On Tuesday, 10 May 2016 10:11:58 UTC+1, Simon Brooke wrote: > > On Monday, 9 May 2016 16:55:59 UTC+1, Alex Miller wrote: >> >> Clojure is designed with enough extensibility to modify the printer and >> reader to cover this case. >> >> You can define a custom print strategy for these types by extending the >> print-dup multimethod. If you print it as a tagged literal, you can also >> define a custom reader that can read it back as the appropriate type. Or >> you can just happen to write it as a form that constructs a Java object if >> that's possible. (I don't know the Joda classes well.) >> >> Print methods typically look like this: >> >> (defmethod print-dup org.joda.time.DateTime >> [date-time ^java.io.Writer w] >> (.write w (format "#org.joda.time.DateTime[%d]"))) >> >> That particular format should produce a string like >> #org.joda.time.DateTime[1462809085214] which when read will call the >> DateTime constructor with the long value. >> >> Or you could write your own custom tagged literal format and define and >> install a reader for that tag that refers to a function that does whatever >> you need. >> >> And I would recommend never using Java serialization in either Clojure or >> Java. :) >> > > Fair enough, thanks. I looked for printer macros in the documentation but > didn't find them; I didn't think of multimethods. > > Thanks again. >
Right. I investigated the nippy library but it too needs work to read and write joda time objects, and I didn't have anything to go on (and I'm under time pressure) so I left it. Following Alex Miller's advice above and making use of an excellent blog at http://proofbyexample.com/print-and-read-in-clojure.html I solved the problem as follows: (ns opsdata.persistence "Serialising/deserialsing mixed Clojure/JodaTime data.") ;; I made use of the advice at http://proofbyexample.com/print-and-read-in-clojure.html ;; in writing this file. ;; Make it possible to print joda DateTime instances in re-readable form, for persistence. (defmethod print-dup org.joda.time.DateTime [dt out] (.write out (str "#=" `(org.joda.time.DateTime. ~(.getMillis dt) ~org.joda.time.DateTimeZone/UTC)))) ;; Make it possible to print joda Interval instances in re-readable form, for persistence. (defmethod print-dup org.joda.time.Interval [value out] (.write out (str "#=" `(org.joda.time.Interval. ~(.getStartMillis value) ~(.getEndMillis value) ~org.joda.time.DateTimeZone/UTC)))) ;; Make it possible to print joda DateTimeZone instances in re-readable form, for persistence. (defmethod print-dup org.joda.time.DateTimeZone [value out] (.write out (str "#=" `(org.joda.time.DateTimeZone/forID ~(.getID value))))) (defn persist-to-file "Persist this `value` in the file at this `file-path`." [value file-path] (binding [*print-dup* true] (spit file-path (with-out-str (pr value))))) (defn recover-from-file "Read a persisted value from this `file-path`." [file-path] (binding [*read-eval* true] (read-string (slurp file-path)))) -- You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en --- You received this message because you are subscribed to the Google Groups "Clojure" group. To unsubscribe from this group and stop receiving emails from it, send an email to clojure+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
