Java时间处理

1.获得当前系统时间

          首先System.currentTimeMillis()产生一个当前的毫秒，这个毫秒其实就是自1970年1月1日0时起的毫秒数，Date d = new Date()其实就是相当于Date d = new Date(System.currentTimeMillis());因为Date类还有构造Date(long date)，用来计算long秒与1970年1月1日之间的毫秒差。

    

//获得当前系统时间，格式为yyyy-MM-dd hh:MM:ss，如2010-10-30 21：11:20

   public String getCurrentTime(){
            Date currentTime = new Date();
            SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
            String dateString = sdf.format(currentTime);
            return dateString;
    }

2.时间比较

     (1)判断时间date1是否在时间date2之前   时间格式 2005-4-21 16:16:34

              public  boolean isDateBefore(String date1,String date2){
                  try{
                            DateFormat  df  =  DateFormat.getDateTimeInstance();
                            return   df.parse(date1).before(df.parse(date2));
                  }catch(ParseException e){
                               System.out.println(/"[SYS] /" + e.getMessage());
                               return false;
                  }
             }

     (2)时间比较大小

              public   int   timeCompare(String  t1, String  t2) {                

                          String  s1 = "2008-01-25 09:12:09";
                          String  s2 = "2008-01-29 09:12:11";
                          DateFormat  df = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
                          Calendar  c1 = Calendar.getInstance();    //java.util.Calendar
                          Calendar  c2 = Calendar.getInstance();
                          try{
                                       c1.setTime(df.parse(s1));
                                       c2.setTime(df.parse(s2));
                          }catch(java.text.ParseException e){
                                       System.err.println("格式不正确");
                          }
                          int  result = c1.compareTo(c2);
                          if(result == 0)
                                       System.out.println("c1相等c2");
                          else if( result < 0)
                                       System.out.println("c1小于c2");
                          else
                                       System.out.println("c1大于c2");

               }

3.计算时间差

      比如：现在是2010-10-30 21:23:40
      过去是：2004-01-02 11:30:24
      我现在要获得两个日期差，差的形式为：XX天XX小时XX分XX秒

      方法一：
                  DateFormat df = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");

                  try{
                               Date d1 = df.parse("2010-10-30 21:23:40");
                               Date d2 = df.parse("2004-01-02 11:30:24");
                               long diff = d1.getTime() - d2.getTime();
                               long days = diff / (1000 * 60 * 60 * 24);  //两个日期相差的天数
                  }
                  catch (Exception e){
                  }

     方法二：

                  SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
                  Date now = df.parse("2010-10-30 21:23:40");
                  Date date=df.parse("2004-01-02 11:30:24");
                  long time=now.getTime()-date.getTime();
                  long day=time/(24*60*60*1000);              //两个日期相差的天数
                  long hour=(time/(60*60*1000)-day*24);               //两个日期相差的小时数
                  long min=((time/(60*1000))-day*24*60-hour*60);        //两个日期相差的分钟
                  long s=(time/1000-day*24*60*60-hour*60*60-min*60);  //两个日期相差的秒数
                  System.out.println(""+day+"天"+hour+"小时"+min+"分"+s+"秒");

      方法三：
                  SimpleDateFormat dfs = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
                  Date begin=dfs.parse("2010-10-30 21:23:40");
                  Date end = dfs.parse("2004-03-26 13:31:40");
                long between=(end.getTime()-begin.getTime())/1000;//除以1000是为了转换成秒

                  long day1=between/(24*3600);
                  long hour1=between%(24*3600)/3600;
                  long minute1=between%3600/60;
                  long second1=between%60/60;
                System.out.println(""+day1+"天"+hour1+"小时"+minute1+"分"+second1+"秒");

 

4.获取某个月最后一天

               private int getLastDayOfMonth(String date) {
                           SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM");
                           Date d = null;
                           try {
                                      d = sdf.parse(date);
                           } catch (ParseException e) {
                                      e.printStackTrace();
                           }
                           int day;
                           Calendar cal = Calendar.getInstance();
                           cal.setTime(d);
                           cal.set(Calendar.DAY_OF_MONTH,1);//设置为1号,当前日期既为本月第一天
                           cal.add(Calendar.MONTH,1);//月增加1天
                           cal.add(Calendar.DAY_OF_MONTH,-1);//日期倒数一日,既得到本月最后一天
                           day = cal.get(Calendar.DAY_OF_MONTH);
                           return day;
              }