Adding two streams, or an extra element to a stream

Concat.java

Stream<Foo> stream = stream1.collect(concat(stream2)).collect(concat(element));

Stream<Foo> stream = stream1
                     .filter(x -> x!=0)
                     .collect(concat(stream2))
                     .filter(x -> x!=1)
                     .collect(concat(element))
                     .filter(x -> x!=2);
                     
private static <T,A,R,S> Collector<T,?,S> combine(Collector<T,A,R> collector, Function<? super R, ? extends S> function) {
		return Collector.of(
				collector.supplier(),
				collector.accumulator(),
				collector.combiner(),
				collector.finisher().andThen(function));
	}
	public static <T> Collector<T,?,Stream<T>> concat(Stream<? extends T> other) {
		return combine(Collectors.toList(),
				list -> Stream.concat(list.stream(), other));
	}
	public static <T> Collector<T,?,Stream<T>> concat(T element) {
		return concat(Stream.of(element));
	}