☕ Java Time Handling Guide
Master Java's modern time API (java.time) and avoid the pitfalls of legacy Date/Calendar classes.
⚡ Quick Reference
✅ Use (Java 8+)
- • Instant for UTC timestamps
- • ZonedDateTime for timezone-aware times
- • OffsetDateTime for API serialization
- • LocalDateTime only for timezone-naive data
- • DateTimeFormatter for parsing/formatting
❌ Avoid (Legacy)
- • java.util.Date (mutable, timezone-naive)
- • java.util.Calendar (complex, error-prone)
- • SimpleDateFormat (not thread-safe)
- • Timestamp arithmetic without timezone
- • Hardcoded timezone offsets
🕐 Modern Time API (java.time)
Core Classes and When to Use Them
🌍 Timezone Handling
ZonedDateTime vs OffsetDateTime
📝 Parsing and Formatting
Thread-Safe Date Parsing
⏱️ Duration and Period
Time-Based vs Date-Based Calculations
🗄️ Database Integration
JPA and JDBC with Modern Time API
🧪 Testing Time Logic
Clock Abstraction for Testing
🔄 Migration from Legacy APIs
Converting from Date/Calendar
⚠️ Common Pitfalls
Things That Will Bite You
1. LocalDateTime Timezone Confusion
LocalDateTime has no timezone - don't use it for timestamps!
2. Instant vs ZonedDateTime Confusion
Know when to use each for different scenarios.