MongoDB BSON codec not being used while encoding object

Question

I'm attempting to store an object in a MongoDB database (using MongoDB 3.0.2) and am getting a CodecConfigurationException when attempting to encode the object with error message

Can't find a codec for class java.time.LocalDate. 

I have written and included a codec for the LocalDate objects. Details follow.

The object, DutyBlock, that I'm attempting to store has these member variables:

public class DutyBlock {
    private LocalDate startDate;
    private LocalDate endDate; //Inclusive
    private int blockLength;
    private double pointValue;
    private ArrayList<Ra> assigned;
}

I wrote the following codec to encode the DutyBlock objects within the database:

public class DutyBlockCodec implements Codec<DutyBlock> {

    @Override
    public void encode(BsonWriter writer, DutyBlock t, EncoderContext ec) {
        Document document = new Document();
        document.append("startDate", t.getStartDate());
        document.append("endDate", t.getEndDate());
        document.append("blockLength", t.getBlockLength());
        document.append("pointValue", t.getPointValue());
        document.append("assigned", t.getRasOnDuty());

        writer.writeString(document.toJson());  //Line 27 in the error message.
    }

    @Override
    public Class<DutyBlock> getEncoderClass() {
        return DutyBlock.class;
    }

    @Override
    public DutyBlock decode(BsonReader reader, DecoderContext dc) {
        String json = reader.readString();
        return new DutyBlock(Document.parse(json));
    }

}

Since MongoDB currently does not support the java.time.LocalDate class, I've written the following codec to encode the LocalDate objects within the database:

public class LocalDateCodec implements Codec<LocalDate> {

    @Override
    public void encode(BsonWriter writer, LocalDate t, EncoderContext ec) {
        writer.writeString(t.toString());
    }

    @Override
    public Class<LocalDate> getEncoderClass() {
        return LocalDate.class;
    }

    @Override
    public LocalDate decode(BsonReader reader, DecoderContext dc) {
        String date = reader.readString();
        return LocalDate.parse(date);
    }
}

I've added the two Codec's (along with one for the Ra type) to the CodecRegistry at the MongoClient level while instantiating the MongoClient.

public class DutyScheduleDB {
    private MongoClient mongoClient;
    private MongoDatabase db;

    public DutyScheduleDB() {
        CodecRegistry codecRegistry = 
                CodecRegistries.fromRegistries(
                        CodecRegistries.fromCodecs(new LocalDateCodec(), new DutyBlockCodec(), new RaCodec()),
                        MongoClient.getDefaultCodecRegistry());
        MongoClientOptions options = MongoClientOptions.builder()
                .codecRegistry(codecRegistry).build();
        mongoClient = new MongoClient(new ServerAddress(), options);
        db = mongoClient.getDatabase("DutySchedulerDB");
    }
    . (More code not shown)
    .
    .
}

I attempt to store an ArrayList of DutyBlock objects as part of a org.bson.Document within the MongoDB database.

public void storeScheduledCalendar(String id,
        String calendarName,
        ArrayList<DutyBlock> cal) {
    //Access collection of scheduled calendars.
    MongoCollection collection = db.getCollection("ScheduledCalendars");
    //Query parameter is uuid + calendarName.
    Document doc = new Document("name", id + calendarName);
    doc.append("dutyBlocks", cal);
    //Insert doc to collection.
    collection.insertOne(doc); //Line 59 in the error message.
}

However, I'm running into this error message:

Exception in thread "main" org.bson.codecs.configuration.CodecConfigurationException: Can't find a codec for class java.time.LocalDate.
at org.bson.codecs.configuration.CodecCache.getOrThrow(CodecCache.java:46)
at org.bson.codecs.configuration.ProvidersCodecRegistry.get(ProvidersCodecRegistry.java:63)
at org.bson.codecs.configuration.ProvidersCodecRegistry.get(ProvidersCodecRegistry.java:37)
at org.bson.codecs.DocumentCodec.writeValue(DocumentCodec.java:174)
at org.bson.codecs.DocumentCodec.writeMap(DocumentCodec.java:189)
at org.bson.codecs.DocumentCodec.encode(DocumentCodec.java:131)
at org.bson.codecs.DocumentCodec.encode(DocumentCodec.java:45)
at org.bson.Document.toJson(Document.java:294)
at org.bson.Document.toJson(Document.java:268)
at org.bson.Document.toJson(Document.java:255)
at SchedulingHeuristic.DutyBlockCodec.encode(DutyBlockCodec.java:27)
at SchedulingHeuristic.DutyBlockCodec.encode(DutyBlockCodec.java:16)
at org.bson.codecs.EncoderContext.encodeWithChildContext(EncoderContext.java:91)
at org.bson.codecs.DocumentCodec.writeValue(DocumentCodec.java:175)
at org.bson.codecs.DocumentCodec.writeIterable(DocumentCodec.java:197)
at org.bson.codecs.DocumentCodec.writeValue(DocumentCodec.java:170)
at org.bson.codecs.DocumentCodec.writeMap(DocumentCodec.java:189)
at org.bson.codecs.DocumentCodec.encode(DocumentCodec.java:131)
at org.bson.codecs.DocumentCodec.encode(DocumentCodec.java:45)
at org.bson.codecs.BsonDocumentWrapperCodec.encode(BsonDocumentWrapperCodec.java:63)
at org.bson.codecs.BsonDocumentWrapperCodec.encode(BsonDocumentWrapperCodec.java:29)
at com.mongodb.connection.InsertCommandMessage.writeTheWrites(InsertCommandMessage.java:99)
at com.mongodb.connection.InsertCommandMessage.writeTheWrites(InsertCommandMessage.java:43)
at com.mongodb.connection.BaseWriteCommandMessage.encodeMessageBody(BaseWriteCommandMessage.java:112)
at com.mongodb.connection.BaseWriteCommandMessage.encodeMessageBody(BaseWriteCommandMessage.java:35)
at com.mongodb.connection.RequestMessage.encode(RequestMessage.java:132)
at com.mongodb.connection.BaseWriteCommandMessage.encode(BaseWriteCommandMessage.java:89)
at com.mongodb.connection.WriteCommandProtocol.sendMessage(WriteCommandProtocol.java:170)
at com.mongodb.connection.WriteCommandProtocol.execute(WriteCommandProtocol.java:73)
at com.mongodb.connection.InsertCommandProtocol.execute(InsertCommandProtocol.java:66)
at com.mongodb.connection.InsertCommandProtocol.execute(InsertCommandProtocol.java:37)
at com.mongodb.connection.DefaultServer$DefaultServerProtocolExecutor.execute(DefaultServer.java:155)
at com.mongodb.connection.DefaultServerConnection.executeProtocol(DefaultServerConnection.java:219)
at com.mongodb.connection.DefaultServerConnection.insertCommand(DefaultServerConnection.java:108)
at com.mongodb.operation.MixedBulkWriteOperation$Run$2.executeWriteCommandProtocol(MixedBulkWriteOperation.java:416)
at com.mongodb.operation.MixedBulkWriteOperation$Run$RunExecutor.execute(MixedBulkWriteOperation.java:604)
at com.mongodb.operation.MixedBulkWriteOperation$Run.execute(MixedBulkWriteOperation.java:363)
at com.mongodb.operation.MixedBulkWriteOperation$1.call(MixedBulkWriteOperation.java:148)
at com.mongodb.operation.MixedBulkWriteOperation$1.call(MixedBulkWriteOperation.java:141)
at com.mongodb.operation.OperationHelper.withConnectionSource(OperationHelper.java:186)
at com.mongodb.operation.OperationHelper.withConnection(OperationHelper.java:177)
at com.mongodb.operation.MixedBulkWriteOperation.execute(MixedBulkWriteOperation.java:141)
at com.mongodb.operation.MixedBulkWriteOperation.execute(MixedBulkWriteOperation.java:72)
at com.mongodb.Mongo.execute(Mongo.java:747)
at com.mongodb.Mongo$2.execute(Mongo.java:730)
at com.mongodb.MongoCollectionImpl.executeSingleWriteRequest(MongoCollectionImpl.java:482)
at com.mongodb.MongoCollectionImpl.insertOne(MongoCollectionImpl.java:277)
at DutyScheduleDB.storeScheduledCalendar(DutyScheduleDB.java:59)
at DutyScheduleDB.main(DutyScheduleDB.java:106)

It seems that my codec for LocalDate isn't being used when attempting to encode DutyBlock objects, though I've verified that the collection that I am attempting to store the org.bson.Document in does indeed contain the LocalDateCodec via a

System.out.println(collection.getCodecRegistry().get(LocalDate.class));

Can anyone can provide some insight on why this is happening?

Answer 1

After several days of research, I've figured out a solution.

The DutyBlockCodec depends on the LocalDateCodec (which I created) in order to encode/decode. This dependency isn't satisfied just by adding the two codecs into the same codec registry. The solution is to pass a CodecRegistry object containing the codecs that DutyBlockCodec depends on (e.g. a CodecRegistry containing within it the LocalDateCodec) to the DutyBlockCodec's constructor, which is stored as a member variable. In order to use the LocalDateCodec to encode, I use the EncoderContext.encodeWithChildContext() method, passing in the codec, writer, and element to encode. Additionally, I write individual fields rather than writing a Document as a String (as in my original code). Thus the DutyBlock codec ends up looking like this:

public class DutyBlockCodec implements Codec<DutyBlock> {
    private final CodecRegistry codecRegistry;

    public DutyBlockCodec(final CodecRegistry codecRegistry) {
        this.codecRegistry = codecRegistry;
    }

    @Override
    public void encode(BsonWriter writer, DutyBlock t, EncoderContext ec) {
        writer.writeStartDocument();
            Codec dateCodec = codecRegistry.get(LocalDate.class);
            writer.writeName("startDate");
            ec.encodeWithChildContext(dateCodec, writer, t.getStartDate());
            writer.writeName("endDate");
            ec.encodeWithChildContext(dateCodec, writer, t.getEndDate());
            writer.writeName("blockLength");
            writer.writeInt32(t.getBlockLength());
            writer.writeName("pointValue");
            writer.writeDouble(t.getPointValue());

            //Writing ArrayList of RAs
            writer.writeName("assigned");
            writer.writeStartArray();
                for (Ra ra : t.getRasOnDuty()) {
                    Codec raCodec = codecRegistry.get(Ra.class);
                    ec.encodeWithChildContext(raCodec, writer, ra);
                }
            writer.writeEndArray();
        writer.writeEndDocument();
    }

    @Override
    public Class<DutyBlock> getEncoderClass() {
        return DutyBlock.class;
    }

    @Override
    public DutyBlock decode(BsonReader reader, DecoderContext dc) {
        reader.readStartDocument();
            Codec<LocalDate> dateCodec = codecRegistry.get(LocalDate.class);
            reader.readName();
            LocalDate startDate = dateCodec.decode(reader, dc);
            reader.readName();
            LocalDate endDate = dateCodec.decode(reader, dc);
            reader.readName();
            int blockLength = reader.readInt32();
            reader.readName();
            double pointValue = reader.readDouble();

            //Reading ArrayList of RAs
            reader.readName();
            Codec<Ra> raCodec = codecRegistry.get(Ra.class);
            ArrayList<Ra> rasOnDuty = new ArrayList<>();
            reader.readStartArray();
                while (reader.readBsonType() != BsonType.END_OF_DOCUMENT) {
                    rasOnDuty.add(raCodec.decode(reader, dc));
                }
            reader.readEndArray();
        reader.readEndDocument();

        return new DutyBlock(startDate, endDate, blockLength, pointValue, rasOnDuty);
    }

}

DutyBlockCodec depends on another codec, and so requires a CodecRegistry to be passed in on its constructor. While I believe it is possible to create a CodecRegistry with the LocalDateCodec, then pass this as an argument to DutyBlockCodec's constructor, then create another CodecRegistry containing both LocalDateCodec and DutyBlockCodec, this is rather confusing, and MongoDB provides a functionality, the CodecProvider to facilitate this process.

Using the CodecProvider interface, I wrote a DutyBlockCodecProvider

public class DutyBlockCodecProvider implements CodecProvider {
    @Override
    public <T> Codec<T> get(Class<T> type, CodecRegistry cr) {
        if (type == DutyBlock.class) {
            return (Codec<T>) new DutyBlockCodec(cr);
        }
        return null;
    }
}

I added these CodecProviders to the MongoDB Client using the CodecRegistries.fromProviders() method.

CodecRegistry codecRegistry = CodecRegistries.fromRegistries(
            CodecRegistries.fromCodecs(new LocalDateCodec()),
            CodecRegistries.fromProviders(
                    new RaCodecProvider(),
                    new DutyBlockCodecProvider(),
                    new ScheduledDutyCodecProvider()),
            MongoClient.getDefaultCodecRegistry());  
    MongoClientOptions options = MongoClientOptions.builder()
            .codecRegistry(codecRegistry).build();
    mongoClient = new MongoClient(new ServerAddress(), options);
    db = mongoClient.getDatabase("DutySchedulerDB");

My source code for this project can be found at https://github.com/desrepair/DutyScheduler I'm open to answering any questions people may have.