commons-fileupload如何实现带进度条的断点续传

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commons-fileupload如何实现带进度条的断点续传5

大概要求如题，我已经实现了进度条，用的是dwr和commons-fileupload，但是现在我不知道该怎么实现断线续传，下面的代码是非断点的，该如何修给实现断点呢？求教各位牛人。


public class FileUploadServlet extends HttpServlet {

	private static final long serialVersionUID = 1L;

	private static final String FILE_UPLOAD_JSP = "/jsp/FileUploadForm.jsp";

	private static final long MAX_LENGTH = 1000 * 1024 * 1024L; // 1000MB

	private static final int HTTP_REDUNDANT_LENGTH = 1024; // 1KB

	protected void doGet(HttpServletRequest request, 
			HttpServletResponse response) throws ServletException, IOException {
		RequestDispatcher rd = request.getRequestDispatcher(FILE_UPLOAD_JSP);
		rd.forward(request, response);

	}

	protected void doPost(HttpServletRequest request,
			HttpServletResponse response) throws ServletException, IOException {

		ProgressInfo pi = new ProgressInfo();
		
		try {
			this.doUpload(request, pi);
		} catch (Exception e) {
			pi.setInProgress(false);
			Util.info("FileUploadServlet", "cancelled or interrupted!");
			e.printStackTrace();
			throw new ServletException(e);
		}
	}

	private String getFileName(String fileName) {
		String name = fileName.substring(fileName.lastIndexOf("\\") + 1);
		return System.getProperty("java.io.tmpdir") + "/" + name;
	}

	private void doUpload(HttpServletRequest request, ProgressInfo pi)
			throws Exception {

		String fldName = "";
		FileItemStream item = null;
		BufferedInputStream stream = null;

		boolean isMultipart = ServletFileUpload.isMultipartContent(request);

		if (isMultipart) {
			int filesSize = request.getContentLength() - HTTP_REDUNDANT_LENGTH;
			if (filesSize >= MAX_LENGTH) {
				String errorMsg = "Error: Current files size is " + filesSize
						/ (1024 * 1024) + "MB which has exceeded max " + MAX_LENGTH + "MB";
				pi.setCompleted(true);
				pi.setErrorMsg(errorMsg);
				throw new Exception(errorMsg);
			}
			ServletFileUpload upload = new ServletFileUpload();
			upload.setHeaderEncoding("UTF-8");
			upload.setFileSizeMax(MAX_LENGTH);
			upload.setSizeMax(MAX_LENGTH);
			UploadListener uploadListener = new UploadListener(pi);
			upload.setProgressListener(uploadListener);
			// Parse the request
			FileItemIterator fIter = upload.getItemIterator(request);
			
			while (fIter.hasNext()) {
				item = fIter.next();
				fldName = item.getFieldName();
				Util.info("FileUploadServlet", fldName + ", "
						+ item.isFormField() + ", " + item.getContentType()
						+ ", " + item.getName() + ", " + item.getHeaders());

				if (!item.isFormField()) {
					fldName = item.getFieldName();
					if (item.getName() == null
							|| "".equals(item.getName().trim())) {
						continue;
					}

					pi.setCurFileName(item.getName());
					pi.setUploadedFiles(pi.getUploadedFiles() + "<b>"
							+ item.getName() + "</b><br/>");
					
					File file = new File(this.getFileName(item.getName()));
					Long size = file.length();
					if (file.exists()) {
						pi.setBytesRead(size);
					}
					stream = new BufferedInputStream(item.openStream());
					stream.skip(file.length());
					Util.info("FileUploadServlet", this.getFileName(item
							.getName()));	
					
					BufferedOutputStream bos = new BufferedOutputStream(new FileOutputStream(file));
					Streams.copy(stream, bos, true);
				}

			}
		}

	}

}

这个是listener代码：


public class UploadListener implements ProgressListener {

	private static final long UPDATE_THRESHOLD = 50 * 1024L; // 

	private static WebContext wctx = null;

	private ScriptProxy sp = null;

	private long megaBytes = -1;

	private ProgressInfo pi = null;

	public UploadListener() {
		wctx = WebContextFactory.get();
	}

	public UploadListener(ProgressInfo pi) {
		this.pi = pi;
	}

	public void update(long pBytesRead, long pContentLength, int pItems) {

		try {
			// Make the upload more slowly, so we can see the progress bar for small file.
			// In Prod env. it should be removed.
			Thread.sleep(10);
		} catch (Exception ex) {
			ex.printStackTrace();
		}

		if(pBytesRead + 2000 > pContentLength){
			pi.setBytesRead(pContentLength);
			sp.addFunctionCall("updateProgress", pi);
			return;
		}
		long mBytes = pBytesRead / UPDATE_THRESHOLD;
		if (megaBytes == mBytes && megaBytes > 0) {
			return;
		}
		
		megaBytes = mBytes;
		pi.setBytesRead(pBytesRead);
		pi.setFileIndex(pItems);
		pi.setTotalSize(pContentLength);

		// WebContext wctx = WebContextFactory.get();
		// org.directwebremoting.proxy.dwr.Util utilThis = new
		// org.directwebremoting.proxy.dwr.Util(wctx.getScriptSession());
		// utilThis.setValue("text", String.valueOf(pBytesRead));
		if(sp == null){
			sp = new ScriptProxy(wctx.getScriptSessionsByPage(wctx.getCurrentPage()));
		}
		sp.addFunctionCall("updateProgress", pi);

	}

	public void go() {
		System.out.println("---------go!");
	}
}

问题补充：

hu437 写道

使用commons-fileupload实现断点续传不好的，原因如下：

1、断点续传原理：首先获取文件的整个长度，然后查询已经上传了多少长度，下次读取的时候从上传完成的部分开始读取（复杂的还有文件分片等）

2、js无法获取本地硬盘上的文件信息，所以他不能从指定的大小位置可始读取文件，这个只有每次都是重新上传，这样的断点续传也没意义

建议使用flash组件进行上传，可以看一下swfupload这个组件，实现进度条等也非常方便

我简单用过swfupload，但是好像看不到它的上传代码吧？！看不到的话我应该怎么改动呢？

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