java.io.FileNotFoundException：/storage/emulated/0/downloadedFilem.jpg（权限被拒绝）

Question

我正试图在android中使用异步任务下载和存储图像，当点击下载按钮时得到以下错误。

    W/System.err: java.io.FileNotFoundException: /storage/emulated/0/downloadedfilem.jpg (Permission denied)
12-07 11:01:00.120 28478-28540/myoracle.com.quotes W/System.err:     at java.io.FileOutputStream.open(Native Method)
12-07 11:01:00.120 28478-28540/myoracle.com.quotes W/System.err:     at java.io.FileOutputStream.<init>(FileOutputStream.java:221)
12-07 11:01:00.120 28478-28540/myoracle.com.quotes W/System.err:     at java.io.FileOutputStream.<init>(FileOutputStream.java:108)
12-07 11:01:00.120 28478-28540/myoracle.com.quotes W/System.err:     at myoracle.com.quotes.WallpaperDeatilsActivity$ImageDownload.doInBackground(WallpaperDeatilsActivity.java:113)
12-07 11:01:00.120 28478-28540/myoracle.com.quotes W/System.err:     at myoracle.com.quotes.WallpaperDeatilsActivity$ImageDownload.doInBackground(WallpaperDeatilsActivity.java:91)

class ImageDownload extends AsyncTask<String, String, String> {

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

            String root = Environment.getExternalStorageDirectory().toString();

            System.out.println("Downloading");
            URL url = new URL(params[0]);

            URLConnection conection = url.openConnection();
            conection.connect();
            // getting file length
            int lenghtOfFile = conection.getContentLength();

            // input stream to read file - with 8k buffer
            InputStream input = new BufferedInputStream(url.openStream(), 8192);

            // Output stream to write file
            System.out.println(root);
            OutputStream output = new FileOutputStream(root+"/downloadedfilem.jpg");
            byte data[] = new byte[1024];
            long total = 0;
            while ((count = input.read(data)) != -1) {
                total += count;
                // writing data to file
                output.write(data, 0, count);
                System.out.println(count);
            }
            // flushing output
            output.flush();
            // closing streams
            output.close();
           input.close();

        } catch (Exception e) {
            e.printStackTrace();
        }

null

Android.permission.write_external_storage

Answer 1

您需要添加OSMarshmallow或以上版本的运行时权限。添加此代码是为了允许运行时操作在splash活动中，在onCreate中或在图像下载过程之前。

if (!checkPermission()) {
    openActivity();
} else {
    if (checkPermission()) {
        requestPermissionAndContinue();
    } else {
        openActivity();
    }
}

在oncreate外添加此方法

private static final int PERMISSION_REQUEST_CODE = 200;
private boolean checkPermission() {

        return ContextCompat.checkSelfPermission(this, WRITE_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED
                && ContextCompat.checkSelfPermission(this, READ_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED
                ;
    }

private void requestPermissionAndContinue() {
    if (ContextCompat.checkSelfPermission(this, WRITE_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED
            && ContextCompat.checkSelfPermission(this, READ_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED) {

        if (ActivityCompat.shouldShowRequestPermissionRationale(this, WRITE_EXTERNAL_STORAGE)
                && ActivityCompat.shouldShowRequestPermissionRationale(this, READ_EXTERNAL_STORAGE)) {
            AlertDialog.Builder alertBuilder = new AlertDialog.Builder(this);
            alertBuilder.setCancelable(true);
            alertBuilder.setTitle(getString(R.string.permission_necessary));
            alertBuilder.setMessage(R.string.storage_permission_is_encessary_to_wrote_event);
            alertBuilder.setPositiveButton(android.R.string.yes, new DialogInterface.OnClickListener() {
                @TargetApi(Build.VERSION_CODES.JELLY_BEAN)
                public void onClick(DialogInterface dialog, int which) {
                    ActivityCompat.requestPermissions(SplashActivity.this, new String[]{WRITE_EXTERNAL_STORAGE
                            , READ_EXTERNAL_STORAGE}, PERMISSION_REQUEST_CODE);
                }
            });
            AlertDialog alert = alertBuilder.create();
            alert.show();
            Log.e("", "permission denied, show dialog");
        } else {
            ActivityCompat.requestPermissions(SplashActivity.this, new String[]{WRITE_EXTERNAL_STORAGE,
                    READ_EXTERNAL_STORAGE}, PERMISSION_REQUEST_CODE);
        }
    } else {
        openActivity();
    }
}

@Override
public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {

    if (requestCode == PERMISSION_REQUEST_CODE) {
        if (permissions.length > 0 && grantResults.length > 0) {

            boolean flag = true;
            for (int i = 0; i < grantResults.length; i++) {
                if (grantResults[i] != PackageManager.PERMISSION_GRANTED) {
                    flag = false;
                }
            }
            if (flag) {
                openActivity();
            } else {
                finish();
            }

        } else {
            finish();
        }
    } else {
        super.onRequestPermissionsResult(requestCode, permissions, grantResults);
    }
}

private void openActivity() {
  //add your further process after giving permission or to download images from remote server.
}