Date date= new Date();
Calendar calendar = Calendar.getInstance();
//设置日期为当前日期,也可以设置其他日期
calendar.setTime(date);
int days = calendar.get(Calendar.DATE);
//计算前一天的日期
calendar.set(Calendar.DATE, days - 1);
//得到前一天的日期Date
Date dayBefore = calendar.getTime();