JSON Concepts

Internal

• JSON

Top-Level Element

The top level element has always one of the JSON data types. If it's a boolean, number or string, the entire content consists of that sole element. For a complex, recursive content, the top element is either an Object, so it starts with "{" or an Array, so it starts with "[".

Data Types

JSON data types are: null, Booleans, Strings, Numbers, Objects (which can be thought of as Maps) and Arrays.

null

null is represented as a lowercase literal:

null

Booleans

Booleans are represented as lowercase literals:

true
false

and they are not quoted.

Strings

Strings are represented as:

"this is a string"

and they must be quoted.

Always use double quotes ("), never use single quotes ('). Single quotes are only accepted if the parser was configured so, which is not the default. See "Single Quotes vs. Double Quotes" below.

Numbers

Numbers are represented as:

10

and they are not quoted.

Objects

Objects are enclosed in curly brackets "{}" and contain fields.

The field name and the value are separated by colon (":"). The pairs are delimited by commas (",").

The field name is always a string, so it must be quoted.

{
  "id" : 42,
  "name" : "John Doe",
  "married" : true
  "kids" : [ "Alice", "Bob" ]
}

Fields

A field is a key-value pair, where the key, or the field name, is always a string.

The JSON RFC refers to the key as "names". Jackson refers to them as "field names".

The field name, is separated by the value by a semicolon (:). The value can have any of the JSON data types.

Fields can only exist inside of a JSON Object.

Arrays

Array elements are enclosed in brackets "[", and they are separated by commas:

[ "one element", "another element" ]

Comments

JSON does not support comments: https://plus.google.com/+DouglasCrockfordEsq/posts/RK8qyGVaGSr

A comment can be simulated as follows:

{
   "comment":"this is a comment",

   ...

} 

Single Quotes vs. Double Quotes

Never use single quotes ('), always use double quotes ("). Single quotes are only accepted if the parser was configured so, which is not the default.

JSON Schema

JSON Schema is a vocabulary that allows to annotate and validate JSON documents. The schema describes the data format, and provides complete structural validation. Example:

{
  "description":"A customer",
  "type":"object",
  "properties":
   {
      "first": {"type": "string"},
      "last" : {"type" : "string"}
   }
}

More http://json-schema.org.

Collection+JSON

Collection+JSON is a JSON-based read/write hypermedia-type designed to support management and querying of simple collections. More details http://amundsen.com/media-types/collection/.