播放2.3.x：无阻塞图像上传到Amazon S3

Question

I am wondering what the correct way with Play 2.3.x (Java) is to upload images to Amazon S3 in a non-blocking way. Right now I am wrapping the amazons3.putObject method inside a promise. However I fear that I am basically just blocking another thread with this logic. My code looks like following:

return Promise.promise(
        new Function0<Boolean>() {
            public Boolean apply() {
                if (S3Plugin.amazonS3 != null) {
                    try {
                        PutObjectRequest putObjectRequest = new PutObjectRequest(
S3Plugin.s3Bucket, name + "." + format, file.getFile());
                        ObjectMetadata metadata = putObjectRequest.getMetadata();
                        if(metadata == null) {
                            metadata = new ObjectMetadata();
                        }
                        metadata.setContentType(file.getContentType());
                        putObjectRequest.setMetadata(metadata);
                        putObjectRequest.withCannedAcl(CannedAccessControlList.PublicRead);
                        S3Plugin.amazonS3.putObject(putObjectRequest);
                        return true;
                    } catch (AmazonServiceException e) {
                        // error uploading image to s3
                        Logger.error("AmazonServiceException: " + e.toString());
                    } catch (AmazonClientException e) {
                        // error uploading image to s3
                        Logger.error("AmazonClientException: " + e.toString());
                    }
                }
                return false;
            }
        }
    );

What is the best way to do the upload process non-blocking? The Amazon library also provides the TransferManager.class for asynchronous uploads but I am not sure how to utilize this in a non-blocking way either...

SOLUTION: After spending quite a while figuring out how to utilize the Promise/Future in Java, I came up with following solution thanks to Will Sargent:

import akka.dispatch.Futures;

final scala.concurrent.Promise<Boolean> promise = Futures.promise();
... create AmazonS3 upload object ...
upload.addProgressListener(new ProgressListener() {
    @Override
    public void progressChanged(ProgressEvent progressEvent) {
        if(progressEvent.getEventCode() == ProgressEvent.COMPLETED_EVENT_CODE) {
            promise.success(true);
        }
        else if(progressEvent.getEventCode() == ProgressEvent.FAILED_EVENT_CODE) {
            promise.success(false);
        }
    }
});
return Promise.wrap(promise.future());

Important to note is that I have to use the scala promise and not the play framework promise. The return value however is a play.libs.F.Promise.

Answer 1

You can do the upload process and return a Future by creating a Promise, returning the promise's future, and only writing to the promise in the TransferManager's progress listener:

Examples of promises / futures: http://docs.scala-lang.org/overviews/core/futures.html

Return the Scala future from Promise: http://www.playframework.com/documentation/2.3.x/api/java/play/libs/F.Promise.html#wrapped()

TransferManager docs: http://docs.aws.amazon.com/AWSJavaSDK/latest/javadoc/com/amazonaws/services/s3/transfer/TransferManager.html