play_with_clojure.clj

(import '(java.util Date Calendar)
        '(java.text SimpleDateFormat))

(defn yesterday-start-as-string []
  "Returns the beginning of yesterday as a formatted string.
   For example 2015-12-21 00:00:00 - hours, minutes and seconds are
   always zeros."
  (let [dt (.getTime (doto (Calendar/getInstance)
                       (.setTime (Date.))
                       (.set Calendar/HOUR_OF_DAY 0)
                       (.set Calendar/MINUTE 0)
                       (.set Calendar/SECOND 0)
                       (.set Calendar/MILLISECOND 0)
                       (.set Calendar/DAY_OF_MONTH -1)))
        ft (SimpleDateFormat. "yyyy-MM-dd HH:mm:ss")]
    (.format ft dt)))