Procedures and Compiled Scripts - Scripting in Java: Integrating with Groovy and JavaScript - page 172

The two versions of the getInterface() method let you get an instance of a Java
interface that is implemented in a scripting languages. I will discuss these functions in
details in the next section. The invokeFunction() method lets you invoke a top-level
function written in a scripting language. The invokeMethod() method lets you invoke
methods of objects written in a scripting language.
It is the responsibility of the developer to check if a script engine implements the
Invocable interface, before invoking a procedure. Invoking a procedure is a four-step
process:

• Check if the script engine supports procedure invocation

Invocable type • Cast the engine reference to the

• Evaluate the script that contains the source code for the

procedure, so the engine compiles and caches the script

invokeFunction() method of the Invocable interface
to invoke procedures and functions; use the invokeMethod()
method to invoke methods of the objects created in a scripting
language

• Use the

The following snippet of code performs the check that the script engine
implementation class implements the Invocable interface:

// Get the Nashorn engine
ScriptEngineManager manager = new ScriptEngineManager();
ScriptEngine engine = manager.getEngineByName("JavaScript");

// Make sure the script engine implements the Invocable interface
if (engine instanceof Invocable) {
System.out.println("Invoking procedures is supported.");
}
else {
System.out.println("Invoking procedures is not supported.");
}

The second step is to cast the engine reference to the Invocable interface type:

if (engine instanceof Invocable) {
Invocable inv = (Invocable)engine;

// More code goes here
}