java.time.DateTimeFormatter：需要始终呈现毫秒的ISO_INSTANT

我正在尝试清理有关日期时间管理的各种代码的混合，以仅将Java 8 java.time命名空间。现在，我对Outstant的默认DateTimeFormatter有一个小问题。DateTimeFormatter.ISO_INSTANT 格式化程序仅在毫秒不等于零时才显示毫秒。

纪元呈现为 而不是 。1970-01-01T00:00:00Z1970-01-01T00:00:00.000Z

我做了一个单元测试来解释这个问题，以及我们需要如何将最终日期相互比较。

@Test
public void java8Date() {
    DateTimeFormatter formatter = DateTimeFormatter.ISO_INSTANT;
    String epoch, almostEpoch, afterEpoch;

    { // before epoch
        java.time.Instant instant = java.time.Instant.ofEpochMilli(-1);
        almostEpoch = formatter.format(instant);
        assertEquals("1969-12-31T23:59:59.999Z", almostEpoch );
    }

    { // epoch
        java.time.Instant instant = java.time.Instant.ofEpochMilli(0);
        epoch = formatter.format(instant);
        // This fails, I get 1970-01-01T00:00:00Z instead
        assertEquals("1970-01-01T00:00:00.000Z", epoch );
    }

    { // after epoch
        java.time.Instant instant = java.time.Instant.ofEpochMilli(1);
        afterEpoch = formatter.format(instant);
        assertEquals("1970-01-01T00:00:00.001Z", afterEpoch );
    }

    // The end game is to make sure this rule is respected (this is how we order things in dynamo):
    assertTrue(epoch.compareTo(almostEpoch) > 0);
    assertTrue(afterEpoch.compareTo(epoch) > 0); // <-- This assert would also fail if the second assert fails

    { // to confirm we're not showing nanos
        assertEquals("1970-01-01T00:00:00.000Z", formatter.format(Instant.EPOCH.plusNanos(1)));
        assertEquals("1970-01-01T00:00:00.001Z", formatter.format(Instant.EPOCH.plusNanos(1000000)));
    }
}