writeTo PipedOutputStream just hangs
aws-java-sdk, groovy, inputstream, java
Solution
When you do os.writeTo(out), it will try to flush an entire stream to out, and since there is nobody reading from the other side of it (i.e. inpipe) yet, the internal buffer fills up and the thread stops.
You have to setup the reader before you write the data, and also make sure that it is executed in a separate thread (see javadoc on PipedOutputStream).
Problem
My goal is to: - reading a file from S3, - changing its metadata - Push it out to S3 again AWS java SDK doesn't allow outputstreams to be pushed. Therefore, I have to convert the `outputstream` from step2 to `inputstream`. For this I decided to use `PipedInputStream`. However, my code just hangs in the `writeTo(out);` step. This code is in a grails application. When the code hangs the CPU is not in high consumption: ``` import org.apache.commons.imaging.formats.jpeg.xmp.JpegXmpRewriter; AmazonS3Client client = nfile.getS3Client() //get S3 client S3Object object1 = client.getObject( new GetObjectRequest("test-bucket", "myfile.jpg")) //get the object. InputStream isNew1 = object1.getObjectContent(); //create input stream ByteArrayOutputStream os = new ByteArrayOutputStream(); PipedInputStream inpipe = new PipedInputStream(); final PipedOutputStream out = new PipedOutputStream(inpipe); try { String xmpXml = "<x:xmpmeta>" + "\n<Lifeshare>" + "\n\t<Date>"+"some date"+"</Date>" + "\n</Lifeshare>" + "\n</x:xmpmeta>";/ JpegXmpRewriter rewriter = new JpegXmpRewriter(); rewriter.updateXmpXml(isNew1,os, xmpXml); //This is step2 try { new Thread(new Runnable() { public void run () { try { // write the original OutputStream to the PipedOutputStream println "starting writeto" os.writeTo(out); println "ending writeto" } catch (IOException e) { // logging and exception handling should go here } } }).start(); ObjectMetadata metadata = new ObjectMetadata(); metadata.setContentLength(1024); //just testing client.putObject(new PutObjectRequest("test-bucket", "myfile_copy.jpg", inpipe, metadata)); os.writeTo(out); os.close(); out.close(); } catch (IOException e) { // logging and exception handling should go here } } finally { isNew1.close() os.close() out.close() } ``` The above code just prints `starting writeto` and hangs. it does not print `ending writeto` Update By putting the `writeTo` in a separate thread, the file is now being written to S3, however, only 1024 bytes of it being are written. The file is incomplete. How can I write everything from outputstream to S3?