Java - Date format for Multiple Scenarios

Question

I have a java component to format the date that I retrieve. Here is my code:

    Format formatter      = new SimpleDateFormat("yyyyMMdd");
        String s = "2019-04-23 06:57:00.0";
        SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyy-mm-dd hh:mm:ss.S");
        try
        {
            Date date = simpleDateFormat.parse(s);
            System.out.println("Formatter: "+formatter.format(date));
        }
        catch (ParseException ex)
        {
            System.out.println("Exception "+ex);
        }

The code works great as long as the String s has the format "2019-04-23 06:57:00.0";

My Question is, how to tweak this code so it will work for below scenarios ex, my s string may have values like


String s = "2019-04-23 06:57:00.0";
or 
String s = "2019-04-23 06:57:00";

Or 
String s = "2019-04-23";

right now it fails if I don't pass the ms.. Thanks!

Possible duplicate of [How to parse dates in multiple formats using SimpleDateFormat](https://stackoverflow.com/questions/4024544/how-to-parse-dates-in-multiple-formats-using-simpledateformat) — Stephan Hogenboom, May 08 '19 at 16:49
Use Joda Date API. Same question is already there in stackoverflow and solution as well. I've overcome same challenges long time back. FYI, This functionality is lagging in Java 8 DateTime API. So recommend you to dig in JODA Datetime. — Yanish Pradhananga, May 08 '19 at 17:23
FYI, the terribly troublesome date-time classes such as [`java.util.Date`](https://docs.oracle.com/javase/10/docs/api/java/util/Date.html), [`java.util.Calendar`](https://docs.oracle.com/javase/10/docs/api/java/util/Calendar.html), and `java.text.SimpleDateFormat` are now [legacy](https://en.wikipedia.org/wiki/Legacy_system), supplanted by the [*java.time*](https://docs.oracle.com/javase/10/docs/api/java/time/package-summary.html) classes built into Java 8 and later. See [*Tutorial* by Oracle](https://docs.oracle.com/javase/tutorial/datetime/TOC.html). — Basil Bourque, May 08 '19 at 18:20
I recommend you don’t use `SimpleDateFormat` and `Date`. Those classes are poorly designed and long outdated, the former in particular notoriously troublesome. Instead use `LocalDate`, `LocalDateTime` and `DateTimeFormatter`, all from [java.time, the modern Java date and time API](https://docs.oracle.com/javase/tutorial/datetime/). — Ole V.V., May 09 '19 at 05:42

score 4 · Answer 1 · edited Jun 20 '20 at 09:12

Different types

String s = "2019-04-23 06:57:00";

String s = "2019-04-23";

These are two different kinds of information. One is a date with time-of-day, the other is simply a date. So you should be parsing each as different types of objects.

`LocalDateTime.parse`

To comply with the ISO 8601 standard format used by default in the LocalDateTime class, replace the SPACE in the middle with a T. I suggest you educate the publisher of your data about using only ISO 8601 formats when exchanging date-time values as text.

LocalDateTime ldt1 = LocalDateTime.parse( "2019-04-23 06:57:00".replace( " " , "T" ) ) ;

The fractional second parses by default as well.

LocalDateTime ldt2 = LocalDateTime.parse( "2019-04-23 06:57:00.0".replace( " " , "T" ) ) ;

See this code run live at IdeOne.com.

ldt1.toString(): 2019-04-23T06:57

ldt2.toString(): 2019-04-23T06:57

`LocalDate.parse`

Your date-only input already complies with ISO 8601.

LocalDate ld = LocalDate.parse( "2019-04-23" ) ;

See this code run live at IdeOne.com.

ld.toString(): 2019-04-23

Date with time-of-day

You can strip out the time-of-day from the date.

LocalDate ld = ldt.toLocalDate() ;

And you can add it back in.

LocalTime lt = LocalTime.parse( "06:57:00" ) ;
LocalDateTime ldt = ld.with( lt ) ;

Moment

However, be aware that a LocalDateTime does not represent a moment, is not a point on the timeline. Lacking the context of a time zone or offset-from-UTC, a LocalDateTime cannot hold a moment, as explained in its class JavaDoc.

For a moment, use the ZonedDateTime, OffsetDateTime, or Instant classes. Teach the publisher of your data to include the offset, preferably in UTC.

Avoid legacy date-time classes

The old classes SimpleDateFormat, Date, and Calendar are terrible, riddled with poor design choices, written by people not skilled in date-time handling. These were supplanted years ago by the modern java.time classes defined in JSR 310.

thank you.. the values are from the database so I think it comply the standards. I will verify this aspect. — Anto, May 10 '19 at 13:40
@Anto If you are receiving data from a database, you should be extracting date-time objects rather than mere strings. Use `ResultSet::getObject` with a JDBC 4.2 or later driver to get `LocalDate` objects from a `DATE` column and `LocalDateTime` objects from a `TIMESTAMP WITHOUT TIME ZONE` column. This has been covered many times already on Stack Overflow. You should have noted the database as source in your Question. — Basil Bourque, May 10 '19 at 13:48

score 1 · Accepted Answer · answered May 09 '19 at 07:32

In case of you have optional parts in pattern you can use [ and ].

For example

public static Instant toInstant(final String timeStr){
    final DateTimeFormatter formatter = DateTimeFormatter
            .ofPattern("yyyy-MM-dd HH[:mm[:ss[ SSSSSSSS]]]")
            .withZone(ZoneId.of("UTC"));
    try {
        return Instant.from(formatter.parse(timeStr));
    }catch (DateTimeException e){
        final DateTimeFormatter formatter2 = DateTimeFormatter
                .ofPattern("yyyy-MM-dd")
                .withZone(ZoneId.of("UTC"));
        return LocalDate.parse(timeStr, formatter2).atStartOfDay().atZone(ZoneId.of("UTC")).toInstant();
    }
}

cover

yyyy-MM-dd
yyyy-MM-dd HH
yyyy-MM-dd HH:mm
yyyy-MM-dd HH:mm:ss
yyyy-MM-dd HH:mm:ss SSSSSSSS