Serve result from java.io.OutputStream

Play Framework
1

I’m using a PDF library which writes data into an OutputStream. How can I serve this outputstream as a Result?

I used stuff from play-iteratees for this, but it seems that it no longer exists for Scala 2.13. I guess there might be something in StreamConverters, but I can’t figure out how to use it.

2

As far I I’m able to figure out

StreamConverters.asOutputStream().mapMaterializedValue { os => myRenderMethod(os) }

should be a possible solution.

However, that gives:

Rendering of response failed because response entity stream materialization failed with 'java.util.concurrent.TimeoutException'

That is with iText. When using the same technique for rendering Excel files using Apache POI I get a different error, but the common thing is that neither works.

So I’ve resorted to simply using a ByteArrayOutputStream and just serving it with .toByteArray. Which works perfectly.

3

This is an example in Java, not Scala, but this is how you “convert” an OutputStream to an InputStream.

	public static InputStream foo(Consumer<OutputStream> outputStreamConsumer) throws IOException {
		final PipedInputStream pipedIn = new PipedInputStream();
		final PipedOutputStream pipedOut = new PipedOutputStream(pipedIn);
		new Thread(() -> {
			try {
				outputStreamConsumer.accept(pipedOut);
			} catch (Exception e) {
				// uh oh
			}
		}).start();
		return pipedIn;
	}

It obviously needs to be polished up but that’s the basic idea of how you do it. Once you have an InputStream, it should be easy to pipe it to Play.