时间减去n秒

public class Today {
public static void main(String[] args) {
// TODO Auto-generated method stub
//Date date = new Date();
//SimpleDateFormat sm = new SimpleDateFormat("yyyyMMdd");
//String time= sm.format(date);
//String s = time.substring(4);
//System.out.println(time+" "+s);

String recvtime="20170704171011";
Date dt= null;
try {
dt = new SimpleDateFormat("yyyyMMddHHmmss").parse(recvtime);
System.out.println(dt);
} catch (ParseException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
long ms = dt.getTime()-2000;
Date dt2 =null;
try {
dt2 = new SimpleDateFormat("yyyyMMddHHmmss").parse(ms+"");
System.out.println("减去2秒的时间"+dt2);
} catch (ParseException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}

String time="";
SimpleDateFormat tmp = new SimpleDateFormat("yyMMddHHmmss");
try {
time= tmp.format(dt);
System.out.println(time);
} catch (Exception E) {
time = "";
}


String time2="";
SimpleDateFormat tmp2 = new SimpleDateFormat("yyMMddHHmmss");
try {
time2= tmp2.format(dt2);
System.out.println("减去2秒的时间"+time2);
} catch (Exception E) {
time2 = "";
}


//-------------------------------------------------------
//Format f = new SimpleDateFormat("yyyyMMddHHmmss");
       Calendar c = Calendar.getInstance();
       // 重置 Calendar 显示当前时间  
       c.setTime(dt);
       c.add(Calendar.SECOND,-2);
       System.out.println("##############"+c.getTime());
       //long a = c.getTimeInMillis()-2000;
       //c.setTimeInMillis(a);
       //System.out.println();
       String str = (new SimpleDateFormat("yyyy-MM-dd HH:mm:ss")).format(c.getTime());  
      System.out.println("00000000000000:::"+str); 

}
}