java - 下载文件到 SD 卡不起作用

Question

想知道是否有人知道为什么这不起作用。首先，代码会获取网站上 pdf 的链接，并且 pdf 的链接肯定是正确的，但它不正确似乎正在将其下载到我的 SD 卡上。不确定它是否是按照我从设备上的 android studio 运行它的方式完成的？链接只是一个容器对象我有 pdf 的 URL 以及一些给出的方法只是文件名、整个 URL 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);

    }

}

我的 list 中的权限

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

编辑:在异常堆栈跟踪中找到以下内容，这应该有助于 java.io.FileNotFoundException:/storage/emulated/0/29-11-16.pdf:打开失败:EACCES(权限被拒绝)

Answer 1

对于 Android 6+，您需要请求运行时权限。这是一个例子

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
    }
}

像这样使用它

btnFetchData.setOnClickListener(new View.OnClickListener() {

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