下载文件到sd卡不工作

Question

想知道是否有人有任何洞察力，为什么这不起作用。首先代码去并获得一个链接到一个pdf在一个网站上，并链接到PDF是绝对正确，但它似乎并没有下载到我的SD卡上。不知道如果它是从我的设备上的Android工作室运行它的方式完成的？链接只是一个容器对象我有URL用一些方法给了刚刚的文件名，整个URL的PDF等

public class MainActivity extends AppCompatActivity { 



@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_main); 

    Button btnFetchData = (Button) findViewById(R.id.buttonTest); 
    btnFetchData.setOnClickListener(new View.OnClickListener() { 

     @Override 
     public void onClick(View v) { 
      new FetchWebsiteData().execute(); 


     } 
    }); 

} 
private class FetchWebsiteData extends AsyncTask<Void, Void, Void> { 

    private String pdfLink = "didnt work"; 
    private Link foundLink = new Link(""); 
    String fileLocation= ""; 

    @Override 
    protected void onPreExecute() { 
     super.onPreExecute(); 


    } 

    @Override 
    protected Void doInBackground(Void... params) { 
     int count; 
     try { 

      Document doc = Jsoup.connect("http://www.dunnesstores.com/offer20/food-wine/fcp-category/home").userAgent("Mozilla/5.0 (Windows NT 6.1; WOW64; rv:5.0) Gecko/20100101 Firefox/5.0").get(); 
      //Elements links = doc.select("a[title=\"Download offers in store\"]"); 
      Element links = doc.select("a[title=\"Download offers in store\"]").first(); 
      foundLink = new Link(links.attr("href")); 

      URL url = new URL(foundLink.getUrlWithDomain()); 

      //create the new connection 
      HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection(); 

      //set up some things on the connection 
      urlConnection.setRequestMethod("GET"); 
      urlConnection.setDoOutput(true); 

      //and connect! 
      urlConnection.connect(); 

      //set the path where we want to save the file 
      //in this case, going to save it on the root directory of the 
      //sd card. 
      File SDCardRoot = Environment.getExternalStorageDirectory(); 
      //create a new file, specifying the path, and the filename 
      //which we want to save the file as. 
      File file = new File(SDCardRoot,foundLink.getFileNameOnly()); 
      fileLocation = file.toString(); 
      //this will be used to write the downloaded data into the file we created 
      FileOutputStream fileOutput = new FileOutputStream(file); 

      //this will be used in reading the data from the internet 
      InputStream inputStream = urlConnection.getInputStream(); 

      //this is the total size of the file 
      int totalSize = urlConnection.getContentLength(); 
      //variable to store total downloaded bytes 
      int downloadedSize = 0; 

      //create a buffer... 
      byte[] buffer = new byte[1024]; 
      int bufferLength = 0; //used to store a temporary size of the buffer 

      //now, read through the input buffer and write the contents to the file 
      while ((bufferLength = inputStream.read(buffer)) > 0) { 
       //add the data in the buffer to the file in the file output stream (the file on the sd card 
       fileOutput.write(buffer, 0, bufferLength); 
       //add up the size so we know how much is downloaded 
       downloadedSize += bufferLength; 
       //this is where you would do something to report the progress, like this maybe 


      } 
      //close the output stream when done 
      fileOutput.close(); 





     } catch (IOException e) { 
      //e.printStackTrace(); 
     } 
     return null; 
    } 

    @Override 
    protected void onPostExecute(Void result) { 
     TextView txttitle = (TextView) findViewById(R.id.resultTextView); 
     //testing the file location 
     txttitle.setText(fileLocation); 

    } 

} 

在我的清单

<uses-permission android:name="android.permission.INTERNET"/> 
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/> 

的权限

编辑：发现的异常堆栈跟踪这应有助于java.io.FileNotFoundException如下：/storage/emulated/0/29-11-16.pdf：打开失败：EACCES（拒绝）

Answer 1

借助Android 6+您需要询问运行时权限。下面是一个例子

private void checkPermission() { 
    final String permissionWrite = Manifest.permission.WRITE_EXTERNAL_STORAGE; 
    final String permissionRead = Manifest.permission.READ_EXTERNAL_STORAGE; 

    if (ContextCompat.checkSelfPermission(getActivity(), permissionWrite) != PermissionChecker.PERMISSION_GRANTED 
      || ContextCompat.checkSelfPermission(getActivity(), permissionRead) != PermissionChecker.PERMISSION_GRANTED) { 
     requestPermissions(new String[]{permissionWrite, permissionRead}, 0); 
     return; 
    } 
    new FetchWebsiteData().execute(); 
} 

@Override 
public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) { 
    if (requestCode != 0) return; 
    if (grantResults.length > 0 && grantResults[0] == PackageManager.PERMISSION_GRANTED 
      && grantResults[1] == PackageManager.PERMISSION_GRANTED) { 
     new FetchWebsiteData().execute(); 
    } else { 
     // well no permission granted 
    } 
} 

而且使用这样的

btnFetchData.setOnClickListener(new View.OnClickListener() { 

    @Override 
    public void onClick(View v) { 
     checkPermission(); 
    } 
});