ExternalStorage.java

package com.frogsparks.mytrails.util;

import android.os.Environment;
import com.frogsparks.mytrails.MyTrails;

import java.io.File;
import java.util.*;

// http://stackoverflow.com/a/15612964/304876

public class ExternalStorage {
	public static final String TAG = "ExternalStorage: ";

	public static final String SD_CARD = "sdCard";
	public static final String EXTERNAL_SD_CARD = "externalSdCard";

	/**
	 * @return True if the external storage is available. False otherwise.
	 */
	public static boolean isAvailable() {
		String state = Environment.getExternalStorageState();
		if (Environment.MEDIA_MOUNTED.equals(state) || Environment.MEDIA_MOUNTED_READ_ONLY.equals(state)) {
			return true;
		}
		return false;
	}

	public static String getSdCardPath() {
		return Environment.getExternalStorageDirectory().getPath() + "/";
	}

	/**
	 * @return True if the external storage is writable. False otherwise.
	 */
	public static boolean isWritable() {
		String state = Environment.getExternalStorageState();
		if (Environment.MEDIA_MOUNTED.equals(state)) {
			return true;
		}
		return false;

	}

	/**
	 * @return A map of all storage locations available
	 */
	public static Map<String, File> getAllStorageLocations() {
		Map<String, File> map = new HashMap<String, File>(10);

		List<String> mMounts = new ArrayList<String>(10);
		List<String> mVold = new ArrayList<String>(10);
		mMounts.add("/mnt/sdcard");
		mVold.add("/mnt/sdcard");

		try {
			File mountFile = new File("/proc/mounts");
			if (mountFile.exists()) {
				Scanner scanner = new Scanner(mountFile);
				while (scanner.hasNext()) {
					String line = scanner.nextLine();

					Log1.d(MyTrails.APPTAG, TAG + "getAllStorageLocations /proc/mounts " + line);

					if (line.startsWith("/dev/block/vold/")) {
						String[] lineElements = line.split(" ");
						String element = lineElements[1];

						// don't add the default mount path
						// it's already in the list.
						if (!element.equals("/mnt/sdcard"))
							mMounts.add(element);
					}
				}
			} else {
				Log1.d(MyTrails.APPTAG, TAG + "getAllStorageLocations no /proc/mounts");
			}
		} catch (Exception e) {
			Log1.e(MyTrails.APPTAG, TAG + "getAllStorageLocations", e);
		}

		boolean voldExists;
		try {
			File voldFile = new File("/system/etc/vold.fstab");
			if (voldFile.exists()) {
				voldExists = true;
				Scanner scanner = new Scanner(voldFile);
				while (scanner.hasNext()) {
					String line = scanner.nextLine();

					Log1.d(MyTrails.APPTAG, TAG + "getAllStorageLocations vold.fstab " + line);

					if (line.startsWith("dev_mount")) {
						String[] lineElements = line.split(" ");
						String element = lineElements[2];

						if (element.contains(":"))
							element = element.substring(0, element.indexOf(":"));
						if (!element.equals("/mnt/sdcard"))
							mVold.add(element);
					}
				}
			} else {
				voldExists = false;
				Log1.d(MyTrails.APPTAG, TAG + "getAllStorageLocations no /system/etc/vold.fstab");
			}
		} catch (Exception e) {
			voldExists = false;
			Log1.e(MyTrails.APPTAG, TAG + "getAllStorageLocations", e);
		}

		if (voldExists) {
			for (int i = 0; i < mMounts.size(); i++) {
				String mount = mMounts.get(i);
				if (!mVold.contains(mount))
					mMounts.remove(i--);
			}
			mVold.clear();
		}

		List<String> mountHash = new ArrayList<String>(10);

		for (String mount : mMounts) {
			File root = new File(mount);
			if (root.exists() && root.isDirectory() && root.canWrite()) {
				File[] list = root.listFiles();
				String hash = "[";
				if (list != null) {
					for (File f : list) {
						hash += f.getName().hashCode() + ":" + f.length() + ", ";
					}
				}
				hash += "]";
				if (!mountHash.contains(hash)) {
					String key = SD_CARD + "_" + map.size();
					if (map.size() == 0) {
						key = SD_CARD;
					} else if (map.size() == 1) {
						key = EXTERNAL_SD_CARD;
					}
					mountHash.add(hash);
					map.put(key, root);
				}
			}
		}

		mMounts.clear();

		if (map.isEmpty()) {
			map.put(SD_CARD, Environment.getExternalStorageDirectory());
		}

		Log1.d(MyTrails.APPTAG, TAG + "getAllStorageLocations " + map);

		return map;
	}
}

I tried your method, but in my platform, the path could be /mnt/media_rw/udisk/sda4 or /storage/udisk/sda4.But the question is when I use this /mnt/media_rw/udisk/sda4, the root.exists() return false, but when I use /storage/udisk/sda4, root return true.

Here is my /proc/mounts:

rootfs / rootfs ro,relatime 0 0
devtmpfs /dev devtmpfs rw,seclabel,relatime,size=111156k,nr_inodes=22811,mode=755 0 0
tmpfs /dev tmpfs rw,seclabel,nosuid,relatime,mode=755 0 0
devpts /dev/pts devpts rw,seclabel,relatime,mode=600,ptmxmode=000 0 0
proc /proc proc rw,relatime 0 0
sysfs /sys sysfs rw,seclabel,relatime 0 0
selinuxfs /sys/fs/selinux selinuxfs rw,relatime 0 0
debugfs /sys/kernel/debug debugfs rw,relatime 0 0
none /mnt/media_rw tmpfs rw,seclabel,relatime,mode=700,uid=1023,gid=1023 0 0
none /storage tmpfs rw,seclabel,relatime,mode=751,uid=1028,gid=1028 0 0
tmpfs /mnt/secure tmpfs rw,seclabel,relatime,mode=700 0 0
tmpfs /tmp tmpfs rw,seclabel,relatime,size=20480k,mode=771 0 0
tmpfs /mnt/asec tmpfs rw,seclabel,relatime,mode=755,gid=1000 0 0
tmpfs /mnt/obb tmpfs rw,seclabel,relatime,mode=755,gid=1000 0 0
/dev/block/mmcblk0p1 /system ext4 rw,seclabel,relatime,data=ordered 0 0
/dev/block/mmcblk0p2 /data ext4 rw,seclabel,nosuid,nodev,noatime,nomblk_io_submit,errors=panic,data=ordered 0 0
/dev/block/mmcblk0p3 /cache ext4 rw,seclabel,nosuid,nodev,noatime,nomblk_io_submit,errors=panic,data=ordered 0 0
/dev/fuse /mnt/shell/emulated fuse rw,nosuid,nodev,relatime,user_id=1023,group_id=1023,default_permissions,allow_other 0 0
/dev/block/vold/8:4 /mnt/media_rw/udisk/sda4 vfat rw,dirsync,nosuid,nodev,noexec,relatime,uid=1023,gid=1023,fmask=0007,dmask=0007,allow_utime=0020,codepage=cp437,iocharset=iso8859-1,shortname=mixed,usefree,utf8,errors=remount-ro 0 0
/dev/fuse /storage/udisk/sda4 fuse rw,nosuid,nodev,relatime,user_id=1023,group_id=1023,default_permissions,allow_other 0 0

Why did you use /dev/block/vold instead of /dev/fuse in your code?