exception in thread timer-0 java.lang.nullpointerexception

[peppej89]

Salve a tutti
ho un problema che non riesco proprio a risolvere...
Questo è il mio codice:

class FileUploadProgressListener implements ProgressListener {

    private Collection<ResumableGDataFileUploader> trackedUploaders =    Lists.newArrayList();
    private int pendingRequests;
    PrintStream output;
    Map<String, DocumentListEntry> uploaded = Maps.newHashMap();
    Map<String, String> failed = Maps.newHashMap();

    boolean processed;

    public FileUploadProgressListener() 
    {
      this.pendingRequests = 0;
    }

    public void listenTo(Collection<ResumableGDataFileUploader> uploaders)
    {
      this.trackedUploaders.addAll(uploaders);
      this.pendingRequests = trackedUploaders.size();
    }

    public synchronized void progressChanged(ResumableHttpFileUploader uploader)
    {
      String fileId = ((FileUploadData) uploader.getData()).getFileName();
      switch(uploader.getUploadState()) {
        case COMPLETE:
        case CLIENT_ERROR:
          pendingRequests -= 1;
          output.println(fileId + ": Completed");
          break;
        case IN_PROGRESS:
          output.println(fileId + ":"
              + String.format("%3.0f", uploader.getProgress() * 100) + "%");
          break;
        case NOT_STARTED:
          output.println(fileId + ":" + "Not Started");
          break;
      }
    }

    public synchronized boolean isDone() {
      // not done if there are any pending requests.
      if (pendingRequests > 0) {
        return false;
      }
      // if all responses are processed., nothing to do.
      if (processed) {
        return true;
      }
      // check if all response streams are available.
      for (ResumableGDataFileUploader uploader : trackedUploaders) {
        if (!uploader.isDone()) {
          return false;
        }
      }
      // process all responses
      for (ResumableGDataFileUploader uploader : trackedUploaders) {
        String fileId = ((FileUploadData) uploader.getData()).getFileName();
        switch(uploader.getUploadState()) {
          case COMPLETE:
            try {
              DocumentListEntry entry =
                  uploader.getResponse(DocumentListEntry.class);
              uploaded.put(fileId, entry);
            } catch (IOException e) {
              failed.put(fileId, "Upload completed, but unexpected error "
                  + "reading server response");
            } catch (ServiceException e) {
              failed.put(fileId,
                  "Upload completed, but failed to parse server response");
            }
            break;
          case CLIENT_ERROR:
            failed.put(fileId, "Failed at " + uploader.getProgress());
            break;
        }
      }
      processed = true;
      output.println("All requests done");
      return true;
    }

    public synchronized Collection<DocumentListEntry> getUploaded() {
      if (!isDone()) {
        return null;
      }
      return uploaded.values();
    }

    public synchronized void printResults() {
      if (!isDone()) {
        return;
      }
      output.println("Result: " + uploaded.size() + ", " + failed.size());
      if (uploaded.size() > 0) {
        output.println(" Successfully Uploaded:");
        for (Map.Entry<String, DocumentListEntry> entry : uploaded.entrySet()) {
          printDocumentEntry(entry.getValue());
        }
      }
      if (failed.size() > 0) {
        output.println(" Failed to upload:");
        for (Map.Entry entry : failed.entrySet()) {
          output.println("  " + entry.getKey() + ":" + entry.getValue());
        }
      }
    }

    /**
     * Prints out the specified document entry.
     *
     * @param doc the document entry to print.
     */
    public void printDocumentEntry(DocumentListEntry doc) {
      StringBuffer buffer = new StringBuffer();

      buffer.append(" -- " + doc.getTitle().getPlainText() + " ");
      if (!doc.getParentLinks().isEmpty()) {
        for (Link link : doc.getParentLinks()) {
          buffer.append("[" + link.getTitle() + "] ");
        }
      }
      buffer.append(doc.getResourceId());

      output.println(buffer);
    }

  }		// CHIUSURA CLASSE

	try
	{
		DocsService client = new DocsService("Google Docs API");
		client.setUserCredentials(usr, psw);
		String percorsoFile = request.getParameter("file");
		
	    	int MAX_CONCURRENT_UPLOADS = 10;
	    	int PROGRESS_UPDATE_INTERVAL = 1000;
	    	int DEFAULT_CHUNK_SIZE = 10485760;
	    	File file = new File(percorsoFile);
	    	
	    	FileUploadProgressListener listener = new FileUploadProgressListener();
	        ExecutorService executor = Executors.newFixedThreadPool(MAX_CONCURRENT_UPLOADS);
	    	
	        List<ResumableGDataFileUploader> uploaders = Lists.newArrayList();
	    	String contentType = DocumentListEntry.MediaType.fromFileName(file.getName()).getMimeType();
	    	MediaFileSource mediaFile = new MediaFileSource(file, contentType);
	    	URL createUploadUrl = new URL("https://docs.google.com/feeds/upload/create-session/default/private/full");
	    	ResumableGDataFileUploader uploader = new ResumableGDataFileUploader.Builder(client, createUploadUrl, mediaFile, null)
	    	              			  .chunkSize(DEFAULT_CHUNK_SIZE).executor(executor)
				    	              .title(mediaFile.getName())
				    	              .trackProgress(listener, PROGRESS_UPDATE_INTERVAL)
				    	              .build();
	    	uploaders.add(uploader);
	    	listener.listenTo(uploaders);
	    	
	    	for (ResumableGDataFileUploader uploader1 : uploaders) 
	    	{
	    		uploader1.start();
	    	}
	    	while (!listener.isDone()) 
	    	{
	    	      try 
	    	      {
	    	        Thread.sleep(100);
	    	      } catch (InterruptedException ie) 
	    	      {
	    	        System.out.println("Interrotto!");
	    	    	listener.printResults();
	    	        throw ie; // rethrow
	    	      }
	    	}
	    	listener.printResults();
	}catch (Exception ex)
		{
	        System.err.println("Eccezzione " + ex.getMessage());
	        ex.printStackTrace();
	     }

Il problema che mi da è:

Exception in thread "Timer-0" java.lang.NullPointerException
	at org.apache.jsp.upload_jsp$1FileUploadProgressListener.progressChanged(upload_jsp.java:138)
	at com.google.gdata.client.uploader.ResumableHttpFileUploader$NotificationTask.run(ResumableHttpFileUploader.java:179)
	at java.util.TimerThread.mainLoop(Unknown Source)
	at java.util.TimerThread.run(Unknown Source)

Qualcuno può aiutarmi???

Grazie a tutti