Here’s my solution, which is guaranteed to work till Android 7.0 Nougat:
/* returns external storage paths (directory of external memory card) as array of Strings */
public String[] getExternalStorageDirectories() {
List<String> results = new ArrayList<>();
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.KITKAT) { //Method 1 for KitKat & above
File[] externalDirs = getExternalFilesDirs(null);
String internalRoot = Environment.getExternalStorageDirectory().getAbsolutePath().toLowerCase();
for (File file : externalDirs) {
if(file==null) //solved NPE on some Lollipop devices
continue;
String path = file.getPath().split("/Android")[0];
if(path.toLowerCase().startsWith(internalRoot))
continue;
boolean addPath = false;
if(Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
addPath = Environment.isExternalStorageRemovable(file);
}
else{
addPath = Environment.MEDIA_MOUNTED.equals(EnvironmentCompat.getStorageState(file));
}
if(addPath){
results.add(path);
}
}
}
if(results.isEmpty()) { //Method 2 for all versions
// better variation of: http://stackoverflow.com/a/40123073/5002496
String output = "";
try {
final Process process = new ProcessBuilder().command("mount | grep /dev/block/vold")
.redirectErrorStream(true).start();
process.waitFor();
final InputStream is = process.getInputStream();
final byte[] buffer = new byte[1024];
while (is.read(buffer) != -1) {
output = output + new String(buffer);
}
is.close();
} catch (final Exception e) {
e.printStackTrace();
}
if(!output.trim().isEmpty()) {
String devicePoints[] = output.split("\n");
for(String voldPoint: devicePoints) {
results.add(voldPoint.split(" ")[2]);
}
}
}
//Below few lines is to remove paths which may not be external memory card, like OTG (feel free to comment them out)
if(Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
for (int i = 0; i < results.size(); i++) {
if (!results.get(i).toLowerCase().matches(".*[0-9a-f]{4}[-][0-9a-f]{4}")) {
Log.d(LOG_TAG, results.get(i) + " might not be extSDcard");
results.remove(i--);
}
}
} else {
for (int i = 0; i < results.size(); i++) {
if (!results.get(i).toLowerCase().contains("ext") && !results.get(i).toLowerCase().contains("sdcard")) {
Log.d(LOG_TAG, results.get(i)+" might not be extSDcard");
results.remove(i--);
}
}
}
String[] storageDirectories = new String[results.size()];
for(int i=0; i<results.size(); ++i) storageDirectories[i] = results.get(i);
return storageDirectories;
}