SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
Calendar c = Calendar.getInstance();
1.过去七天
c.setTime(new Date());
c.add(Calendar.DATE, - 7);
Date d = c.getTime();
String day = format.format(d);
System.out.println("过去七天："+day);
2.过去一月
c.setTime(new Date());
c.add(Calendar.MONTH, -1);
Date m = c.getTime();
String mon = format.format(m);
System.out.println("过去一个月："+mon);
3.过去三个月
c.setTime(new Date());
c.add(Calendar.MONTH, -3);
Date m3 = c.getTime();
String mon3 = format.format(m3);
System.out.println("过去三个月："+mon3);
4.过去一年
c.setTime(new Date());
c.add(Calendar.YEAR, -1);
Date y = c.getTime();
String year = format.format(y);
System.out.println("过去一年："+year);
5.现在时间24小时制  
SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");  
String nowDate=format.format(new Date());  
System.out.println(nowDate);  
6.当天的开始时间  
SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd");  
Calendar c = Calendar.getInstance();  
String start = format.format(c.getTime())+" 00:00:00";  
System.out.println(start);  
7.当天的截止时间  
SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd");  
Calendar calendar = Calendar.getInstance();  
String end = format.format(calendar.getTime())+" 23:59:59";  
System.out.println(end);  
8.当前时间的前一个星期 开始时间  
SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd");  
Calendar c = Calendar.getInstance();  
c.add(Calendar.DAY_OF_MONTH, -6);  
String start = format.format(c.getTime())+" 00:00:00";  
System.out.println(start);  
9.当天日期前一个月  
SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd");  
Calendar c = Calendar.getInstance();  
c.add(Calendar.MONTH, -1);    //得到前一个月    
String start = format.format(c.getTime())+" 00:00:00";  
System.out.println(start);  
10.当前时间的前一年开始时间  
SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd");  
Calendar c = Calendar.getInstance();  
c.add(Calendar.YEAR, -1); //年份减1   
String start =format.format(c.getTime())+" 00:00:00";  
System.out.println(start);  
11.当前时间的周一时间和周末时间 setfirstdayofweek（）方法  
SimpleDateFormat format  = new SimpleDateFormat("YYYY-MM-dd ");  
Calendar c = Calendar.getInstance();  
c.set(Calendar.DAY_OF_WEEK,Calendar.MONDAY);  
String weekStart = format.format(c.getTime())+" 00:00:00";  
System.out.println(weekStart);  
Calendar ca = Calendar.getInstance();  
ca.setFirstDayOfWeek(Calendar.MONDAY);  
ca.set(Calendar.DAY_OF_WEEK, ca.getFirstDayOfWeek() + 6); // Sunday  
String weekEnd = format.format(ca.getTime())+" 23:59:59";  
System.out.println(weekEnd);  
12.当前时所在月份的第一天和最后一天  
SimpleDateFormat format=new SimpleDateFormat("yyyy-MM-dd");  
Calendar c = Calendar.getInstance();      
c.set(Calendar.DAY_OF_MONTH,1);//设置为1号,当前日期既为本月第一天   
String monthStart = format.format(c.getTime())+" 00:00:00";  
System.out.println(monthStart);  
Calendar ca = Calendar.getInstance();      
ca.set(Calendar.DAY_OF_MONTH, ca.getActualMaximum(Calendar.DAY_OF_MONTH));    
String monthEnd = format.format(ca.getTime())+" 23:59:59";  
System.out.println(monthEnd);  
13.当期时间所在年份的开始时间  
SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd");  
Calendar c = Calendar.getInstance();  
c.set(c.get(Calendar.YEAR) ,0, 1);//开始时间日期  
String yearStart = format.format(c.getTime())+" 00:00:00";  
System.out.println(yearStart);  
Calendar ca = Calendar.getInstance();  
ca.set(ca.get(Calendar.YEAR) ,11, ca.getActualMaximum(Calendar.DAY_OF_MONTH));//结束日期  
String yearEnd = format.format(ca.getTime())+" 23:59:59";  
System.out.println(yearEnd);  
14.计算时间差取得两个时间的微秒级的时间差
//得微秒级时间差    
long val = calendarEnd.getTimeInMillis() - calendarBegin.getTimeInMillis();    
//换算后得到天数    
long day = val / (1000 * 60 * 60 * 24);
15.获取某个时间的上周一和周日
Calendar cal = Calendar.getInstance();
//n为推迟的周数，1本周，-1向前推迟一周，2下周，依次类推
int n = 1;
String monday;
cal.add(Calendar.DATE, n*7);
//想周几，这里就传几Calendar.MONDAY（TUESDAY...）
cal.set(Calendar.DAY_OF_WEEK,Calendar.MONDAY);
monday = new SimpleDateFormat("yyyy-MM-dd").format(cal.getTime());
System.out.println(monday);