Java Stream - 如何组合函数使用andThen

import java.util.function.Function;

public class Main {
  public static void main(String... args) {
    Function<String, Integer> toInteger = Integer::valueOf;
    Function<String, String> backToString = toInteger.andThen(String::valueOf);

    System.out.println( backToString.apply("123"));
  }
}