Question

Suppose I have a Javascript file

function js_main(args){
     /* some code */
     var x = api_method1(some_argument);
     /* some code */
}

And I try to run it with javax.scripting the usual way

ScriptEngineManager manager = new ScriptEngineManager();
ScriptEngine engine = manager.getEngineByName("javascript");
engine.eval(...);

Now the I’d like to handle the call to api_method1 in Javascript with my Java class. I’d like to have some kind of mapping/binding of calls i.e. each time the script calls api_method1(arg) a method

public Object api_method1(Object arg){ ... }

(placed in the same class as the engine) would be called.

Can I achieve this?

Answer 1

1. use engine.createBindings() to make a Bindings object;

2. put an object exposing your method into the bindings with some name:

   Bindings b = engine.createBindings();
   b.put("api", yourApiObject);
   engine.setBindings(b, ScriptContext.ENGINE_SCOPE);
   

3. Then in JavaScript there’ll be a global “api” object you can call:

   api.method1( "foo", 14, "whatever" );
   

The facility is easy to use, but be careful with what you pass back and forth; it doesn’t do that much to convert JavaScript types to Java types.