getStorageDirectories.java

 public static String[] getStorageDirectories() {
          final Pattern DIR_SEPARATOR = Pattern.compile("/");

        // Final set of paths
        final Set<String> rv = new HashSet<String>();
        // Primary physical SD-CARD (not emulated)
        final String rawExternalStorage = System.getenv("EXTERNAL_STORAGE");
        // All Secondary SD-CARDs (all exclude primary) separated by ":"
        final String rawSecondaryStoragesStr = System.getenv("SECONDARY_STORAGE");
        // Primary emulated SD-CARD
        final String rawEmulatedStorageTarget = System.getenv("EMULATED_STORAGE_TARGET");
        if (TextUtils.isEmpty(rawEmulatedStorageTarget)) {
            // Device has physical external storage; use plain paths.
            if (TextUtils.isEmpty(rawExternalStorage)) {
                // EXTERNAL_STORAGE undefined; falling back to default.
                rv.add("/storage/sdcard0");
            } else {
                rv.add(rawExternalStorage);
            }
        } else {
            // Device has emulated storage; external storage paths should have
            // userId burned into them.
            final String rawUserId;
            if (Build.VERSION.SDK_INT < Build.VERSION_CODES.JELLY_BEAN_MR1) {
                rawUserId = "";
            } else {
                final String path = Environment.getExternalStorageDirectory().getAbsolutePath();
                final String[] folders = DIR_SEPARATOR.split(path);
                final String lastFolder = folders[folders.length - 1];
                boolean isDigit = false;
                try {
                    Integer.valueOf(lastFolder);
                    isDigit = true;
                } catch (NumberFormatException ignored) {
                }
                rawUserId = isDigit ? lastFolder : "";
            }
            // /storage/emulated/0[1,2,...]
            if (TextUtils.isEmpty(rawUserId)) {
                rv.add(rawEmulatedStorageTarget);
            } else {
                rv.add(rawEmulatedStorageTarget + File.separator + rawUserId);
            }
        }
        // Add all secondary storages
        if (!TextUtils.isEmpty(rawSecondaryStoragesStr)) {
            // All Secondary SD-CARDs splited into array
            final String[] rawSecondaryStorages = rawSecondaryStoragesStr.split(File.pathSeparator);
            Collections.addAll(rv, rawSecondaryStorages);
        }
        return rv.toArray(new String[0]);
    }