如何将本地日期转换为格林尼治标准时间

Question

Calendar cal = Calendar.getInstance(TimeZone.getTimeZone(“GMT”));
java.util.Date fromDate = cal.getTime();
System.out.println(fromDate);

上面的代码不在格林尼治标准时间打印日期，而是在本地时区打印。我如何从当前日期获得与格林尼治标准时间等效的日期（假设程序可以在日本或SFO上运行）

Answer 1

这个怎么样 -

public static void main(String[] args) throws IOException {
    Test test=new Test();
    Date fromDate = Calendar.getInstance().getTime();
    System.out.println("UTC Time - "+fromDate);
    System.out.println("GMT Time - "+test.cvtToGmt(fromDate));
}
private  Date cvtToGmt( Date date ){
    TimeZone tz = TimeZone.getDefault();
    Date ret = new Date( date.getTime() - tz.getRawOffset() );

    // if we are now in DST, back off by the delta.  Note that we are checking the GMT date, this is the KEY.
    if ( tz.inDaylightTime( ret )){
        Date dstDate = new Date( ret.getTime() - tz.getDSTSavings() );

        // check to make sure we have not crossed back into standard time
        // this happens when we are on the cusp of DST (7pm the day before the change for PDT)
        if ( tz.inDaylightTime( dstDate )){
            ret = dstDate;
        }
     }
     return ret;
}

测试结果 ：
UTC时间-5月15日星期二16:24:14 IST 2012
GMT时间-5月15日星期二10:54:14 IST 2012