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October 4, 2009

Groovy Goodness: Join Elements to a String

In Groovy we can join elements in a list or array with the join() method to a String. We can set the separator that needs to be between each element. If we don't define a separator the elements are all concatenated together without any separation. The join() method knows when thet last element of the list is reached and no separator is added at the end of the String. Because the end result is a string, all elements are converted to their string counterparts with the toString() method.

def abc = ['a', 'b', 'c']
assert 'abc' == abc.join()
assert 'a::b::c' == abc.join('::')

def numbers = [0, 1, 2, 3, 4, 5] as Integer[]
assert '012345' == numbers.join()
assert '0 x 1 x 2 x 3 x 4 x 5' == numbers.join(' x ')
assert '0 1 2 3 4 5' == numbers.join(' ')

def objects = [new URL('http://www.mrhaki.com'), 'mrhaki', new Expando(name: 'mrhaki'), new Date(109, 10, 10)]
assert 'http://www.mrhaki.com,mrhaki,{name=mrhaki},Tue Nov 10 00:00:00 UTC 2009' == objects.join(',')

// Also great for creating URL query parameters.
def map = [q: 'groovy', maxResult: 10, start: 0, format: 'xml']
def params = map.inject([]) { result, entry -> 
    result << "${entry.key}=${URLEncoder.encode(entry.value.toString())}"
}.join('&')
assert 'q=groovy&maxResult=10&start=0&format=xml' == params