Non-terminal forEach() in a stream?

Yes there is. It is called peek() (example from the JavaDoc):

Stream.of("one", "two", "three", "four")
     .peek(e -> System.out.println("Original value: " + e))
     .filter(e -> e.length() > 3)
     .peek(e -> System.out.println("Filtered value: " + e))
     .map(String::toUpperCase)
     .peek(e -> System.out.println("Mapped value: " + e))
     .collect(Collectors.toList());