code: public String getReverseDNSCacheType() {
          String value = System.getProperty(REVERSE_DNS_CACHETYPE);
          if (value != null) {
              return value;
          }
          return getProperty(REVERSE_DNS_CACHETYPE, THREADED_CACHE);
      }
docs: Returns the reverse DNS cache type.
  Defaults to a threaded chache.
  
  @return the type of cache for reverse DNS requests