optional_datetime_format.java

    LocalDate expectDate = LocalDate.of(2018,9,10);
    DateTimeFormatter dateTimeFormatter = new DateTimeFormatterBuilder()
      .append(DateTimeFormatter.ofPattern("[yyyy M d]"))
      .append(DateTimeFormatter.ofPattern("[d M yyyy]"))
      .append(DateTimeFormatter.ofPattern("[d.M.yyyy]"))
      .append(DateTimeFormatter.ofPattern("[d/M/yyyy]"))
      .toFormatter();
    assertThat(LocalDate.parse("2018 09 10",dateTimeFormatter)).isEqualTo(expectDate);
    assertThat(LocalDate.parse("10 9 2018",dateTimeFormatter)).isEqualTo(expectDate);
    assertThat(LocalDate.parse("10.09.2018",dateTimeFormatter)).isEqualTo(expectDate);
    assertThat(LocalDate.parse("10/9/2018",dateTimeFormatter)).isEqualTo(expectDate);