How can I serve a PDF to a browser without storing

问题:

I have two methods. One that generates a PDF at the server side and another that downloads the PDF at the client side.

How can i do this without storing it in the Server side and allow the client side to directly download this.

The Following are the two methods:

public void downloadPDF(HttpServletRequest request, HttpServletResponse response) throws IOException{

    response.setContentType("application/pdf");
    response.setHeader("Content-disposition","attachment;filename="+ "testPDF.pdf");
    FileInputStream fis = null;
    DataOutputStream os = null;

    try {
        File f = new File("C://New folder//itext3.pdf");
        response.setHeader("Content-Length",String.valueOf(f.length()));

        fis = new FileInputStream(f);
        os = new DataOutputStream(response.getOutputStream());
        byte[] buffer = new byte[1024];
        int len = 0;
        while ((len = fis.read(buffer)) >= 0) {
            os.write(buffer, 0, len);
        }

    } catch (Exception e) {
        e.printStackTrace();
    } finally {
        fis.close();
        os.flush();
        os.close();
    }
    response.setHeader("X-Frame-Options", "SAMEORIGIN");
}

And:

public Document generatePDF() {

    Document doc = new Document();
     try {
            File file = new File("C://New folder//itext_Test2.pdf");
            FileOutputStream pdfFileout = new FileOutputStream(file);
            PdfWriter.getInstance(doc, pdfFileout);

            doc.addAuthor("TestABC");
            doc.addTitle("Aircraft Details");
            doc.open();


            Anchor anchor = new Anchor("Aircraft Report");
            anchor.setName("Aircraft Report");

            Chapter catPart = new Chapter(new Paragraph(anchor), 1);

            Paragraph para1 = new Paragraph();
            Section subCatPart = catPart.addSection(para1);
            para1.add("This is paragraph 1");

            Paragraph para2 = new Paragraph();
            para2.add("This is paragraph 2");


            doc.add(catPart);

            doc.close();


        } catch (Exception e) {
            e.printStackTrace();
        }
     return doc;
}

回答1:

The people who advise you to use response.getOutputStream() instead of creating a FileOutputStream are right. See for instance the Hello Servlet from Chapter 9 of my book:

public class Hello extends HttpServlet {
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
        response.setContentType("application/pdf");
        try {
            // step 1
            Document document = new Document();
            // step 2
            PdfWriter.getInstance(document, response.getOutputStream());
            // step 3
            document.open();
            // step 4
            document.add(new Paragraph("Hello World"));
            document.add(new Paragraph(new Date().toString()));
            // step 5
            document.close();
        } catch (DocumentException de) {
            throw new IOException(de.getMessage());
        }
    }
}

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 PdfServlet extends HttpServlet {

    protected void service(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
        try {
            // 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.";
            }
            // step 1
            Document document = new Document();
            // step 2
            ByteArrayOutputStream baos = new ByteArrayOutputStream();
            PdfWriter.getInstance(document, baos);
            // step 3
            document.open();
            // step 4
            document.add(new Paragraph(String.format(
                "You have submitted the following text using the %s method:",
                request.getMethod())));
            document.add(new Paragraph(text));
            // step 5
            document.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();
        }
        catch(DocumentException e) {
            throw new IOException(e.getMessage());
        }
    }
}

For the full source code, see PdfServlet. You can try the code here: http://demo.itextsupport.com/book/

回答2:

You are creating a FileOutputStream to generate pdf. But what you can do is to use the stream that is present in HttpServletResponse on server side method and write the file directly to it.

回答3:

You can receive an OutputStream in your generatePDF method. If you pass the response.getOutputStream() to the generate method then the PDF will be written to the response directly.

回答4:

Just call this method appropriately from downloadPDF(); e.g.:

generatePDF(response.getOutputStream());

that calls this method:

public void generatePDF(OutputStream pdfOutputStream) {

    Document doc = new Document();
     try {
            PdfWriter.getInstance(doc, pdfOutputStream);

            doc.addAuthor("TestABC");
            doc.addTitle("Aircraft Details");
            doc.open();


            Anchor anchor = new Anchor("Aircraft Report");
            anchor.setName("Aircraft Report");

            Chapter catPart = new Chapter(new Paragraph(anchor), 1);

            Paragraph para1 = new Paragraph();
            Section subCatPart = catPart.addSection(para1);
            para1.add("This is paragraph 1");

            Paragraph para2 = new Paragraph();
            para2.add("This is paragraph 2");


            doc.add(catPart);

            doc.close();


        } catch (Exception e) {
            e.printStackTrace();
        }
}