How to stream an endless InputStream with JAX-RS

Question

I have an endless InputStream with some data, which I want to return in response to a GET HTTP request. I want my web/API client to read from it endlessly. How can I do it with JAX-RS? I'm trying this:

@GET
@Path("/stream")
@Produces(MediaType.TEXT_PLAIN)
public StreamingOutput stream() {
    final InputStream input = // get it
    return new StreamingOutput() {
        @Override
        public void write(OutputStream out) throws IOException {
            while (true) {
                out.write(input.read());
                out.flush();
            }
        }
    };
}

But content doesn't appear for the client. However, if I add OutputStream#close(), the server delivers the content at that very moment. How can I make it truly streamable?

Chanson

I've only used it for finite files, but perhaps you could try producing MediaType.APPLICATION_OCTET_STREAM – Efferent

tried that, no effect :( – Chanson

Which JAX-RS implementation are you using? – Jonna

I'm using Jersey 1.17.1 – Chanson

There is a nice example now at dzone.com/articles/jax-rs-streaming-response – Dett

Answer 1

Simply use the StreamingOutput of JAX-RS

@Path("/numbers")
public class NumbersResource {

    @GET
    public Response streamExample(){
        StreamingOutput stream = new StreamingOutput() {
            @Override
            public void write(OutputStream out) throws IOException, WebApplicationException {
                Writer writer = new BufferedWriter(new OutputStreamWriter(out));
                for (int i = 0; i < 10000000 ; i++){
                    writer.write(i + " ");
                }
                writer.flush();
            }
        };
        return Response.ok(stream).build();
    }
}

Sunn

Thank you for this answer. It really helped me. The method signature of Response.ok(Object entity) is so unhelpful and misleading. It is unbelievable to me that this "modern" API from 2007 uses Object. And, the Javadoc gives no hint about StreamingOutput. Simply dreadful. – Closemouthed

Answer 2

So, you have flush issues, you could try to get the ServletResponse as the spec says:

The @Context annotation can be used to indicate a dependency on a Servlet-defined resource. A Servlet- based implementation MUST support injection of the following Servlet-defined types: ServletConfig, ServletContext, HttpServletRequest and HttpServletResponse.

An injected HttpServletResponse allows a resource method to commit the HTTP response prior to returning. An implementation MUST check the committed status and only process the return value if the response is not yet committed.

Then flushing everything you can, like this:

@Context
private HttpServletResponse context;

@GET
@Path("/stream")
@Produces(MediaType.TEXT_PLAIN)
public String stream() {
    final InputStream input = // get it
    ServletOutputStream out = context.getOutputStream();
            while (true) {
                out.write(input.read());
                out.flush();
                context.flushBuffer();
            }
    return "";
}

Amygdalate

Answer 3

Just a wild guess:

@GET
@Path("/stream")
@Produces(MediaType.TEXT_PLAIN)
public Response stream() {
    final InputStream input = getit();
    return Response.ok(input, MediaType.TEXT_PLAIN_TYPE).build();        
}

Amygdalate

As explained above, InputStream will be read entirely into memory first, and then delivered to the client. This is not what I'm looking for – Chanson

Trying to use Response was a far guess, I thought it would flush this way. – Amygdalate

Answer 4

Folks should be using Java 9 or later can use transferTo to copy the input stream to the output stream so do this:

@GET
@Path("/stream")
@Produces(MediaType.TEXT_PLAIN)
public StreamingOutput stream() {
    final InputStream input = // get it

        StreamingOutput stream = output -> {
            try {
                is.transferTo(output);
            }
            catch (Exception e) {
                throw new WebApplicationException(e);
            } finally {
                is.close();
            }
        };

        return Response.ok(stream, MediaType.APPLICATION_OCTET_STREAM).build();
    }

Coreen