Java DateTimeFormatter Example: A Complete Guide to Date Formatting

If you’re working with dates in Java, the DateTimeFormatter class is your ultimate tool for converting between human-readable date strings and machine-friendly LocalDateTime objects. In this comprehensive guide, we’ll explore practical Java DateTimeFormatter examples to master date formatting, parsing, and customization.

Why DateTimeFormatter Matters in Java

Java introduced DateTimeFormatter in Java 8 as part of the modern Date/Time API to replace the legacy SimpleDateFormat. Key advantages include:

• Thread-safe design (no concurrency issues)
• Immutable formatters (safe to reuse)
• Built-in formats (ISO standards, localized styles)
• Flexible pattern-based formatting

Creating DateTimeFormatter Instances

1. Predefined Formatters

Use built-in formats like ISO dates:

DateTimeFormatter isoDate = DateTimeFormatter.ISO_LOCAL_DATE;  
LocalDate date = LocalDate.now();  
System.out.println(date.format(isoDate)); // Output: 2020-08-15  

2. Custom Pattern-Based Formatters

Define your own patterns using ofPattern():

DateTimeFormatter customFormatter = DateTimeFormatter.ofPattern("dd/MM/yyyy HH:mm");  
LocalDateTime now = LocalDateTime.now();  
System.out.println(now.format(customFormatter)); // Output: 15/08/2020 14:30  

3. Localized Formatters

Format dates for specific locales:

DateTimeFormatter germanFormatter = DateTimeFormatter  
    .ofLocalizedDate(FormatStyle.MEDIUM)  
    .withLocale(Locale.GERMAN);  
System.out.println(LocalDate.now().format(germanFormatter)); // Output: 15. Aug. 2020  

Common DateTimeFormatter Patterns

Parsing Dates with DateTimeFormatter

Convert strings to date objects:

DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd");  
LocalDate parsedDate = LocalDate.parse("2020-08-15", formatter);  
System.out.println(parsedDate.getDayOfWeek()); // Output: TUESDAY  

Best Practices

1. Reuse formatters to avoid recreating instances.
2. Specify a Locale for localized patterns (e.g., month names).
3. Handle exceptions like DateTimeParseException for invalid inputs.
4. Use predefined formatters (e.g., ISO_LOCAL_DATE) when possible.

FAQ