Date时间的格式化、计算、字符串的转换

Date与字符串间的转换
Date进行计算
获取每个月的第一天和最后一天等等

package test;

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.Calendar;
import java.util.Date;
import java.util.List;

import sun.misc.Launcher;

/**
 * @author zhengtian
 * 
 * @date 2011-6-17 下午02:39:24
 */
@SuppressWarnings("all")
public class test {
	private static final String yyyy_MM = "yyyy-MM";
	private static final String yyyy_MM_dd = "yyyy-MM-dd";

	public static void main(String[] args) {
		String dateStr = "2012-3";
		System.out.println(getFirstDayTime(dateStr));
		System.out.println(getLastDayTime(dateStr));
	}

	/**
	 * 得到每个月第一天
	 * 
	 * @param dateStr
	 * @return
	 */
	public static String getFirstDayTime(String dateStr) {
		Date date = convertStrToDate(dateStr, yyyy_MM);
		Calendar calendar = Calendar.getInstance();
		calendar.setTime(date);
		int firstDay = calendar.getActualMinimum(Calendar.DAY_OF_MONTH);
		calendar.set(Calendar.DAY_OF_MONTH, firstDay);
		return convertDateToStr(calendar.getTime(), yyyy_MM_dd);
	}

	/**
	 * 得到每个月的最后一天
	 * 
	 * @param dateStr
	 * @return
	 */
	public static String getLastDayTime(String dateStr) {
		Date date = convertStrToDate(dateStr, yyyy_MM);
		Calendar calendar = Calendar.getInstance();
		calendar.set(Calendar.DATE, 1);
		calendar.setTime(date);
		int lastDay = calendar.getActualMaximum(Calendar.DAY_OF_MONTH);
		calendar.set(Calendar.DAY_OF_MONTH, lastDay);
		return convertDateToStr(calendar.getTime(), yyyy_MM_dd);
	}

	/**
	 * Date转换为字符串
	 * 
	 * @param date
	 * @param formatStr
	 * @return
	 */
	public static String convertDateToStr(Date date, String formatStr) {
		SimpleDateFormat format = new SimpleDateFormat(formatStr);
		return format.format(date);
	}

	/**
	 * 字符串转换为Date
	 * 
	 * @param dateStr
	 * @param formatStr
	 * @return
	 */
	public static Date convertStrToDate(String dateStr, String formatStr) {
		SimpleDateFormat format = new SimpleDateFormat(formatStr);
		try {
			return format.parse(dateStr);
		} catch (ParseException e) {
			return null;
		}
	}
}