Nasgen is a tool for processing Java classes that implement native

JavaScript objects. It does so by looking for the

com.oracle.nashorn.objects.annotations.ScriptClass annotation and other

annotations in that package.

For each  class "C", nasgen instruments the original class and generates

two additional classes: a "C$Prototype" class for the JavaScript

prototype object, and a "C$Constructor" class for the JavaScript

constructor function.

Each class instrumented or generated by nasgen contains a private static

"$nasgenmap$" field of type com.oracle.nashorn.runtime.PropertyMap and

static initializer block to initialize the field to the object's

JavaScript properties.

Members annotated with @Function, @Property, @Getter, and @Setter are

mapped to the $Constructor, $Prototype, or main class, depending on the

value of the annotation's 'where' field. By default, @Property, @Getter,

and @Setter belong to the main class while @Function methods without

explicit 'where' field belong to the $Prototype class. The @Constructor

annotation marks a method to be invoked as JavaScript constructor.

Nasgen enforces all @Function/@Getter/@Setter/@Constructor annotated

methods to be declared as static. Static final @Property fields remain

in the main class while other @Property fields are moved to respective

classes depending on the annotation's 'where' value. For functions

mapped to the $Prototype or $Constructor class, nasgen also generates

getters and setters prefixed by G$ and S$, respectively.

Nasgen-generated classes are hidden from normal ClassLoaders by giving

them a ".clazz" file name extension instead of the standard ".class"

extension. This allows script classes to be loaded independently by each

Nashorn context through the com.oracle.nashorn.runtime.StructureLoader

class loader.