|
|
| Line 1: |
Line 1: |
| − | {{JSON}} | + | {{JSON(ctg)}} |
| − | | |
| − | == Overview ==
| |
| − | [http://www.json.org JSON] (JavaScript Object Notation) is a form of data representation that provides a standardised data exchange format using simple text. As the name suggests, it is based on a subset of the JavaScript programming language; however, it is completely language-agnostic. Besides being easy for humans to read and write, it is also easy for machines to parse and generate.
| |
| − | | |
| − | Compared to [[XML]], it is more human-readable.
| |
| − | | |
| − | == JSON Object ==
| |
| − | A JSON Object is nothing more than a collection of comma-separated name/value pairs (often called members) enclosed in curly brackets:
| |
| − | | |
| − | <syntaxhighlight lang="javascript">
| |
| − | {"name1":value1, "name2":value2 ...}
| |
| − | </syntaxhighlight>
| |
| − | | |
| − | To make it easier for humans to read and visualize, the name/value pairs are often listed vertically:
| |
| − | | |
| − | <syntaxhighlight lang="javascript">
| |
| − | {
| |
| − | "name1": value1,
| |
| − | "name2": value2
| |
| − | }</syntaxhighlight>
| |
| − | | |
| − | The name is supposed to be a string in double quotes, while the value can be any of the following:
| |
| − | | |
| − | * a simple string, numeric, boolean or null value (strings are enclosed in double quotes):<br /><code>{"id":1, "name":"John Doe", "married":false}</code>
| |
| − | | |
| − | * an array; which is a collection of comma-separated values in square brackets:<br /><code>{"primeNumbers":[2, 3, 5, 7, 11, 13, 17], "oddNumbers":[1,3,5,7]}</code>
| |
| − | | |
| − | * an object; which is a collection of name:value pairs enclosed in curly brackets:<br /><code>{"address":{"street":"145 Koinange Street", "City":"Nairobi", "Country":"Kenya"}}</code>
| |
| − | | |
| − | | |
| − | JSON objects can always be nested arbitrarily to create even more complex objects:
| |
| − | | |
| − | <syntaxhighlight lang="javascript">
| |
| − | {"user":
| |
| − | { "userid": 1900,
| |
| − | "username": "jsmith",
| |
| − | "password": "secret",
| |
| − | "groups": [ "admins", "users", "maintainers"]
| |
| − | }
| |
| − | }
| |
| − | </syntaxhighlight>
| |
| − | | |
| − | | |
| − | == Valid JSON format ==
| |
| − | | |
| − | There are a few rules and guidelines that define the JSON syntax (see RFC 4627):
| |
| − | | |
| − | * JSON objects are encapsulated within opening and closing brackets <code>{ }</code>. An empty object can be represented by <code>{ }</code>
| |
| − | * Arrays are encapsulated within opening and closing square brackets <code>[ ]</code>. An empty array can be represented by <code>[ ]</code>
| |
| − | * A member is represented by a key-value pair
| |
| − | * The key of a member should be contained in double quotes
| |
| − | * Each member SHOULD have a unique key within an object structure
| |
| − | * The value of a member must be contained in double quotes if it is a string
| |
| − | * Boolean values are represented using the '''true''' or '''false''' literals in lower case
| |
| − | * Number values are represented using double-precision floating-point format; Scientific notation is supported; Numbers should not have leading zeroes
| |
| − | * "Offensive" characters in a string need to be escaped using the backslash character
| |
| − | * Null values are represented by the '''null''' literal in lower case
| |
| − | * Other object types, such as dates, are not natively supported and should be converted to strings; to be managed by the parser/client
| |
| − | * Each member of an object or each array value must be followed by a comma if it is not the last one
| |
| − | * The common extension for json files is '''.json'''
| |
| − | * The MIME type for json files is '''application/json'''
| |
| − | | |
| − | == Implementations ==
| |
| − | JSON implementation is not very strict, and a lot of leeway is granted to the client application and/or parser to enforce the guidelines. As usual when writing code:
| |
| − | * be liberal in what you accept
| |
| − | * be strict (adhering to the standard) in what you send.
| |
| − | | |
| − | There are two main implementations of JSON:
| |
| − | | |
| − | === The official JSON Specification syntax ===
| |
| − | This implementation adheres strictly to the RFC 4627 guidelines above and does not allow deviation from the specification.
| |
| − | | |
| − | === The Javascript syntax ===
| |
| − | This implementation follows the implementation of the Javascript programming language and as such allows for a few deviations from the official specification. For example:
| |
| − | | |
| − | #allows un-quoted keys eg <code> {name: "John Doe" }</code>
| |
| − | #allows single quotes for keys and/or string values; and a liberal mix of single and double quotes eg <code>{'name': "John Doe", "language":'Pascal'}</code>
| |
| − | #allows trailing comma after the last member of an array and/or object eg <code>{"keywords":["if","begin","for",], "IDEs":["Lazarus","fpIDE","MSEide"],}</code>
| |
| − | | |
| − | == See also ==
| |
| − | | |
| − | * [[fcl-json]] package that implements JSON for FreePascal and Lazarus
| |
| − | * [http://www.json.org Official JSON website]
| |
| − | * [[Streaming JSON/de]] - (Original German article)
| |
| − | * [[Streaming JSON/ru]] - (Russian translation from English )
| |
| − | * [[Streaming JSON]] - (English translation from original German)
| |
| − | | |
| − | [[Category:JSON]]
| |
| − | [[Category:JSON/ru]]
| |
