Java 日期处理 技巧

Java日期处理还是比较麻烦的。不像ruby on rails 通过对数字的扩展，相当方便。
假设我想知道这个礼拜的周一，月底，月初的具体时间，五天前又是几号？因此专门写了个类封装了下。其实如果组合使用其内部函数，还是很方便的。
需要注意的是这里的函数返回日期都是精确到秒的。
getDayBegine()的结果是：
Mon Jun 08 00:00:00 CST 2009 形式的
而 getDayEnd()的结果为：
Sun Jun 07 23:59:59 CST 2009 形式
废话不说，看代码（详单简单）

package com.snail.gequ.action;

import java.util.Calendar;
import java.util.Date;

import org.apache.log4j.Logger;
import org.hibernate.criterion.Expression;
import org.hibernate.criterion.Projections;

import com.snail.commons.basedao.IBaseDAO;
import com.snail.component.beans.Gequ;
import com.snail.component.beans.Gequzhuanji;
import com.snail.component.beans.Huiyuan;
import com.snail.component.beans.Renqirecord;

public class RenQiRecordUtil {

	private static final long serialVersionUID = 3193922028309094171L;
	private final static Logger logger = Logger
			.getLogger(RenQiRecordUtil.class);




	protected Integer getMonthOfThisYear() {
		Calendar cal = Calendar.getInstance();
		cal.setTime(new Date());
		return cal.get(Calendar.MONTH) + 1;

	}

	protected Date getTimeByMonth(Integer month) {
		Calendar cal = Calendar.getInstance();
		cal.setTime(new Date());
		cal.set(Calendar.MONTH, month - 1);
		return cal.getTime();
	}

	protected Date getMonthBegin(Date date) {
		Calendar cal = Calendar.getInstance();
		cal.setTime(date);
		cal.set(cal.get(Calendar.YEAR), cal.get(Calendar.MONTH), 1, 0, 0, 0);
		return cal.getTime();
	}

	protected Date getMonthEnd(Date date) {
		Calendar cal = Calendar.getInstance();
		cal.setTime(date);
		cal
				.set(cal.get(Calendar.YEAR), cal.get(Calendar.MONTH) + 1, 1, 0,
						0, 0);
		cal.set(Calendar.SECOND, cal.get(Calendar.SECOND) - 1);

		return cal.getTime();
	}
	protected Date getWeekBegin(Date date) {
		Calendar cal = Calendar.getInstance();
		cal.setTime(date);
		Date mm=nDaysAgo(cal.get(Calendar.DAY_OF_WEEK)-2,date);
		return getDayBegin(mm);
	}

	protected Date getWeekEnd(Date date) {
		Calendar cal = Calendar.getInstance();
		cal.setTime(date);
		Date mm=nDaysAfter(cal.get(8-Calendar.DAY_OF_WEEK),date);
		return getDayEnd(mm);

	}
	protected Date nDaysAfter(int n,Date date) {
		Calendar cal = Calendar.getInstance();
		cal.setTime(date);
		cal.set(Calendar.DAY_OF_MONTH, cal.get(Calendar.DAY_OF_MONTH)+n);
		return cal.getTime();
	}

	protected Date getDayBegin(Date date) {
		Calendar cal = Calendar.getInstance();
		cal.setTime(date);
		cal.set(cal.get(Calendar.YEAR), cal.get(Calendar.MONTH), cal.get(Calendar.DAY_OF_MONTH), 0, 0, 0);
		return cal.getTime();
	}

	protected Date getDayEnd(Date date) {
		Calendar cal = Calendar.getInstance();
		cal.setTime(date);
		cal
				.set(cal.get(Calendar.YEAR), cal.get(Calendar.MONTH),cal.get(Calendar.DAY_OF_MONTH)+1, 0,
						0, 0);
		cal.set(Calendar.SECOND, cal.get(Calendar.SECOND) - 1);

		return cal.getTime();
	}

	protected Date nMonthsAgo(Integer n,Date date) {
		Calendar cal = Calendar.getInstance();
		cal.setTime(date);
		cal.set(Calendar.MONTH, cal.get(Calendar.MONTH) - n);
		return cal.getTime();
	}
	protected Date nDaysAgo(Integer n,Date date) {
		Calendar cal = Calendar.getInstance();
		cal.setTime(date);
		cal.set(Calendar.DAY_OF_MONTH, cal.get(Calendar.DAY_OF_MONTH) -n);
		return cal.getTime();
	}
	public RenQiRecordUtil() {
		// TODO Auto-generated constructor stub
	}


}

恩 现在我们来看下一个例子：

如果我要拿到上个礼拜的第一天，怎么拿？

RenQiRecordUtil util=new RenQiRecordUtil();
System.out.println(util.nDaysAgo(7,util.getWeekBegin(new Date())));

那如果要拿到上个笔来的周末呢？

System.out.println(util.getDayEnd(util.nDaysAgo(1,util.getWeekBegin(new Date()))));