How to check and request read, write permission for sd card in platform >= 23 of Android

Question

I have the following code to request read,write permission for external(shared) storage known as emulated. Now I also want to read and write to SD Card. But i am getting the error "permission denied" in logs.

//We are calling this method to check the read permission status
public boolean isReadWriteStorageAllowed() {
    //Getting the permission status
    int resultRead   = ContextCompat.checkSelfPermission(this, Manifest.permission.READ_EXTERNAL_STORAGE);
    int resultWrite  = ContextCompat.checkSelfPermission(this, Manifest.permission.WRITE_EXTERNAL_STORAGE);

    //If permission is granted returning true
    if (resultRead == PackageManager.PERMISSION_GRANTED && resultWrite == PackageManager.PERMISSION_GRANTED)
        return true;

    //If permission is not granted returning false
    return false;
}

public void requestStoragePermission(int code){

    if (ActivityCompat.shouldShowRequestPermissionRationale(this, Manifest.permission.WRITE_EXTERNAL_STORAGE)) {
    }
    ActivityCompat.requestPermissions(this, new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE}, code);
}

The logs for the error are as below

    10-12 14:23:03.998 8550-8550/com.free W/System.err: java.io.FileNotFoundException: /storage/8E14-3919/database.db (Permission denied)
10-12 14:23:03.998 8550-8550/com.free W/System.err:     at java.io.FileOutputStream.open(Native Method)
10-12 14:23:03.998 8550-8550/com.free W/System.err:     at java.io.FileOutputStream.<init>(FileOutputStream.java:221)
10-12 14:23:03.998 8550-8550/com. free W/System.err:     at java.io.FileOutputStream.<init>(FileOutputStream.java:108)
10-12 14:23:03.998 8550-8550/com.free W/System.err:     at com. DatabaseManage.exportDatabase(DatabaseManage.java:140)
10-12 14:23:03.998 8550-8550/com.free W/System.err:     at com. DatabaseManage.access$000(DatabaseManage.java:50)
10-12 14:23:03.998 8550-8550/com.free W/System.err:     at com. DatabaseManage$1.onClick(DatabaseManage.java:106)
10-12 14:23:03.999 8550-8550/com.free W/System.err:     at com.android.internal.app.AlertController$AlertParams$3.onItemClick(AlertController.java:1244)
10-12 14:23:03.999 8550-8550/com.free W/System.err:     at android.widget.AdapterView.performItemClick(AdapterView.java:339)
10-12 14:23:03.999 8550-8550/com.free W/System.err:     at android.widget.AbsListView.performItemClick(AbsListView.java:1695)
10-12 14:23:03.999 8550-8550/com.free W/System.err:     at android.widget.AbsListView$PerformClick.run(AbsListView.java:4171)
10-12 14:23:03.999 8550-8550/com.free W/System.err:     at android.widget.AbsListView$13.run(AbsListView.java:6772)
10-12 14:23:03.999 8550-8550/com.free W/System.err:     at android.os.Handler.handleCallback(Handler.java:751)
10-12 14:23:03.999 8550-8550/com.free W/System.err:     at android.os.Handler.dispatchMessage(Handler.java:95)
10-12 14:23:03.999 8550-8550/com.free W/System.err:     at android.os.Looper.loop(Looper.java:154)
10-12 14:23:03.999 8550-8550/com.free W/System.err:     at android.app.ActivityThread.main(ActivityThread.java:6692)
10-12 14:23:03.999 8550-8550/com.free W/System.err:     at java.lang.reflect.Method.invoke(Native Method)
10-12 14:23:03.999 8550-8550/com.free W/System.err:     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1468)
10-12 14:23:03.999 8550-8550/com.free W/System.err:     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1358)

My question is 'if asking the storage permissions for external storage' will also grant the permissions for 'sd card'? If not then whats wrong in my code or what am i missing? I need a solution!

The code is as under

public void exportDB(){
    int size, pathSize = 0;
    String[] storageLocations = null;

    final File dbFile = context.getDatabasePath(DATABASE_NAME);//existing database file path

    File device = Environment.getExternalStorageDirectory();//device storage
    String[] sdCard = getExternalStorageDirectories();//sd cards

    size = sdCard.length;

    if(size == 0)
        pathSize = 0;
    else if(size > 0)
        pathSize = size + 1;

    pathForExports   = new String[pathSize];
    storageLocations = new String[pathSize];

    if(sdCard.length == 0){
        pathForExports[0]   = device.getAbsolutePath() + "/" + DATABASE_NAME;
        storageLocations[0] = "1) Device Storage";
    }
    else if(sdCard.length > 0) {
        pathForExports[0] = device.getAbsolutePath() + "/" + DATABASE_NAME;
        storageLocations[0] = "1) Device Storage";

        for (int i=0;i<sdCard.length; i++) {
            File file = new File(sdCard[i]);
            pathForExports[i+1] = file.getAbsolutePath() + "/" + DATABASE_NAME;
            if(sdCard.length > 1) {
                storageLocations[i+1] = (i+2) + ") Sd Card - " + (i+1);
            }
            else
                storageLocations[i+1] = (i+2) + ") Sd Card";
        }
    }
    //File file = new File(Environment.getExternalStorageDirectory() + File.separator + SAMPLE_DB_NAME);

    AlertDialog.Builder builder = new AlertDialog.Builder(context);
    builder.setTitle("Choose Export Location");
    builder.setItems(pathForExports, new DialogInterface.OnClickListener() {
        @Override
        public void onClick(DialogInterface dialog, int which) {
            exportDatabase(dbFile, which);
        }
    });
    AlertDialog alertDialog = builder.create();
    alertDialog.show();
}

private void exportDatabase(File dbFile, int whichButton) {

    FileChannel source = null;
    FileChannel destination = null;

    try {
        source = new FileInputStream(dbFile).getChannel();
        destination = new FileOutputStream(pathForExports[whichButton]).getChannel();
        destination.transferFrom(source, 0, source.size());
        source.close();
        destination.close();

        if(whichButton == 0)
            alert("Database is exported to device storage");
        else
            alert("Database is exported to sd Card");
    } catch(IOException e) {
        e.printStackTrace();
        if(whichButton == 0)
            alert("Failed to export database to device storage");
        else
            alert("Failed to export database to sd card");
    }
}

Answer 1

    /storage/8E14-3919/database.db .

Even if you have all the permissions for external storage then still you will not be able to write on the micro SD card on that place.

You can only write in the app specific directory on the card.

To find that path use getExternalFilesDirs(). If you are lucky it is one of the entries returned.

For you the path would look like

 /storage/8E14-3919/Android/data/<packagename>/files

Have a look with a file explorer app. It is probably already there.

If you want to write everywhere on the card use the storage access framework.