Download CSV file via Rest

Question

Using OpenCSV, I can successfully create a CSV file on disc, but what I really need is to allow users download the CSV with a download button, I don't need to save on disk, just download. Any ideas?

@GET
@Path("/downloadCsv")
public Object downloadCsv() {
        CSVWriter writer;
        FileWriter wr; 
      //Or should I use outputstream here?   
        wr= new FileWriter("MyFile.csv");
        writer = new CSVWriter(wr,',');
        for (Asset elem: assets) {
            writer.writeNext(elem.toStringArray());
        }
        writer.close();


}

EDIT: I do NOT want to save/read file on disc EVER

Answer 1

To force "save as", you need to set the content disposition HTTP header in the response. It should look like this:

Content-Disposition: attachment; filename="whatever.csv"

It looks like you're using JAX-RS. This question shows how to set the header. You can either write the CSV to the HTTP response stream and set the header there or return a Response object like so:

return Response.ok(myCsvText).header("Content-Disposition", "attachment; filename=" + fileName).build();

You do not need to write to a File object in the middle of this process so can avoid writing to disk.