JSON Questions et reponses d'entretien
Differences associees
Question 6. Explain JSON Structures.
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)
Question 7. Compare JSON with JavaScript.
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
Question 8. What is the Security and JSON Parser?
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
Question 9. What are the JSON Tools for Java Developer?
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"}
Question 10. How to Generate or Send JSON Data at the Server Side?
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"}
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