从Amazon S3下载部件的大文件

I would like to download big file from Amazon S3 into RAM. File is bigger then RAM size. Seems, I need to load it by parts. Each part would be return in endpoint. Also I can not use hard drive, to store downloaded file there. I have InputStream object and I am trying to load object like below:

我想从Amazon S3下载大文件到RAM。文件大于RAM大小。似乎，我需要按部件加载它。每个部分都将在端点返回。另外，我不能使用硬盘，存储下载的文件。我有InputStream对象，我正在尝试加载如下所示的对象：

    inputStream.skip(totalBytes);
    long downloadedBytesCount = 0;
    ByteArrayOutputStream result = new ByteArrayOutputStream();
    byte[] buffer = new byte[1024];
    int length;
    do {
        length = inputStream.read(buffer);
        result.write(buffer, 0, length);
        downloadedBytesCount += length;
    }
    while (downloadedBytesCount <= partOfFileSize && (length != -1));
    totalBytes += downloadedBytesCount;

but that code contains problems: each new request will start download file from the begin,so last request for downloading (for example 20 MB) will download all the file (for example 1 GB). So, method skip(long) doesn't work as I expected.

但该代码包含问题：每个新请求将从开始下载文件，因此上次下载请求（例如20 MB）将下载所有文件（例如1 GB）。因此，方法skip（long）不能像我预期的那样工作。

How can I download file from inputStream by parts? Any suggestions?

如何通过部件从inputStream下载文件？有什么建议么？

1 个解决方案

#1

The standard S3 library can transfer whatever parts of the file you want:

标准S3库可以传输所需文件的任何部分：

(taken from the AWS docs)

（摘自AWS文档）

GetObjectRequest rangeObjectRequest = new GetObjectRequest(
        bucketName, key);
rangeObjectRequest.setRange(0, 10); // retrieve 1st 11 bytes.
S3Object objectPortion = s3Client.getObject(rangeObjectRequest);

InputStream objectData = objectPortion.getObjectContent();

In your program you could, for example, read 1000 bytes at a time by moving the range.

例如，在程序中，您可以通过移动范围一次读取1000个字节。

#1