public synchronized Value get(String key) throws IOException {
    checkNotClosed();
    Entry entry = lruEntries.get(key);
    if (entry == null) {
      return null;
    }

    if (!entry.readable) {
      return null;
    }

    for (File file : entry.cleanFiles) {
        // A file must have been deleted manually!
        if (!file.exists()) {
            return null;
        }
    }

    redundantOpCount++;
    journalWriter.append(READ);
    journalWriter.append(' ');
    journalWriter.append(key);
    journalWriter.append('\n');
    if (journalRebuildRequired()) {
      executorService.submit(cleanupCallable);
    }

    return new Value(key, entry.sequenceNumber, entry.cleanFiles, entry.lengths);
  }
Returns a snapshot of the entry named {@code key}, or null if it doesn't
exist is not currently readable. If a value is returned, it is moved to
the head of the LRU queue.
core/src/main/java/com/bumptech/glide/disklrucache/DiskLruCache.java