Check if SD card storage is available

public static boolean hasStorage(boolean requireWriteAccess) {
String state = Environment.getExternalStorageState();

if (Environment.MEDIA_MOUNTED.equals(state)) {
return true;
} else if (!requireWriteAccess
&& Environment.MEDIA_MOUNTED_READ_ONLY.equals(state)) {
return true;
}
return false;
}

Reference:
Android: Check if SD card storage is available