UTC的相互轉換(java)

        SimpleDateFormat foo = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss");
        System.out.println("foo:"+foo.format(new Date()));
        
        Calendar gc = GregorianCalendar.getInstance();
        System.out.println("gc.getTime():"+gc.getTime());
        System.out.println("gc.getTimeInMillis():"+new Date(gc.getTimeInMillis()));
        
        //當前系統默認時區的時間：
        Calendar calendar=new GregorianCalendar();
        System.out.print("時區："+calendar.getTimeZone().getID()+"  ");
        System.out.println("時間："+calendar.get(Calendar.HOUR_OF_DAY)+":"+calendar.get(Calendar.MINUTE));
        //美國洛杉磯時區
        TimeZone tz=TimeZone.getTimeZone("America/Los_Angeles");
        //時區轉換
        calendar.setTimeZone(tz);
        System.out.print("時區："+calendar.getTimeZone().getID()+"  ");
        System.out.println("時間："+calendar.get(Calendar.HOUR_OF_DAY)+":"+calendar.get(Calendar.MINUTE));
        Date time=new Date();
        
        //1、取得本地時間：
        java.util.Calendar cal = java.util.Calendar.getInstance();

        //2、取得時間偏移量：
        int zoneOffset = cal.get(java.util.Calendar.ZONE_OFFSET);

        //3、取得夏令時差：
        int dstOffset = cal.get(java.util.Calendar.DST_OFFSET);

        //4、從本地時間里扣除這些差量，即可以取得UTC時間：
        cal.add(java.util.Calendar.MILLISECOND, -(zoneOffset + dstOffset));

        //之后調用cal.get(int x)或cal.getTimeInMillis()方法所取得的時間即是UTC標准時間。
        System.out.println("UTC:"+new Date(cal.getTimeInMillis()));
        
        Calendar calendar1 = Calendar.getInstance();
        TimeZone tztz = TimeZone.getTimeZone("GMT");       
        calendar1.setTimeZone(tztz);
        System.out.println(calendar.getTime());
        System.out.println(calendar.getTimeInMillis());