Question

I have a List of javascript objects on my client side, which are a list of “events” that a user has executed. When the user is ready, I want to send this to the server. The order of events is important, so preserving the list order is necessary.

What I would like to do is to have a JSON library (don’t mind which one) to bind the JSON to some Event objects in my Java code, where Event is an abstract class, and I have 3 concrete classes that all extend Event (lets say EventA, EventB and EventC).

Ideal scenario would be something like

List<Event> events = jsonlibrary.deserialise(jsonString);

which may contain a list of items such as

[eventA, eventC, eventA, eventA, eventB]

Is this possible, or do I have to inspect the JSON tree manually, and deserialise the individual elements of the json array?

Answer 1

JSON objects are just key/value pairs and contain no type information. That means identifying the type of a JSON object automatically isn’t possible. You have to implement some logic on the server-side to find out what kind of event you are dealing with.

I would suggest to use a factory method which takes a json string, parses it to find out what kind of Event it is, builds an Event object of the correct subclass and returns it.