{
  "shouldBeIgnored1": "string",
  "shouldBeIgnored2": "string",
  "key1": {
             "id": 1,
             "value": "value"
           },
  "key2": {
             "id": 2,
             "value": "another value"
           }
    ...
}

class Item {
    private int id;
    private String value;

    //getters setters
}

JsonMappingException: Can not instantiate value of type [simple type, class Item] from String value ('string'); no single-String constructor/factory method

String json = "...";
ObjectMapper objectMapper = new ObjectMapper();
ObjectNode objectNode = (ObjectNode) objectMapper.readTree(json);

Iterator<Map.Entry<String, JsonNode>> fields = objectNode.fields();
Set<String> fieldsToRemove = new HashSet<>();
while (fields.hasNext()) {
    Map.Entry<String, JsonNode> field = fields.next();
    String fieldName = field.getKey();
    JsonNode fieldValue = field.getValue();
    if (!fieldValue.isObject()) {
        fieldsToRemove.add(fieldName);
    }
}

objectNode.remove(fieldsToRemove);

TypeReference typeReference = new TypeReference<Map<String, Item>>() { };
Map<String, Item> map = objectMapper.convertValue(objectNode, typeReference);