Module: JSON

Sets create identifier, which is used to decide if the json_create hook of a class should be called; initial value is json_class:

JSON.create_id # => 'json_class'

Sets or returns the default options for the .dump method. Initially:

opts = JSON.dump_default_options
opts # => {:max_nesting=>false, :allow_nan=>true, :escape_slash=>false}

Returns the JSON generator module that is used by JSON. This is either ::JSON::Ext::Generator or JSON::Pure::Generator:

JSON.generator # => JSON::Ext::Generator

::Set the module generator to be used by JSON.

Sets or returns default options for the .load method. Initially:

opts = JSON.load_default_options
opts # => {:max_nesting=>false, :allow_nan=>true, :allow_blank=>true, :create_additions=>true}

Returns the JSON parser class that is used by JSON. This is either ::JSON::Ext::Parser or JSON::Pure::Parser:

JSON.parser # => JSON::Ext::Parser

::Set the JSON parser class parser to be used by JSON.

Sets or Returns the JSON generator state class that is used by JSON. This is either ::JSON::Ext::Generator::State or JSON::Pure::Generator::State:

JSON.state # => JSON::Ext::Generator::State

Return the constant located at path. The format of path has to be either ::A::B::C or A::B::C. In any case, A has to be located at the top level (absolute namespace path?). If there doesn’t exist a constant at the given path, an ArgumentError is raised.

Dumps obj as a JSON string, i.e. calls generate on the object and returns the result.

The default options can be changed via method .dump_default_options.

• Argument io, if given, should respond to method write; the JSON String is written to io, and io is returned. If io is not given, the JSON String is returned.

• Argument limit, if given, is passed to .generate as option max_nesting.

When argument io is not given, returns the JSON String generated from obj:

obj = {foo: [0, 1], bar: {baz: 2, bat: 3}, bam: :bad}
json = JSON.dump(obj)
json # => "{\"foo\":[0,1],\"bar\":{\"baz\":2,\"bat\":3},\"bam\":\"bad\"}"

When argument io is given, writes the JSON String to io and returns io:

path = 't.json'
File.open(path, 'w') do |file|
  JSON.dump(obj, file)
end # => #<File:t.json (closed)>
puts File.read(path)

Output:

{"foo":[0,1],"bar":{"baz":2,"bat":3},"bam":"bad"}

Arguments obj and opts here are the same as arguments obj and opts in .generate.

By default, generates JSON data without checking for circular references in obj (option max_nesting set to false, disabled).

Raises an exception if obj contains circular references:

a = []; b = []; a.push(b); b.push(a)
# Raises SystemStackError (stack level too deep):
JSON.fast_generate(a)

Returns a String containing the generated JSON data.

See also .fast_generate, .pretty_generate.

Argument obj is the Ruby object to be converted to JSON.

Argument opts, if given, contains a Hash of options for the generation. See Generating Options.

When obj is an Array, returns a String containing a JSON array:

obj = ["foo", 1.0, true, false, nil]
json = JSON.generate(obj)
json # => '["foo",1.0,true,false,null]'

When obj is a Hash, returns a String containing a JSON object:

obj = {foo: 0, bar: 's', baz: :bat}
json = JSON.generate(obj)
json # => '{"foo":0,"bar":"s","baz":"bat"}'

For examples of generating from other Ruby objects, see Generating JSON from Other Objects.

Raises an exception if any formatting option is not a String.

Raises an exception if obj contains circular references:

a = []; b = []; a.push(b); b.push(a)
# Raises JSON::NestingError (nesting of 100 is too deep):
JSON.generate(a)

Encodes string using String.encode.

Returns the Ruby objects created by parsing the given source.

• Argument source must be, or be convertible to, a String:

  • If source responds to instance method to_str, source.to_str becomes the source.

  • If source responds to instance method to_io, source.to_io.read becomes the source.

  • If source responds to instance method read, source.read becomes the source.

  • If both of the following are true, source becomes the String 'null':

    • Option allow_blank specifies a truthy value.

    • The source, as defined above, is nil or the empty String ''.

  • Otherwise, source remains the source.

• Argument proc, if given, must be a Proc that accepts one argument. It will be called recursively with each result (depth-first order). See details below. BEWARE: This method is meant to serialise data from trusted user input, like from your own database server or clients under your control, it could be dangerous to allow untrusted users to pass JSON sources into it.

• Argument opts, if given, contains a Hash of options for the parsing. See Parsing Options. The default options can be changed via method JSON.load_default_options=.

When no proc is given, modifies source as above and returns the result of parse(source, opts); see #parse.

Source for following examples:

source = <<-EOT
{
"name": "Dave",
  "age" :40,
  "hats": [
    "Cattleman's",
    "Panama",
    "Tophat"
  ]
}
EOT

Load a String:

ruby = JSON.load(source)
ruby # => {"name"=>"Dave", "age"=>40, "hats"=>["Cattleman's", "Panama", "Tophat"]}

Load an IO object:

require 'stringio'
object = JSON.load(StringIO.new(source))
object # => {"name"=>"Dave", "age"=>40, "hats"=>["Cattleman's", "Panama", "Tophat"]}

Load a File object:

path = 't.json'
File.write(path, source)
File.open(path) do |file|
  JSON.load(file)
end # => {"name"=>"Dave", "age"=>40, "hats"=>["Cattleman's", "Panama", "Tophat"]}

When proc is given:

• Modifies source as above.

• Gets the result from calling parse(source, opts).

• Recursively calls proc(result).

• Returns the final result.

Example:

require 'json'

# Some classes for the example.
class Base
  def initialize(attributes)
    @attributes = attributes
  end
end
class User    < Base; end
class Account < Base; end
class Admin   < Base; end
# The JSON source.
json = <<-EOF
{
  "users": [
      {"type": "User", "username": "jane", "email": "jane@example.com"},
      {"type": "User", "username": "john", "email": "john@example.com"}
  ],
  "accounts": [
      {"account": {"type": "Account", "paid": true, "account_id": "1234"}},
      {"account": {"type": "Account", "paid": false, "account_id": "1235"}}
  ],
  "admins": {"type": "Admin", "password": "0wn3d"}
}
EOF
# Deserializer method.
def deserialize_obj(obj, safe_types = %w(User Account Admin))
  type = obj.is_a?(Hash) && obj["type"]
  safe_types.include?(type) ? Object.const_get(type).new(obj) : obj
end
# Call to JSON.load
ruby = JSON.load(json, proc {|obj|
  case obj
  when Hash
    obj.each {|k, v| obj[k] = deserialize_obj v }
  when Array
    obj.map! {|v| deserialize_obj v }
  end
})
pp ruby

Output:

{"users"=>
   [#<User:0x00000000064c4c98
     @attributes=
       {"type"=>"User", "username"=>"jane", "email"=>"jane@example.com"}>,
     #<User:0x00000000064c4bd0
     @attributes=
       {"type"=>"User", "username"=>"john", "email"=>"john@example.com"}>],
 "accounts"=>
   [{"account"=>
       #<Account:0x00000000064c4928
       @attributes={"type"=>"Account", "paid"=>true, "account_id"=>"1234"}>},
    {"account"=>
       #<Account:0x00000000064c4680
       @attributes={"type"=>"Account", "paid"=>false, "account_id"=>"1235"}>}],
 "admins"=>
   #<Admin:0x00000000064c41f8
   @attributes={"type"=>"Admin", "password"=>"0wn3d"}>}

Calls:

parse(File.read(path), opts)

See method #parse.

Calls:

JSON.parse!(File.read(path, opts))

See method #parse!

Returns the Ruby objects created by parsing the given source.

Argument source contains the String to be parsed.

Argument opts, if given, contains a Hash of options for the parsing. See Parsing Options.

When source is a JSON array, returns a Ruby Array:

source = '["foo", 1.0, true, false, null]'
ruby = JSON.parse(source)
ruby # => ["foo", 1.0, true, false, nil]
ruby.class # => Array

When source is a JSON object, returns a Ruby Hash:

source = '{"a": "foo", "b": 1.0, "c": true, "d": false, "e": null}'
ruby = JSON.parse(source)
ruby # => {"a"=>"foo", "b"=>1.0, "c"=>true, "d"=>false, "e"=>nil}
ruby.class # => Hash

For examples of parsing for all JSON data types, see Parsing JSON.

Parses nested JSON objects:

source = <<-EOT
{
"name": "Dave",
  "age" :40,
  "hats": [
    "Cattleman's",
    "Panama",
    "Tophat"
  ]
}
EOT
ruby = JSON.parse(source)
ruby # => {"name"=>"Dave", "age"=>40, "hats"=>["Cattleman's", "Panama", "Tophat"]}

Raises an exception if source is not valid JSON:

# Raises JSON::ParserError (783: unexpected token at ''):
JSON.parse('')

Calls

parse(source, opts)

with source and possibly modified opts.

Differences from .parse:

• Option max_nesting, if not provided, defaults to false, which disables checking for nesting depth.

• Option allow_nan, if not provided, defaults to true.

Arguments obj and opts here are the same as arguments obj and opts in .generate.

Default options are:

{
  indent: '  ',   # Two spaces
  space: ' ',     # One space
  array_nl: "\n", # Newline
  object_nl: "\n" # Newline
}

Example:

obj = {foo: [:bar, :baz], bat: {bam: 0, bad: 1}}
json = JSON.pretty_generate(obj)
puts json

Output:

{
  "foo": [
    "bar",
    "baz"
  ],
  "bat": {
    "bam": 0,
    "bad": 1
  }
}

Recursively calls passed Proc if the parsed data structure is an Array or Hash