jackson-core: Dependent pair, where type family exists before quantifier in Json data

Question

I have some incoming JSON (the field-order of which is not my choice) that embeds a dependent pair:

{
  "data": {...},
  "evt": "READY",
  ...
}

and what type I should read data into depends on the value of evt . With just a JsonParser this is impossible because there's no way to store data for later so that it can be returned to once evt is reached.

All of the data I'm parsing (unfortunately) already exists in a ByteBuffer , so is there a better interface to use than JsonParser ? I don't want to bring in any more dependencies than jackson-core if it can be helped.

Answer 1

Looks like there is no simple way to achieve this without any additional dependencies.

I suppose, you need to add at least jackson-databind (and also jackson-annotations if not added automatically via Maven/Gradle). Then you can use an ObjectMapper as an ObjectCodec for the parser and parse the complete JSON either into a TreeNode structure that can be partically parsed later into the correct type or - if you have objects for all types of data - you maybe can directly parse the complete object with matching data type. If needed, a custom ObjectCodec could be implemented to first collect the unknown data and then later process it when the type is known, but implementing an ObjectCode does not seem to be that easy.

Instead of Jackson you could use GSON which can either parse the data into the complete object structure or a generic JSON object tree without any additional dependencies.

If you really cannot add additional dependencies, then you could implement a SAX-XML-Parser-like logic using JsonParser.nextToken , but I suppose that would require a lot of custom logic.