How to get BigDecimal to behave in MongoDb

BigDecimalCodec.java

public class BigDecimalCodec implements Codec<BigDecimal> {
  // Note that you may not want it to be double -- choose your own type.
    @Override
    public void encode(final BsonWriter writer, final BigDecimal value, final EncoderContext encoderContext) {
        writer.writeDouble(value);
    }

    @Override
    public BigDecimal decode(final BsonReader reader, final DecoderContext decoderContext) {
        return reader.readDouble();
    }

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

BigDecimalCodecProvider.java

class BigDecimalCodecProvider implements CodecProvider{
    @Override
    def <T> Codec<T> get(Class<T> aClass, CodecRegistry codecRegistry) {
        if (aClass==BigDecimal.class) {
            return new BigDecimalCodec() as Codec<T>
        }

        return null
    }
}

BigDecimalTransformer.java

class BigDecimalTransformer implements Transformer{
	@Override
	Object transform(Object objectToTransform) {
		BigDecimal value = (BigDecimal) objectToTransform;
    
    //Again, you may not want a double.
		return value.doubleValue();
	}
}

YourMongoConfig.java

// when you are configuring your Mongo options. 
// And, yes, you need both the Codec and the Transformer
  BSON.addEncodingHook(BigDecimal.class, new BigDecimalTransformer());

    CodecRegistry codecRegistry = CodecRegistries.fromRegistries(
      CodecRegistries.fromProviders(new BigDecimalCodecProvider()),
      MongoClient.getDefaultCodecRegistry()
    );

    MongoClientOptions.Builder builder = MongoClientOptions.builder()
       .codecRegistry(codecRegistry);
    [....]            

    return builder.build();

I use Java 8 and I couldn't see an implicit conversion between double and Bigdecimal and I just fancied to use our hero "String" type

public class BigDecimalCodec implements Codec<BigDecimal> {
    @Override
    public void encode(final BsonWriter writer, final BigDecimal value, final EncoderContext encoderContext) {
        writer.writeString(value+"");
    }
    
    @Override
    public BigDecimal decode(final BsonReader reader, final DecoderContext ecoderContext) {
        return new BigDecimal(Double.parseDouble(reader.readString()));
    }

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