File sdcard = Environment.getExternalStorageDirectory();
File f=new File(sdcard+"/dor");
f.mkdir();
this will create a folder named dor in your sdcard. then to fetch file for eg- filename.json which is manually inserted in dor folder. Like:
File file1 = new File(sdcard,"/dor/fitness.json");
.......
.....
< uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
and don't forget to add code in manifest