JSON Quick Guide

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JSON or JavaScript Object Notation is a lightweight is a text-based open standard designed for human-readable data interchange. Conventions used by JSON are known to programmers which include C, C++, Java, Python, Perl etc.

  • JSON stands for JavaScript Object Notation.

  • This format was specified by Douglas Crockford.

  • This was designed for human-readable data interchange

  • JSON has been extended from the JavaScript scripting language.

  • JSON filename extension is .json

  • JSON Internet Media type is application/json

  • The Uniform Type Identifier is public.json

Uses of JSON

  • JSON is used when writing JavaScript based application which includes browser extension and websites.

  • JSON format is used for serializing & transmitting structured data over network connection.

  • JSON is primarily used to transmit data between server and web application.

  • Web Services and API.s use JSON format to provide public data.

  • JSON can be used with modern programming languages.

Characteristics of JSON

  • It is easy to read and write JSON.

  • JSON is lightweight text based interchange format

  • JSON is language independent.

Simple Example in JSON

Example shows Books information stored using JSON considering language of books and there editions:

{
    "book": [
    {
       "id":"01",
       "language": "Java",
       "edition": "third",
       "author": "Herbert Schildt"
    },
    {
       "id":"07",
       "language": "C++",
       "edition": "second"
       "author": "E.Balagurusamy"
    }]
}

After understanding the above program we will try another example, let's save the below code as json.htm:

<html>
<head>
<title>JSON example</title>
<script language="javascript" >
  
  var object1 = { "language" : "Java", "author"  : "herbert schildt" };
  document.write("<h1>JSON with JavaScript example</h1>");
  document.write("<br>");
  document.write("<h3>Language = " + object1.language+"</h3>");  
  document.write("<h3>Author = " + object1.author+"</h3>");   

  var object2 = { "language" : "C++", "author"  : "E-Balagurusamy" };
  document.write("<br>");
  document.write("<h3>Language = " + object2.language+"</h3>");  
  document.write("<h3>Author = " + object2.author+"</h3>");   
  
  document.write("<hr />");
  document.write(object2.language + " programming language can be studied " +
  "from book written by " + object2.author);
  document.write("<hr />");
  
</script>
</head>
<body>
</body>
</html>

Now let's try to open json.htm using IE or any other javascript enabled browser, this produces the following result:

json example

JSON - Syntax

Let's have a quick look on JSON basic syntax. JSON syntax is basically considered as subset of JavaScript syntax, it includes the following:

  • Data is represented in name/value pairs

  • Curly braces hold objects and each name is followed by ':'(colon), the name/value pairs are separated by , (comma).

  • Square brackets hold arrays and values are separated by ,(comma).

Below is a simple example:

{
    "book": [
    {
       "id":"01",
       "language": "Java",
       "edition": "third",
       "author": "Herbert Schildt"
    },
    {
       "id":"07",
       "language": "C++",
       "edition": "second"
       "author": "E.Balagurusamy"
    }]
}

JSON supports following two data structures:

  • Collection of name/value pairs: This Data Structure is supported by different programming language.

  • Ordered list of values: It includes array, list, vector or sequence etc.

JSON - DataTypes

There are following datatypes supported by JSON format:

TypeDescription
Numberdouble- precision floating-point format in JavaScript
Stringdouble-quoted Unicode with backslash escaping
Booleantrue or false
Arrayan ordered sequence of values
Valueit can be a string, a number, true or false, null etc
Objectan unordered collection of key:value pairs
Whitespacecan be used between any pair of tokens
nullempty

Number

  • It is a double precision floating-point format in JavaScript and it depends on implementation.

  • Octal and hexadecimal formats are not used.

  • No NaN or Infinity is used in Number.

The following table shows number types:

TypeDescription
IntegerDigits 1-9, 0 and positive or negative
FractionFractions like .3, .9
ExponentExponent like e, e+, e-,E, E+, E-

Syntax:

var json-object-name = { string : number_value, .......}

Example:

Example showing Number Datatype, value should not be quoted:

var obj = {marks: 97}

String

  • It is a sequence of zero or more double quoted Unicode characters with backslash escaping.

  • Character is a single character string i.e. a string with length 1.

The table shows string types:

TypeDescription
" double quotation
\ reverse solidus
/ solidus
b backspace
f form feed
n new line
r carriage return
t horizontal tab
u four hexadecimal digits

Syntax:

var json-object-name = { string : "string value", .......}

Example:

Example showing String Datatype:

var obj = {name: 'Amit'}

Boolean

It includes true or false values.

Syntax:

var json-object-name = { string : true/false, .......}

Example:

var obj = {name: 'Amit', marks: 97, distinction: true}

Array

  • It is an ordered collection of values.

  • These are enclosed square brackets which means that array begins with .[. and ends with .]..

  • The values are separated by ,(comma).

  • Array indexing can be started at 0 or 1.

  • Arrays should be used when the key names are sequential integers.

Syntax:

[ value, .......]

Example:

Example showing array containing multiple objects:

{
  "books": [
   { "language":"Java" , "edition":"second" },
   { "language":"C++" , "lastName":"fifth" },
   { "language":"C" , "lastName":"third" }
  ]
}

Object

  • It is an unordered set of name/value pairs.

  • Object are enclosed in curly braces that is it starts with '{' and ends with '}'.

  • Each name is followed by ':'(colon) and the name/value pairs are separated by , (comma).

  • The keys must be strings and should be different from each other.

  • Objects should be used when the key names are arbitrary strings

Syntax:

{ string : value, .......}

Example:

Example showing Object:

{
 "id": "011A",
 "language": "JAVA",
 "price": 500,
}

Whitespace

It can be inserted between any pair of tokens. It can be added to make code more readable. Example shows declaration with and without whitespace:

Syntax:

{string:"   ",....}

Example:

var i= "   sachin";
var j = "  saurav"

null

It means empty type.

Syntax:

null

Example:

var i = null;

if(i==1) 
{
   document.write("<h1>value is 1</h1>");	
}
else
{
   document.write("<h1>value is null</h1>");
}

JSON Value

It includes:

  • number (integer or floating point)

  • string

  • boolean

  • array

  • object

  • null

Syntax:

String | Number | Object | Array | TRUE | FALSE | NULL

Example:

var i =1;
var j = "sachin";
var k = null;

JSON - Objects

Creating Simple Objects

JSON objects can be created with Javascript. Let's us see various ways of creating JSON objects using Javascript:

  • Creation of an empty Object:

var JSONObj = {};
  • Creation of new Object:

var JSONObj = new Object();
  • Creation of an object with attribute bookname with value in string, attribute price with numeric value. Attributes is accessed by using '.' Operator:

var JSONObj = { "bookname ":"VB BLACK BOOK", "price":500 };

This is an example which shows creation of an object in javascript using JSON, save the below code as json_object.htm:

<html>
<head>
<title>Creating Object JSON with JavaScript</title>
<script language="javascript" >

  var JSONObj = { "name" : "tutorialspoint.com", "year"  : 2005 };
  document.write("<h1>JSON with JavaScript example</h1>");
  document.write("<br>");
  document.write("<h3>Website Name="+JSONObj.name+"</h3>");  
  document.write("<h3>Year="+JSONObj.year+"</h3>");  

</script>
</head>
<body>
</body>
</html>

Now let's try to open json_object.htm using IE or any other javascript enabled browser, this produces the following result:

json objects

Creating Array Objects

Below example shows creation of an array object in javascript using JSON, save the below code as json_array_object.htm:

<html>
<head>
<title>Creation of array object in javascript using JSON</title>
<script language="javascript" >

document.writeln("<h2>JSON array object</h2>");

var books = { "Pascal" : [ 
      { "Name"  : "Pascal Made Simple", "price" : 700 },
      { "Name"  : "Guide to Pascal", "price" : 400 }
   ],                       
   "Scala"  : [
      { "Name"  : "Scala for the Impatient", "price" : 1000 }, 
      { "Name"  : "Scala in Depth", "price" : 1300 }
   ]    
}    

var i = 0
document.writeln("<table border='2'><tr>");
for(i=0;i<books.Pascal.length;i++)
{	
   document.writeln("<td>");
   document.writeln("<table border='1' width=100 >");
   document.writeln("<tr><td><b>Name</b></td><td width=50>"
   + books.Pascal[i].Name+"</td></tr>");
   document.writeln("<tr><td><b>Price</b></td><td width=50>"
   + books.Pascal[i].price +"</td></tr>");
   document.writeln("</table>");
   document.writeln("</td>");
}

for(i=0;i<books.Scala.length;i++)
{
   document.writeln("<td>");
   document.writeln("<table border='1' width=100 >");
   document.writeln("<tr><td><b>Name</b></td><td width=50>"
   + books.Scala[i].Name+"</td></tr>");
   document.writeln("<tr><td><b>Price</b></td><td width=50>"
   + books.Scala[i].price+"</td></tr>");
   document.writeln("</table>");
   document.writeln("</td>");
}
document.writeln("</tr></table>");
</script>
</head>
<body>
</body>
</html>

Now let's try to open json_array_object.htm using IE or any other javascript enabled browser, this produces the following result:

json array objects

JSON - Schema

JSON Schema is a specification for JSON based format for defining structure of JSON data. It was written under IETF draft which expired in 2011. JSON Schema:

  • Describes your existing data format.

  • Clear, human- and machine-readable documentation.

  • Complete structural validation, useful for automated testing.

  • Complete structural validation, validating client-submitted data.

JSON Schema Validation Libraries

There are several validators currently available for different programming languages. Currently the most complete and compliant JSON Schema validator available is JSV

LanguagesLibraries
CWJElement (LGPLv3)
Javajson-schema-validator (LGPLv3)
.NETJson.NET (MIT)
ActionScript 3Frigga (MIT)
Haskellaeson-schema (MIT)
PythonJsonschema
Rubyautoparse (ASL 2.0); ruby-jsonschema (MIT)
PHPphp-json-schema (MIT). json-schema (Berkeley)
JavaScriptOrderly (BSD); JSV; json-schema; Matic (MIT); Dojo; Persevere (modified BSD or AFL 2.0); schema.js.

JSON Schema Example

Following is a basic JSON schema which covers a classical product catalog description:

{
    "$schema": "http://json-schema.org/draft-04/schema#",
    "title": "Product",
    "description": "A product from Acme's catalog",
    "type": "object",
    "properties": {
        "id": {
            "description": "The unique identifier for a product",
            "type": "integer"
        },
        "name": {
            "description": "Name of the product",
            "type": "string"
        },
        "price": {
            "type": "number",
            "minimum": 0,
            "exclusiveMinimum": true
        }
    },
    "required": ["id", "name", "price"]
}

Let's check various important keywords which can be used in this schema:

KeywordsDescription
$schemaThe $schema keyword states that this schema is written according to the draft v4 specification.
title You will use this to give a title to your schema
descriptionA little description of the schema
typeThe type keyword defines the first constraint on our JSON data: it has to be a JSON Object.
propertiesDefines various keys and their value types, minimum and maximum values to be used in JSON file.
requiredThis keeps a list of required properties.
minimumThis is the constraint to be put on the value and represents minimum acceptable value.
exclusiveMinimumIf "exclusiveMinimum" is present and has boolean value true, the instance is valid if it is strictly greater than the value of "minimum".
maximumThis is the constraint to be put on the value and represents maximum acceptable value.
exclusiveMaximumIf "exclusiveMaximum" is present and has boolean value true, the instance is valid if it is strictly lower than the value of "maximum".
multipleOfA numeric instance is valid against "multipleOf" if the result of the division of the instance by this keyword's value is an integer.
maxLengthThe length of a string instance is defined as the maximum number of its characters.
minLengthThe length of a string instance is defined as the minimum number of its characters.
patternA string instance is considered valid if the regular expression matches the instance successfully.

You can check a http://json-schema.org for complete list of keywords which can be used in defining JSON schema. Above schema can be used to test the validity of the below given JSON code:

[
    {
        "id": 2,
        "name": "An ice sculpture",
        "price": 12.50,
    },
    {
        "id": 3,
        "name": "A blue mouse",
        "price": 25.50,
    }
]

JSON - Comparison with XML

JSON and XML are human readable formats and are language independent. They both have support for creation, reading and decoding in real world situations. We can compare JSON with XML based on the following factors:

Verbose

XML is more verbose than JSON, so it's faster to write JSON for humans.

Arrays Usage

XML is used to describe structured data which doesn't include arrays whereas JSON include arrays.

Parsing

JavaScript's eval method parses JSON. When applied to JSON, eval returns the described object.

Example

This shows individual examples of XML and JSON:

JSON

{
   "company": Volkswagen,
   "name": "Vento",
   "price": 800000
}

XML

<car>
   <company>Volkswagen</company>
   <name>Vento</name>
   <price>800000</price>
</car>

JSON with PHP

This chapter will teach you how to encode and decode JSON objects using PHP programming language. Let's start with preparing environment to start our programming with PHP for JSON.

Environment

As of PHP 5.2.0, the JSON extension is bundled and compiled into PHP by default.

JSON Functions

FunctionLibraries
json_encode Returns the JSON representation of a value
json_decodeDecodes a JSON string
json_last_errorReturns the last error occurred

Encoding JSON in PHP (json_encode)

PHP json_encode() function is used for encoding JSON in PHP. This function returns the JSON representation of a value on success or FALSE on failure.

Syntax:

string json_encode ( $value [, $options = 0 ] )

Parameters:

  • value: The value being encoded. This function only works with UTF-8 encoded data.

  • options: This optional value is a bitmask consisting of JSON_HEX_QUOT, JSON_HEX_TAG, JSON_HEX_AMP, JSON_HEX_APOS, JSON_NUMERIC_CHECK,JSON_PRETTY_PRINT, JSON_UNESCAPED_SLASHES, JSON_FORCE_OBJECT

Example

The following example shows how to convert an arrays into JSON with PHP:

<?php
   $arr = array('a' => 1, 'b' => 2, 'c' => 3, 'd' => 4, 'e' => 5);
   echo json_encode($arr);
?>

While executing, this will produce following result:

{"a":1,"b":2,"c":3,"d":4,"e":5}

The following example shows how PHP objects can be converted into JSON:

<?php
   class Emp {
       public $name = "";
       public $hobbies  = "";
       public $birthdate = "";
   }
   $e = new Emp();
   $e->name = "sachin";
   $e->hobbies  = "sports";
   $e->birthdate = date('m/d/Y h:i:s a', strtotime("8/5/1974 12:20:03"));

   echo json_encode($e);
?>

While executing, this will produce following result:

{"name":"sachin","hobbies":"sports","birthdate":"08\/05\/1974 12:20:03 pm"}

Decoding JSON in PHP (json_decode)

PHP json_decode() function is used for decoding JSON in PHP. This function returns the value decoded from json to appropriate PHP type.

Syntax:

mixed json_decode ($json [,$assoc = false [, $depth = 512 [, $options = 0 ]]])

Paramaters:

  • json_string: It is encoded string which must be UTF-8 encoded data

  • assoc: It is a boolean type parameter, when set to TRUE, returned objects will be converted into associative arrays.

  • depth: It is an integer type parameter which specifies recursion depth

  • options: It is an integer type bitmask of JSON decode, JSON_BIGINT_AS_STRING is supported.

Example

The following example shows how PHP can be used to decode JSON objects:

<?php
   $json = '{"a":1,"b":2,"c":3,"d":4,"e":5}';

   var_dump(json_decode($json));
   var_dump(json_decode($json, true));
?>

While executing, this will produce following result:

object(stdClass)#1 (5) {
    ["a"] => int(1)
    ["b"] => int(2)
    ["c"] => int(3)
    ["d"] => int(4)
    ["e"] => int(5)
}

array(5) {
    ["a"] => int(1)
    ["b"] => int(2)
    ["c"] => int(3)
    ["d"] => int(4)
    ["e"] => int(5)
}

JSON with Perl

This chapter will teach you how to encode and decode JSON objects using Perl programming language. Let's start with preparing environment to start our programming with Perl for JSON.

Environment

Before you start with encoding and decoding JSON using Perl, you will need to install JSON module which can be obtained from CPAN. Once you downloaded JSON-2.53.tar.gz or any other latest version, follow the following steps:

$tar xvfz JSON-2.53.tar.gz
$cd JSON-2.53
$perl Makefile.PL
$make
$make install

JSON Functions

FunctionLibraries
encode_json Converts the given Perl data structure to a UTF-8 encoded, binary string.
decode_jsonDecodes a JSON string.
to_jsonConverts the given Perl data structure to a json string.
from_jsonExpects a json string and tries to parse it, returning the resulting reference.
convert_blessedUse this function with true value so that Perl can use TO_JSON method on the object's class to convert an object into JSON.

Encoding JSON in Perl (encode_json)

Perl encode_json() function converts the given Perl data structure to a UTF-8 encoded, binary string.

Syntax:

$json_text = encode_json ($perl_scalar );

or

$json_text = JSON->new->utf8->encode($perl_scalar);

Example

The following example shows arrays under JSON with Perl:

#!/usr/bin/perl
use JSON;

my %rec_hash = ('a' => 1, 'b' => 2, 'c' => 3, 'd' => 4, 'e' => 5);
my $json = encode_json \%rec_hash;
print "$json\n";

While executing, this will produce following result:

{"e":5,"c":3,"a":1,"b":2,"d":4}

The following example shows how Perl objects can be converted into JSON:

#!/usr/bin/perl

package Emp;
sub new
{
    my $class = shift;
    my $self = {
        name => shift,
        hobbies  => shift,
        birthdate  => shift,
    };
    bless $self, $class;
    return $self;
}
sub TO_JSON { return { %{ shift() } }; }

package main;
use JSON;

my $JSON  = JSON->new->utf8;
$JSON->convert_blessed(1);

$e = new Emp( "sachin", "sports", "8/5/1974 12:20:03 pm");
$json = $JSON->encode($e);
print "$json\n";

While executing, this will produce following result:

{"birthdate":"8/5/1974 12:20:03 pm","name":"sachin","hobbies":"sports"}

Decoding JSON in Perl (decode_json)

Perl decode_json() function is used for decoding JSON in Perl. This function returns the value decoded from json to appropriate Perl type.

Syntax:

$perl_scalar = decode_json $json_text

or

$perl_scalar = JSON->new->utf8->decode($json_text)

Example

The following example shows how Perl can be used to decode JSON objects. Here you will need to install Data::Dumper module if you already do not have it on your machine.

#!/usr/bin/perl
use JSON;
use Data::Dumper;

$json = '{"a":1,"b":2,"c":3,"d":4,"e":5}';

$text = decode_json($json);
print  Dumper($text);

While executing, this will produce following result:

$VAR1 = {
          'e' => 5,
          'c' => 3,
          'a' => 1,
          'b' => 2,
          'd' => 4
        };

JSON with Python

This chapter will teach you how to encode and decode JSON objects using Python programming language. Let's start with preparing environment to start our programming with Python for JSON.

Environment

Before you start with encoding and decoding JSON using Python, you will need to install any of the JSON modules available. For this tutorial I downloaded and installed Demjson as follows:

$tar xvfz demjson-1.6.tar.gz
$cd demjson-1.6
$python setup.py install

JSON Functions

FunctionLibraries
encode Encodes the Python object into a JSON string representation.
decodeDecodes a JSON-endoded string into a Python object

Encoding JSON in Python (encode)

Python encode() function encodes the Python object into a JSON string representation.

Syntax:

demjson.encode(self, obj, nest_level=0)

Example

The following example shows arrays under JSON with Python

#!/usr/bin/python
import demjson

data = [ { 'a' : 1, 'b' : 2, 'c' : 3, 'd' : 4, 'e' : 5 } ]

json = demjson.encode(data)
print json

While executing, this will produce following result:

[{"a":1,"b":2,"c":3,"d":4,"e":5}]

Decoding JSON in Python (decode)

Python can use demjson.decode() function for decoding JSON. This function returns the value decoded from json to appropriate Python type.

Syntax:

demjson.decode(self, txt)

Example

The following example shows how Python can be used to decode JSON objects.

#!/usr/bin/python
import demjson

json = '{"a":1,"b":2,"c":3,"d":4,"e":5}';

text = demjson.decode(json)
print  text

While executing, this will produce following result:

{u'a': 1, u'c': 3, u'b': 2, u'e': 5, u'd': 4}

JSON with Ruby

This chapter will teach you how to encode and decode JSON objects using Ruby programming language. Let's start with preparing environment to start our programming with Ruby for JSON.

Environment

Before you start with encoding and decoding JSON using Ruby, you will need to install any of the JSON modules available for Ruby. You may need to install Ruby gem, but if yo are running latest version of Ruby then you must have gem already installed on your machine, otherwise let's follow the following single step assuming you already have gem installed:

$gem install json

Parsing JSON using Ruby

The following example shows that the first 2 keys hold string values and the last 3 keys hold arrays of strings. Let's keep the following content in a file called input.json

{
  "President": "Alan Isaac",
  "CEO": "David Richardson",
  
  "India": [
    "Sachin Tendulkar",
    "Virender Sehwag",
    "Gautam Gambhir",
  ],

  "Srilanka": [
    "Lasith Malinga",
    "Angelo Mathews",
    "Kumar Sangakkara"
  ],

  "England": [
    "Alastair Cook",
    "Jonathan Trott",
    "Kevin Pietersen"
  ]
}

The following is ruby program which will be used to parse above mentioned JSON document:

#!/usr/bin/ruby
require 'rubygems'
require 'json'
require 'pp'

json = File.read('input.json')
obj = JSON.parse(json)

pp obj

While executing, this will produce following result:

{"President"=>"Alan Isaac",
 "CEO"=>"David Richardson",

 "India"=>
  ["Sachin Tendulkar", "Virender Sehwag", "Gautam Gambhir"],

"Srilanka"=>
  ["Lasith Malinga ", "Angelo Mathews", "Kumar Sangakkara"],

 "England"=>
  ["Alastair Cook", "Jonathan Trott", "Kevin Pietersen"]
}

JSON with Java

This chapter will teach you how to encode and decode JSON objects using Java programming language. Let's start with preparing environment to start our programming with Java for JSON.

Environment

Before you start with encoding and decoding JSON using Java, you will need to install any of the JSON modules available. For this tutorial I downloaded and installed JSON.simple and add the location of json-simple-1.1.1.jar file to environment variable CLASSPATH:

Mapping between JSON and Java entities

JSON.simple maps entities from the left side to the right side while decoding or parsing, and maps entities from the right to the left while encoding.

JSONJava
stringjava.lang.String
numberjava.lang.Number
true|falseava.lang.Boolean
nullnull
array java.util.List
objectjava.util.Map

While decoding, default concrete class of java.util.List is org.json.simple.JSONArray and default concrete class of java.util.Map is org.json.simple.JSONObject.

Encoding JSON in Java

Following is a simple example to encode a JSON object using Java JSONObject which is a subclass of java.util.HashMap. No ordering is provided. If you need strict ordering of elements use JSONValue.toJSONString( map ) method with ordered map implementation such as java.util.LinkedHashMap.

import org.json.simple.JSONObject;

class JsonEncodeDemo 
{
   public static void main(String[] args) 
   {
      JSONObject obj = new JSONObject();

      obj.put("name", "foo");
      obj.put("num", new Integer(100));
      obj.put("balance", new Double(1000.21));
      obj.put("is_vip", new Boolean(true));

      System.out.print(obj);
   }
}

While compile and executing above program, this will produce following result:

{"balance": 1000.21, "num":100, "is_vip":true, "name":"foo"}

Following is another example which shows JSON object streaming using Java JSONObject:

import org.json.simple.JSONObject;

class JsonEncodeDemo 
{
   public static void main(String[] args) 
   {
      JSONObject obj = new JSONObject();

      obj.put("name","foo");
      obj.put("num",new Integer(100));
      obj.put("balance",new Double(1000.21));
      obj.put("is_vip",new Boolean(true));

      StringWriter out = new StringWriter();
      obj.writeJSONString(out);
      
      String jsonText = out.toString();
      System.out.print(jsonText);
   }
}

While compile and executing above program, this will produce following result:

{"balance": 1000.21, "num":100, "is_vip":true, "name":"foo"}

Decoding JSON in Java

Following example makes use of JSONObject and JSONArray where JSONObject is a java.util.Map and JSONArray is a java.util.List, so you can access them with standard operations of Map or List.

import org.json.simple.JSONObject;
import org.json.simple.JSONArray;
import org.json.simple.parser.ParseException;
import org.json.simple.parser.JSONParser;

class JsonDecodeDemo 
{
   public static void main(String[] args) 
   {
      JSONParser parser=new JSONParser();
      String s = "[0,{\"1\":{\"2\":{\"3\":{\"4\":[5,{\"6\":7}]}}}}]";
      try{
         Object obj = parser.parse(s);
         JSONArray array = (JSONArray)obj;
         System.out.println("The 2nd element of array");
         System.out.println(array.get(1));
         System.out.println();

         JSONObject obj2 = (JSONObject)array.get(1);
         System.out.println("Field \"1\"");
         System.out.println(obj2.get("1"));    

         s = "{}";
         obj = parser.parse(s);
         System.out.println(obj);

         s= "[5,]";
         obj = parser.parse(s);
         System.out.println(obj);

         s= "[5,,2]";
         obj = parser.parse(s);
         System.out.println(obj);
      }catch(ParseException pe){
         System.out.println("position: " + pe.getPosition());
         System.out.println(pe);
      }
   }
}

While compile and executing above program, this will produce following result:

The 2nd element of array
{"1":{"2":{"3":{"4":[5,{"6":7}]}}}}

Field "1"
{"2":{"3":{"4":[5,{"6":7}]}}}
{}
[5]
[5,2]

JSON with Ajax

Ajax is Asynchronous JavaScript and XML which is used on client side as group of interrelated web development techniques in order to create asynchronous web applications. According to Ajax model, web applications can send data and retrieve data from a server asynchronously without interfering with the display, behavior of existing page.

Many developers use JSON to pass AJAX updates between client and server. Websites updating live sports scores can be considered as an example of AJAX. If these scores have to be updated on the website, then they must be stored on the server so that the webpage can retrieve the score when it is required. This is where we can make use of JSON formatted data.

Any data that is updated using AJAX can be stored using the JSON format on web server. Ajax is used so that javascript can retrieve these JSON files when necessary, they parse them and then does of the two:

  • Store the parsed values in variables for further processing before displaying them on the webpage

  • It directly assign the data to the DOM elements in the webpage, so that it gets displayed on the website.

Example

The below code shows JSON with Ajax, save it in ajax.htm file. Here loading function loadJSON() will be used asynchronously to upload JSON data.

<html>
<head>
<meta content="text/html; charset=ISO-8859-1" http-equiv="content-type">
<script type="application/javascript">
function loadJSON()
{
   var data_file = "http://www.tutorialspoint.com/json/data.json";
   var http_request = new XMLHttpRequest();
   try{
      // Opera 8.0+, Firefox, Chrome, Safari
      http_request = new XMLHttpRequest();
   }catch (e){
      // Internet Explorer Browsers
      try{
         http_request = new ActiveXObject("Msxml2.XMLHTTP");
      }catch (e) {
         try{
            http_request = new ActiveXObject("Microsoft.XMLHTTP");
         }catch (e){
            // Something went wrong
            alert("Your browser broke!");
            return false;
         }
      }
   }
   http_request.onreadystatechange  = function(){
      if (http_request.readyState == 4  )
      {
        // Javascript function JSON.parse to parse JSON data
        var jsonObj = JSON.parse(http_request.responseText);

        // jsonObj variable now contains the data structure and can
        // be accessed as jsonObj.name and jsonObj.country.
        document.getElementById("Name").innerHTML =  jsonObj.name;
        document.getElementById("Country").innerHTML = jsonObj.country;
      }
   }
   http_request.open("GET", data_file, true);
   http_request.send();
}
</script>
<title>tutorialspoint.com JSON</title>
</head>
<body>
<h1>Cricketer Details</h1>
<table class="src">
<tr><th>Name</th><th>Country</th></tr>
<tr><td><div id="Name">Sachin</div></td>
<td><div id="Country">India</div></td></tr>
</table>

<div class="central">
<button type="button" onclick="loadJSON()">Update Details </button>
</body>
</html>

Following is the input file data.json having data in JSON format which will be uploaded asynchronously when we click Update Detail button. This file is being kept in http://www.tutorialspoint.com/json/

{"name": "brett", "country": "Australia"}

Above HTML code will generate following screen, where you can check AJAX in action:

Cricketer Details

NameCountry
Sachin
India

When you click on Update Detail button, you should get a result something as follows, you can try it yourself JSON with AJAX provided your browser supports Javascript.

Cricketer Details

NameCountry
brett
Australia


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