jackson delay deserializing field

Question

I have a class like this:

public class DeserializedHeader
    int typeToClassId;
    Object obj

I know what type of object obj is based on

Answer 1

This is really complex and painful problem. I do not know any sophisticated and elegant solution, but I can share with you my idea which I developed. I have created example program which help me to show you how you can solve your problem. At the beginning I have created two simple POJO classes:

class Product {

    private String name;

        // getters/setters/toString
}

and

class Entity {

    private long id;

    // getters/setters/toString
}

Example input JSON for those classes could look like this. For Product class:

{
  "typeToClassId" : 33,
  "obj" : {
    "name" : "Computer"
  }
}

and for Entity class:

{
  "typeToClassId" : 45,
  "obj" : {
    "id" : 10
  }
}

The main functionality which we want to use is "partial serializing/deserializing". To do this we will enable FAIL_ON_UNKNOWN_PROPERTIES feature on ObjectMapper. Now we have to create two classes which define typeToClassId and obj properties.

class HeaderType {

    private int typeToClassId;

    public int getTypeToClassId() {
        return typeToClassId;
    }

    public void setTypeToClassId(int typeToClassId) {
        this.typeToClassId = typeToClassId;
    }

    @Override
    public String toString() {
        return "HeaderType [typeToClassId=" + typeToClassId + "]";
    }
}

class HeaderObject<T> {

    private T obj;

    public T getObj() {
        return obj;
    }

    public void setObj(T obj) {
        this.obj = obj;
    }

    @Override
    public String toString() {
        return "HeaderObject [obj=" + obj + "]";
    }
}

And, finally source code which can parse JSON:

// Simple binding
Map<Integer, Class<?>> classResolverMap = new HashMap<Integer, Class<?>>();
classResolverMap.put(33, Product.class);
classResolverMap.put(45, Entity.class);

ObjectMapper mapper = new ObjectMapper();
mapper.disable(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES);

String json = "{...}";

// Parse type
HeaderType headerType = mapper.readValue(json, HeaderType.class);
// Retrieve class by integer value
Class<?> clazz = classResolverMap.get(headerType.getTypeToClassId());
// Create dynamic type
JavaType type = mapper.getTypeFactory().constructParametricType(HeaderObject.class, clazz);
// Parse object
HeaderObject<?> headerObject = (HeaderObject<?>) mapper.readValue(json, type);
// Get the object
Object result = headerObject.getObj();

System.out.println(result);

Helpful links:

1. How To Convert Java Map To / From JSON (Jackson).
2. java jackson parse object containing a generic type object.