Java转换GMT/UTC到本地时间不能按预期工作

Question

为了显示可重现的场景,我正在做以下事情

1. 获取当前系统时间(当地时间)

2. 将本地时间转换为UTC //在这里工作正常

3. 反转UTC时间,返回当地时间.遵循3种不同的方法(如下所列),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());
   

   }

Answer 1

我还建议使用前面提到的Joda.

使用标准Java Date对象解决问题的方法如下:

    // **** 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