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

/**
 * 时间处理工具类 <br>
 * 
 * @author Davint
 * @since 5.0
 * @version 1.0
 */
public class TimerUtil {

	private SimpleDateFormat sp = new SimpleDateFormat("yyyy-MM-dd");
	private static TimerUtil cc = new TimerUtil();

	public static TimerUtil getInstance() {
		return cc;
	}

	public static void main(String[] args) {
		TimerUtil timer=TimerUtil.getInstance();
		System.out.println(timer.getDaysByDate(timer.getDate("2012-04-01", "yyyy-MM-dd")));
		
	}
	
	//根据日期得到当月天数
	public int getDaysByDate(Date date) {
		Calendar ca=Calendar.getInstance();
		ca.setTime(date);
		int year=ca.get(Calendar.YEAR);
		int month=ca.get(Calendar.MONDAY)+1;
		int day=0;
		if (year % 4 == 0 && year % 100 != 0 || year % 400 == 0) {
			if (month==2) {
				day=29;
			}
		}else {
			if (month==2) {
				day=28;
			} 
		}
		
		if (month==4||month==6||month==9||month==11) {
			day=30;
		}
		
		if (month==1||month==3||month==5||month==7||month==8||month==10||month==12) {
			day=31;
		}
		return day;
	}
	

	/**
	 * 上周一的日期
	 * 将周一作为一周的第一天
	 */
	public Date getLastWeekFirstDay() {
		Calendar ca = Calendar.getInstance();
		if (ca.get(Calendar.DAY_OF_WEEK)-1==0) {
			ca.add(Calendar.DATE, -1 * 7*2);
			ca.set(Calendar.DAY_OF_WEEK, Calendar.MONDAY);
			return ca.getTime();
		}
		ca.add(Calendar.DATE, -1 * 7);
		ca.set(Calendar.DAY_OF_WEEK, Calendar.MONDAY);
		return ca.getTime();
	}

	// 本周一日期
	public Date getThisWeekFirstDay() {
		Calendar ca=Calendar.getInstance();
		if (ca.get(Calendar.DAY_OF_WEEK)-1==0) {
			ca.add(Calendar.DATE, -1);
			ca.set(Calendar.DAY_OF_WEEK, Calendar.MONDAY);
			return ca.getTime();
		}
		ca.add(Calendar.DATE, 0);
		ca.set(Calendar.DAY_OF_WEEK, Calendar.MONDAY);
		return ca.getTime();
	}
	
	//两个月前的第一天
	public Date getLast2MonFirstDay() {
		Calendar cal=Calendar.getInstance();
		Date now=new Date();
		cal.setTime(now);
		cal.add(Calendar.MONTH, -1);
		int year=cal.get(Calendar.YEAR);
		int month=cal.get(Calendar.MONTH);
		String resultTime=year+"-"+month+"-01";
		Date date =null;
		try {
			date=sp.parse(resultTime);
		} catch (ParseException e) {
			e.printStackTrace();
		}
		return date;
	}
	
	// 上个月第一天日期
	public Date getLastMonFirstDay() {
		Calendar cal=Calendar.getInstance();
		Date now=new Date();
		cal.setTime(now);
		int year=cal.get(Calendar.YEAR);
		int month=cal.get(Calendar.MONTH);
		String resultTime=year+"-"+month+"-01";
		Date date =null;
		try {
			date=sp.parse(resultTime);
		} catch (ParseException e) {
			e.printStackTrace();
		}
		return date;
	}

	// 本月第一天
	public Date getThisMonFirstDay() {
		Calendar cal = Calendar.getInstance();
		int year = cal.get(Calendar.YEAR);
		int month = cal.get(Calendar.MONTH) + 2;
		cal.set(Calendar.DAY_OF_MONTH, 1);
		cal.add(Calendar.DAY_OF_MONTH, -1);
		int day = cal.get(Calendar.DAY_OF_MONTH);
		String months = "";
		String days = "";
		if (month > 1) {
			month--;
		} else {
			year--;
			month = 12;
		}
		if (!(String.valueOf(month).length() > 1)) {
			months = "0" + month;
		} else {
			months = String.valueOf(month);
		}
		if (!(String.valueOf(day).length() > 1)) {
			days = "0" + day;
		} else {
			days = String.valueOf(day);
		}
		String firstDay = "" + year + "-" + months + "-01";
		String[] lastMonth = new String[2];
		lastMonth[0] = firstDay;
		try {
			return sp.parse(firstDay);
		} catch (ParseException e) {
		}
		return null;
	}
	
	// 昨天日期
	public String getYesterday() {
		Date today = new Date();
		Calendar ca = Calendar.getInstance();
		ca.setTime(today);
		ca.add(Calendar.DAY_OF_YEAR, -1);
		return sp.format(ca.getTime());
	}

	// 7天前日期
	public String getSevenDayAgo() {
		Date today = new Date();
		Calendar ca = Calendar.getInstance();
		ca.setTime(today);
		ca.add(Calendar.DAY_OF_YEAR, -7);
		return sp.format(ca.getTime());
	}

	// 3天前日期
	public String getThreeDayAgo() {
		Date today = new Date();
		Calendar ca = Calendar.getInstance();
		ca.setTime(today);
		ca.add(Calendar.DAY_OF_YEAR, -3);
		return sp.format(ca.getTime());
	}

	// 一月前日期
	public String getOneMonthAgo() {
		Calendar cal = Calendar.getInstance();
		cal.add(Calendar.MONTH, -1); // 得到前一个月
		long date = cal.getTimeInMillis();
		Date kk = new Date(date);
		return sp.format(kk);
	}

	// 3月前日期
	public String getThreeMonthAgo() {
		Calendar cal = Calendar.getInstance();
		cal.add(Calendar.MONTH, -3);
		long date = cal.getTimeInMillis();
		Date kk = new Date(date);
		return sp.format(kk);
	}

	/**
	 * getDate<br>
	 * 格式：yyyy-MM-dd 00:00:00 eg.2013-08-19 00:00:00<br>
	 * @param type -1表示昨天；-2表示前天；以此类推-N表示前N天
	 * @return java.util.Date
	 */
	public Date getDate(int type) {
		Date resultDate = null;
		Date today = new Date();
		Calendar ca = Calendar.getInstance();
		ca.setTime(today);
		ca.add(Calendar.DAY_OF_YEAR, type);
		// 将时间转换成00:00:00
		try {
			resultDate = sp.parse(sp.format(ca.getTime()));
			return resultDate;
		} catch (ParseException e) {
			e.printStackTrace();
		}
		return resultDate;
	}

	/**
	 * N天前的具体时间
	 * 
	 * @param n  0 表示今天，-1代表昨天
	 * @param type yyyyMMddHHmmss、yyyy-MM-dd HH:mm:ss
	 * @return
	 */
	public String getSomeDaysAgoString(int n, String type) {
		Date today = new Date();
		SimpleDateFormat sp = new SimpleDateFormat();
		sp.applyPattern(type);
		Calendar ca = Calendar.getInstance();
		ca.setTime(today);
		ca.add(Calendar.DAY_OF_YEAR, n);
		return sp.format(ca.getTime());
	}

	/**
	 * N天前的具体时间
	 * 
	 * @param n 0 表示今天，-1代表昨天
	 * @return
	 */
	public Date getSomeDaysAgoDate(int n) {
		Date today = new Date();
		Calendar ca = Calendar.getInstance();
		ca.setTime(today);
		ca.add(Calendar.DAY_OF_YEAR, n);
		return ca.getTime();
	}

	/**
	 * 格式化某一时间
	 * 
	 * @param date
	 * @param type
	 * @return
	 */
	public String getString(Date date, String type) {
		SimpleDateFormat sp = new SimpleDateFormat();
		sp.applyPattern(type);
		if (date != null && type != null) {
			return sp.format(date);
		}
		return "时间格式化异常！";
	}

	/**
	 * 格式化某一时间字符串
	 * 
	 * @param date
	 * @param type
	 * @return
	 */
	public Date getDate(String date, String type) {
		SimpleDateFormat sp = new SimpleDateFormat();
		sp.applyPattern(type);
		try {
			if (date != null && type != null) {
				return sp.parse(date);
			}
			return null;
		} catch (ParseException e) {
			e.printStackTrace();
		}
		return null;
	}
	
	/**
	 * 某日期前、后N天的日期
	 * @param date 某一日期
	 * @param type N天 0表示当天，N或+N表示后N天的日期，-N表示前N天的日期
	 * @return java.util.Date
	 */
	public Date getDate(Date date,int type) {
		Calendar cal=Calendar.getInstance();
		cal.setTime(date);
		cal.add(Calendar.DAY_OF_YEAR, type);
		return cal.getTime();
	}

}

java 日期工具类