Creating Global Groovy Closure

Question

I'm trying to learn how to create a global closure in groovy (like the println closure). I have the following code:

a.groovy

def header = Tools.&header
header 'groovy script a'

b.groovy

def header = Tools.&header
header 'groovy script b'

tools.groovy

class Tools {
    def static header(String str) {
        println("\n${str}")
        println("-" * 80)
    }
}

I would like to avoid:

def header = Tools.&header

in every groovy script where I would like to use the Tools.header() (and just use header closure when I import the tools package). I tried to put the definition after the Tools class, but that did not work. Can this be done? Is there a better way to handle this?

EDIT: (using a metaClass and the evaluate method unless there is a simpler way to include an external script):

a.groovy

evaluate(new File("Tools.groovy"))
header 'groovy script a'

b.groovy

evaluate(new File("Tools.groovy"))
header 'groovy script b'

tools.groovy

Object.metaClass.header = {str ->
    println("\n${str}")
    println("-" * 80)
}

Dónal Dónal · Accepted Answer · 2011-04-06T08:57:48

println is not actually a global closure. It's a method that is added to java.lang.Object using groovy metaprogramming. Because all classes extend Object - including the script class that wraps code run in the groovy console - println can be called from anywhere.

You can add your own methods to Object. Run this code in the Groovy console to see it in action:

// Add a global sayHello() method
Object.metaClass.sayHello = {-> println 'hello' }

// Try it out
sayHello()

Creating Global Groovy Closure

2 Answers