Question

我下面的代码下载文件工作正常时没有实现resume，在阅读了更多解决方案来实现并解决问题我知道我必须检查Last-Modified标头并设置它用于连接，

但我无法做到这一点，因为我收到android Cannot set request property after connection is made或null的{{1}}错误，

我正在使用此reference

httpURLConnection heaser返回：

getHeaderField

现在我如何设置恢复下载文件？

GitHub Link

{
  null=[HTTP/1.1 200 OK], 
  Cache-Control=[public], 
  Connection=[keep-alive], 
  Content-Length=[8037404], 
  Content-Md5=[VEqXHCc/Off7a6D0gRFpiQ==], 
  Content-Type=[image/jpeg], 
  Date=[Tue, 19 Jan 2016 07:24:36 GMT], 
  Etag=["544a971c273f39f7fb6ba0f481116989"], 
  Expires=[Sat, 29 Jul 2017 10:07:00 GMT], 
  Last-Modified=[Thu, 18 Dec 2014 08:44:34 GMT], 
  Server=[bws], 
  X-Android-Received-Millis=[1501063623576], 
  X-Android-Response-Source=[NETWORK 200], 
  X-Android-Selected-Protocol=[http/1.1], 
  X-Android-Sent-Millis=[1501063623532]
}

我还得到public void run() { final URL url; HttpURLConnection httpURLConnection = null; try { try { url = new URL(mUrl); String lastModified = httpURLConnection.getHeaderField("Last-Modified"); if (!lastModified.isEmpty()) { httpURLConnection.setRequestProperty("If-Range", lastModified); } httpURLConnection = (HttpURLConnection) url.openConnection(); if (mFile.exists()) { downloadedLength = mFile.length(); Log.e("downloadedLength ", downloadedLength + ""); httpURLConnection.setRequestProperty("Range", "bytes=" + downloadedLength + "-"); fileOutputStream = new FileOutputStream(mFile, true); } else { fileOutputStream = new FileOutputStream(mFile); } httpURLConnection.setConnectTimeout(30000); httpURLConnection.setReadTimeout(30000); httpURLConnection.setRequestMethod("GET"); } catch (IOException e) { } final int responseCode; final int total; try { responseCode = httpURLConnection.getResponseCode(); total = httpURLConnection.getContentLength(); } catch (IOException e) { e.printStackTrace(); Log.e("ER UPDATE ", e.getMessage()); } if (responseCode == 200) { try { inputStream = httpURLConnection.getInputStream(); } catch (IOException e) { e.printStackTrace(); Log.e("IOException ", e.getMessage()); } final byte[] buffer = new byte[4 * 1024]; int length = -1; int finished = 0; long start = System.currentTimeMillis(); try { while ((length = inputStream.read(buffer)) != -1) { if (!isDownloading()) { throw new CanceledException("canceled"); } fileOutputStream.write(buffer, 0, length); finished += length; if (System.currentTimeMillis() - start > 1000) { onDownloadProgressing(finished, total); start = System.currentTimeMillis(); } } onDownloadCompleted(); } catch (IOException e) { e.printStackTrace(); Log.e("ER UPDATE ", e.getMessage()); } } else { Log.e("responseCode ", responseCode + ""); } } catch (DownloadException e) { e.printStackTrace(); Log.e("ER UPDATE ", e.getMessage()); } catch (CanceledException e) { e.printStackTrace(); Log.e("ER UPDATE ", e.getMessage()); } }响应代码，而不是206

Answer 1

1- httpURLConnection为空，因为您在初始化之前尝试调用它，

即，这一行

httpURLConnection = (HttpURLConnection) url.openConnection();

应该在这一行之前：

String lastModified = httpURLConnection.getHeaderField("Last-Modified");

2-您可以在connect()上致电httpURLConnection之前设置标头所以你需要设置你想要的任何东西，然后连接（）。这样你不应该得到错误（android连接后无法设置请求属性）

3- 206 为perfectly right，这是Range使用httpURLConnection.setRequestProperty("If-Range", lastModified);时的含义，表示部分内容成功< / strong>以及您正在做的事情，您正在获取部分内容，如果您获得完整内容，您将获得 200 。

总而言之，您的代码可能如下所示： 注意：按照// ***查看所需的更改。

编辑：这一切都来到了这一行

public void run() { myLastModified = getLastModified(mFile.getName()); // get last stored value for this file (use file name or other key) int total =0; final URL url; HttpURLConnection httpURLConnection = null; try { try { url = new URL(mUrl); httpURLConnection = (HttpURLConnection) url.openConnection(); httpURLConnection.setDoInput(true); httpURLConnection.setConnectTimeout(30000); httpURLConnection.setReadTimeout(30000); httpURLConnection.setRequestMethod("GET"); //*** new way to handle download process total = httpURLConnection.getContentLength(); if(mFile.exists()){ if(mFile.length() == total){ //we are done, return. return; }else{ //file was not completly donwloaded, now check lastModified: long lastModified = httpURLConnection.getLastModified();//this gets the header "Last-Modified" and convert to long if (lastModified == myLastModified) { //myLastModified should be retrived on each download and stored locally on ur system downloadedLength = mFile.length(); Log.e("downloadedLength ", downloadedLength + ""); httpURLConnection = (HttpURLConnection) url.openConnection(); httpURLConnection.setDoInput(true); httpURLConnection.setConnectTimeout(30000); httpURLConnection.setReadTimeout(30000); httpURLConnection.setRequestMethod("GET"); httpURLConnection.setRequestProperty("Range", "bytes=" + downloadedLength + "-"+ total); //add + total (TO) //append mode fileOutputStream = new FileOutputStream(mFile, true); }else{ //file was modified after 1st uncompleted-download: storeLastModified(lastModified, mFile.getName()); // use file name as key. can store in db or file ... //don't set ant Range ... we want full download, with a fresh file fileOutputStream = new FileOutputStream(mFile); }//last mod IF }//Length check }else{ //file not exist at all, create new file, set no Range we want full download... mFile.createNewFile(); fileOutputStream = new FileOutputStream(mFile); }//file exists. } catch (IOException e) { e.printStackTrace(); } final int responseCode; try { responseCode = httpURLConnection.getResponseCode(); } catch (IOException e) { e.printStackTrace(); Log.e("ER UPDATE ", e.getMessage()); } //***** if (responseCode == 200 || responseCode == 206) { try { inputStream = httpURLConnection.getInputStream(); } catch (IOException e) { e.printStackTrace(); Log.e("IOException ", e.getMessage()); } final byte[] buffer = new byte[4 * 1024]; int length = -1; int finished = 0; long start = System.currentTimeMillis(); try { while ((length = inputStream.read(buffer)) != -1) { if (!isDownloading()) { throw new CanceledException("canceled"); } fileOutputStream.write(buffer, 0, length); finished += length; if (System.currentTimeMillis() - start > 1000) { onDownloadProgressing(finished, total); start = System.currentTimeMillis(); } } onDownloadCompleted(); } catch (IOException e) { e.printStackTrace(); Log.e("ER UPDATE ", e.getMessage()); } } else { Log.e("responseCode ", responseCode + ""); } } catch (DownloadException e) { e.printStackTrace(); Log.e("ER UPDATE ", e.getMessage()); } catch (CanceledException e) { e.printStackTrace(); Log.e("ER UPDATE ", e.getMessage()); } }

设置该属性时会抛出错误，

无论如何，当你看到这个，它没有意义时，你会问最后修改是否等于你从连接中得到的值！如果你想这样做，你需要在你的系统中存储 lastModified ，然后将它与您从URLConn获得的那个进行比较，并将其与您的文件长度（已下载）进行比较然后继续完整下载或继续下载。

在下面找到新代码：

for ($i=0; $i <2 ; $i++) { //two sheet create excel workbook $newsheet = $objPHPExcel->createSheet();//sheet create $newsheet->setTitle("week". $i); //sheet name use looping }

Answer 2

查看this的POMATu回答。但无论如何，如果您通过HTTP协议下载文件，您可以使用DownloadManager - 系统服务（自API级别9），以便在后台长时间运行下载。它处理HTTP连接，连接更改，重新启动，并确保每次下载成功完成。它已经支持恢复并且还会提前通知。

您可以找到许多教程，例如this或that等示例，以及stackoverflow标记android-download-manager上的许多解决方案。

通过互联网实现下载文件的简历

2 个答案: