S3 download pdf - REST API

Question

I am trying to serve one of my PDF stored on S3 using Spring Boot Rest API.

Following is my code :

        byte[] targetArray = null;

        InputStream is = null;

        S3Object object = s3Client
                    .getObject(new GetObjectRequest("S3_BUCKET_NAME", "prefixUrl"));

        InputStream objectData = object.getObjectContent();

    BufferedReader reader = new BufferedReader(new InputStreamReader(objectData));

    char[] charArray = new char[8 * 1024];
    StringBuilder builder = new StringBuilder();
    int numCharsRead;
    while ((numCharsRead = reader.read(charArray, 0, charArray.length)) != -1) {

        builder.append(charArray, 0, numCharsRead);
    }
    reader.close();

    objectData.close();
    object.close();
    targetArray = builder.toString().getBytes();

    is = new ByteArrayInputStream(targetArray);


    return ResponseEntity.ok().contentLength(targetArray.length).contentType(MediaType.APPLICATION_PDF)
                    .cacheControl(CacheControl.noCache()).header("Content-Disposition", "attachment; filename=" + "testing.pdf")
                    .body(new InputStreamResource(is));

When I hit my API using postman, I am able to download PDF file but the problem is it is totally blank. What might be the issue ?

S3 streams the data and does not keep buffer and the data is in binary ( PDF ) so how to server such data to using Rest API.

How to solve this ?

why don't you use Amazon AWS SDK? https://docs.aws.amazon.com/sdk-for-java/v1/developer-guide/examples-s3-objects.html — Red Boy, Apr 26 '18 at 13:42
@kryger Yes I have gone through the above link but still I am facing this issue. — Shivkumar Mallesappa, Apr 27 '18 at 03:59
@kryger Actually I was trying to send the contents directly. As Red Boy has solved my problem, so I am deleting the other question posted in java group.Thank you for your support and help. — Shivkumar Mallesappa, Apr 27 '18 at 13:23
Here is a link which is also helpful https://stackoverflow.com/questions/5616014/aws-s3-java-sdk-download-pdf-getting-corrupted — Shivkumar Mallesappa, Apr 27 '18 at 18:08

score 14 · Accepted Answer · edited Oct 10 '19 at 05:43

14

Following simple code should work for you, not sure why are you trying to convert characters to bytes and vice-versa? Try this one, it works fine. Both PostMan/Browser.

@GET
@RequestMapping("/document")
@Consumes(MediaType.APPLICATION_OCTET_STREAM)
@Produces("application/pdf")
public ResponseEntity<InputStreamResource> getDocument() throws IOException {

    final AmazonS3 s3 = AmazonS3ClientBuilder.defaultClient();

    S3Object object = s3.getObject("BUCKET-NAME", "DOCUMENT-URL");
    S3ObjectInputStream s3is = object.getObjectContent();

    return ResponseEntity.ok()
                .contentType(org.springframework.http.MediaType.APPLICATION_PDF)
                .cacheControl(CacheControl.noCache())
                .header("Content-Disposition", "attachment; filename=" + "testing.pdf")
                .body(new InputStreamResource(s3is));
}

edited Oct 10 '19 at 05:43

akokskis

1,486
15
32

answered Apr 27 '18 at 13:09

Red Boy

5,429
3
28
41

You deserve a treat . This is what I was trying to achieve ,directly send contents rather than storing on local machine then reading and sending. I was confused between the S3ObjectInputStream and InputStream since I was reading binary data directly from S3 . Thanks a ton. – Shivkumar Mallesappa Apr 27 '18 at 13:21
1

Is it safe to return an InputStreamResource in controller? Will this InputStream be closed automatically after successful download? Because there is one warning in AWS documentation of the getObjectContent() method, that makes me suspicious about your approach: "If you retrieve an S3Object, you should close this input stream as soon as possible, because the object contents aren't buffered in memory and stream directly from Amazon S3. Further, failure to close this stream can cause the request pool to become blocked." – ilja Nov 20 '19 at 17:10
@ilja have you got an answer to that question? (safety and stream closing) – evgeniy44 Jan 03 '20 at 13:01
@evgeniy44 not yet, should I maybe ask this in separate question? – ilja Jan 03 '20 at 15:28
@ilja it would be great because I'm facing the same question as well and it seems to me like a very reasonable and not obvious question – evgeniy44 Jan 03 '20 at 15:40
@evgeniy44 here you go: https://stackoverflow.com/q/59582243/5305936 – ilja Jan 03 '20 at 16:47

S3 download pdf - REST API

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