JSON parsing and printing



Parsing and printing JSON in pure Julia.

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Installation: julia> Pkg.add("JSON")

Basic Usage

import JSON

# JSON.parse - string or stream to Julia data structures
s = "{\"a_number\" : 5.0, \"an_array\" : [\"string\", 9]}"
j = JSON.parse(s)
#  Dict{AbstractString,Any} with 2 entries:
#    "an_array" => {"string",9}
#    "a_number" => 5.0

# JSON.json - Julia data structures to a string
#  "[2,3]"
#  "{\"an_array\":[\"string\",9],\"a_number\":5.0}"


JSON.print(io::IO, s::AbstractString)
JSON.print(io::IO, s::Union{Integer, AbstractFloat})
JSON.print(io::IO, n::Nothing)
JSON.print(io::IO, b::Bool)
JSON.print(io::IO, a::AbstractDict)
JSON.print(io::IO, v::AbstractVector)
JSON.print{T, N}(io::IO, v::Array{T, N})

Writes a compact (no extra whitespace or indentation) JSON representation to the supplied IO.

JSON.print(a::AbstractDict, indent)
JSON.print(io::IO, a::AbstractDict, indent)

Writes a JSON representation with newlines, and indentation if specified. Non-zero indent will be applied recursively to nested elements.


Returns a compact JSON representation as an AbstractString.

JSON.parse(s::AbstractString; dicttype=Dict, inttype=Int64)
JSON.parse(io::IO; dicttype=Dict, inttype=Int64)
JSON.parsefile(filename::AbstractString; dicttype=Dict, inttype=Int64, use_mmap=true)

Parses a JSON AbstractString or IO stream into a nested Array or Dict.

The dicttype indicates the dictionary type (<: Associative), or a function that returns an instance of a dictionary type, that JSON objects are parsed to. It defaults to Dict (the built-in Julia dictionary), but a different type can be passed for additional functionality. For example, if you import DataStructures (assuming the DataStructures package is installed)

  • you can pass dicttype=DataStructures.OrderedDict to maintain the insertion order of the items in the object;
  • or you can pass ()->DefaultDict{String,Any}(Missing) to having any non-found keys return missing when you index the result.

The inttype argument controls how integers are parsed. If a number in a JSON file is recognized to be an integer, it is parsed as one; otherwise it is parsed as a Float64. The inttype defaults to Int64, but, for example, if you know that your integer numbers are all small and want to save space, you can pass inttype=Int32. Alternatively, if your JSON input has integers which are too large for Int64, you can pass inttype=Int128 or inttype=BigInt. inttype can be any subtype of Real.


A wrapper around a Julia string representing JSON-formatted text, which is inserted as-is in the JSON output of JSON.print and JSON.json.

JSON.lower(p::Point2D) = [p.x, p.y]

Define a custom serialization rule for a particular data type. Must return a value that can be directly serialized; see help for more details.

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