How to add extra fields to an Object during Jackson's json serialization?

Question

I need to add new property to an object, when serializing to JSON. The value for the property is calculated on runtime and does not exist in the object. Also the same object

Answer 1

Can you not just add a method in value class? Note that it does not have to be either public, or use getter naming convention; you could do something like:

public class MyStuff {
   // ... the usual fields, getters and/or setters

   @JsonProperty("sum") // or whatever name you need in JSON
   private int calculateSumForJSON() {
        return 42; // calculate somehow
   }
}

Otherwise you could convert POJO into JSON Tree value:

JsonNode tree = mapper.valueToTree(value);

and then modify it by adding properties etc.