Question

我正在尝试创建然后在我的Vaadin应用程序中下载pdf文件（使用vaadin-archetype-application生成），但不知怎的，我无法弄清楚它为什么不工作以及为什么我会得到它例外以下是我如何构建pdf文件（使用iText）：

String fileName = "file.pdf";
String relativePath = VaadinServlet.getCurrent().getServletContext().getRealPath("");

    try {
        Document document = new Document(PageSize.LETTER.rotate());

        PdfWriter.getInstance(document, new FileOutputStream(relativePath + "\\" + fileName));
        document.open();
        table = new PdfPTable(6);
        addMetaData(document);
        addTitlePage(document);
        addContent(document, table);
        System.out.println("dupa add content la scrierea documentului pdf");
        document.close();
    } catch (Exception e) {
        e.printStackTrace();
    }

以下是我尝试下载请求的方法：

if(_ui!=null){
    getUI().getPage().open("http://localhost:8080/project/download?ext=.pdf", "_blank", false);
}

这是我得到空指针异常的行我用if子句包围它，因为起初我认为_ui参数为null

这是我必须处理请求的代码：

private void registerRequestHandler() {
    // A request handler for generating some content
    VaadinSession.getCurrent().addRequestHandler(new RequestHandler() {
        private static final long serialVersionUID = 1L;

        @Override
        public boolean handleRequest(VaadinSession session, VaadinRequest request, VaadinResponse response)
                throws IOException {
            System.out.println("req: "+request.getPathInfo());         //not shown in console
            if ("/download".equals(request.getPathInfo())) {

                // reads input file from an absolute path
                String extension = request.getParameter("ext");
                System.out.println("extension: "+extension);
                String filePath = VaadinServlet.getCurrent().getServletContext().getRealPath("") + "\\file"
                        + extension;
                File downloadFile = new File(filePath);
                FileInputStream inStream = new FileInputStream(downloadFile);

                // if you want to use a relative path to context root:
                System.out.println("filePath = " + filePath);

                // obtains ServletContext
                ServletContext context = VaadinServlet.getCurrent().getServletContext();

                // gets MIME type of the file
                String mimeType = context.getMimeType(filePath);
                if (mimeType == null) {
                    // set to binary type if MIME mapping not found
                    mimeType = "application/octet-stream";
                }
                System.out.println("MIME type: " + mimeType);

                // modifies response
                response.setContentType(mimeType);
                response.setContentLength((int) downloadFile.length());

                // forces download
                String headerKey = "Content-Disposition";
                String headerValue = String.format("attachment; filename=\"%s\"", downloadFile.getName());
                response.setHeader(headerKey, headerValue);

                // obtains response's output stream
                OutputStream outStream = response.getOutputStream();

                byte[] buffer = new byte[4096];
                int bytesRead = -1;

                while ((bytesRead = inStream.read(buffer)) != -1) {
                    outStream.write(buffer, 0, bytesRead);
                }

                inStream.close();
                outStream.close();

                return true; // We wrote a response
            } else
                return false; // No response was written
        }
    });
}

这部分代码在我的MyUi类中。没有打印出system.out.printlns。任何帮助/想法/建议深表感谢。

Vaadin请求下载pdf返回空指针异常

0 个答案: