改用 SimpleDateFormat:

Use SimpleDateFormat instead:

private String toDate(long timestamp) {
    Date date = new Date(timestamp * 1000);
    return new SimpleDateFormat("yyyy-MM-dd").format(date);
}

更新:Java 8 解决方案:

Updated: Java 8 solution:

private String toDate(long timestamp) {
    LocalDate date = Instant.ofEpochMilli(timestamp * 1000).atZone(ZoneId.systemDefault()).toLocalDate();
    return date.format(DateTimeFormatter.ofPattern("yyyy-MM-dd"));
}