class Ideone {
static void main(String[] args) {
def redirectQuery = "&callbackUri=someValue"
def callbackUriMatch = redirectQuery =~ /(?<=[&?]callbackUri=)[^&]*/
if (callbackUriMatch) {
println callbackUriMatch.group()
}
}
}
Y2xhc3MgSWRlb25lIHsKICAgIHN0YXRpYyB2b2lkIG1haW4oU3RyaW5nW10gYXJncykgewogICAgCWRlZiByZWRpcmVjdFF1ZXJ5ID0gIiZjYWxsYmFja1VyaT1zb21lVmFsdWUiCgkJZGVmIGNhbGxiYWNrVXJpTWF0Y2ggPSByZWRpcmVjdFF1ZXJ5ID1+IC8oPzw9WyY/XWNhbGxiYWNrVXJpPSlbXiZdKi8KCQlpZiAoY2FsbGJhY2tVcmlNYXRjaCkgewoJCQlwcmludGxuIGNhbGxiYWNrVXJpTWF0Y2guZ3JvdXAoKQoJCX0KICAgIH0KfQo=