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Clojure JSON and JSON SMILE (binary json format) encoding/decoding

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'Cheshire Puss,' she began, rather timidly, as she did not at all know whether it would like the name: however, it only grinned a little wider. 'Come, it's pleased so far,' thought Alice, and she went on. 'Would you tell me, please, which way I ought to go from here?'

'That depends a good deal on where you want to get to,' said the Cat.

'I don't much care where--' said Alice.

'Then it doesn't matter which way you go,' said the Cat.

'--so long as I get SOMEWHERE,' Alice added as an explanation.

'Oh, you're sure to do that,' said the Cat, 'if you only walk long enough.'

Cheshire is fast JSON encoding, based off of clj-json and clojure-json, with additional features like Date/UUID/Set/Symbol encoding and SMILE support.

Clojure code with docs


clojure-json had really nice features (custom encoders), but was slow; clj-json had almost no features, but was very fast. I wanted the best of both worlds.


[cheshire "1.1.2"]


;; generate some json
(generate-string {:foo "bar" :baz 5})

;; write some json to a stream
(generate-stream ( "/tmp/foo") {:foo "bar" :baz 5})

;; generate some SMILE
(generate-smile {:foo "bar" :baz 5})

;; generate some JSON with Dates
;; the Date will be encoded as a string using
;; the default date format: yyyy-MM-dd'T'HH:mm:ss'Z'
(generate-string {:foo "bar" :baz (Date. 0)})

;; generate some JSON with Dates with custom Date encoding
(generate-string {:baz (Date. 0)} "yyyy-MM-dd")


;; parse some json
(parse-string "{\"foo\":\"bar\"}")
;; => {"foo" "bar"}

;; parse some json and get keywords back
(parse-string "{\"foo\":\"bar\"}" true)
;; => {:foo "bar"}

;; parse some SMILE (keywords option also supported)
(parse-smile <your-byte-array>)

;; parse a stream (keywords option also supported)
(parse-stream ( "/tmp/foo"))

;; parse a stream lazily (keywords option also supported)
(parsed-seq ( "/tmp/foo"))

;; parse a SMILE stream lazily (keywords option also supported)
(parsed-smile-seq ( "/tmp/foo"))

There are also a few aliases for commonly used functions:

encode -> generate-string
encode-stream -> generate-stream
encode-smile -> generate-smile
decode -> parse-string
decode-stream -> parse-stream
decode-smile -> parse-smile


Cheshire supports encoding standard clojure datastructures, but with a few addons. Right now it does not support custom encoders, but a few helpers were added to support commonly encoded classes.

Cheshire encoding supports:

Clojure data structures

  • strings
  • lists
  • vectors
  • sets (clj-json does not yet support sets)
  • maps
  • symbols (clj-json does not yet support symbols)
  • booleans
  • numbers (Integer, Long, BigInt, Double, Float)

Java classes

  • Date
  • UUID

Also supports

Work is underway to have custom object encoders while still being fast.


Clojure version:  1.2.1
Num roundtrips:   100000

Trail:  1
clj-json                               2.16
clj-json w/ keywords                   2.43
clj-serializer                         2.13
cheshire                               2.19
cheshire-smile                         2.20
cheshire w/ keywords                   2.12
clojure printer/reader                 7.16
clojure printer/reader w/ print-dup    12.29
clojure-json                           20.55

Trail:  2
clj-json                               1.23
clj-json w/ keywords                   2.17
clj-serializer                         1.58
cheshire                               1.49
cheshire-smile                         1.49
cheshire w/ keywords                   1.99
clojure printer/reader                 5.97
clojure printer/reader w/ print-dup    11.17
clojure-json                           20.42

Cheshire is right up there with clj-json.

Future Ideas/TODOs

  • move away from using Java entirely, use Protocols for the encoder
  • allow custom encoders (this should be doable once switched over to protocols)


Release under the MIT license. See LICENSE for the full license.


Thanks go to Mark McGranaghan for allowing me to copy the clj-json code to get started on this and Jim Duey for the name. :)

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