@Override
                        public void failed(final Exception ex) {
                            System.out.println(httpget1 + "->" + ex);
                        }
This is an example demonstrating how to control execution of cache
operation and determine its outcome using the async HTTP cache API.
httpclient5-cache/src/test/java/org/apache/hc/client5/http/cache/example/AsyncClientCacheControl.java