[FIXED] How can I reuse JAX-RS Response into HttpServletResponse?

Issue

I have a Servlet which makes a request to my Rest API, and I want it to return the API Response content to the final user through the HttpServletResponse.

The content is actually a .xls file to download which I put in the Response with the StreamingOutput Object.

How can I do that ? I can't cast the Response into a HttpServletResponse

Rest API method :

@GET
@Produces( MediaType.APPLICATION_JSON )
@Path("bla")
public Response getTopicByName() {

    final Workbook wb = new HSSFWorkbook();
    StreamingOutput stream = new StreamingOutput() {
        @Override
        public void write(OutputStream output) throws IOException, WebApplicationException {
            wb.write(output);
        }
    };
    responseBuilder = responseBuilder.entity(stream);
    responseBuilder = responseBuilder.status(Response.Status.OK);
    responseBuilder = responseBuilder.header("Content-Disposition", "attachment; filename=" + device + ".xls");

    return responseBuilder.build();
}

Servlet POST method :

@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

    Client client = ClientBuilder.newClient();
    WebTarget target = client.target(url);
    Response res = target. request().get();
    if (res.getStatus() == 200) {
        // how to put res stream into response stream ?
        ServletOutputStream stream = response.getOutputStream();
    }
    client.close();
}

EDIT :

I tried TedTrippin method and after finding out the way to recover an InputStream from the Response, it worked well.

But I keep getting corrupted xls files. And it is quite annoying. I don't get those corrupted files when I make the request directly from the browser. Got any clues where it comes from ?

POST method :

@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

    Client client = ClientBuilder.newClient();
    WebTarget target = client.target(url + param + format);
    Response res = target.request().get();
    if (res.getStatus() == 200) {
        response.setHeader("Content-Disposition", "attachment; filename=test.xls");
        InputStream in = res.readEntity(InputStream.class);
        ServletOutputStream out = response.getOutputStream();
        byte[] buffer = new byte[1024];
        while (in.read(buffer) >= 0) {
            out.write(buffer);
        }
        out.flush();
    }
    client.close();
}

Solution

Simplest way is to read the response stream and write it straight to the response output stream. Either use a library function from IOUtils or Guava or pure java...

try (InputStream in = ...;
     OutputStream out = ...) {
  byte[] buffer = new byte[1024];
  while (in.read(buffer) >= 0)
    out.write(buffer);
} catch (IOException ex) {
  ...
}

A nicer (depending on your view) way would be to read/save the response as a temporary file then you could return that or write it to the output stream.

Third approach would be to create a pipe, but I don't think that would be applicable here.

Answered By - TedTrippin