java获取当前月第一天和最后一天，上个月第一天和最后一天

package com.test.packager;

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Calendar;

public class Test {
  private static String firstDay;
  private static String lastDay;
    public static void main(String[] args) {
        SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd"); 

        //获取前月的第一天
        Calendar   cal_1=Calendar.getInstance();//获取当前日期 
        cal_1.add(Calendar.MONTH, -1);
        cal_1.set(Calendar.DAY_OF_MONTH,1);//设置为1号,当前日期既为本月第一天 
        firstDay = format.format(cal_1.getTime());
        System.out.println("-----1------firstDay:"+firstDay);
        //获取前月的最后一天
        Calendar cale = Calendar.getInstance();   
        cale.set(Calendar.DAY_OF_MONTH,0);//设置为1号,当前日期既为本月第一天 
        lastDay = format.format(cale.getTime());
        System.out.println("-----2------lastDay:"+lastDay);


        //获取当前月第一天：
        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 
        String first = format.format(c.getTime());
        System.out.println("===============first:"+first);

        //获取当前月最后一天
        Calendar ca = Calendar.getInstance();    
        ca.set(Calendar.DAY_OF_MONTH, ca.getActualMaximum(Calendar.DAY_OF_MONTH));  
        String last = format.format(ca.getTime());
        System.out.println("===============last:"+last);

    }
    /** 
   * 字符串的日期格式的计算 
   */ 
  public static int daysBetween(String smdate,String bdate) throws ParseException{ 
          SimpleDateFormat sdf=new SimpleDateFormat("yyyy-MM-dd"); 
          Calendar cal = Calendar.getInstance(); 
          cal.setTime(sdf.parse(smdate)); 
          long time1 = cal.getTimeInMillis(); 
          cal.setTime(sdf.parse(bdate)); 
          long time2 = cal.getTimeInMillis(); 
          long between_days=(time2-time1)/(1000*3600*24); 
          return Integer.parseInt(String.valueOf(between_days)); 
  }
}

//获取指定日期的最后一天

<pre name="code" class="java">    public String getLastDay(String datadate)throws Exception{        Date date = null;        String day_last = null;        SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd");        date = format.parse(datadate);                //创建日历        Calendar calendar = Calendar.getInstance();        calendar.setTime(date);        calendar.add(Calendar.MONTH, 1);    //加一个月        calendar.set(Calendar.DATE, 1);     //设置为该月第一天        calendar.add(Calendar.DATE, -1);    //再减一天即为上个月最后一天        day_last = format.format(calendar.getTime());        return day_last;    }    //获取指定日期的第一天    public String getFirstDay(String datadate)throws Exception{        Date date = null;        String day_first = null;        SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd");        date = format.parse(datadate);                //创建日历        Calendar calendar = Calendar.getInstance();        calendar.setTime(date);        calendar.set(Calendar.DAY_OF_MONTH, 1);        day_first = format.format(calendar.getTime());        return day_first;    }