public static DiskLruCache open(File directory, int appVersion, int valueCount, long maxSize)
      throws IOException {
    if (maxSize <= 0) {
      throw new IllegalArgumentException("maxSize <= 0");
    }
    if (valueCount <= 0) {
      throw new IllegalArgumentException("valueCount <= 0");
    }

    // If a bkp file exists, use it instead.
    File backupFile = new File(directory, JOURNAL_FILE_BACKUP);
    if (backupFile.exists()) {
      File journalFile = new File(directory, JOURNAL_FILE);
      // If journal file also exists just delete backup file.
      if (journalFile.exists()) {
        backupFile.delete();
      } else {
        renameTo(backupFile, journalFile, false);
      }
    }

    // Prefer to pick up where we left off.
    DiskLruCache cache = new DiskLruCache(directory, appVersion, valueCount, maxSize);
    if (cache.journalFile.exists()) {
      try {
        cache.readJournal();
        cache.processJournal();
        return cache;
      } catch (IOException journalIsCorrupt) {
        System.out
            .println("DiskLruCache "
                + directory
                + " is corrupt: "
                + journalIsCorrupt.getMessage()
                + ", removing");
        cache.delete();
      }
    }

    // Create a new empty cache.
    directory.mkdirs();
    cache = new DiskLruCache(directory, appVersion, valueCount, maxSize);
    cache.rebuildJournal();
    return cache;
  }
@Test public void constructorDoesNotAllowZeroValuesPerEntry() throws Exception {
    try {
      DiskLruCache.open(cacheDir, appVersion, 0, 10);
      Assert.fail();
    } catch (IllegalArgumentException expected) {
    }
  }