CODEWITHSUNDEEP
javadatesimpledateformatmilliseconds
Egor
Egor

Reputation: 561

What does Java's SimpleDateFormat make with milli/micro-seconds?

I have simple test

@SuppressWarnings("deprecation")
@Test
public void test_NO_MILLIS() throws ParseException {
    String rabbit = "22-OCT-15 06.37.35";
    final String PATTERN = "dd-MMM-yy HH.mm.ss";
    Date dateObject = new SimpleDateFormat(PATTERN).parse(rabbit);
    Assert.assertNotNull(dateObject);
    Assert.assertEquals(22, dateObject.getDate());
    Assert.assertEquals(10, dateObject.getMonth() + 1);
    Assert.assertEquals(2015, dateObject.getYear() + 1900);
    Assert.assertEquals(6, dateObject.getHours());
    Assert.assertEquals(37, dateObject.getMinutes());
    Assert.assertEquals(35, dateObject.getSeconds());
}

And everything goes right. I get 22 as day in result.

But after I am adding microseconds both to pattern and to string value to be parsed

    @Test
public void test_MILLIS() throws ParseException {
    String rabbit = "22-OCT-15 06.37.35.586173000";
    final String PATTERN = "dd-MMM-yy HH.mm.ss.SSSSSSSSS";
    Date dateObject = new SimpleDateFormat(PATTERN).parse(rabbit);
    Assert.assertNotNull(dateObject);
    Assert.assertEquals(22, dateObject.getDate());
    Assert.assertEquals(10, dateObject.getMonth() + 1);
    Assert.assertEquals(2015, dateObject.getYear() + 1900);
    Assert.assertEquals(6, dateObject.getHours());
    Assert.assertEquals(37, dateObject.getMinutes());
    Assert.assertEquals(35, dateObject.getSeconds());
}

I get an assert failure

junit.framework.AssertionFailedError: expected:<22> but was:<29>
at junit.framework.Assert.fail(Assert.java:57)
at junit.framework.Assert.failNotEquals(Assert.java:329)
at junit.framework.Assert.assertEquals(Assert.java:78)
at junit.framework.Assert.assertEquals(Assert.java:234)
at junit.framework.Assert.assertEquals(Assert.java:241)
at main.TestDateFormatTest.test_MILLIS(TestDateFormatTest.java:36)
...

Which means that day has become 29 instead of 22. What has gone wrong? Tested Platforms: mac osx 10.9, ubuntu, win7 jdk: 7,6

Upvotes: 0

Views: 204

Answers (1)

rgettman
rgettman

Reputation: 178293

The format pattern S for milliseconds doesn't take into account mathematical placement values; it just sees 586173000 as the number of milliseconds to add to the rest of the date. That number is equivalent to about 6.784 days, so that explains why the date became 29 instead of 22.

Before parsing, cut off the milliseconds at 3 digits, e.g. "22-OCT-15 06.37.35.586", so it's interpreted as 586 milliseconds.

Upvotes: 4

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