Java 将 GMT/UTC 转换为本地时间无法按预期工作

date-formatting utc java timestamp-with-timezone simpledateformat

2022-09-01 05:06:28

为了显示可重现的场景，我正在执行以下操作

获取当前系统时间（本地时间）
将本地时间转换为UTC // 工作正常直到这里

反转 UTC 时间，返回到本地时间。遵循了 3 种不同的方法（下面列出），但所有 3 种方法仅保留 UTC 时间。

{

long ts = System.currentTimeMillis();
Date localTime = new Date(ts);
String format = "yyyy/MM/dd HH:mm:ss";
SimpleDateFormat sdf = new SimpleDateFormat (format);

// Convert Local Time to UTC (Works Fine) 
sdf.setTimeZone(TimeZone.getTimeZone("UTC"));
Date gmtTime = new Date(sdf.format(localTime));
System.out.println("Local:" + localTime.toString() + "," + localTime.getTime() + " --> UTC time:" + gmtTime.toString() + "-" + gmtTime.getTime());

// Reverse Convert UTC Time to Locale time (Doesn't work) Approach 1
sdf.setTimeZone(TimeZone.getDefault());        
localTime = new Date(sdf.format(gmtTime));
System.out.println("Local:" + localTime.toString() + "," + localTime.getTime() + " --> UTC time:" + gmtTime.toString() + "-" + gmtTime.getTime());

// Reverse Convert UTC Time to Locale time (Doesn't work) Approach 2 using DateFormat
DateFormat df = new SimpleDateFormat (format);
df.setTimeZone(TimeZone.getDefault());
localTime = df.parse((df.format(gmtTime)));
System.out.println("Local:" + localTime.toString() + "," + localTime.getTime() + " --> UTC time:" + gmtTime.toString() + "-" + gmtTime.getTime());

// Approach 3
Calendar c = new GregorianCalendar(TimeZone.getDefault());
c.setTimeInMillis(gmtTime.getTime());
System.out.println("Local Time " + c.toString());

}

答案 1

我也建议使用前面提到的Joda。

仅使用标准 Java 对象解决您的问题可以按如下方式完成：Date

    // **** YOUR CODE **** BEGIN ****
    long ts = System.currentTimeMillis();
    Date localTime = new Date(ts);
    String format = "yyyy/MM/dd HH:mm:ss";
    SimpleDateFormat sdf = new SimpleDateFormat(format);

    // Convert Local Time to UTC (Works Fine)
    sdf.setTimeZone(TimeZone.getTimeZone("UTC"));
    Date gmtTime = new Date(sdf.format(localTime));
    System.out.println("Local:" + localTime.toString() + "," + localTime.getTime() + " --> UTC time:"
            + gmtTime.toString() + "," + gmtTime.getTime());

    // **** YOUR CODE **** END ****

    // Convert UTC to Local Time
    Date fromGmt = new Date(gmtTime.getTime() + TimeZone.getDefault().getOffset(localTime.getTime()));
    System.out.println("UTC time:" + gmtTime.toString() + "," + gmtTime.getTime() + " --> Local:"
            + fromGmt.toString() + "-" + fromGmt.getTime());

输出：

Local:Tue Oct 15 12:19:40 CEST 2013,1381832380522 --> UTC time:Tue Oct 15 10:19:40 CEST 2013,1381825180000
UTC time:Tue Oct 15 10:19:40 CEST 2013,1381825180000 --> Local:Tue Oct 15 12:19:40 CEST 2013-1381832380000

答案 2

您有一个具有已知时区（此处）的日期和一个目标时区（Europe/MadridUTC)

你只需要两个 SimpleDateFormats：

        long ts = System.currentTimeMillis();
        Date localTime = new Date(ts);

        SimpleDateFormat sdfLocal = new SimpleDateFormat ("yyyy/MM/dd HH:mm:ss");
        sdfLocal.setTimeZone(TimeZone.getTimeZone("Europe/Madrid"));

        SimpleDateFormat sdfUTC = new SimpleDateFormat ("yyyy/MM/dd HH:mm:ss");
        sdfUTC.setTimeZone(TimeZone.getTimeZone("UTC"));

        // Convert Local Time to UTC
        Date utcTime = sdfLocal.parse(sdfUTC.format(localTime));
        System.out.println("Local:" + localTime.toString() + "," + localTime.getTime() + " --> UTC time:" + utcTime.toString() + "-" + utcTime.getTime());

        // Reverse Convert UTC Time to Locale time
        localTime = sdfUTC.parse(sdfLocal.format(utcTime));
        System.out.println("UTC:" + utcTime.toString() + "," + utcTime.getTime() + " --> Local time:" + localTime.toString() + "-" + localTime.getTime());

因此，在看到它工作之后，您可以将此方法添加到您的实用程序中：

    public Date convertDate(Date dateFrom, String fromTimeZone, String toTimeZone) throws ParseException {
        String pattern = "yyyy/MM/dd HH:mm:ss";
        SimpleDateFormat sdfFrom = new SimpleDateFormat (pattern);
        sdfFrom.setTimeZone(TimeZone.getTimeZone(fromTimeZone));

        SimpleDateFormat sdfTo = new SimpleDateFormat (pattern);
        sdfTo.setTimeZone(TimeZone.getTimeZone(toTimeZone));

        Date dateTo = sdfFrom.parse(sdfTo.format(dateFrom));
        return dateTo;
    }