JSON or JavaScript Object Notation is a lightweight 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.
The format was specified by Douglas Crockford.
It was designed for human-readable data interchange.
It has been extended from the JavaScript scripting language.
The filename extension is .json.
JSON Internet Media type is application/json.
The Uniform Type Identifier is public.json.
Uses of JSON
It is used while writing JavaScript based applications that includes browser extensions and websites.
JSON format is used for serializing and transmitting structured data over network connection.
It is primarily used to transmit data between a server and web applications.
Web services and APIs use JSON format to provide public data.
It can be used with modern programming languages.
Characteristics of JSON
JSON is easy to read and write.
It is a lightweight text-based interchange format.
JSON is language independent.
Simple Example in JSON
The following example shows how to use JSON to store information related to books based on their topic and edition.
Now let's try to open Json Array Object using IE or any other javaScript enabled browser. It produces the following result −
JSON - Schema
JSON Schema is a specification for JSON based format for defining the 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.
There are several validators currently available for different programming languages. Currently the most complete and compliant JSON Schema validator available is JSV.
Given below 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 the check various important keywords that can be used in this schema −
Sr.No.
Keyword & Description
1
$schema
The $schema keyword states that this schema is written according to the draft v4 specification.
2
title
You will use this to give a title to your schema.
3
description
A little description of the schema.
4
type
The type keyword defines the first constraint on our JSON data: it has to be a JSON Object.
5
properties
Defines various keys and their value types, minimum and maximum values to be used in JSON file.
6
required
This keeps a list of required properties.
7
minimum
This is the constraint to be put on the value and represents minimum acceptable value.
8
exclusiveMinimum
If "exclusiveMinimum" is present and has boolean value true, the instance is valid if it is strictly greater than the value of "minimum".
9
maximum
This is the constraint to be put on the value and represents maximum acceptable value.
10
exclusiveMaximum
If "exclusiveMaximum" is present and has boolean value true, the instance is valid if it is strictly lower than the value of "maximum".
11
multipleOf
A numeric instance is valid against "multipleOf" if the result of the division of the instance by this keyword's value is an integer.
12
maxLength
The length of a string instance is defined as the maximum number of its characters.
13
minLength
The length of a string instance is defined as the minimum number of its characters.
14
pattern
A string instance is considered valid if the regular expression matches the instance successfully.
You can check a http://json-schema.org for the complete list of keywords that can be used in defining a JSON schema. The above schema can be used to test the validity of the following JSON code −
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 is faster to write JSON for programmers.
Arrays Usage
XML is used to describe the 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.
This chapter covers how to encode and decode JSON objects using PHP programming language. Let's start with preparing the 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
Function
Libraries
json_encode
Returns the JSON representation of a value.
json_decode
Decodes a JSON string.
json_last_error
Returns 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 array into JSON with PHP −
This chapter covers how to encode and decode JSON objects using Perl programming language. Let's start with preparing the environment to start our programming with Perl for JSON.
Environment
Before you start encoding and decoding JSON using Perl, you 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 steps mentioned below −
Perl decode_json() function is used for decoding JSON in Perl. This function returns the value decoded from json to an 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);
This chapter covers how to encode and decode JSON objects using Python programming language. Let's start with preparing the environment to start our programming with Python for JSON.
Environment
Before you start with encoding and decoding JSON using Python, you need to install any of the JSON modules available. For this tutorial we have downloaded and installed Demjson as follows −
While executing, this will produce the 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 an 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
On executing, it will produce the following result −
{u'a': 1, u'c': 3, u'b': 2, u'e': 5, u'd': 4}
JSON with Ruby
This chapter covers how to encode and decode JSON objects using Ruby programming language. Let's start with preparing the environment to start our programming with Ruby for JSON.
Environment
Before you start with encoding and decoding JSON using Ruby, you need to install any of the JSON modules available for Ruby. You may need to install Ruby gem, but if you 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.
This chapter covers how to encode and decode JSON objects using Java programming language. Let's start with preparing the environment to start our programming with Java for JSON.
Environment
Before you start with encoding and decoding JSON using Java, you need to install any of the JSON modules available. For this tutorial we have downloaded and installed JSON.simple and have added the location of json-simple-1.1.1.jar file to the 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.
JSON
Java
string
java.lang.String
number
java.lang.Number
true|false
java.lang.Boolean
null
null
array
java.util.List
object
java.util.Map
On decoding, the default concrete class of java.util.List is org.json.simple.JSONArray and the 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 the 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);
}
}
On compiling and executing the above program the following result will be generated −
The 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);
}
}
}
On compiling and executing the above program, the following result will be generated −
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 the client side as a group of interrelated web development techniques, in order to create asynchronous web applications. According to the AJAX model, web applications can send and retrieve data from a server asynchronously without interfering with the display and the behavior of the existing page.
Many developers use JSON to pass AJAX updates between the client and the 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 the web server. AJAX is used so that javascript can retrieve these JSON files when necessary, parse them, and perform one of the following operations −
Store the parsed values in the variables for further processing before displaying them on the webpage.
It directly assigns the data to the DOM elements in the webpage, so that they are displayed on the website.
Example
The following code shows JSON with AJAX. Save it as ajax.htm file. Here the loading function loadJSON() is 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.howcodex.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>howcodex.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>
</div>
</body>
</html>
Given below is the input file data.json, having data in JSON format which will be uploaded asynchronously when we click the Update Detail button. This file is being kept in http://www.howcodex.com/json/
{"name": "Brett", "country": "Australia"}
The above HTML code will generate the following screen, where you can check AJAX in action −
Cricketer Details
Name
Country
Sachin
India
When you click on the Update Detail button, you should get a result something as follows. You can try JSON with AJAX yourself, provided your browser supports Javascript.
