如何在不将文件存储在服务器端的情况下将 PDF 提供给浏览器？

Question

我有两种方法。一个在服务器端生成 PDF，另一个在客户端下载 PDF。

如何在不将其存储在服务器端并允许客户端直接下载的情况下做到这一点。

以下是两种方法：

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");
}

还有：

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;
}

Answer 1

您正在创建一个 FileOutputStream 来生成 pdf。但是您可以做的是在服务器端方法上使用 HttpServletResponse 中存在的流并将文件直接写入它。

Answer 2

您可以在generatePDF 方法中收到OutputStream。如果您将response.getOutputStream() 传递给 generate 方法，则 PDF 将直接写入响应。

Answer 3

只需从downloadPDF() 适当调用此方法即可；例如：

generatePDF(response.getOutputStream());

调用这个方法的：

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();
        }
}

Answer 4

建议您使用response.getOutputStream() 而不是创建FileOutputStream 的人是对的。例如，参见我的书第 9 章中的 Hello Servlet：

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());
        }
    }
}

但是，当您像这样直接发送字节时，某些浏览器会遇到问题。使用ByteArrayOutputStream 在内存中创建文件并告诉浏览器它可以在内容头中预期多少字节会更安全：

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());
        }
    }
}

完整源代码见PdfServlet。你可以在这里试试代码：http://demo.itextsupport.com/book/