Upload file from applet to servlet using apache fileupload

Question

To accomplish: Upload a file from my local to server using an applet and servlet using apache fileupload jar.

Tried: I have used a simple jsp, with a browse button and posted the action to my servlet (where I used apache fileupload). I was successful in uploading the file to the server.

Issue: I am trying to upload a file, from my local machine, using an applet. I do not want to manually select files, instead upload files that are present in a specific folder. For now I have hardcoded the folder. I am able to look at the folder and get the list of files I want to upload. Also, I have successfully established a connection from my applet to servlet.

Issue arises at the upload.parseRequest(request) in the servlet. I'm thinking its because the applet cannot post to servlet's request object. Also, I have set the request type to multipart/form-data in my applet. Right now, I am trying to pass the absolute path of the file to servlet and upload.

I have seen other posts where byte stream data is passed from applet to servlet, but the servlet uses the traditional File.write. For me, it is mandatory to achieve this using apache fileupload.

Please suggest on how to pass a file/file path from applet to servlet, where the upload is handled by apache fileupload.

Below are my FileUploadHandler (where the HTTP requests are handled) and FileUpload(which is my applet)

Below is my FileUpload Handler:

@WebServlet(name = "FileUploadHandler", urlPatterns = { "/upload" })
@MultipartConfig
public class FileUploadHandler extends HttpServlet {
    String uploadFolder ="";
    @Override
    protected void doPost(HttpServletRequest request,
            HttpServletResponse response) throws ServletException, IOException {

        System.out.println("doPost-servlet URL is: "
                + request.getRequestURL());
        try {
            uploadFolder = fileToUpload(request);
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
          uploadFolder = getServletContext().getRealPath("")+ File.separator;

        //   Create a factory for disk-based file items 
        DiskFileItemFactory factory = new DiskFileItemFactory();

        // Create a new file upload handler 
        ServletFileUpload upload = new ServletFileUpload(factory);
        // process only if its multipart content

    if (ServletFileUpload.isMultipartContent(request)) {
        System.out.println("Yes, it is a multipart request...");
        try {
                List<FileItem> multiparts = upload.parseRequest(request);

                System.out.println("Upload.parseRequest success !");

                for (FileItem item : multiparts) {
                    if (!item.isFormField()) {
                        String name = new File(item.getName()).getName();
                        item.write(new File(uploadFolder + File.separator
                                + name));
                    }
                }
                System.out.println("File uploaded to server !");
                // File uploaded successfully
                request.setAttribute("message", "File Uploaded Successfully");
            } catch (Exception ex) {
                request.setAttribute("message", "File Upload Failed due to "
                        + ex);
            }

        }  if(!ServletFileUpload.isMultipartContent(request)){
            throw new ServletException("Content type is not multipart/form-data");
        }


        doGet(request, response);
        //request.getRequestDispatcher("/result.jsp").forward(request, response);
        OutputStream outputStream = response.getOutputStream();
         ObjectOutputStream objectOutputStream = new ObjectOutputStream(outputStream);
          objectOutputStream.writeObject("Success !");
          objectOutputStream.flush();
          objectOutputStream.close();
    }


    private String fileToUpload(HttpServletRequest request) throws IOException,
            ClassNotFoundException {
            ServletInputStream servletIn = request.getInputStream();
            ObjectInputStream in = new ObjectInputStream(servletIn);
            String uploadFile = (String) in.readObject();
            System.out.println("Value in uploadFolder is: " + uploadFile);
            return uploadFile;
    }

Below is the fileupload applet:

public class FileUpload extends Applet {
private JButton capture;
private JTextField textField;
private final String pathDirectory = "C:\\";
private final String captureConfirmMessage = "Are you sure you want to continue?";
private final String confirmDialogTitle = "Confirm upload";
final File folder = new File(pathDirectory);

public void init() {
    upload= new JButton("Upload");
    textField = new JTextField();
    capture.addActionListener(new ActionListener() {

        @Override
        public void actionPerformed(ActionEvent e) {
            int selection = JOptionPane.showConfirmDialog(upload,
                    uploadConfirmMessage, confirmDialogTitle,
                    JOptionPane.YES_NO_OPTION);

            if (selection == JOptionPane.OK_OPTION) {
                listFilesForFolder(folder);

            } else if (selection == JOptionPane.CANCEL_OPTION) {
                JOptionPane.showMessageDialog(upload,
                        "You have aborted upload", "Upload Cancelled", 2);
            }

        }
    });

    add(upload);
    add(textField);
}

public void listFilesForFolder(final File folder) {
    for (final File fileEntry : folder.listFiles()) {
        if (fileEntry.isDirectory()) {
            listFilesForFolder(fileEntry);
        } else {
            try {
                onSendData(fileEntry.getAbsolutePath());
                System.out.println(fileEntry.getAbsolutePath());

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

        }
    }
}

private URLConnection getServletConnection() throws MalformedURLException,
        IOException {
    // Open the servlet connection
    URL urlServlet = new URL("http://localhost:8081/UploadFile/upload");
    HttpURLConnection servletConnection = (HttpURLConnection) urlServlet
            .openConnection();
    // Config
    servletConnection.setDoInput(true);
    servletConnection.setDoOutput(true);

    servletConnection.setUseCaches(false);
    servletConnection.setDefaultUseCaches(false);
    servletConnection.setRequestProperty("Content-Type", "multipart/form-data;");
    servletConnection.connect();

    return servletConnection;
}

private void onSendData(String fileEntry) {
    try {
        // Send data to the servlet
        HttpURLConnection servletConnection = (HttpURLConnection) getServletConnection();
        OutputStream outstream = servletConnection.getOutputStream();
        ObjectOutputStream objectOutputStream= new ObjectOutputStream(
                outstream);
        objectOutputStream.writeObject(fileEntry);

                    // Receive result from servlet
        InputStream inputStream = servletconnection.getInputStream();
        ObjectInputStream objectInputStream = new ObjectInputStream(
                inputStream);
        String result = (String) objectInputStream.readObject();
        objectInputStream.close();
        inputStream.close();
        out.flush();
        out.close();

        // Display result on the applet
        textField.setText(result);
    } catch (java.net.MalformedURLException mue) {
        mue.printStackTrace();
        textField.setText("Invalid serlvetUrl, error: " + mue.getMessage());

    } catch (java.io.IOException ioe) {
        ioe.printStackTrace();
        textField.setText("Couldn't open a URLConnection, error: "
                + ioe.getMessage());
    } catch (Exception e) {
        e.printStackTrace();
        textField.setText("Exception caught, error: " + e.getMessage());
    }
}

public void paint(Graphics g) {
    g.drawString("Click the button above to capture", 5, 50);
}

Answer 1

I could finally succeed posting the request to the servlet from the applet. It was a simple logic that I was missing. I did not add the header and trailer while posting to the servlet, which was the key, in the servlet to identify the incoming request as a multipart data.

            FileInputStream fileInputStream = new FileInputStream(new File(
                fileEntry));
        dataOutputStream.writeBytes(twoHyphens + boundary + lineEnd);
        dataOutputStream
                .writeBytes("Content-Disposition: form-data; name=\"upload\";"
                        + " filename=\"" + fileEntry + "\"" + lineEnd);
        dataOutputStream.writeBytes(lineEnd);

        // create a buffer of maximum size
        bytesAvailable = fileInputStream.available();
        bufferSize = Math.min(bytesAvailable, maxBufferSize);
        buffer = new byte[bufferSize];
        // read file and write it into form
        bytesRead = fileInputStream.read(buffer, 0, bufferSize);
        while (bytesRead > 0) {
            dataOutputStream.write(buffer, 0, bufferSize);
            bytesAvailable = fileInputStream.available();
            bufferSize = Math.min(bytesAvailable, maxBufferSize);
            bytesRead = fileInputStream.read(buffer, 0, bufferSize);
            System.out.println(fileEntry + " uploaded.");
        }

        // send multipart form data necesssary after file data
        dataOutputStream.writeBytes(lineEnd);
        dataOutputStream.writeBytes(twoHyphens + boundary + twoHyphens
                + lineEnd);

I added the header and trailer and also used this to create the URL connection.

private URLConnection getServletConnection() throws MalformedURLException,
        IOException {
    // Open the servlet connection
    URL urlServlet = new URL("http://localhost:8083/UploadFile/upload");
    HttpURLConnection servletConnection = (HttpURLConnection) urlServlet
            .openConnection();
    // Config
    servletConnection.setDoInput(true);
    servletConnection.setDoOutput(true);
    servletConnection.setUseCaches(false);
    servletConnection.setDefaultUseCaches(false);
    servletConnection.setRequestMethod("POST");
    servletConnection.setRequestProperty("Content-Type",
            "multipart/form-data;boundary=" + this.boundary);
    servletConnection.setRequestProperty("Connection", "Keep-Alive");
    servletConnection.connect();
    return servletConnection;
}

Then, in the servlet, I was just reading the data using upload.ParseRequest(request). Thank you for the help.