JSON (JavaScript Object Notation)
JSON 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.
Features of JSON
Simplicity
Openness
Self Describing
Internationalization
Extensibility
Interoperability
Exchanging Data
When exchanging data between a browser and a server, the data can only be text.
JSON is text, and we can convert any JavaScript object into JSON, and send JSON to the server.
We can also convert any JSON received from the server into JavaScript objects.
This way we can work with the data as JavaScript objects, with no complicated parsing and translations.
Sending Data
If you have data stored in a JavaScript object, you can convert the object into JSON, and send it to a server:
Example
var myObj = { "name":"John", "age":31, "city":"New York" };
var myJSON = JSON.stringify(myObj);
window.location = "demo_json.php?x=" + myJSON;
Receiving Data
If you receive data in JSON format, you can convert it into a JavaScript object:
Example
var myJSON = '{ "name":"John", "age":31, "city":"New York" }';
var myObj = JSON.parse(myJSON);
document.getElementById("demo").innerHTML = myObj.name;
Storing Data
When storing data, the data has to be a certain format, and regardless of where you choose to store it, text is always one of the legal formats.
JSON makes it possible to store JavaScript objects as text.
Example
Storing data in local storage
//Storing data:
myObj = { "name":"John", "age":31, "city":"New York" };
myJSON = JSON.stringify(myObj);
localStorage.setItem("testJSON", myJSON);
//Retrieving data:
text = localStorage.getItem("testJSON");
obj = JSON.parse(text);
document.getElementById("demo").innerHTML = obj.name;
JSON Syntax
The JSON syntax is a subset of the JavaScript syntax.
JSON Syntax Rules
JSON syntax is derived from JavaScript object notation syntax:
Data is in name/value pairs
Data is separated by commas
Curly braces hold objects
Square brackets hold arrays
JSON Data - A Name and a Value
JSON data is written as name/value pairs.
A name/value pair consists of a field name (in double quotes), followed by a colon, followed by a value:
Example
"name":"John"
JSON names require double quotes. JavaScript names don't.
JSON - Evaluates to JavaScript Objects
The JSON format is almost identical to JavaScript objects.
In JSON, keys must be strings, written with double quotes:
JSON
{ "name":"John" }
In JavaScript, keys can be strings, numbers, or identifier names:
JavaScript
{ name:"John" }
JSON Values
In JSON, values must be one of the following data types:
a string
a number
an object (JSON object)
an array
a boolean
null
In JavaScript values can be all of the above, plus any other valid JavaScript expression, including:
a function
a date
undefined
In JSON, string values must be written with double quotes:
JSON
{ "name":"John" }
In JavaScript, you can write string values with double or single quotes:
JavaScript
{ name:'John' }
JSON Uses JavaScript Syntax
Because JSON syntax is derived from JavaScript object notation, very little extra software is needed to work with JSON within JavaScript.
With JavaScript you can create an object and assign data to it, like this:
Example
var person = { "name":"John", "age":31, "city":"New York" };
You can access a JavaScript object like this:
Example
// returns John
person.name;
It can also be accessed like this:
Example
// returns John
person["name"];
Data can be modified like this:
Example
person.name = "Gilbert";
It can also be modified like this:
Example
person["name"] = "Gilbert";
You will learn how to convert JavaScript objects into JSON later in this tutorial.
JavaScript Arrays as JSON
The same way JavaScript objects can be used as JSON, JavaScript arrays can also be used as JSON.
You will learn more about arrays as JSON later in this tutorial.
JSON Files
The file type for JSON files is ".json"
The MIME type for JSON text is "application/json"
JSON Data Types
In JSON, values must be one of the following data types:
a string
a number
an object (JSON object)
an array
a boolean
null
JSON values cannot be one of the following data types:
a function
a date
undefined
JSON Strings
Strings in JSON must be written in double quotes.
Example
{ "name":"John" }
JSON Numbers
Numbers in JSON must be an integer or a floating point.
Example
{ "age":30 }
JSON Objects
Values in JSON can be objects.
Example
{
"employee":{ "name":"John", "age":30, "city":"New York" }
}
Objects as values in JSON must follow the same rules as JSON objects.
JSON Arrays
Values in JSON can be arrays.
Example
{
"employees":[ "John", "Anna", "Peter" ]
}
JSON Booleans
Values in JSON can be true/false.
Example
{ "sale":true }
JSON null
Values in JSON can be null.
Example
{ "middlename":null }
JSON Objects
Object Syntax
Example
{ "name":"John", "age":30, "car":null }
JSON objects are surrounded by curly braces {}.
JSON objects are written in key/value pairs.
Keys must be strings, and values must be a valid JSON data type (string, number, object, array, boolean or null).
Keys and values are separated by a colon.
Each key/value pair is separated by a comma.
Accessing Object Values
You can access the object values by using dot (.) notation:
Example
myObj = { "name":"John", "age":30, "car":null };
x = myObj.name;
You can also access the object values by using bracket ([]) notation:
Example
myObj = { "name":"John", "age":30, "car":null };
x = myObj["name"];
JSON Arrays
Arrays as JSON Objects
Example
[ "Ford", "BMW", "Fiat" ]
Arrays in JSON are almost the same as arrays in JavaScript.
In JSON, array values must be of type string, number, object, array, boolean or null.
In JavaScript, array values can be all of the above, plus any other valid JavaScript expression, including functions, dates, and undefined.
Arrays in JSON Objects
Arrays can be values of an object property:
Example
{
"name":"John",
"age":30,
"cars":[ "Ford", "BMW", "Fiat" ]
}
Accessing Array Values
You access the array values by using the index number:
Example
x = myObj.cars[0];
Looping Through an Array
You can access array values by using a for-in loop:
Example
for (i in myObj.cars) {
x += myObj.cars[i];
}
JSON vs XML
The following JSON and XML examples both defines an employees object, with an array of 3 employees:
JSON Example
{"employees":[
{ "firstName":"John", "lastName":"Doe" },
{ "firstName":"Anna", "lastName":"Smith" },
{ "firstName":"Peter", "lastName":"Jones" }
]}
XML Example
<employees>
<employee>
<firstName>John</firstName> <lastName>Doe</lastName>
</employee>
<employee>
<firstName>Anna</firstName> <lastName>Smith</lastName>
</employee>
<employee>
<firstName>Peter</firstName> <lastName>Jones</lastName>
</employee>
</employees>
A list of differences between JSON and XML are given below.
Similarities between JSON and XML
Both are simple and open.
Both supports unicode. So internationalization is supported by JSON and XML both.
Both represents self describing data.
Both are interoperable or language-independent.
Why JSON is Better Than XML
XML is much more difficult to parse than JSON.
JSON is parsed into a ready-to-use JavaScript object.
For AJAX applications, JSON is faster and easier than XML:
Using XML
Fetch an XML document
Use the XML DOM to loop through the document
Extract values and store in variables
Using JSON
Fetch a JSON string
JSON.Parse the JSON string
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.
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.
JSON Schema Example
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 −
JSON with Java
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.
On decoding, the default concrete class of java.util.List isorg.json.simple.JSONArray and the default concrete class of java.util.Map isorg.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 −
{"balance": 1000.21, "num":100, "is_vip":true, "name":"foo"}
Following is another example that shows a 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);
}
}
On compiling and executing the above program, the following result is generated −
{"balance": 1000.21, "num":100, "is_vip":true, "name":"foo"}
Decoding JSON in Java
The following example makes use of JSONObject
import org.json.simple.JSONObject;
import org.json.simple.JSONValue;
public class JsonDecode {
public static void main(String[] args) {
String s="{\"name\":\"sycs\",\"salary\":600000.0,\"age\":27}";
Object obj=JSONValue.parse(s);
JSONObject jsonObject = (JSONObject) obj;
String name = (String) jsonObject.get("name");
double salary = (Double) jsonObject.get("salary");
long age = (Long) jsonObject.get("age");
System.out.println(name+" "+salary+" "+age);
}
}
Reviewed by Asst. Prof. Sunita Rai
on
March 27, 2022
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