Writing Scripts in Nashorn - Scripting in Java: Integrating with Groovy and JavaScript - page 128

Serializing Objects
Nashorn supports serializing and desterilizing of object using a built-in object called
JSON . JSON is also an acronym that stands for J ava S cript O bject N otation that specifies
how a JavaScript object is converted to a string and vice versa. JSON is a Data Interchange
Format described in RFC 4627 at http://www.ietf.org/rfc/rfc4627.txt . The JSON
object contains two methods:

JSON.stringify(value, replacer, indentation)

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JSON.parse(text, reviver)
The JSON.stringify() method converts a Nashorn value into a string. The JSON.
parse() method converts a string in JSON format into a Nashorn value.
The value parameter in the stringify() method can be an object or a primitive
value. Not all types of values can be stringified. For example, undefined cannot be
stringified. NaN and Infinity are stringified as null .
The replacer argument is a function or an array. If replacer is a function, it is takes
two parameter. The first parameter is the name of the property being stringified and the
second one is the value of the property. The returned value of the function is used as the
final value to be stringified. If the function returns undefined or no value, the property is not
stringified. The first time replacer is called with the empty string as the property name
and the object being stringified as the value. Subsequent calls pass the property
name and the property value of the property being stringified. If replacer is an array, it
contains the names of the properties to be stringified. Any properties not appearing in the
array will not be stringified.
The indentation is a number or a string used for indentation in the output. If it is a
number, it is the number of spaces to be used for indentation. Its value is capped at 10.
If it is a string such as "\t" , it is used for indentation at each level. The replacer and
indentation parameters are optional in the stringify() method.
The reviver is a function that is called when the JSON text is being parsed into an
object. It takes two parameters. The first parameter is the name of the property being
parsed and the second one is the value of the property. If the function returns null or
undefined , the corresponding property is deleted.
Listing 4-19 demonstrates the use of the JSON object. It stringifies an object. During
stringification, it multiplies the values of the properties by 2. During parsing, it applies the
reverse logic to restore the object.

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Listing 4-19. Using the JSON Object to Stringify and Parse Objects

// json.js
var point = {x: 10, y: 20};

function replacer (key, value) {
if (key === "x" || key === "y") {
// Multiply the value by 2
return value * 2;
}