Decode Document to a Java Class using custom Mongo Codec

Question

I am trying to use the MongoDB Codec functionality to read and write a Java ZonedDateTime object to Mongo in a custom format.

Inserting documents works just fine, but I'm struggling to understand how to get Mongo to return a ZonedDateTime.

I've written the following test case to try and demonstrate:

public class ZonedDateTimeTest {

    @Test
    public void serializeAndDeserializeZonedDateTime() throws Exception {
        CodecRegistry codecRegistry = fromRegistries(
                CodecRegistries.fromCodecs(new ZonedDateTimeCodec()),
                MongoClient.getDefaultCodecRegistry()
        );
        MongoClient mongoClient = new MongoClient(
                "localhost:27017",
                MongoClientOptions.builder()
                        .codecRegistry(codecRegistry)
                        .build()
        );
        ZonedDateTime zonedDateTime = ZonedDateTime.now(ZoneId.of("Europe/London"));

        MongoCollection<Document> collection = mongoClient
                .getDatabase("test")
                .getCollection("test");

        // Insert a document
        collection.insertOne(new Document("_id", 1).append("zonedDateTime", zonedDateTime));

        // Find the document just inserted
        Document document = collection
                .find(new Document("_id", 1))
                .first();

        // How to "get" a ZonedDateTime?
        document.get("zonedDateTime");
    }

    private static class ZonedDateTimeCodec implements Codec<ZonedDateTime> {
        @Override
        public Class<ZonedDateTime> getEncoderClass() {
            return ZonedDateTime.class;
        }

        @Override
        public void encode(BsonWriter writer, ZonedDateTime value,
                           EncoderContext encoderContext) {
            writer.writeStartDocument();
            writer.writeString("dateTime", DateTimeFormatter.ISO_LOCAL_DATE_TIME.format(value));
            writer.writeString("offset", value.getOffset().toString());
            writer.writeString("zone", value.getZone().toString());
            writer.writeEndDocument();
        }

        @Override
        public ZonedDateTime decode(BsonReader reader, DecoderContext decoderContext) {
            reader.readStartDocument();
            ZonedDateTime zonedDateTime = ZonedDateTime.ofInstant(
                    LocalDateTime.from(DateTimeFormatter.ISO_LOCAL_DATE_TIME.parse(reader.readString("dateTime"))),
                    ZoneOffset.of(reader.readString("offset")),
                    ZoneId.of(reader.readString("zone"))
            );
            reader.readEndDocument();
            return zonedDateTime;
        }
    }
}

Answer 1

I've made a test here, and checked that document.get("zonedDateTime") returns a org.bson.Document instance. So, I've just passed this object to the codec:

import org.bson.BsonReader;
import org.bson.Document;
import org.bson.json.JsonReader;
import org.bson.codecs.DecoderContext;

Object object = document.get("zonedDateTime");

ZonedDateTimeCodec codec = (ZonedDateTimeCodec) codecRegistry.get(ZonedDateTime.class);
BsonReader reader = new JsonReader(((Document) object).toJson());
ZonedDateTime zdt = codec.decode(reader, DecoderContext.builder().build());
System.out.println(zdt);

The ZonedDateTime variable (zdt) will be correctly created (in my test, I've got 2017-07-13T18:07:13.603+01:00[Europe/London]) (the current date/time in London timezone).