使用Jackson反序列化自引用对象

Question

I have a JSON string looking like that (simplified):

[
  { "id":1, "friends":[2] },
  { "id":2, "friends":[1,3] },
  { "id":3, "friends":[] }
]

The content of friends are ids of other users in the list.

Is it possible somehow to create a Java class like the one below from the JSON just with Data Binding using Jackson or do I need an intermediate step for that?

public class User {
  private long userid;
  private List<User> friends;
// ... getters/setters

Thanks for your help.

Answer 1

There is no fully annotative way to do this, so you would need custom JsonSerializer / JsonDeserializer. Jackson 1.9 adds two new features that might help:

• ValueInstantiators, so you can add constructors for deserializer to convert from basic integer into POJO
• Value injection so you could pass additional context object (which you would need to find ids of already deserializer objects, to map then from integer to instance)

However I am not 100% sure how to combine these two features for specific use case...