code: protected boolean isCacheValid(final Long lastModified) {
          return (lastModified != null && lastModified <= this.lastModifiedTime) ||
                  (lastModified == null && (this.lastModifiedTime + this.noLastModifiedReloadPeriod) <= System.currentTimeMillis());
      }
docs: Determines if the cached unmarshalled object is still valid
  
  @param lastModified last modified timestamp of the resource, null if not known.
  @return true if the cached object should be used