关于java：如何将本地日期转换为GMT

How to convert a local date to GMT

本问题已经有最佳答案，请猛点这里访问。

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

上面的代码不会在GMT中打印日期，而是在本地时区打印。如何从当前日期获得GMT等效日期(假设该程序可以在日本或SFO运行)

这个怎么样 -

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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 Time - Tue May 15 10:54:14 IST 2012