GPath example from 'Groovy in Action'.

class Invoice {
    List items
    Date date
}

class LineItem {
    Product    product
    int        count
    int total() {
        return product.dollar * count
    }
}

class Product {
    String name
    def dollar
}

def ulcDate = new Date(107, 0, 1)
def ulc = new Product(dollar:1499, name:'ULC')
def ve = new Product(dollar:499, name:'Visual Editor')

def invoices = [
    new Invoice(date:ulcDate, items: [
        new LineItem(count:5, product:ulc),
        new LineItem(count:1,  product:ve)
    ]),
    new Invoice(date:[107,1,2], items: [
        new LineItem(count:4, product:ve)
    ])
]

assert [5*1499, 499, 4*499] == invoices.items.flatten()*.total() //1

assert ['ULC'] == invoices.items.flatten().grep{it.total() > 7000}.product.name //2

def searchDates = invoices.grep{
    it.items.any{ it.product == ulc }
}.date*.toString()                        //3

assert [ulcDate.toString()] == searchDates