groovy/groovy-core/xdocs/embedding.wiki

1 Embedding Groovy

Groovy has been designed to be very lightweight and easy to embed into any Java application
or system.

You can use {link:BSF|bsf.html} to embed any scripting language into your Java code; however Groovy offers
a lighter weight and closer integration. There are two main approaches


1.1 Evaluate scripts or expressions using the shell

You can evaluate any expression or script in Groovy using the {link:GroovyShell|apidocs/groovy/lang/GroovyShell.html}.
The GroovyShell allows you to pass in and out variables via the {link:Binding|apidocs/groovy/lang/Binding.html} object.

{code:java}
// call groovy expressions from Java code
Binding binding = new Binding();
binding.setVariable("foo", new Integer(2));
GroovyShell shell = new GroovyShell(binding);

Object value = shell.evaluate("println 'Hello World!'; x = 123; return foo * 10");
assert value.equals(new Integer(20));
assert binding.getVariable("x").equals(new Integer(123))
{code}


1.1 Dynamically loading and running Groovy code inside Java

You can use the {link:GroovyClassLoader|apidocs/groovy/lang/GroovyClassLoader.html} 
to load classes dynamically into a Java program and execute them (or use them) directly.
The following Java code shows an example... 

{code:java}
ClassLoader parent = getClass().getClassLoader();
GroovyClassLoader loader = new GroovyClassLoader(parent);
Class groovyClass = loader.parseClass(new File("src/test/groovy/script/HelloWorld.groovy"));

// lets call some method on an instance
GroovyObject groovyObject = (GroovyObject) groovyClass.newInstance();
Object[] args = {};
groovyObject.invokeMethod("run", args);
{code}

If you have an interface you wish to use which you implement in the Groovy script you can use it as follows

{code:java}
GroovyClassLoader gcl = new GroovyClassLoader();
Class clazz = gcl.parseClass(myStringwithGroovyClassSource "SomeName.groovy");
Object aScript = clazz.newInstance();
MyInterface myObject = (MyInterface) aScript;
myObject.interfaceMethod();
  ...
{code}

This works fine if the Groovy class implements the inferface MyInterface.
myObject can from then on be used as every other Java object implementing
MyInterface.


1.1 Runtime dependencies

As well as Java 1.4 and the Groovy jar we also depend at runtime on the ASM library. Thats it.
So just add these 2 jars to your classpath and away you go, you can happily embed Groovy into your application.