code: public HashMap<String,Object> getKeys(T item) {
          HashMap<String,Object> keys = new HashMap<String,Object>();
  
          for( String key: caches.keySet() ) {
              keys.put(key, getValue(key, item));
          }
          return keys;
      }
docs: Provides the values for all of the unique identifiers managed by the cache.
  @param item the item whose key values are being sought
  @return a mapping of key names to item values