Problem Statement

Sort an array (or list) of strings in order of descending length, and in ascending lexicographic order for strings of equal length. Use a sorting facility provided by the language/library, combined with your own callback comparison function.

Note:   Lexicographic order is case-insensitive.

Let's start with the solution:

def strings = "Here are some sample strings to be sorted".split()
strings.sort { x, y ->
    y.length() <=> x.length() ?: x.compareToIgnoreCase(y)
}
println strings