How to deserialize JSON array with different types?

Question

I have a JSON array like this:

[
  "0",
  {
    "number": 1,
    "field": "value"
  },
  {
    "number": 2,
    "field": "value"
  }
]

The first element to the array is a string.

Is it possible to deserialize it with FasterXML Jackson?

I know how to do it with different objects.
I need to use @JsonSubTypes (Here is an example https://stackoverflow.com/a/38877862/2564509)

The problem with this array is that the first element is String type.

I'm not set up to test it, but the "only" issue I see compared to the linked solution, is that String is final and can not be made to extend a custom interface. But 1) do you really need a single, custom interface (e.g. List<Object>) ? 2) What about creating a StringWrapper class that holds a String (maybe with a custom (De)Serializer ? 3) What about cheating by extending something not final and String-like, e.g. a CharSequence implementation (sadly, StringBuilder is final too) ? — GPI
– GPI, Commented Dec 16, 2021 at 14:26
@GPI Yes, the String class is final. Because of that, I cannot have a common interface for String and other classes. 1) I get an array from an API like in the question. I cannot change it. 2) I haven't tried it. So this is the next to try. 3) For my case, it is not a good approach because other elements (objects) are not String-related (they are more specific, like user data). — djm.im
– djm.im, Commented Dec 16, 2021 at 14:39

DwB · Accepted Answer · 2021-12-16 19:06:12Z

2

Caveat: Your situation is an unfortunate edge case. As such, the solution is likely to be not wonderful.

This works, but is not wonderful:

First, deserialize as a List<Object>. In your case, this will result in a List of three elements; String, LinkedHashMap, and LinkedHashMap
Next, process each element in the array and, process based on the element type; a String will be your String element, a LinkedHashMap will be the representation of your number-field class.

answered Dec 16, 2021 at 19:06

DwB

38.6k11 gold badges62 silver badges86 bronze badges

Sign up to request clarification or add additional context in comments.

1 Answer 1