Use the AWS SDK for Java and Apache Commons IO as such:

//import org.apache.commons.io.IOUtils

AmazonS3 s3  = new AmazonS3Client(credentials);  // anonymous credentials are possible if this isn't your bucket
S3Object object = s3.getObject("bucket", "key"); 
byte[] byteArray = IOUtils.toByteArray(object.getObjectContent());

Not sure what you mean by "get it removed", but IOUtils will close the object's input stream when it's done converting it to a byte array. If you mean you want to delete the object from s3, that's as easy as:

s3.deleteObject("bucket", "key"); 

You are right on one thing. You should never completely load a file to memory. Files have sizes which may exceed the total RAM capacity (5 Gb, 10 Gb) thus it is not a reliable way to handle files. Using IOUtils.toByteArray() reads an InputStream and loads it to a single byte array which is not a good thing.

What you should do is read chunk by chunk and write whenever you finish reading a chunk. More like streaming. See code change below. Here for any given time for a image there will be only 8 * 2048 bytes or 2 Kb of RAM will be used. You can increase it if you want stream faster.

@RequestMapping(value = "/image/{id}/{quality}/{pageNumber}", method = RequestMethod.GET, produces = MediaType.IMAGE_PNG_VALUE)
public void retrieveImage(@PathVariable Long id, @PathVariable String quality, @PathVariable Integer pageNumber,
        HttpServletResponse response) throws Exception{

    //Open connection
    S3Object s3Object = imageService.getS3Object(quality, pageNumber, id)
    S3ObjectInputStream s3ObjectIS = s3Object.getObjectContent();

    byte[] data = new byte[2048];
    int read = 0;
    OutputStream out = response.getOutputStream();
    while((read = s3ObjectIS.read(data)) > 0) {
        out.write(data, 0, read);
        out.flush();
    }
    out.close();

    //Then close connection to amazon......
}

Based on S3ObjectInputStream API doc S3ObjectInputStream is sub class of java.io.InputStream. In that case you should be able to do

    S3ObjectInputStream s3ImageResource = ... 
    StreamResource res = new StreamResource("filename.jpg", () -> {
        InputStream is = s3ImageResource;
        return is;
    });
    Image image = new Image(res,"Image");

Alternatively if that does not work, based on other questions here in StackOverflow, I assume you can convert S3ObjectInputStream to byte array.

    byte[] bytes = // get bytes from S3ObjectInputStream 
    StreamResource res = new StreamResource("filename.jpg", () -> {
        InputStream is = new ByteArrayInputStream(bytes);
        return is;
    });
    Image image = new Image(res,"Image");

👨🏿 👨 🙍🏼‍♀️

👨🏿👨🙍 If I tell Notepad++ that it is UTF-8.

Since Java 7 (published back in July 2011), there’s a better way: Files.copy() utility from java.util.nio.file.

Copies all bytes from an input stream to a file.

So you need neither an external library nor rolling your own byte array loops. Two examples below, both of which use the input stream from S3Object.getObjectContent().

InputStream in = s3Client.getObject("bucketName", "key").getObjectContent();

1) Write to a new file at specified path:

Files.copy(in, Paths.get("/my/path/file.jpg"));

2) Write to a temp file in system's default tmp location:

File tmp = File.createTempFile("s3test", "");
Files.copy(in, tmp.toPath(), StandardCopyOption.REPLACE_EXISTING);

(Without specifying the option to replace existing file, you'll get a FileAlreadyExistsException.)

Also note that getObjectContent() Javadocs urge you to close the input stream:

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.

So it should be safest to wrap everything in try-catch-finally, and do in.close(); in the finally block.

The above assumes that you use the official SDK from Amazon (aws-java-sdk-s3).