java 时间字符串中毫秒值时有时无,怎么解析

• 针对某个值 时有时无的情况,可用 [xxx] 括起来,标识

  public void testDate2() {
  
          // 针对某个值 时有时无的情况,可用 [] 括起来,标识
          DateTimeFormatter settleTimeFormatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss[.SSS]");
          String date = "2021-02-26 07:35:23";
          String date2 = "2021-02-26 07:35:23.121";
  
          TemporalAccessor parse = settleTimeFormatter.parse(date);
          TemporalAccessor parse2 = settleTimeFormatter.parse(date2);
          System.out.println(parse);
          System.out.println(parse2);
  
  
      }
  

• 针对 某个值位数不一定的时候,用SimpleDateFormat 解析不报错,用DateTimeFormatter 解析报错的处理
  说明:针对某个值的位数不固定的情况,可用用 ParsePosition 规定,从某个索引开始,按索引值与对应的时间值区匹配,而不是字段的长度与匹配格式不匹配就抛出异常

  	public void testDate3() throws ParseException {
  
      
  
      DateTimeFormatter settleTimeFormatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss[.S]");
      String date = "2021-02-26 10:50:07";
      String date1 = "2021-02-26 10:50:07.1";
      String date2 = "2021-02-26 10:50:07.17";
      String date3 = "2021-02-26 10:50:07.172";
  
      // 针对某个值的位数不固定的情况,可用用 ParsePosition 规定,从某个索引开始,按索引值与对应的时间值区匹配
      TemporalAccessor parse = settleTimeFormatter.parse(date,new ParsePosition(0));
      TemporalAccessor parse1 = settleTimeFormatter.parse(date1,new ParsePosition(0));
      TemporalAccessor parse2 = settleTimeFormatter.parse(date2,new ParsePosition(0));
      TemporalAccessor parse3 = settleTimeFormatter.parse(date3,new ParsePosition(0));
      System.out.println(parse);
      System.out.println(parse1);
      System.out.println(parse2);
      System.out.println(parse3);
  
  
  }