Java SimpleDateFormat 解析结果延迟一小时(是的，我设置了时区)

Question

给我一​​个谜:为什么这个简单的 JUnit 断言会失败？

public void testParseDate() throws ParseException {
    final SimpleDateFormat formatter = new SimpleDateFormat(
            "yyyy-MM-dd HH:mm:ss z");
    formatter.setTimeZone(UTC);
    final Calendar c = new GregorianCalendar();
    c.setTime(formatter.parse("2013-03-02 11:59:59 UTC"));

    assertEquals(11, c.get(HOUR_OF_DAY));
}

我原以为一天中的小时是 11 点，但根据 JUnit，一天中的小时是 12 点。

junit.framework.AssertionFailedError: expected:<11> but was:<12>
at junit.framework.Assert.fail(Assert.java:47)
    ... snip ...

Answer 1

公历的默认构造函数使用机器的本地时区。如果这与 UTC 不同，您会得到这种行为。尝试使用 GregorianCalendar(TimeZone) 构造函数并将 UTC 传递给它。

这会起作用:

public void testParseDate() throws Exception {

    TimeZone UTC = TimeZone.getTimeZone("UTC");

    // Create a UTC formatter
    final SimpleDateFormat formatter = new SimpleDateFormat(
            "yyyy-MM-dd HH:mm:ss z");
    formatter.setTimeZone(UTC);

    // Create a UTC Gregorian Calendar (stores internally in UTC, so
    // get(Calendar.HOUR_OF_DAY) returns in UTC instead of in the
    // local machine's timezone.
    final Calendar c = new GregorianCalendar(UTC);

    // Ask the formatter for a date representation and pass that
    // into the GregorianCalendar (which will convert it into
    // it's internal timezone, which is also UTC.
    c.setTime(formatter.parse("2013-03-02 11:59:59 UTC"));

    // Output the UTC hour of day
    assertEquals(11, c.get(Calendar.HOUR_OF_DAY));
}