Hidden features of Groovy?

Answer 1

Destructuring

It might be called something else in Groovy; it's called destructuring in clojure. You'll never believe how handy it can come.

def list = [1, 'bla', false]
def (num, str, bool) = list
assert num == 1
assert str == 'bla'
assert !bool

Answer 2

For testing java code with groovy, object graph builder is amazing:

def company = builder.company( name: 'ACME' ) {
   address( id: 'a1', line1: '123 Groovy Rd', zip: 12345, state: 'JV' )
   employee(  name: 'Duke', employeeId: 1 ){
      address( refId: 'a1' )
   }
}

Standard feature, but still really nice.

ObjectGraphBuilder

(You do need to give any properties of your POJO that are Lists a default value of an empty list rather than null for builder support to work.)

Answer 3

println 
"""
Groovy has "multi-line" strings.
Hooray!
"""

Answer 4

Anyone know about Elvis?

def d = "hello";
def obj = null;

def obj2 = obj ?: d;   // sets obj2 to default
obj = "world"

def obj3 = obj ?: d;  // sets obj3 to obj (since it's non-null)

Answer 5

Using the Spaceship Operator

I like the Spaceship operator, useful for all sorts of custom sorting scenarios. Some examples of usage are here. One situation in which it's particularly helpful is in creating a comparator on the fly of an object using multiple fields. e.g.

def list = [
    [ id:0, first: 'Michael', last: 'Smith', age: 23 ],
    [ id:1, first: 'John', last: 'Smith', age: 30 ],
    [ id:2, first: 'Michael', last: 'Smith', age: 15 ],    
    [ id:3, first: 'Michael', last: 'Jones', age: 15 ],   
]

// sort list by last name, then first name, then by descending age
assert (list.sort { a,b -> a.last <=> b.last ?: a.first <=> b.first ?: b.age <=> a.age })*.id == [ 3,1,0,2 ]

Answer 6

Multiple variables deceleration

1)Multiple variables declarations in single line

def (a,b,c) = [1,2,3]

2)Using different type declarations.

def (String a, int b) = ['Groovy', 1]