CODEWITHSUNDEEP
javajackson
user1596371
user1596371

Reputation:

How to change Jackson's default concrete map type?

I have a very simple Jackson code to deserialize a nested JSON object:

public class MapTest
{
  public static void main(String ... args) throws Exception
  {
    final String ser = "{\"nested\":{\"k1\":\"v1\",\"k2\":\"v2\",\"k3\":\"v3\"}}";
    final Map<String, Object> deser = new ObjectMapper().readValue(ser, new TypeReference<TreeMap<String, Object>>(){});
    System.out.println("Class of deser's nested object is " + deser.get("nested").getClass().getSimpleName());
  }
}

When I run this I obtain the following output:

Class of deser's nested object is LinkedHashMap

However I want the nested map to be deserialized as a TreeMap rather than as a LinkedHashMap as per the output. How can I tell Jackson to default to use a TreeMap when deserializing?

Reading through the documentation the closest thing I found was the ability to define concrete classes for abstract types through addAbstractTypeMapping() in a module but I've tried every superclass and instance of LinkedHashMap in an attempt to do this and nothing seems to work.

This is using Jackson 2.4.2, although if there is a way to do this that requires a higher version I would be able to upgrade.

Upvotes: 5

Views: 3090

Answers (1)

StaxMan
StaxMan

Reputation: 116502

Module's addAbstractTypeMapping() is indeed the way to achive mapping in general. But the problem may be due to recursive nature of deserialization; because inner values are considered to be of type java.lang.Object.

However, I think there were indeed fixes to this part in 2.5, so I would specifically checking to see if 2.5.0 would work, once you add abstract mapping from Map to TreeMap. If this does not work, please file a bug at https://github.com/FasterXML/jackson-databind/issues since it should work.

Upvotes: 2

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