How to get the generic type for the Jackson ObjectMapper


Java erases normally the Generics data on compilation, but there is a possibility to get that information (the Jackson ObjectMapper does that pretty well).

My Problem: I have a Class with a property of List:

public class User {
    public List<Long> listProp;//it is public only to keep the example simple

How can I get the correct TypeReference (or JavaType ?) so that I can map programatically a JSON String to the correct List Type, having the instance of the Class class (User.class) and the property name (listProp)? What I mean is this:

TypeReference typeReference = ...;//how to get the typeReference?
List<Long> correctList = om.readValue(jsonEntry.getValue(), typeReference);//this should return a List<Long> and not eg. a List<Integer>

Have you tried the mappers constructType method?

Type genericType = User.class.getField("listProp").getGenericType();
List<Long> correctList = om.readValue(jsonEntry.getValue(), om.constructType(genericType));