Writing clojure maps/arrays to a file and reading them back

Question

I need to save clojure maps to a file and read them back later to process them.

This is what I could come up with. Is there a better way to accomplish the same thing?

Answer 1

It is easiest to read a single form to and from the file, so I usually put my data into a vector. I also prefer to use pr or pr-str rather than print because it is guaranteed to produce readable data,

(def my-data [{:a "foo" :b [1 2 3]} "asdf" 42 #{1 2 3}]) 
(spit "/tmp/data.edn" (with-out-str (pr my-data)))
nil
(read-string (slurp "/tmp/data.edn"))
[{:a "foo", :b [1 2 3]} "asdf" 42 #{1 2 3}] 

vs:

(spit "/tmp/data.edn" (with-out-str (print my-data)))
(read-string (slurp "/tmp/data.edn"))
[{:a foo, :b [1 2 3]} asdf 42 #{1 2 3}] 

notice how the string `"asdf" was read back as a symbol.

.toString also works fine:

(spit "/tmp/data.edn" (.toString my-data)) 
(read-string (slurp "/tmp/data.edn"))
[{:a "foo", :b [1 2 3]} "asdf" 42 #{1 2 3}]