class JSON::PullParser

Overview

This class allows you to consume JSON on demand, token by token.

Eachread_* method consumes the next token. Sometimes it consumes only one token (like#read_begin_array), sometimes it consumes a full valid value (like#read_array).

You must be careful when calling those methods, as they move forward into the JSON input you are pulling. Calling#read_string twice will return the next two strings (if possible), not twice the same.

If you try to read a token which is not the one currently under the cursor location, an exceptionParseException will be raised.

Example:

input = %(
  {
    "type": "event",
    "values": [1, 4, "three", 10]
  }
)
pull = JSON::PullParser.new(input)
pull.read_begin_object
pull.read_object_key # => "type"
pull.read_string     # => "event"
# Actually you can also use `read_string` to read a key
pull.read_string # => "values"
pull.read_begin_array
pull.read_int    # => 1
pull.read_int    # => 4
pull.read_string # => "three"
pull.read_int    # => 10
pull.read_end_array
pull.read_end_object

Another example reading the same object:

pull = JSON::PullParser.new(input)
pull.read_object do |key|
  case key
  when "type"
    pull.read_string # => "event"
  when "values"
    pull.read_array do
      if v = pull.read?(Int8)
        v
      else
        pull.read_string
      end
    end
  end
end

This example fails:

pull = JSON::PullParser.new(input)
pull.read_begin_object
pull.read_object_key # => "type"
pull.read_string     # => "event"
pull.read_end_object # => raise an exception. The current token is a string ("values"), not the end of an object.

Defined in:

json/pull_parser.cr

Constructors

Instance Method Summary

Instance methods inherited from class Reference

==(other : self)
==(other : JSON::Any)
==(other : YAML::Any)
==(other) ==, dup dup, hash(hasher) hash, initialize initialize, inspect(io : IO) : Nil inspect, object_id : UInt64 object_id, pretty_print(pp) : Nil pretty_print, same?(other : Reference) : Bool
same?(other : Nil) same?, to_s(io : IO) : Nil to_s

Constructor methods inherited from class Reference

new new, unsafe_construct(address : Pointer, *args, **opts) : self unsafe_construct

Class methods inherited from class Reference

pre_initialize(address : Pointer) pre_initialize

Instance methods inherited from class Object

! : Bool !, !=(other) !=, !~(other) !~, ==(other) ==, ===(other : JSON::Any)
===(other : YAML::Any)
===(other) ===, =~(other) =~, as(type : Class) as, as?(type : Class) as?, class class, dup dup, hash(hasher)
hash hash, in?(collection : Object) : Bool
in?(*values : Object) : Bool in?, inspect(io : IO) : Nil
inspect : String inspect, is_a?(type : Class) : Bool is_a?, itself itself, nil? : Bool nil?, not_nil!(message)
not_nil! not_nil!, pretty_inspect(width = 79, newline = "\n", indent = 0) : String pretty_inspect, pretty_print(pp : PrettyPrint) : Nil pretty_print, responds_to?(name : Symbol) : Bool responds_to?, tap(&) tap, to_json(io : IO) : Nil
to_json : String to_json, to_pretty_json(indent : String = " ") : String
to_pretty_json(io : IO, indent : String = " ") : Nil to_pretty_json, to_s(io : IO) : Nil
to_s : String to_s, to_yaml(io : IO) : Nil
to_yaml : String to_yaml, try(&) try, unsafe_as(type : T.class) forall T unsafe_as

Class methods inherited from class Object

from_json(string_or_io : String | IO, root : String)
from_json(string_or_io : String | IO) from_json, from_yaml(string_or_io : String | IO) from_yaml

Macros inherited from class Object

class_getter(*names, &block) class_getter, class_getter!(*names) class_getter!, class_getter?(*names, &block) class_getter?, class_property(*names, &block) class_property, class_property!(*names) class_property!, class_property?(*names, &block) class_property?, class_setter(*names) class_setter, def_clone def_clone, def_equals(*fields) def_equals, def_equals_and_hash(*fields) def_equals_and_hash, def_hash(*fields) def_hash, delegate(*methods, to object) delegate, forward_missing_to(delegate) forward_missing_to, getter(*names, &block) getter, getter!(*names) getter!, getter?(*names, &block) getter?, property(*names, &block) property, property!(*names) property!, property?(*names, &block) property?, setter(*names) setter

Constructor Detail

def self.new(input) #

Creates a PullParser which will consume the JSONinput.

input must be aString or anIO.


Instance Method Detail

def bool_value : Bool #

def column_number #

Returns the current column number.


def column_number_i64 #

Returns the current column number.

EXPERIMENTAL


def float_value : Float64 #

def int_value : Int64 #

def kind : Kind #

def line_number : Int32 #

Returns the current line number.


def line_number_i64 : Int64 #

Returns the current line number.

EXPERIMENTAL


def location : Tuple(Int32, Int32) #

Returns the current location.

The location is a tuple{line number, column number}.


def location_i64 : Tuple(Int64, Int64) #

Returns the current location.

The location is a tuple{line number, column number}.

EXPERIMENTAL


def max_nesting : Int32 #

def max_nesting=(max_nesting : Int32) #

def on_key(key, & : self -> _) #

Reads an object keys and yield whenkey is found.

All the other object keys are skipped.

Returns the return value of the block orNil if the key was not read.


def on_key!(key, & : self -> _) #

Reads an object keys and yield whenkey is found. If not found, raise anException.

All the other object keys are skipped.

Returns the return value of the block.


def raise(message : String) : NoReturn #

RaisesParseException withmessage at current location.


def raw_value : String #

def read?(klass : Bool.class) : Bool | Nil #

Reads aBool value and returns it.

If the value is not aBool, returnsnil.


def read?(klass : Int128.class) : Int128 | Nil #

Reads anInt128 value and returns it.

If the value is not an integer or does not fit in anInt128, it returnsnil.


def read?(klass : Int16.class) : Int16 | Nil #

Reads anInt16 value and returns it.

If the value is not an integer or does not fit in anInt16, it returnsnil.


def read?(klass : Int32.class) : Int32 | Nil #

Reads anInt32 value and returns it.

If the value is not an integer or does not fit in anInt32, it returnsnil.


def read?(klass : Int64.class) : Int64 | Nil #

Reads anInt64 value and returns it.

If the value is not an integer or does not fit in anInt64, it returnsnil.


def read?(klass : Int8.class) : Int8 | Nil #

Reads anInt8 value and returns it.

If the value is not an integer or does not fit in anInt8, it returnsnil.


def read?(klass : UInt128.class) : UInt128 | Nil #

Reads anUInt128 value and returns it.

If the value is not an integer or does not fit in anUInt128, it returnsnil.


def read?(klass : UInt16.class) : UInt16 | Nil #

Reads anUInt16 value and returns it.

If the value is not an integer or does not fit in anUInt16, it returnsnil.


def read?(klass : UInt32.class) : UInt32 | Nil #

Reads anUInt32 value and returns it.

If the value is not an integer or does not fit in anUInt32, it returnsnil.


def read?(klass : UInt64.class) : UInt64 | Nil #

Reads anUInt64 value and returns it.

If the value is not an integer or does not fit in anUInt64, it returnsnil.


def read?(klass : UInt8.class) : UInt8 | Nil #

Reads anUInt8 value and returns it.

If the value is not an integer or does not fit in anUInt8, it returnsnil.


def read?(klass : Float32.class) : Float32 | Nil #

Reads anFloat32 value and returns it.

If the value is not an integer or does not fit in anFloat32, it returnsnil. If the value was actually an integer, it is converted to a float.


def read?(klass : Float64.class) : Float64 | Nil #

Reads anFloat64 value and returns it.

If the value is not an integer or does not fit in aFloat64 variable, it returnsnil. If the value was actually an integer, it is converted to a float.


def read?(klass : String.class) : String | Nil #

Reads aString value and returns it.

If the value is not aString, returnsnil.


def read_array(&) #

Reads a whole array.

It reads the beginning of the array, yield each value of the array, and reads the end of the array. You have to consumes the values, if any, so the pull parser does not fail when reading the end of the array.

If the array is empty, it does not yield.


def read_array_or_null(&) #

Reads an array or a null value, and returns it.


def read_begin_array : JSON::PullParser::Kind #

Reads the beginning of an array.


def read_begin_object : JSON::PullParser::Kind #

Reads the beginning of an object.


def read_bool : Bool #

Reads aBool value.


def read_bool_or_null : Bool | Nil #

Reads aBool or a null value, and returns it.


def read_end_array : JSON::PullParser::Kind #

Reads the end of an array.


def read_end_object : JSON::PullParser::Kind #

Reads the end of an object.


def read_float : Float64 #

Reads a float value.

If the value is actually an integer, it is converted to float.


def read_float_or_null : Float64 | Nil #

Reads a float or a null value, and returns it.


def read_int : Int64 #

Reads an integer value.


def read_int_or_null : Int64 | Nil #

Reads an integer or a null value, and returns it.


def read_next : Kind #

Reads the next lexer's token.

Contrary to#read_raw, it does not read a full value. For example if the next token is the beginning of an array, it will stop there, while#read_raw would have read the whole array.


def read_null : Nil #

Reads a null value and returns it.


def read_null? : Bool #

Reads the current token if its value is null.

Returnstrue if the token was read.


def read_null_or(&) #

Reads a null value and returns it, or executes the given block if the value is not null.


def read_object(&) #

Reads a whole object.

It reads the beginning of the object, yield each key and key location, and reads the end of the object. You have to consumes the values, if any, so the pull parser does not fail when reading the end of the object.

If the object is empty, it does not yield.


def read_object_key : String #

Reads an object's key and returns it.


def read_object_or_null(&) #

Reads an object or a null value, and returns it.


def read_raw(json : JSON::Builder) : Nil #

Reads the new value and fill the a JSON builder with it.

Use this method with aJSON::Builder to read a JSON while building another one.


def read_raw : String #

Read the next value and returns it.

The value is returned as a json string. If the value is an array or an object, it returns a string representing the full value. If the value in unknown, it raises aParseException.

pull = JSON::PullParser.new %([null, true, 1, "foo", [1, "two"], {"foo": "bar"}])
pull.read_begin_array
pull.read_raw # => "null"
pull.read_raw # => "true"
pull.read_raw # => "1"
pull.read_raw # => "\"foo\""
pull.read_raw # => "[1,\"two\"]"
pull.read_raw # => "{\"foo\":\"bar\"}"
pull.read_end_array

def read_string : String #

Reads a string and returns it.


def read_string_or_null : String | Nil #

Reads a string or a null value, and returns it.


def skip : Nil #

Skips the next value.

It skips the whole value, not only the next lexer's token. For example if the next value is an array, the whole array will be skipped.


def string_value : String #