java - GridFSDownloadStream无法读取所有数据

Question

我尝试从 mongodb 下载文件。上传文件的大小为 2106 字节，chunkSize=2048 字节，因此 GridFS 将文件分为 2 个 block 。当我执行downloadStream.read(bytesToWriteTo)代码时，只能读取第一个 block 的数据，无法读取第二个 block 的数据。如何读取所有数据？

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

Answer 1

我知道这是一个很晚的回复，您可以尝试使用以下实现

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));
    }
}