java 程序中判断过去的某一天离现在相差多少天的程序

public static String formatDateTime(Date dateTime){

String newDateTime="";

SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");

SimpleDateFormat dateformat1=new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");

Date dateNow=new Date();

        String date=sdf.format(dateTime);

        String dateNowStr=sdf.format(dateNow);

        

        Date resDate=null;

        Date sysDate=null;

        try {

resDate=dateformat1.parse(date+" 00:00:01");

sysDate=dateformat1.parse(dateNowStr+" 00:00:01");

} catch (ParseException e) {

// TODO Auto-generated catch block

e.printStackTrace();

}

//Date sysDate=new Date();

if(dateTime!=null){

//Long s1=System.currentTimeMillis();

long s1=sysDate.getTime();

long s2=resDate.getTime();

long diff = s2 - s1; 

double diffDays = (double)diff / (double)(24 * 60 * 60 * 1000); 

if (diffDays<=0 && diffDays>-1)

{

newDateTime="今天";

}else if (diffDays<=1 && diffDays>0)

{

newDateTime="明天";

}else if (diffDays==-1)

{

newDateTime="昨天";

}else if (diffDays<=2 && diffDays>1)

{

newDateTime="后天";

}else if (diffDays>=-2 && diffDays<-1)

{

newDateTime="前天";

}else if (diffDays>2)

{

newDateTime= (int)diffDays+"天后";

}else if (diffDays<-2)

{

newDateTime= (int)(-diffDays)+"天前";

}

}

return newDateTime;

}