获取当月的第一天和最后一天

 public static void main(String args[]){
    SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
         Calendar c = Calendar.getInstance();   
         c.add(Calendar.MONTH, 0);
         c.set(Calendar.DAY_OF_MONTH,1);//设置为1号,当前日期既为本月第一天
         c.set(Calendar.HOUR_OF_DAY, 0);
         c.set(Calendar.MINUTE, 0);
         c.set(Calendar.SECOND, 0);
         String first = format.format(c.getTime());
         System.out.println("===============first:"+first);

   
         Calendar ca = Calendar.getInstance();   
         ca.set(Calendar.DAY_OF_MONTH, ca.getActualMaximum(Calendar.DAY_OF_MONTH));
         ca.set(Calendar.HOUR_OF_DAY, ca.getActualMaximum(Calendar.HOUR_OF_DAY));
         ca.set(Calendar.MINUTE, ca.getActualMaximum(Calendar.MINUTE));
         ca.set(Calendar.SECOND, ca.getActualMaximum(Calendar.SECOND));
         String last = format.format(ca.getTime());
         System.out.println("===============last:"+last);

 }