Collectors.counting is implemented as follows:

    public static <T> Collector<T, ?, Long>
    counting() {
        return reducing(0L, e -> 1L, Long::sum);
    }

As Tagir states here:

http://mail.openjdk.java.net/pipermail/core-libs-dev/2015-September/035255.html

That implementation results in much boxing.The implementation could use summingLong instead:

    public static <T> Collector<T, ?, Long>
    counting() {
        return summingLong(e -> 1L);
    }