为什么不在java servlet中创建pdf文档？ [英] Why doesn'n create pdf-documents in java servlet?

问题描述

我使用iText / Pdfbox创建PDF文档。当我使用像这样的独立Java类创建PDF时，一切正常：

I use iText/Pdfbox to create a PDF document. Everything works when I create the PDF using a standalone Java class like this:

public static void main(String[] args){
...
...
...
}

文档已正确创建。

但我需要从Servlet创建PDF文档。我将代码粘贴到get或post方法中，在服务器上运行该servlet，但未创建PDF文档！

But I need create a PDF document from a Servlet. I paste the code into the get or post method, run that servlet on the server, but the PDF document isn't created!

此代码作为独立应用程序运行：

This code works as a standalone application:

此代码不起作用：

推荐答案

请阅读文档。例如，问题的答案如何在不在服务器端存储文件的情况下将PDF提供给浏览器？

Please read the documentation. For instance the answer to the question How can I serve a PDF to a browser without storing a file on the server side?

您当前正在文件系统上创建文件。您没有使用响应对象，这意味着您没有向浏览器发送任何字节。这解释了为什么浏览器中没有任何反应。

You are currently creating a file on your file system. You aren't using the response object, meaning you aren't sending any bytes to the browser. This explains why nothing happens in the browser.

这是一个简单的例子：

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，某些浏览器遇到问题当你像这样直接发送字节时。使用 ByteArrayOutputStream 在内存中创建文件更安全，并告诉浏览器在内容标题中可以预期多少字节：

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());
        }
    }
}

有关完整源代码，请参阅 PdfServlet 。您可以在此处尝试以下代码： http://demo.itextsupport.com/book/

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

您在评论中写道

此演示将PDF文件写入浏览器。我想将PDF保存在硬盘上。

This demo writes the PDF file into the browser. I want to save the PDF on my hard drive.

这个问题可以通过两种不同的方式解释：

This question could be interpreted in two different ways:

1. 您希望将文件写入用户磁盘驱动器上的特定目录，而无需任何用户交互。这是禁止！如果服务器可以强制将文件写入用户磁盘驱动器的任何位置，那将是一个严重的安全隐患。


2. 您想要显示一个对话框，以便用户可以保存PDF在他选择的目录中的磁盘驱动器上，而不是仅在浏览器中显示PDF。在这种情况下，请仔细查看文档。你会看到这一行： response.setHeader（Content-disposition，attachment; filename =+testPDF.pdf）; 你可以设置内容处置到内联如果你想在浏览器中打开PDF，但在问题中，内容处置设置为附件，触发一个对话框打开。

1. You want to write the file to a specific directory on the user's disk drive without any user interaction. This is forbidden! It would be a serious security hazard if a server could force a file to be written anywhere on a user's disk drive.
2. You want to show a dialog box so that the user can save the PDF on his disk drive in a directory of his choice instead of just showing the PDF in the browser. In this case, please take a closer look at the documentation. You'll see this line: response.setHeader("Content-disposition","attachment;filename="+ "testPDF.pdf"); You can set the Content-disposition to inline if you want the PDF to open in the browser, but in the question, the Content-disposition is set to attachment which triggers a dialog box to open.

另见如何为iText生成的PDF显示另存为对话框？

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