Adding default methods with a Groovy BaseScript

Having talked about nouns in our DSL by adding new variables from the Binding, it’s time to talk a little bit about verbs – there’s a number of ways to do this in Groovy, so let’s start by looking at a BaseScript for Scripts.

A BaseScript is, effectively, the super class for the Script that’s executed dynamically from GroovyShell.    To use a BaseScript, create an abstract class that extends Script, implementing the methods you want to enable in your scripts.  Here’s a very simple example:

package basescripttest;

import groovy.lang.Script;

abstract public class BaseScript extends Script {
    void hello(String name) {
        System.out.println("hello "+name);
    }
}

This BaseScript will provide a single method to your script: hello – taking a single argument, a String.  Note that you could just as easily use a Groovy class for the same purpose:

package basescripttest

abstract class BaseScript extends Script{
    def hello(name) {
        println "hello $name"
    }
}

Which does the same thing.  To use it in a program, use the CompilerConfiguration class, which allows various modifications of how the GroovyShell parser acts at runtime.  Note that you need to pass the fully qualified name of the class as a String to the setScriptBaseClass.

CompilerConfiguration config = new CompilerConfiguration();
config.setScriptBaseClass("basescripttest.BaseScript");
GroovyShell shell = new GroovyShell(config);
Script script = shell.parse("hello('Jim')");
script.run();

 

So, to recap, we’re executing the following script:

hello('Jim')

Which is outputting the following text to stdout:

Jim

In this example, we just use the (now default provided) hello function in the BaseScript from within the provided class. This is a very simple example – we’ll go into more detail next time.