Java SimpleDateFormat将结果解析一小时（是的，我设置了时区）

Question

让我感到困惑：为什么这个简单的JUnit断言失败？

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));
}

我本来希望一天中的小时为11，但根据JUnit，一天中的小时为12。

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

Answer 1

阳历的默认构造函数使用计算机的本地时区。如果与UTC不同，则会出现此现象。尝试使用GregorianCalendar（TimeZone）构造函数并将UTC传递给该构造函数。

这将起作用：

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));
}