How to parse custom multiple Date formats in Java

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I want to parse custom multiple Date formats in Java. Here is my code

Scenario 1: Order of patterns:

  • yyMMdd'h'HH
  • yyMMdd

DateTimeFormatter formatter = new DateTimeFormatterBuilder() .appendOptional(DateTimeFormatter.ofPattern("yyMMdd'h'HH")) .appendOptional(DateTimeFormatter.ofPattern("yyMMdd")).toFormatter();

Works:

String dateString1 = "201028h05";

LocalDateTime date1 = LocalDateTime.parse(dateString1, formatter);

Doesn't works:

String dateString2 = "201028";

LocalDateTime date1 = LocalDateTime.parse(dateString2, formatter);

Scenario 2: Order of patterns:

  • yyMMdd
  • yyMMdd'h'HH

DateTimeFormatter formatter = new DateTimeFormatterBuilder() .appendOptional(DateTimeFormatter.ofPattern("yyMMdd")).toFormatter(); .appendOptional(DateTimeFormatter.ofPattern("yyMMdd'h'HH"))

Doesn't Work:

  String dateString1 = "201028h05";
    
    LocalDateTime date1 = LocalDateTime.parse(dateString1, formatter);

Works:

String dateString2 = "201028";

LocalDateTime date1 = LocalDateTime.parse(dateString2, formatter);

How to make it work for both of the date patterns irrespective of any input pattern order. I don't want to use any external dependency for this.

java-time java
1 Answers

You can use [] to define the optional parts within a pattern. Additionally you need to set defaults to not get an exception when no time is supplied.

DateTimeFormatter formatter = new DateTimeFormatterBuilder()
        .appendPattern("yyMMdd['h'HH]")
        .parseDefaulting(ChronoField.HOUR_OF_DAY, 0)
        .parseDefaulting(ChronoField.MINUTE_OF_HOUR, 0)
        .parseDefaulting(ChronoField.SECOND_OF_MINUTE, 0)
        .toFormatter();

String dateString1 = "201028h05";
LocalDateTime date1 = LocalDateTime.parse(dateString1, formatter);
System.out.println(date1);

String dateString2 = "201028";
LocalDateTime date2 = LocalDateTime.parse(dateString2, formatter);
System.out.println(date2);

Output:

2020-10-28T05:00
2020-10-28T00:00
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