How to Use DateTimeFormatter to Parse Multiple Dates into One with the Java Time Library

Question

How can I use DateTimeFormatter to accept multiple date formats and convert them into a standardized date using the java.time library?

LocalDate date = LocalDate.parse(dateString, formatter);

Answer

In Java, the `DateTimeFormatter` class from the `java.time` package allows you to parse and format dates in various formats. If you need to handle multiple date formats and standardize them into one format, you can create a custom formatter that tries to parse these formats in sequence.

import java.time.LocalDate;
import java.time.format.DateTimeFormatter;
import java.time.format.DateTimeParseException;

public class DateParser {
    public static void main(String[] args) {
        String[] dateStrings = {"2023-10-12", "12/10/2023", "Oct 12 2023"};
        DateTimeFormatter[] formatters = new DateTimeFormatter[] {
            DateTimeFormatter.ofPattern("yyyy-MM-dd"),
            DateTimeFormatter.ofPattern("dd/MM/yyyy"),
            DateTimeFormatter.ofPattern("MMM dd yyyy")
        };

        for (String dateString : dateStrings) {
            LocalDate date = parseDate(dateString, formatters);
            if (date != null) {
                System.out.println("Parsed date: " + date);
            } else {
                System.out.println("Failed to parse date: " + dateString);
            }
        }
    }

    private static LocalDate parseDate(String dateString, DateTimeFormatter[] formatters) {
        for (DateTimeFormatter formatter : formatters) {
            try {
                return LocalDate.parse(dateString, formatter);
            } catch (DateTimeParseException e) {
                // Ignore and try next formatter
            }
        }
        return null; // Return null if no formatters succeeded
    }
}

Causes

The need to handle various date formats in user input.
Flexibility in accepting different date representations, especially in applications with internationalization.

Solutions

Create multiple `DateTimeFormatter` instances for each expected date format.
Utilize a loop to attempt parsing each date format until one succeeds. Here’s an example implementation:

Common Mistakes

Mistake: Not handling DateTimeParseException when parsing dates.

Solution: Wrap the parsing code in a try-catch block and provide fallbacks.

Mistake: Assuming a single format is used for all date inputs.

Solution: Implement multiple formatters to accommodate a variety of formats.

Helpers

DateTimeFormatter
Java Date Parsing
java.time library
multiple date formats
LocalDate parsing
Java examples