SimpleDateFormat df=new SimpleDateFormat("yyyy-MM-dd");//格式
//今天
String today=df.format(new Date());
System.out.println(today);
//昨天
Calendar cal = Calendar.getInstance();//日历
cal.add(Calendar.DATE, -1);
String yesterday = new SimpleDateFormat( "yyyy-MM-dd ").format(cal.getTime());
System.out.println(yesterday);
//前天
cal.add(Calendar.DATE, -1);
String vorgestern = new SimpleDateFormat( "yyyy-MM-dd ").format(cal.getTime());
System.out.println(vorgestern);