"Java DateFormat is not threadsafe" what does this leads to?

user_487244 0
Viewed 64545

Everybody cautions regarding Java DateFormat not being thread safe and I understand the concept theoretically.

But I'm not able to visualize what actual issues we can face due to this. Say, I've a DateFormat field in a class and the same is used in different methods in the class (formatting dates) in a multi-threaded environment.

Will this cause:

  • any exception like format exception
  • discrepancy in data
  • any other issue?

Also, please explain why.

date-format multithreading java
11 Answers

This will cause ArrayIndexOutOfBoundsException

Apart from the incorrect result, it will give you a crash from time to time. It depends on the speed your machine; in my laptop, it happens once in 100,000 calls on average:

SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");

ExecutorService executorService = Executors.newFixedThreadPool(2);
Future<?> future1 = executorService.submit(() -> {
  for (int i = 0; i < 99000; i++) {
    sdf.format(Date.from(LocalDate.parse("2019-12-31").atStartOfDay().toInstant(UTC)));
  }
});

executorService.submit(() -> {
  for (int i = 0; i < 99000; i++) {
    sdf.format(Date.from(LocalDate.parse("2020-04-17").atStartOfDay().toInstant(UTC)));
  }
});

future1.get();

the last line sould trigger the postponed executor exception:

java.lang.ArrayIndexOutOfBoundsException: Index 16 out of bounds for length 13
  at java.base/sun.util.calendar.BaseCalendar.getCalendarDateFromFixedDate(BaseCalendar.java:453)
  at java.base/java.util.GregorianCalendar.computeFields(GregorianCalendar.java:2394)
  at java.base/java.util.GregorianCalendar.computeFields(GregorianCalendar.java:2309)
  at java.base/java.util.Calendar.complete(Calendar.java:2301)
  at java.base/java.util.Calendar.get(Calendar.java:1856)
  at java.base/java.text.SimpleDateFormat.subFormat(SimpleDateFormat.java:1150)
  at java.base/java.text.SimpleDateFormat.format(SimpleDateFormat.java:997)
  at java.base/java.text.SimpleDateFormat.format(SimpleDateFormat.java:967)
  at java.base/java.text.DateFormat.format(DateFormat.java:374)
user_6018440
Related