70. Useful Methods That Use Closures

Groovy adds a number of methods to java.lang.Object that gives you the power of closures baked into many of the data types you’ll use on a daily basis.

any

The any method is passed a closure that evaluates a criteria (condition). If any element in the collection meets that criteria, true is returned. Importantly, any will only iterate through the list until it the criteria is met.

def scores = [10, 8, 11, 6]
assert scores.any {it > 10} == true

find and findAll

The find method locates the first item in a collection that meets the criteria set in the closure:

def animals = ['dog', 'rat', 'cat', 'mouse']
assert animals.find {it in ['rat', 'mouse', 'wild pig'] } == 'rat'

The findAll method is similar to find but returns all collection items that meet the criteria set by the closure:

def animals = ['dog', 'rat', 'cat', 'mouse']
assert animals.findAll {it in ['rat', 'mouse', 'wild pig'] } == ['rat', 'mouse']

split

The split method splits a collection into two lists: the first list contains all items that meet the criteria set by the closure parameter and the second list contains all remaining items.

In the example below I use the split method to get a list of those who got a score over 100 and those that didn’t.

Using split
def players = [
        [ name: 'Fred', topScore: 120 ],
        [ name: 'Sally', topScore: 200 ],
        [ name: 'Felix', topScore: 101 ],
        [ name: 'Albert', topScore: 12 ],
        [ name: 'Jane', topScore: 20 ]
]

def result = players.split { it.topScore > 100 }

result[0].each { println "$it.name is in the hall of fame" }

result[1].each { println "$it.name missed out" }

with

The with method provides a handy approach to calling several methods and manipulating fields for an object.

In the example below I use with to perform a set of operations on an instance of the Person class:

Using with
class Person {
    def name
    def email
    def mobile

    def printBusinessCard() {
        println "$name"
        println "e: $email"
        println "m: $mobile"
    }
}

def john = new Person()

john.with {
    name = 'John Smith'
    email = 'john@example.com'
    mobile = '0401 999 888'
    printBusinessCard()
}

This approach can be really useful when creating an object. In the snippet below I create a new Person and set up their details at the same time:

Using with at instantiation time
class Person {
    def name
    def email
    def mobile

    def printBusinessCard() {
        println "$name"
        println "e: $email"
        println "m: $mobile"
    }
}

def stacey = new Person().with {
    name = 'Stacey Jane'
    email = 'stacy@example.com'
    mobile = '0401 333 666'
    //This is the same as saying 'return it':
    it
}
stacey.printBusinessCard()

Up next

71. Closure scope