Mongodb 3.0 Java driver output Document to byte array

[Aplomb Chen]

I have a question that is it possible to output Document into byte array, so that I can transfer the Document into another server through any type of RPC. 

I know I can convert Document into JSON format, but I am a bit worried about the penaty of parsing JSON string back to Document. 

I have tried the API, but no luck, so please help me to clarify whether it is possible to output a Document directly into byte array for sending to another server and another server can convert the byte array back to Document? 

Many thanks!

Aplomb

Best regards 

[Ross Lawley]

Hi Aplomb,

Apologies for the delay, this is not easily achievable via the api but if you follow the logic from the Document.toJson and the Document.parse methods you can use the BsonBinaryReader / Writer to achieve your goals.

The following is an example of creating static helpers to write to an InputStream and to read from an InputStream:

import org.bson.BsonBinaryReader;
import org.bson.BsonBinaryWriter;
import org.bson.Document;
import org.bson.codecs.Codec;
import org.bson.codecs.DecoderContext;
import org.bson.codecs.DocumentCodec;
import org.bson.codecs.EncoderContext;
import org.bson.io.BasicOutputBuffer;

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.nio.ByteBuffer;

import static java.util.Arrays.asList;

public class DocumentToBinary {

    private static Codec<Document> DOCUMENT_CODEC = new DocumentCodec();

    public static void main(final String[] args) {
        Document myDocument = new Document("_id", 1).append("key1", asList(1, 2, 3, 4));

        try {
            Document myCopiedDocument = fromInputStream(toInputStream(myDocument));
            assert myCopiedDocument.equals(myDocument);
        } catch (IOException e) {
            e.printStackTrace();
        }

    }

    public static InputStream toInputStream(final Document document) {
        BasicOutputBuffer outputBuffer = new BasicOutputBuffer();
        BsonBinaryWriter writer = new BsonBinaryWriter(outputBuffer);
        DOCUMENT_CODEC.encode(writer, document, EncoderContext.builder().isEncodingCollectibleDocument(true).build());
        return new ByteArrayInputStream(outputBuffer.toByteArray());
    }

    public static Document fromInputStream(final InputStream input) throws IOException {
        ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
        byte[] buffer = new byte[1024];
        int len;
        while ((len = input.read(buffer)) != -1) {
            outputStream.write(buffer, 0, len);
        }
        outputStream.close();
        BsonBinaryReader bsonReader = new BsonBinaryReader(ByteBuffer.wrap(outputStream.toByteArray()));
        return DOCUMENT_CODEC.decode(bsonReader, DecoderContext.builder().build());
    }
}

This is also available as a gist: https://gist.github.com/rozza/9c94808ed5b4f1edca75

I've added this as a feature request to our issue tracker https://jira.mongodb.org/browse/JAVA-1975, please click "watch" on the ticket to follow updates.

Ross