java 实现断点续传

/**
     * 下载服务器已存在的文件,支持断点续传
     * 
     * @param request
     *            请求对象
     * @param response
     *            响应对象
     * @param path
     *            文件路径(绝对)
     */
    public static void download(HttpServletRequest request, HttpServletResponse response, File proposeFile) {
        LOGGER.debug("下载文件路径：" + proposeFile.getPath());
        InputStream inputStream = null;
        OutputStream bufferOut = null;
        try {
            // 设置响应报头
            long fSize = proposeFile.length();
            response.setContentType("application/x-download");
            String isoFileName = URLEncoder.encode(proposeFile.getName(), ENCODING);
            response.addHeader("Content-Disposition", "attachment; filename=" + isoFileName);
            response.addHeader("Content-Length", String.valueOf(fSize));
            response.setHeader("Accept-Ranges", "bytes");
            long pos = 0, last = fSize - 1;
            if (null != request.getHeader("Range")) {
                // 断点续传
                response.setStatus(HttpServletResponse.SC_PARTIAL_CONTENT);
                try {
                    // 情景一：RANGE: bytes=2000070- 情景二：RANGE: bytes=2000070-2000970
                    String numRang = request.getHeader("Range").replaceAll("bytes=", "");
                    String[] strRange = numRang.split("-");
                    if (strRange.length == 2) {
                        pos = Long.parseLong(strRange[0].trim());
                        last = Long.parseLong(strRange[1].trim());
                    } else {
                        pos = Long.parseLong(numRang.replaceAll("-", "").trim());
                    }
                } catch (NumberFormatException e) {
                    LOGGER.error(request.getHeader("Range") + " is not Number!");
                    pos = 0;
                }
            }
            String contentRange = new StringBuffer("bytes ").append(new Long(pos).toString()).append("-").append(new Long(fSize - 1).toString()).append("/").append(new Long(fSize).toString()).toString();
            response.setHeader("Content-Range", contentRange);

            // 跳过已经下载的部分，进行后续下载
            bufferOut = new BufferedOutputStream(response.getOutputStream());
            inputStream = new BufferedInputStream(new FileInputStream(proposeFile));
            inputStream.skip(pos);
            byte[] buffer = new byte[5 * 1024];
            long rangLength = last - pos + 1, sum = 0;// sum记录总共已经读取了多少字节
            int length = 0;
            while ((length = inputStream.read(buffer, 0, ((rangLength - sum) <= buffer.length ? ((int) (rangLength - sum)) : buffer.length))) != -1 && sum < rangLength) {
                sum = sum + length;
                bufferOut.write(buffer, 0, length);
            }
        } catch (Throwable e) {
            if (e instanceof ClientAbortException) {
                // 浏览器点击取消
                LOGGER.info("用户取消下载!");
            } else {
                LOGGER.info("下载文件失败....");
                e.printStackTrace();
            }
        } finally {
            try {
                if (bufferOut != null) {
                    bufferOut.close();
                }
                if (inputStream != null) {
                    inputStream.close();
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }