code: private boolean isCacheValid()
    {
      long now = CurrentTime.currentTime();
  
      if ((now - _lastTime < 100) && ! CurrentTime.isTest())
        return true;
  
      long oldLastModified = _lastModified;
      long oldLength = _length;
      
      long newLastModified = getBacking().getLastModified();
      long newLength = getBacking().length();
      
      _lastTime = now;
  
      if (newLastModified == oldLastModified && newLength == oldLength) {
        _lastTime = now;
        return true;
      }
      else {
        _changeSequence.incrementAndGet();
        
        // If the file has changed, close the old file
        clearCache();
        
        _zipEntryCache.clear();
        
        _lastModified = newLastModified;
        _length = newLength;
        
        _lastTime = now;
  
        return false;
      }
    }
docs: Returns the last modified time for the path.
  
  
  @return the last modified time of the jar in milliseconds.