面试题与答案

Douglas Crockford is the Creator or Father of JSON.

JSON full form is JavaScript Object Notation. JSON is a lightweight text-based open standard designed for human-readable data interchange. It is derived from the JavaScript programming language for representing simple data structures and associative arrays, called objects. And JSON is language-independent, with parsers available for virtually every programming language. Uses conventions that are familiar to programmers of the C-family of languages, including C, C++, C#, Java, JavaScript, Perl, Python,php
The JSON format is often used for serializing and transmitting structured data over a network connection. When third party data interchane(REST Services) then JSON may used there LIKE SHOP .It is primarily used to transmit data between a server and web application, serving as an alternative to XML.

The JSON filename extension is .json.

Json is too much easy with php There is no installation needed to use these functions; they are part of the PHP core. nothing more need to know just only use { ,[ and create json format string and use three php function json_encode() to get JSON representation of a value, json_decode() for Decodes a JSON string, �json_last_error() to get the last error occurred in process.

Example:
$string='{
"firstName": "Rohit",
"lastName": "Singh",
"age": 26,
"address": {
"streetAddress": "Mira Road Thane ",
"city": "Mumbai",
"state": "maharshtra",
"postalCode": "401107"
},
"phoneNumber": [
{ "type": "home", "number": "022 333-1234" },
{ "type": "fax", "number": "022 444-4567" }
]
}';

$decodeString = json_decode($string);
echo 'First Name - '.$decode->{"firstName"};
echo 'Last Name - '.$decode->{"lastName"};
echo 'Address - '.$decode->{"address"}->{"streetAddress"};

Out put : Print below

First Name - Rohit
Last Name - Singh
Address - Mira Road Thane

Some of JSON tools for java developer is
� Parser
> Parse JSON text files and convert these to a Java model
� Renderer
> Render a Java representation into text
� Serializer
> Serialize plain POJO clusters to a JSON representation
� Validator
> Validate the contents of a JSON file using a JSON schema
JSONObject Java Class
� A JSONObject is an unordered collection of name/value pairs
� The put methods adds a name/value pair to an object
� The texts produced by the toString methods strictly conform to the JSON syntax rules
myString = new JSONObject().put("JSON", "Hello, World!").toString();
// myString is {"JSON": "Hello, World"}

� Lighter and faster than XML as on-the-wire data format
� JSON objects are typed while XML data is typeless
> JSON types: string, number, array, boolean,
> XML data are all string
� Native data form for JavaScript code
> Data is readily accessible as JSON objects in your JavaScript
code vs. XML data needed to be parsed and assigned to variables through tedious DOM APIs
> Retrieving values is as easy as reading from an object property in your JavaScript code

� A collection of name/value pairs
> In various languages, this is realized as an object, record, struct, dictionary, hash table, keyed list, or associative array
� An ordered list of values
> In most languages, this is realized as an array, vector, list, or sequence
� These are universal data structures supported
� A JSON object is an unordered set of name/value pairs
� A JSON object begins with { (left brace) and ends with } (right brace)
� Each name is followed by : (colon) and the name/value pairs are separated by , (comma)

� JSON is a subset of the object literal notation of JavaScript
> JSON can be used in the JavaScript language with no muss or fuss
Example: JSON Object
var myJSONObject = {"bindings": [ {"ircEvent": "PRIVMSG", "method": "newURI", "regex": "^http://.*"},
{"ircEvent": "PRIVMSG", "method": "deleteURI", "regex": "^delete.*"},
{"ircEvent": "PRIVMSG", "method": "randomURI", "regex": "^random.*"}
]
};
� In this example, a JSON JavaScript object is created
containing a single member "bindings", which contains
an array containing three objects, each containing
"ircEvent", "method", and "regex" members
� Members can be retrieved using dot or subscript
operators myJSONObject.bindings[0].method // "newURI"
Text to Object Conversion in
JavaScript code
var myObject = eval('(' + myJSONtext + ')');
� To convert a JSON text into an JSON object, use
the eval() function > eval() invokes the JavaScript compiler
> Since JSON is a proper subset of JavaScript, the compiler will
correctly parse the text and produce an object structure

� Create JSON Java object
� Add name and value pairs using put method
� Convert it to String type using toString method and send it to the client with content-type as "text/xml" or "text/plain"
myString = new JSONObject().put("JSON", "Hello, World!").toString();
// myString is {"JSON": "Hello, World"}

� JSON data is received as a string
� Calling eval() will generate JSON object in JavaScript code
var JSONdata = eval(req.responseText);
� Once you have JSON object, you can use . notation to access its properties
var name = JSONdata.name;
var address = JSONdata.addresses[3];
var streetname = JSONdata.addresses[3].street;

� Create JSON JavaScript object
� Use "POST" HTTP method in the open method of the XMLHttpRequest object
� Pass JSON JavaScript object in the send method of XMLHttpRequest object
var carAsJSON = JSON.stringify(car);
var url = "JSONExample?timeStamp=" + new Date().getTime(); createXMLHttpRequest();
xmlHttp.open("POST", url, true);
xmlHttp.onreadystatechange = handleStateChange;
xmlHttp.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");
xmlHttp.send(carAsJSON);

� Read the JSON data as a String type
� Create JSONObject Java object from the string String json = readJSONStringFromRequestBody(request);
//Use the JSON-Java binding library to create a JSON object in Java JSONObject jsonObject = null;
try {
jsonObject = new JSONObject(json);
}
catch(ParseException pe) {
}

Security and JSON Parser to understand by below examples
// Include http://www.json.org/json.js
var myObject = myJSONtext.parseJSON();
� eval() can compile and execute any JavaScript program, so there can be security issues (cross-site scripting)
Use eval() when the source can be trusted
� When security is a concern - the source cannot be trusted -, it is better to use a JSON parser
A JSON parser will only recognize JSON text and so is much safer
Object to Text Conversion
var myJSONText = myObject.toJSONString();
� You can convert JSON object into JSON text
� JSON does not support cyclic data structure
Do not give cyclical structures to the JSON stringifier

� JSON-RPC is a simple remote procedure call protocol similar to XML-RPC although it uses the lightweight JSON format instead of XML
� JSON-RPC-Java is a Java implementation of the JSON-RPC protocol

� It allows you to transparently call server-side Java code from JavaScript with an included lightweight JSON-RPC JavaScript client.
� It is designed to run in a Servlet container such as Tomcat and can be used with J2EE Application servers to allow calling of plain Java or EJB methods from within a JavaScript DHTML web application.

� Dynamically call server-side Java methods from JavaScript DHTML web applications. No Page reloading.
� Asynchronous communications.
� Transparently maps Java objects to JavaScript objects.
� Lightweight protocol similar to XML-RPC although much faster.
� Leverages J2EE security model with session specific exporting of objects.
� Supports Internet Explorer, Mozilla, Firefox, Safari, Opera.