public synchronized T get(String key) {
        try {
            key = URLEncoder.encode(key, "UTF-8");

            T obj = cache.getIfPresent(key);
            if (obj == null) {
                obj = persistentTable.get(key);
            }
            return obj;
        } catch (Exception e) {
            logger.error("Failed to get key from hashtable.", e);
            return null;
        }
    }
DEPRECATED: may cause OutOfMemoryError on large crawls.

@return
ache/src/main/java/achecrawler/util/persistence/PersistentHashtable.java