Jackson JsonNode to string with sorted keys

Question

I'm using Jackson 2.2.3 and need to convert a JsonNode tree into a string with sorted field keys. It's completely unclear to me how to do this, especially since the opposite is so simple - JsonNode jn = ObjectMapper.readTree(String s).

It appears the correct method is void writeTree(JsonGenerator jgen,JsonNode rootNode). However, I see no way to then get the serialized String from the JsonGenerator. I presume that SerializationFeature.ORDER_MAP_ENTRIES_BY_KEYS will still apply, since the JsonGenerator.Features don't have that option. Is there a simpler way to do this - or if not, how do I retrieve the serialized string from the JsonGenerator?

Answer 1

This is the easiest way to do it, as provided by one of Jackson's authors. There's currently no way to go straight from JsonNode to String with sorted keys.

private static final ObjectMapper SORTED_MAPPER = new ObjectMapper();
static {
    SORTED_MAPPER.configure(SerializationFeature.ORDER_MAP_ENTRIES_BY_KEYS, true);
}

private String convertNode(final JsonNode node) throws JsonProcessingException {
    final Object obj = SORTED_MAPPER.treeToValue(node, Object.class);
    final String json = SORTED_MAPPER.writeValueAsString(obj);
    return json;
}