url 断点续传

通过url下载文件，中间服务器可能中断，需要断点续传 private void copyUrlPartly( URL url) throws IOException { List<PartETag> partETags = new ArrayList<PartETag>(); long totalUplod = 0L; int index = 1; long remain = fileSize; int retry = 0; HttpURLConnection httpURLConnection = (HttpURLConnection)url.openConnection(); long fileSize = httpURLConnection.getContentLengthLong(); /*如果下载的size小于size那么，就重新请求连接*/ while (totalUplod < fileSize && retry < 5) { byte readBuffer[] = new byte[1024]; HttpURLConnection httpURLConnection = (HttpURLConnection) url.openConnection(); httpURLConnection.setRequestProperty("RANGE", "bytes="+totalUplod+"-"); httpURLConnection.connect(); InputStream stream = httpURLConnection.getInputStream(); BufferedInputStream bis = new BufferedInputStream(stream); if(remain <= 0) { break; } while (remain > 0) { long partSize = 0L; File tmpFile = null; try { /* 使用临时文件作为中转 */ tmpFile = File.createTempFile( "test", null); /* 将part拷贝到临时文件夹下面的临时文件 */  partSize = downloadPart(bis, readBuffer, tmpFile);   // 在这可以对tmpFile处理你 省略不写 remain -= partSize;   totalUplod += partSize; retry = 0; } catch (Exception e) {  retry++; logger.error("copyUrlPartly failed. ", e); break; } finally { if (null != tmpFile) { tmpFile.delete(); } } } }  } //将网上下载部分保存到临时文件tmpFile中 private long downloadPart(BufferedInputStream bis, byte[] buffer, File tmpFile) throws Exception { BufferedOutputStream bos = null; long total = 0; try { bos = new BufferedOutputStream(new FileOutputStream(tmpFile)); int count; while ((count = bis.read(buffer)) > 0) { total += count; bos.write(buffer, 0, count); } } finally { try { if (null != bos) { bos.close(); } } catch (Exception e) { logger.debug("IoCloseException", e); } } return total; } Range头域   　　Range头域可以请求实体的一个或者多个子范围。例如，   　　表示头500个字节：bytes=0-499   　　表示第二个500字节：bytes=500-999   　　表示最后500个字节：bytes=-500   　　表示500字节以后的范围：bytes=500-   　　第一个和最后一个字节：bytes=0-0,-1   　　同时指定几个范围：bytes=500-600,601-999