How can I serve a PDF to a browser without storing a file on the server side?

How can I serve the PDF file to the client without storing the file on the server side and allow the client side to directly download the file that is generated?

public void generatePDF() throws Exception {
    Document doc = new Document();
    File file = new File("C://New folder//itext_Test.pdf");
    FileOutputStream pdfFileout = new FileOutputStream(file);
    PdfWriter.getInstance(doc, pdfFileout);
    doc.open();
    Paragraph para = new Paragraph("Test");
    doc.add(catPart);
    doc.close();
}
 
public void downloadPDF(HttpServletRequest request, HttpServletResponse response)
    throws IOException{
    response.setContentType("application/pdf");
    response.setHeader("Content-disposition","attachment;filename="+ "testPDF.pdf");
    try {
        File f = new File("C://New folder//itext_Test.pdf");
        FileInputStream fis = new FileInputStream(f);
        DataOutputStream os = new DataOutputStream(response.getOutputStream())
        response.setHeader("Content-Length",String.valueOf(f.length()));
        byte[] buffer = new byte[1024];
        int len = 0;
        while ((len = fis.read(buffer)) >= 0) {
            os.write(buffer, 0, len);
        }
    } catch (Exception e) {
        e.printStackTrace();
    }
}

You can use any OutputStream when creating a PDF file, so in theory, you could use a response.getOutputStream(). See for instance the Hello Servlet from Chapter 9 of "iText in Action - Second Edition":

public class Listing_09_01_Hello extends HttpServlet {
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        response.setContentType("application/pdf");
        PdfDocument pdfDoc = new PdfDocument(new PdfWriter(response.getOutputStream()));
        Document doc = new Document(pdfDoc);
        doc.add(new Paragraph("Hello World"));
        doc.add(new Paragraph(new Date().toString()));
        doc.close();
    }
}

However, some browsers experience problems when you send bytes directly like this. It's safer to create the file in memory using a ByteArrayOutputStream and to tell the browser how many bytes it can expect in the content header:

public class Listing_09_03_PdfServlet extends HttpServlet {
    protected void service(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        // Get the text that will be added to the PDF
        String text = request.getParameter("text");
        if (text == null || text.trim().length() == 0) {
            text = "You didn't enter any text.";
        }
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        PdfDocument pdfDoc = new PdfDocument(new PdfWriter(baos));
        Document doc = new Document(pdfDoc);
        doc.add(new Paragraph(String.format(
                "You have submitted the following text using the %s method:",
                request.getMethod())));
        doc.add(new Paragraph(text));
        doc.close();

        // setting some response headers
        response.setHeader("Expires", "0");
        response.setHeader("Cache-Control",
                "must-revalidate, post-check=0, pre-check=0");
        response.setHeader("Pragma", "public");
        // setting the content type
        response.setContentType("application/pdf");
        // the contentlength
        response.setContentLength(baos.size());
        // write ByteArrayOutputStream to the ServletOutputStream
        OutputStream os = response.getOutputStream();
        baos.writeTo(os);
        os.flush();
        os.close();
    }
}

For the full source code, see PdfServlet.

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