Groovy Closure to Callable

gistfile1.java

// anonymously invoke a closure into callable and submit to executor
// this fails w/o the explicit (Callable) since it converts it to Runnable

def executor = java.util.concurrent.Executors.newFixedThreadPool(5)
def future = executor.submit((java.util.concurrent.Callable) {
    'TEST'
})

assert('TEST' == future.get())

can also do

def future = executor.submit({ 'TEST' } as Callable)