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;;; json/write.clj: JavaScript Object Notation (JSON) generator
;; by Stuart Sierra, http://stuartsierra.com/
;; January 26, 2009
;; Copyright (c) Stuart Sierra, 2009. All rights reserved. The use
;; and distribution terms for this software are covered by the Eclipse
;; Public License 1.0 (http://opensource.org/licenses/eclipse-1.0.php)
;; which can be found in the file epl-v10.html at the root of this
;; distribution. By using this software in any fashion, you are
;; agreeing to be bound by the terms of this license. You must not
;; remove this notice, or any other, from this software.
(ns
#^{:author "Stuart Sierra",
:doc "JavaScript Object Notation (JSON) generator.
This is a low-level implementation of JSON. It only supports basic
types, arrays, Collections, and Maps.
You can extend the library to handle new types by adding methods to
the print-json multimethod.
This library does NOT attempt to preserve round-trip equality between
JSON and Clojure data types. That is, if you write a JSON string with
this library, then read it back with clojure.contrib.json.read, you
won't necessarily get the exact same data structure.
If you want round-trip equality and/or indented output, try Dan
Larkin's clojure-json library at
http://github.com/danlarkin/clojure-json
This implementation attempts to follow the description of JSON at
<http://json.org/>. Maps become JSON objects, all other collections
become JSON arrays. JSON object keys are always converted to strings.
Within strings, all non-ASCII characters are hexadecimal escaped.
",
:see-also [["http://json.org/", "JSON Home Page"]]}
clojure.contrib.json.write
(:require [clojure.contrib.java-utils :as j])
(:use [clojure.contrib.test-is :only (deftest- is)]))
(defmulti
#^{:doc "Prints Clojure data types as JSON. Nil becomes JSON null.
Keywords become strings, without the leading colon. Maps become
JSON objects, all other collection types become JSON arrays.
Strings and numbers print as with pr."
:arglists '([x])}
print-json (fn [x] (cond
(nil? x) nil ;; prevent NullPointerException on next line
(.isArray (class x)) ::array
:else (type x))))
;; Primitive types can be printed with Clojure's pr function.
(derive java.lang.Boolean ::pr)
(derive java.lang.Byte ::pr)
(derive java.lang.Short ::pr)
(derive java.lang.Integer ::pr)
(derive java.lang.Long ::pr)
(derive java.lang.Float ::pr)
(derive java.lang.Double ::pr)
;; Collection types can be printed as JSON objects or arrays.
(derive java.util.Map ::object)
(derive java.util.Collection ::array)
;; Symbols and keywords are converted to strings.
(derive clojure.lang.Symbol ::symbol)
(derive clojure.lang.Keyword ::symbol)
(defmethod print-json ::pr [x] (pr x))
(defmethod print-json nil [x] (print "null"))
(defmethod print-json ::symbol [x] (pr (name x)))
(defmethod print-json ::array [s]
(print "[")
(loop [x s]
(when-let [fst (first x)]
(print-json fst)
(when-let [nxt (next x)]
(print ",")
(recur nxt))))
(print "]"))
(defmethod print-json ::object [m]
(print "{")
(loop [x m]
(when (first x)
(let [[k v] (first x)]
(print-json (j/as-str k))
(print ":")
(print-json v))
(when (next x)
(print ",")
(recur (next x)))))
(print "}"))
(defmethod print-json java.lang.CharSequence [s]
(print \")
(dotimes [i (count s)]
(let [cp (Character/codePointAt s i)]
(cond
;; Handle printable JSON escapes before ASCII
(= cp 34) (print "\\\"")
(= cp 92) (print "\\\\")
(= cp 47) (print "\\/")
;; Print simple ASCII characters
(< 31 cp 127) (print (.charAt s i))
;; Handle non-printable JSON escapes
(= cp 8) (print "\\b")
(= cp 12) (print "\\f")
(= cp 10) (print "\\n")
(= cp 13) (print "\\r")
(= cp 9) (print "\\t")
;; Any other character is printed as Hexadecimal escape
:else (printf "\\u%04x" cp))))
(print \"))
(defn json-str
"Converts Clojure data structures to a JSON-formatted string."
[x]
(with-out-str (print-json x)))
;;; TESTS
;; Run these tests with
;; (clojure.contrib.test-is/run-tests 'clojure.contrib.print-json)
;; Bind clojure.contrib.test-is/*load-tests* to false to omit these
;; tests from production code.
(deftest- can-print-json-strings
(is (= "\"Hello, World!\"" (json-str "Hello, World!")))
(is (= "\"\\\"Embedded\\\" Quotes\"" (json-str "\"Embedded\" Quotes"))))
(deftest- can-print-unicode
(is (= "\"\\u1234\\u4567\"" (json-str "\u1234\u4567"))))
(deftest- can-print-json-null
(is (= "null" (json-str nil))))
(deftest- can-print-json-arrays
(is (= "[1,2,3]" (json-str [1 2 3])))
(is (= "[1,2,3]" (json-str (list 1 2 3))))
(is (= "[1,2,3]" (json-str (sorted-set 1 2 3))))
(is (= "[1,2,3]" (json-str (seq [1 2 3])))))
(deftest- can-print-java-arrays
(is (= "[1,2,3]" (json-str (into-array [1 2 3])))))
(deftest- can-print-empty-arrays
(is (= "[]" (json-str [])))
(is (= "[]" (json-str (list))))
(is (= "[]" (json-str #{}))))
(deftest- can-print-json-objects
(is (= "{\"a\":1,\"b\":2}" (json-str (sorted-map :a 1 :b 2)))))
(deftest- object-keys-must-be-strings
(is (= "{\"1\":1,\"2\":2") (json-str (sorted-map 1 1 2 2))))
(deftest- can-print-empty-objects
(is (= "{}" (json-str {}))))
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