Java获取月份第一天和最后一天日期

package test;

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;
import java.util.GregorianCalendar;
import java.util.HashMap;
import java.util.Map;

public class Test {

/**
* @param args
* @throws ParseException
*/
public static void main(String[] args) throws ParseException {
SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd");
String str = "2012-05-02";
Date date = df.parse(str);
Map<String, String> map = getFirstday_Lastday_Month(date);
System.out.println("当月第一天：" + getFirstDay());
System.out.println("当月最后一天：" + getLastDay());

System.out.println("一个月前第一天：" + map.get("first"));
System.out.println("一个月前最后一天：" + map.get("last"));
}

/**
* 某一个月第一天和最后一天
* @param date
* @return
*/
private static Map<String, String> getFirstday_Lastday_Month(Date date) {
SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd");
Calendar calendar = Calendar.getInstance();
calendar.setTime(date);
calendar.add(Calendar.MONTH, -1);
Date theDate = calendar.getTime();

//上个月第一天
GregorianCalendar gcLast = (GregorianCalendar) Calendar.getInstance();
gcLast.setTime(theDate);
gcLast.set(Calendar.DAY_OF_MONTH, 1);
String day_first = df.format(gcLast.getTime());
StringBuffer str = new StringBuffer().append(day_first).append(" 00:00:00");
day_first = str.toString();

//上个月最后一天
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
String day_last = df.format(calendar.getTime());
StringBuffer endStr = new StringBuffer().append(day_last).append(" 23:59:59");
day_last = endStr.toString();

Map<String, String> map = new HashMap<String, String>();
map.put("first", day_first);
map.put("last", day_last);
return map;
}

/**
* 当月第一天
* @return
*/
private static String getFirstDay() {
SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd");
Calendar calendar = Calendar.getInstance();
Date theDate = calendar.getTime();

GregorianCalendar gcLast = (GregorianCalendar) Calendar.getInstance();
gcLast.setTime(theDate);
gcLast.set(Calendar.DAY_OF_MONTH, 1);
String day_first = df.format(gcLast.getTime());
StringBuffer str = new StringBuffer().append(day_first).append(" 00:00:00");
return str.toString();

}

/**
* 当月最后一天
* @return
*/
private static String getLastDay() {
SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd");
Calendar calendar = Calendar.getInstance();
Date theDate = calendar.getTime();
String s = df.format(theDate);
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
String day_last = df.format(calendar.getTime());
StringBuffer endStr = new StringBuffer().append(day_last);
day_last = endStr.toString();
StringBuffer str = new StringBuffer().append(day_last);
return str.toString();

}

}