those would work for you.

[kenston]

The properties does not have or are not settable using a setXx method. My class have one or more usable constructors; thus, I can't just pick one over the other by placing the JsonCreator annotation. I also want to keep my classes clean from annotations just like how Spring supports it that way.

[ErikLundJensen]

We have the same issue. When Genson selects a constructor then it should at least select one that does not fail. Today it selects one constructor and then fails with NullPointerException if not all arguments are available.
Genson should continue to the next constructor to see if that one matches.

[EugenCepoi]

Initially we had support for multiple constructors, here is why I removed it:

• When two constructors match the defined properties, then we again don't know which one to pick.
• If we imagine there are setters for the other properties then maybe it wouldn't matter what constructor we choose. But in this case why not have a single constructor (or many but this one annotated with JsonCreator) that takes all the required properties and uses setters for the ones that are optional?
• It added complexity and performance overhead

What do you think, especially about point 2?

@ErikLundJensen I prefer we first discuss all this a bit before considering an implementation. I am not necessarily against it, but if we do so then it must add very low overhead to the performances.

[ErikLundJensen]

Sorry for not returning before. I understand that you want to keep the code smooth and fast.
And you are right, you should not solve problems caused by others not using annotations correctly.

I suggest that I delete my pull request and thereby make sure it is not used by others. Is that Okay?

[EugenCepoi]

I am going to close your PR for now, but again, if this is a feature you strongly need let's discuss it. I am open to consider it :)