Thanks to everyone for their suggestions. This is what I have used finally:
(defn parse-date [date-str]
(when-not (blank? date-str)
(let [clean-date-str (trim date-str)
parse-or-nil
(fn [format]
(try
(.parse format clean-date-str)
(catch java.text.ParseException e nil)))]
(some parse-or-nil
[full-date-format date-format-wo-tz short-date-format-wo-tz]))))
Using some is better than using map because it will stop at the first
successful parsing.
Regards,
Abhinav
On Sat, Jul 31, 2010 at 3:05 AM, ataggart <[email protected]> wrote:
> Untested, but maybe this:
>
> (def- parse-date [date-str]
> (when-not (blank? date-str)
> (let [date-str (trim date-str)]
> (take 1
> (filter identity
> (map #(try (.parse % date-str) (catch ParseException e nil))
> [full-date-format date-format-wo-tz short-date-format-wo-
> tz]))))))
>
> WARNING: SimpleDateFormat is not thread-safe, so it's probably a bad
> idea to stick one in a shared context like def.
>
>
> On Jul 29, 10:35 pm, abhinav sarkar <[email protected]> wrote:
> > Hi,
> > I am just starting to learn Clojure by writing a small library. I came
> > across a situation in which I have to parse a String for getting a Date.
> Now
> > the string can be in one of the three formats. So I wrote this functions
> to
> > parse it:
> >
> > (def #^{:private true :tag SimpleDateFormat} full-date-format
> > (doto (SimpleDateFormat. "EEE, dd MMMM yyyy HH:mm:ss +0000")
> > (.setTimeZone (TimeZone/getTimeZone "GMT"))))
> >
> > (def #^{:private true :tag SimpleDateFormat} date-format-wo-tz
> > (doto (SimpleDateFormat. "EEE, dd MMMM yyyy HH:mm:ss")
> > (.setTimeZone (TimeZone/getTimeZone "GMT"))))
> >
> > (def #^{:private true :tag SimpleDateFormat} short-date-format-wo-tz
> > (doto (SimpleDateFormat. "dd MMM yyyy, HH:mm")
> > (.setTimeZone (TimeZone/getTimeZone "GMT"))))
> >
> > (defn- parse-date [date-str]
> > (if (some #(% date-str) [nil? blank?])
> > nil
> > (let [clean-date-str (trim date-str)]
> > (try
> > (.parse full-date-format clean-date-str)
> > (catch java.text.ParseException e
> > (try
> > (.parse date-format-wo-tz clean-date-str)
> > (catch java.text.ParseException e
> > (.parse short-date-format-wo-tz clean-date-str))))))))
> >
> > I can't help but think that there must be a better way to do the same
> > without so many nested try catch blocks. If this were Java, I could have
> > looped over all the date formats and used an explicit return in the try
> > block and continue in catch block. I don't understand how to do explicit
> > return in Clojure.
> >
> > Also as the number of formats grows, I'll have to add more nested try
> catch
> > blocks. Please suggest a cleaner way to do this.
> >
> > Regards,
> > Abhinav
>
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