Datei auf eine Micro-SD-Card speichern

package de.abc.trytowriteonmicrosd;
import android.Manifest;
import android.content.pm.PackageManager;
import android.os.Environment;
import android.support.v4.app.ActivityCompat;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;




public class MainActivity extends AppCompatActivity {


    static final int REQUEST_EXTERNAL_STORAGE_RESULT = 2;
    String dasWirdDieNachricht = "Hallo";
    String filename = "Hi.txt";


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


        //Überprüfe ob Berechtigung vorhanden
        if (ActivityCompat.checkSelfPermission(this, Manifest.permission.WRITE_EXTERNAL_STORAGE) == PackageManager.PERMISSION_GRANTED){
            Log.i("MainActvity", "Permission grant save now!");
            //Datei speichern
            save();
        }
        else{
            Log.i("MainActvity", "No Permission, request it!");
            // Berechtigung abfragen
            requestPermissions(new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE},REQUEST_EXTERNAL_STORAGE_RESULT);
        }
    }


    @Override
    public void onRequestPermissionsResult(int requestCode, String permissions[], int[] grantResults) {
        //Überprüfen welcher Request/Berechtigung ankam
        switch (requestCode) {
            case REQUEST_EXTERNAL_STORAGE_RESULT: {
                if (grantResults.length > 0 && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
                    //Berechtigung bekommen, save aufrufen
                    Log.i("MainActvity", "Permission grant save now!");
                    save();
                } else {
                    //Berechtigung nicht bekommen
                    Log.i("MainActvity", "Failed to get Permission!");
                }
            }
        }
    }


    public void save() {
        Log.i("MainActvity", "Save called!");


        //Primären externe Pfad bekommen
        File root = Environment.getExternalStorageDirectory();
        //Alle externe Pfade bekommen
        File[] externalFilesDir = getExternalFilesDirs(null);
        for(File externalFileDir : externalFilesDir){
            Log.i("MainActvity", "File-Dir: " + externalFileDir.getAbsolutePath());
        }
        //Wenn SD Karte vorhanden, dann sd-karte setzen (statt dem primären)
        if(externalFilesDir.length > 1){
            root = externalFilesDir[1];
        }


        File writeFile = new File(root, filename);
        Log.i("MainActvity", "Save Path: " + writeFile.getAbsolutePath());


        //Überprüfe ob Datei schon existiert
        if(!writeFile.exists()) {
            //Schreibe Datei
            try {
                FileOutputStream fos = new FileOutputStream(writeFile);
                fos.write(dasWirdDieNachricht.getBytes());
                fos.close();
                Log.i("MainActvity", "File saved!");
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        else{
            Log.i("MainActvity", "File already exists!");
        }
    }
}