Custom serializer in pretty printer for binary fields

[martinpaljak]

Hi! I'd like the pretty printer to print binary as hex instead of base64. I've created a mapper and custom serializer for byte[].class that works in other contexts, but not in the pretty printer derived from that mapper, which still emits base64.

Any hints?

[cowtowncoder]

Pretty printer really should not change serialization aspects; it should invoke all the usual handling so this sounds odd and not at all like expected.
If you could provide a reproduction that'd be good maybe we could help with suggestions.
Filing a separate bug issue is fine too but if repro is small enough can just continue here for now.

[martinpaljak]

My assumption was incorrect. I had a bunch of serializers for special objects "BlahAsBytesSerializer" in a module (for CBORMapper), so by just adding "BinaryAsHex" serializer to the end of same module and using the module with ObjectMapper (used for printing) did not "stack". A member of type Blah was first converted to byte[] and then printed as base64 whereas a simple byte[] was indeed serialized as hex.

"fixed" this by making "BlahAsHex" serializer. Would be cool if the mapper respected such two stage conversions, first from custom object to byte[] and then because same module has a serializer for byte[], would use that?

[cowtowncoder]

Unfortunately there is no way to stack serializers since they take Java Objects and produce JsonToken streams.

There are ways to do 2-phase conversions (using Converter with JsonSerializer) to allow Java Ob to Java Object conversions (on ser or deser) but that's about it; but one cannot dynamically mix and match them; need specific JsonSerializer that applies Converter. This is easy enough to do, but I don't think that'd do what you want here.

[martinpaljak]

Hijacking the same thread for a similar question - things work when pretty-printing a POJO with byte[] fields but reading a generic JsonNode from a stream and sending this to the same pretty printer will fail (read: results in base64). I thought that maybe adding a serializer for BinaryNode would fix it, but this does not get triggered.

How can I make any BinaryNode be pretty-printed in hex with a pretty printer bound to an object mapper?

[cowtowncoder]

@martinpaljak Challenge with BinaryNode serializer is that existence of custom serializer might not be checked properly yet -- for performance reasons delegation is likely used directly as JsonNode implementations implement JsonSerializable. I think override does work for ArrayNode and ObjectNode but not other types.
So you may want to file an issue here to make custom serializer override work (along with simple reproduction); it may be easy enough to add support.

Alternatively what is available now.... you could use wrapper type POJONode for values that implement JsonSerializable -- if so, matching method will get called. You can see

    public final void serialize(JsonGenerator gen, SerializerProvider ctxt) throws IOException

of POJONode for details. Actually, looks like you might be able to use RawValue as thing to pass: JsonNodeFactory has:

    @Override
    public ValueNode rawValueNode(RawValue value) {
        return new POJONode(value);
    }

which basically supports, I think, "injection" of RawValues where you can pre-format output (but ensuring to use surrounding double-quotes; it's literally embedded in output).