Java Cookbook, 4th Edition

Chapter 14. Processing JSON Data

14.0 Introduction

JSON, or JavaScript Object Notation, is all of the following:

• A simple, lightweight data interchange format.

• A simpler, lighter alternative to XML.

• Easy to generate with println() or with one of several APIs.

• Recognized directly by the JavaScript parser in all web browsers.

• Supported with add-on frameworks for all common languages (Java, C/C++, Perl, Ruby, Python, Lua, Erlang, Haskell, to name a few); a ridiculously long list of supported languages (including two dozen parsers for Java alone) is right on the home page.

A simple JSON message might look like this:

json/src/main/resources/json/softwareinfo.json/

{
  "name": "robinparse",
  "version": "1.2.3",
  "description": "Another Parser for JSON",
  "className": "RobinParse",
  "contributors": [
        "Robin Smythe",
        "Jon Jenz",
        "Jan Ardann"
    ]
}

As you can see, the syntax is simple, nestable, and amenable to human inspection.

The JSON home page provides a concise summary of JSON syntax. There are two kinds of structure: JSON objects (maps) and JSON arrays (lists). JSON objects are sets of name and value pairs, which can be represented either as a java.util.Map or as the properties of a Java object. For example, the fields of a LocalDate (see Recipe 6.1) object for April 1, 2019, might be represented like this:

{
	"year": 2019,
	"month": 4,
	"day" : 1
}

JSON arrays are ordered lists, represented in Java either as arrays or as java.util.Lists. A list of two dates might look ...