code = 7qqChen
$ redis-cli EXISTS url:7qqChen            # before the first redirect
0
--- after 1st redirect (cache miss, database read, cache filled)
$ redis-cli GET url:7qqChen
https://example.com/cache-demo
$ redis-cli TTL url:7qqChen
3600
cache hits +0, misses +1
--- after 9 more redirects
cache hits +9, misses +1
$ redis-cli GET clicks:7qqChen
10
$ curl -s http://127.0.0.1:8080/api/v1/urls/7qqChen/stats
{"code":"7qqChen","longUrl":"https://example.com/cache-demo","clicks":10,...