I try to download file from mongodb . the size of uploaded file is 2106 bytes,and chunkSize=2048 bytes, so GridFS divides the file into 2 chunks. when I excute the codes of downloadStream.read(bytesToWriteTo), only read data of the first chunk, and can not read the data of second chunk. How can I read all of the data?

public class OpenDownloadStreamDemo {

          public static void main(String[] args) {
            MongoClient mongoClient = new MongoClient("127.0.0.1", 27017);
            MongoDatabase mongoDatabase = mongoClient.getDatabase("demo");
            GridFSBucket gridFSBucket = GridFSBuckets[enter image description here][1].create(mongoDatabase);
            ObjectId fileId = new ObjectId("56f25a8b163b4598987b666b");
            GridFSDownloadStream downloadStream = gridFSBucket.openDownloadStream(fileId);
            int fileLength = (int) downloadStream.getGridFSFile().getLength();
            byte[] bytesToWriteTo = new byte[fileLength];
            downloadStream.read(bytesToWriteTo);
            downloadStream.close();
            System.out.println(new String(bytesToWriteTo, StandardCharsets.UTF_8));
        }
    }

The files Collection

The chunks Collection

I know it is a very late reply, you can try using following implementation

public static void main(String[] args) {
        MongoClient mongoClient = new MongoClient("127.0.0.1", 27017);
        MongoDatabase mongoDatabase = mongoClient.getDatabase("demo");
        GridFSBucket gridFSBucket = GridFSBuckets.create(mongoDatabase);
        ObjectId fileId = new ObjectId("56f25a8b163b4598987b666b");
        GridFSDownloadStream downloadStream = gridFSBucket.openDownloadStream(fileId);
        ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
        int data = downloadStream.read();
        while (data >= 0) {
            outputStream.write((char) data);
            data = downloadStream.read();
        }
        byte[] bytesToWriteTo = outputStream.toByteArray();
        downloadStream.close();
        System.out.println(new String(bytesToWriteTo, StandardCharsets.UTF_8));
    }
}