Java对象可以成为Nashorn中JavaScript对象的原型吗？

Question

Is it possible to make an Java object the prototype of a JavaScript object? Like the following:

var Person = Java.type("Person");
var hans = new Person();
hans.name = "Hans";

var employeeFactory = function() {
    var F = function(){};
    F.prototype = hans;
    return new F();
};

var fritz = employeeFactory();
print(fritz.name);

Here Person is a Java Bean. The variable hans is set as the instance of this Java class. The line hans.name = "Hans" sets the name field in the Java object as expected. But when the object fritz is created in the factory function, it doesn't get linked to the expected prototype. Is there any reason why the Java instance isn't accepted as prototype?

Answer 1

It might work in Rhino, because in Rhino all beans are wrapped into JS native objects before being exposed to the JS program. Nashorn OTOH doesn't create wrappers. You can, however, use Nashorn's non-standard Object.bindProperties that adds properties from one object to another, bound to the original object's instance as its this. That's essentially as close as you can get (well, it's pretty darn close) to a wrapper. The exact specification is:

Object.bindProperties(dst, src)

creates bound properties from all properties in src object, puts them into the dst object, and returns the dst object. Since the properties are bound to src , dst.foo will delegate to src.foo for its value. bindProperties has been coded specifically so that it can handle ordinary Java objects as src .

With that in mind, I believe that if you change the line

F.prototype = hans;

to

F.prototype = Object.bindProperties({}, hans);

you'll get what you wanted. That would work with Object.create too, eg Object.create(Object.bindProperties({}, somePojo)) .