Anwerfor quesion This is how I finally solved the issue

Anwerfor quesion
This is how I finally solved the issue.
First call an intent to let the user grant write permission for whole SD card.
Intent intent = new Intent(Intent.ACTION_OPEN_DOCUMENT_TREE);
intent.addFlags(Intent.FLAG_GRANT_WRITE_URI_PERMISSION);
startActivityForResult(intent, 42);
Then on onActivityResult take write permission.
public void onActivityResult(int requestCode, int resultCode, Intent data) {
treeUri = data.getData();
final int takeFlags = data.getFlags()
& (Intent.FLAG_GRANT_READ_URI_PERMISSION
| Intent.FLAG_GRANT_WRITE_URI_PERMISSION);
getActivity().getContentResolver().takePersistableUriPermission(treeUri, takeFlags);
}
And this is the code I used to copy files to SD card.
public static boolean copy(File copy, String directory, Context con) {
static FileInputStream inStream = null;
static OutputStream outStream = null;
DocumentFile dir= getDocumentFileIfAllowedToWrite(new File(directory), con);
String mime = mime(copy.toURI().toString());
DocumentFile copy1= dir.createFile(mime, copy.getName());
try {
inStream = new FileInputStream(copy);
outStream =
con.getContentResolver().openOutputStream(copy1.getUri());
byte[] buffer = new byte[16384];
int bytesRead;
while ((bytesRead = inStream.read(buffer)) != -1) {
outStream.write(buffer, 0, bytesRead);


}
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally {
try {


inStream.close();


outStream.close();
return true;
} catch (IOException e) {
e.printStackTrace();
}
}
return false;
}
The above code uses the following two methods.
getDocumentFileIfAllowedToWrite method which returns DocumentFile if allowed to write.
public static DocumentFile getDocumentFileIfAllowedToWrite(File file, Context con) {
List permissionUris = con.getContentResolver().getPersistedUriPermissions();


for (UriPermission permissionUri : permissionUris) {
Uri treeUri = permissionUri.getUri();
DocumentFile rootDocFile = DocumentFile.fromTreeUri(con, treeUri);
String rootDocFilePath = FileUtil.getFullPathFromTreeUri(treeUri, con);


if (file.getAbsolutePath().startsWith(rootDocFilePath)) {


ArrayList pathInRootDocParts = new ArrayList();
while (!rootDocFilePath.equals(file.getAbsolutePath())) {
pathInRootDocParts.add(file.getName());
file = file.getParentFile();
}


DocumentFile docFile = null;


if (pathInRootDocParts.size() == 0) {
docFile = DocumentFile.fromTreeUri(con, rootDocFile.getUri());
} else {
for (int i = pathInRootDocParts.size() - 1; i >= 0; i--) {
if (docFile == null) {
docFile = rootDocFile.findFile(pathInRootDocParts.get(i));
} else {
docFile = docFile.findFile(pathInRootDocParts.get(i));
}
}
}
if (docFile != null && docFile.canWrite()) {
return docFile;
} else {
return null;
}


}
}
return null;
}
And mime method which returns the mime type of the file.
public static String mime(String URI) {
static String type;
String extention = MimeTypeMap.getFileExtensionFromUrl(URI);
if (extention != null) {
type = MimeTypeMap.getSingleton().getMimeTypeFromExtension(extention);
}
return type;
}
I have tested the above code with Android Lollipop and Marshmallow