如何从android中的URL下载文件的一部分？

我试图使用setRequestProperty（“Range”，“bytes =”+ startbytes +“ – ”+ endbytes）下载给定下载URL的文件的一部分; 以下代码段显示了我要执行的操作。

protected String doInBackground(String... aurl) { int count; Log.d(TAG,"Entered"); try { URL url = new URL(aurl[0]); HttpURLConnection connection =(HttpURLConnection) url.openConnection(); int lengthOfFile = connection.getContentLength(); Log.d(TAG,"Length of file: "+ lengthOfFile); connection.setRequestProperty("Range", "bytes=" + 0 + "-" + 1000); 

问题在于，引发了一个exception，即“在建立连接后无法设置请求属性”。 请帮我解决这个问题。

Answer 1

假设您使用HTTP进行下载，您将需要使用HEAD http动词和RANGE http标头。

HEAD将为您提供文件大小（如果可用），然后RANGE允许您下载字节范围。

获得文件大小后，将其划分为大致相等大小的块，并为每个块生成下载线程。 完成所有操作后，按正确的顺序写入文件块。

如果你不知道如何使用RANGE标题，这里有另一个SO答案，解释如何： https ： //stackoverflow.com/a/6323043/1355166

[编辑]

要将文件分成块，请使用此命令，然后开始下载过程，

 private void getBytesFromFile(File file) throws IOException { FileInputStream is = new FileInputStream(file); //videorecorder stores video to file java.nio.channels.FileChannel fc = is.getChannel(); java.nio.ByteBuffer bb = java.nio.ByteBuffer.allocate(10000); int chunkCount = 0; byte[] bytes; while(fc.read(bb) >= 0){ bb.flip(); //save the part of the file into a chunk bytes = bb.array(); storeByteArrayToFile(bytes, mRecordingFile + "." + chunkCount);//mRecordingFile is the (String)path to file chunkCount++; bb.clear(); } } private void storeByteArrayToFile(byte[] bytesToSave, String path) throws IOException { FileOutputStream fOut = new FileOutputStream(path); try { fOut.write(bytesToSave); } catch (Exception ex) { Log.e("ERROR", ex.getMessage()); } finally { fOut.close(); } } 

Answer 2

选项1

如果您不需要知道内容长度：

[注意，不要调用connection.getContentLength() 。 如果你打电话，你会得到例外。 如果你需要打电话，那么检查第二个选项]

 URL url = new URL(aurl[0]); HttpURLConnection connection =(HttpURLConnection) url.openConnection(); connection.setRequestProperty("Range", "bytes=" + 0 + "-" + 1000); //Note that, response code will be 206 (Partial Content) instead of usual 200 (OK) if(connection.getResponseCode() == HttpURLConnection.HTTP_PARTIAL){ //Your code here to read response data } 

选项2

如果您需要知道内容长度：

 URL url = new URL(aurl[0]); //First make a HEAD call to get the content length HttpURLConnection connection =(HttpURLConnection) url.openConnection(); connection.setRequestMethod("HEAD"); if(connection.getResponseCode() == HttpURLConnection.HTTP_OK){ int lengthOfFile = connection.getContentLength(); Log.d("ERF","Length of file: "+ lengthOfFile); connection.disconnect(); //Now that we know the content lenght, make the GET call connection =(HttpURLConnection) url.openConnection(); connection.setRequestMethod("GET"); connection.setRequestProperty("Range", "bytes=" + 0 + "-" + 1000); //Note that, response code will be 206 (Partial Content) instead of usual 200 (OK) if(connection.getResponseCode() == HttpURLConnection.HTTP_PARTIAL){ //Your code here to read response data } }