Dynamically load jar in groovy

Question

I have a groovy script createWidget.groovy:

 import com.example.widget

 Widget w = new Widget()

This script runs great when I run it like this:

$ groovy -cp /path/to/widget.jar createWidget.groovy

But, I wanted to hardcode the classpath within the script, so that users do not need to know where it is, so I modified createWidget.groovy as follows (which is one of the ways to modify classpath in groovy):

this.getClass().classLoader.rootLoader.addURL(new File("/path/to/widget.jar").toURL())

import com.example.widget

Widget w = new Widget()

But this always fails with a runtime error on the import: unable to resolve class com.example.widget.

This does look unorthodox and I am thinking you can't mess with the rootLoader prior to an import or is it something else?

Answer 1

// Use the groovy script's classLoader to add the jar file at runtime.
this.class.classLoader.rootLoader.addURL(new URL("/path/to/widget.jar"));

// Note: if widget.jar file is located in your local machine, use following:
// def localFile = new File("/path/tolocal/widget.jar");
// this.class.classLoader.rootLoader.addURL(localFile.toURI().toURL());

// Then, use Class.forName to load the class.
def cls = Class.forName("com.example.widget").newInstance();