Java Cookbook, 3rd Edition

Chapter 19. Processing JSON Data

Introduction

JSON, or JavaScript Object Notation, is:

• A simple, lightweight data interchange format.
• A simpler, lighter alternative to XML (see Chapter 20).
• Easy to generate with printlns 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 homepage.

A simple JSON message might look like this:

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 Finding Today’s Date) object for April 1, 2014, might be represented as:

{
        "year": 2014,
        "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 like this:

{
        [{
                "year": 2014,
                "month": 4,
                "day" : 1
        },{
                "year":