java - xml 文件不更新。这是什么原因呢？

Question

blobstore 中有一个 xml 文件，如下所示:

<?xml version="1.0" encoding="UTF-8"?>

<Blobs>

</Blobs>

以下 Servlet 将文件上传到 blobstore。上传文件后，它获取file键并调用一个Bean，通过添加一个其文本内容为键的节点来更新xml。

public class UploadImagesToAisle extends HttpServlet {

/**
 * Handles the HTTP
 * <code>POST</code> method.
 *
 * @param request servlet request
 * @param response servlet response
 * @throws ServletException if a servlet-specific error occurs
 * @throws IOException if an I/O error occurs
 */
@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
    String path = request.getParameter("Data");
    PrintWriter writer = response.getWriter();
     try {
       boolean isMultipart = ServletFileUpload.isMultipartContent(request);
       if( !isMultipart ) {
           writer.println("File cannot be uploaded !");
       }  else {
           ServletFileUpload upload = new ServletFileUpload();
           FileItemIterator iter = upload.getItemIterator(request);
           List list = null;
           while(iter.hasNext()) {
               FileItemStream item = iter.next();
               String name  = item.getFieldName();
               String fileName = item.getName();
               String mimeType = new MimeType().getMimeType(fileName);
               if(mimeType == null) {
                   response.sendRedirect("error.jsp");
               }
               InputStream stream = item.openStream();
               if(item.isFormField()) {
                   // Process regular form field (input type="text|radio|checkbox|etc", select, etc).
               } else {
                   // Get a file service
                   FileService fileService = FileServiceFactory.getFileService();
                   // Create a new Blob file with mime-type "text/plain"
                   AppEngineFile file = fileService.createNewBlobFile(mimeType, fileName);
                   // Open a channel to write to it
                   boolean lock = true;
                   FileWriteChannel writeChannel = fileService.openWriteChannel(file, lock);
                   // copy byte stream from request to channel
                   byte[] buffer = new byte[10000];
                   int len;
                   while ((len = stream.read(buffer)) > 0) {
                        writeChannel.write(ByteBuffer.wrap(buffer, 0, len));
                   }

                   writeChannel.closeFinally();

                   if(MimeType.isImage) {
                       String key = fileService.getBlobKey(file).getKeyString();
                       // update the xml file with the key
                       new UpdateXml().appendKey(key);  // BEAN CALLED
                   }

                   RequestDispatcher dispatcher = request.getRequestDispatcher("private/cpanel/PcPanel.jsp");
                   dispatcher.forward(request, response);
               }
           }
       }
    }catch(Exception exc) {
        writer.println(exc);
    }
}
}

下面是一个 Bean，由上面的 servlet 调用来更新/写入 xml。

public class UpdateXml {

private final String xmlKey = "AMIfv95NSB_FKs2v6o0dIKkSdmSIJVtE0oq9X4hyTbxOTglDi6XoDaTUBlXxa3OsPfDo8ZQZF8kFb059zg4kJ3lK2MlgudC_nkQdwCpx1kYP9Rwb40s0HClFzzIIUv-UtMbuycxixVtfw-fYyhC3MXvFc1Gh-Cv9mQ";

public void appendKey(String key) {
    try {
        FileService fileService = FileServiceFactory.getFileService();
        AppEngineFile file = fileService.getBlobFile( new BlobKey( xmlKey ) );
        FileReadChannel readChannel = fileService.openReadChannel(file, true);
        InputStream stream = Channels.newInputStream(readChannel);

        DocumentBuilderFactory builderFactory = DocumentBuilderFactory.newInstance();
        DocumentBuilder documentBuilder = builderFactory.newDocumentBuilder();
        Document doc = documentBuilder.parse(stream);
        Element root = doc.getDocumentElement();

        Element blobKey = doc.createElement("blob-key");
        blobKey.setTextContent(key);

        root.appendChild(blobKey);

        GSFileOptionsBuilder optionsBuilder = new GSFileOptionsBuilder();
        optionsBuilder.setBucket("my-bucket");
        optionsBuilder.setKey(xmlKey);
        optionsBuilder.setMimeType("text/html");
        optionsBuilder.setAcl("public_read");
        optionsBuilder.addUserMetadata("suhail", "gupta");

        AppEngineFile writableFile = fileService.createNewGSFile(optionsBuilder.build());
        FileWriteChannel writeChannel = fileService.openWriteChannel(file, true);
        OutputStream output = Channels.newOutputStream(writeChannel);

        TransformerFactory tf = TransformerFactory.newInstance();
        Transformer transformer = tf.newTransformer();
        DOMSource source  = new DOMSource(doc);
        transformer.setOutputProperty(OutputKeys.ENCODING,"UTF-8");
        transformer.setOutputProperty(OutputKeys.INDENT,"yes");
        StreamResult result = new StreamResult(output);
        transformer.transform(source, result);
    }catch(Exception exc) {
        exc.printStackTrace();
    }
}

}

文件上传正常，但未在 xml 文件中添加条目。日志中没有任何错误日志。我不明白这是为什么。有什么问题吗？

Answer 1

我认为该文件未保留，因为您忘记了最终确定:

append to it and when all done writing, you must finalize the file for it to persist

Source

尝试在 transformer.transform(source, result); 之后添加: writeChannel.closeFinally(); 或 writeChannel.close()/p><小时/>

编辑

你永远不会写入writableFile:

FileWriteChannel writeChannel = fileService.openWriteChannel(file, true);

但尝试写入以读取方式打开并锁定的文件。