What is JSON?

JSON (JavaScript Object Notation) is a lightweight data interchange format based on a subset of JavaScript syntax. It is used to represent structured data in a human-readable form and is also easy for machines to parse.

The main elements of JSON are:

1. Objects: Unordered sets of key-value pairs. The key is a string, and the value can be any JSON data type. Objects are enclosed in curly braces {}. Example:

   {
     "name": "Ivan",
     "age": 30
   }
   

2. Arrays: Ordered lists of values. Arrays are enclosed in square brackets []. Values can be of different types. Example:

   [
     "Apple",
     "Banana",
     "Orange"
   ]
   

3. Values: Can be of the following types:
   • String: A sequence of characters in double quotes "".
   • Number: An integer or floating-point number.
   • Boolean: true or false.
   • null: An empty value.
   • Object.
   • Array.

Example of a complete JSON document:

{
  "user": {
    "id": 123,
    "name": "Peter",
    "surname": "Petrov",
    "active": true,
    "roles": ["user", "admin"],
    "address": null,
    "contacts": {
      "email": "petrov@example.com",
      "phone": "111-222-333"
    }
  },
  "products": [
    {
      "code": "A1",
      "name": "Laptop",
      "price": 1200.50
    },
    {
      "code": "B2",
      "name": "Mouse",
      "price": 25.00
    }
  ]
}

JSON is widely used for data exchange between server and web application (AJAX), in configuration files, and as a format for storing unstructured and semi-structured data. In Java, libraries such as Jackson, Gson, org.json, and others are used to work with JSON, allowing conversion between JSON and Java objects (deserialization) and vice versa (serialization).