September 5, 2009

Groovy Goodness: the With Method

Groovy has a with method we can use to group method calls and property access to an object. The with method accepts a closure and every method call or property access in the closure applies to the object if applicable. The method is part of Groovy's extensions to the java.lang.Object class. Let's see this with an example:

class Sample {
    String username
    String email
    List<String> labels = []
    def speakUp() { "I am $username" }
    def addLabel(value) { labels << value }

def sample = new Sample()
sample.with {
    username = 'mrhaki'
    email = 'email@host.com'
    println speakUp()  // Output: I am mrhaki
    addLabel 'Groovy' 
    addLabel 'Java'    
assert 2 == sample.labels.size()
assert 'Groovy' == sample.labels[0]
assert 'Java' == sample.labels[1]
assert 'mrhaki' == sample.username
assert 'email@host.com' == sample.email

def sb = new StringBuilder()
sb.with {
    append 'Just another way to add '
    append 'strings to the StringBuilder '
    append 'object.'    

assert 'Just another way to add strings to the StringBuilder object.' == sb.toString()

// Another example as seen at 
// http://javajeff.blogspot.com/2008/11/getting-groovy-with-with.html
def cal = Calendar.instance
cal.with {
    set(YEAR, 2009)
    set DATE, 4    
    add DATE, 2
assert'September 6, 2009' == cal.time.format('MMMM d, yyyy')