解析：classdef JSON < handle
% v = JSON.parse(json
String) converts a JSON
string to a MATLAB value.
%
% This started out as a recursive descent parser, but JSON is so simple
% that most of
the parser collapsed out.
%
% In
the service of speed, simplicity, and laziness, this code is NOT a
% validator. Its purpose is to convert correct JSON
strings to MATLAB
% values. It does not reject all malformed JSON.
% Copyright 2013
The MathWorks, Inc.
properties (Access = private)
json %
the string
index %
position in
the string
end
methods (Access = private)
function this = JSON(JSON
string)
this.json = JSON
string;
this.index = 1;
end
function value =
getValue(this)
%
get the next value in
the string
token = this.
getNextToken;
if token == '{'
value = this.
getObject;
elseif token == '['
value = this.
getArray;
else
value = token;
end
end
function number =
getNumber(this)
first = this.index;
last =
first;
ch = charAt(this,
first);
if(ch == '-')
last = last + 1;
ch = charAt(this,last);
end
while isDigit(ch)
last = last + 1;
ch = charAt(this,last);
end
if(ch == '.')
last = last + 1;
ch = charAt(this,last);
while isDigit(ch)
last = last + 1;
ch = charAt(this,last);
end
end
if ch == 'e' || ch == 'E'
last = last + 1;
ch = charAt(this,last);
if ismember(ch,'+-')
last = last + 1;
ch = charAt(this,last);
end
while isDigit(ch)
last = last + 1;
ch = charAt(this,last);
end
end
% pull out
the string
str = this.json(
first:(last-1));
number = str2double(str);
% move past it
this.index = last;
% helper functions
function char = charAt(this,
position)
if(
position > length(this.json))
char = 0;
else
char = this.json(
position);
end
end
function tf = isDigit(aChar)
tf = aChar > 47 && aChar < 58;
end
end
function
string =
getString(this)
first = this.index + 1;
last =
first;
str = this.json;
ch = str(last);
while ch ~= '"'
if(ch == '\\') %#ok<STCMP> We KNOW both are single chars
last = last + 2;
else
last = last + 1;
end
ch = str(last);
end
%
get the string without it's quotes
string = str(
first:(last-1));
this.index = last + 1; % skip
the trailing "
end
function array =
getArray(this)
% an array is [ value, ... ]
array = {};
value = this.
getValue;
while ~strcmp(value,']')
% got a value
array{end+1} = value; %#ok<AGROW> final size is unknowable
% followed by a comma or a "]"
value = this.
getValue;
if value == ','
value = this.
getValue;
elseif value == ']'
continue
else
error('JSON parser requires commas between array elements');
end
end
% Arrays of all numbers are turned into
numeric arrays
fcn = @(x) is
numeric(x) && ~isscalar(x);
if all(cellfun(fcn,array))
array = [array{:}];
end
end
function obj =
getObject(this)
% an object is {
string : value, ... }
obj = struct;
value = this.
getValue;
while ~strcmp(value,'}')
fieldname = value;
% make sure its a valid structure field name
fieldname = strrep(fieldname,':','_');
fieldname = strrep(fieldname,'-','_');
% check for colon
value = this.
getValue;
if value ~= ':'
error('JSON parser requires colons between object names and values');
end
%
get the value
value = this.
getValue;
obj.(fieldname) = value;
value = this.
getValue;
if value == ','
value = this.
getValue;
elseif value == '}'
continue
else
error('JSON parser requires commas between object elements');
end
end
end
function token =
getNextToken(this)
%
get whatever is next in
the string
% skip whitespace
ch = this.json(this.index);
while isWhitespace(ch)
this.index = this.index + 1;
ch = this.json(this.index);
end
% is it a special character?
if isSpecial(ch)
token = ch;
this.index = this.index + 1;
return
end
% is it one of
the three keywords?
switch(ch)
case 't'
match(this,'true');
token = true;
return;
case 'f'
match(this,'false');
token = false;
return;
case 'n'
match(this,'null');
token = [];
return;
end
% is it a
string?
if(ch == '"')
token = this.
getString;
return;
end
% well,
then it better be a number
token = this.
getNumber;
function match(this,str)
% find and consume exactly str at
the current location of error
n = length(str);
range = this.index:(this.index + n - 1);
found = this.json(range);
if strcmp(str,found)
this.index = this.index + n;
else
error('
The JSON parser expected "%s" but found %s',str,found)
end
end
function tf = isWhitespace(aChar)
% space, carrage return, linefeed, horizontal tab
tf = aChar == 32 || aChar == 10 || aChar == 13 || aChar == 9;
end
function tf = isSpecial(aChar)
%
the special characters in
the JSON "language"
tf = aChar == '{' || aChar == '}' || aChar == '['|| aChar == ']'|| aChar == ':' || aChar == ',';
end
end
end
methods(Static)
% This is
the one method you should call
from outside
the file.
% JSON.parse(
string)... that should be familiar to Javascrpt
% programmers
function value = parse(JSON
string)
jsonObject = JSON(JSON
string);
value = jsonObject.
getValue;
end
end
end
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