@Override
    public void clear()
    {
        cache.invalidateAll();
    }
Removes all of the mappings from this map (optional operation).
The map will be empty after this call returns.

@throws UnsupportedOperationException if the <tt>clear</tt> operation
                                      is not supported by this map
xmppserver/src/main/java/org/jivesoftware/util/cache/CaffeineCache.java