时间容易出现的问题，就是获取和设置年月日等问题上

我们通常使用 Date和Calander用作时间处理，其实会有两个问题：

1.Date的缺陷，我们知道 Date的setYear和getYear等函数是删除线显示的

原因在：比如今天是2009-01-04日，那么获取的年竟然是109，所以是有问题的

2.Calender常常用于时间的回卷，经常使用的就是roll(Day_of_Year,-7)就是七天前

但是如果是2009-01-04日，那么七天前是2009-12-28日，而非2008年，这是因为它只对天回卷了，年没有回卷

这个时候就会出现1中的问题，难道 Calender获取Date然后再设置天？

我处理的办法如下

static public String getADay(String format,int diff) {

SimpleDateFormat df=new SimpleDateFormat(format);

Calendar now = Calendar.getInstance();

int beforeM=now.get(Calendar.MONTH);

now.roll(Calendar.DAY_OF_YEAR,diff);//

int nowM=now.get(Calendar.MONTH);

//必须进行日期处理，否则2009-01-04日前七天是2009-12-28

if(nowM>beforeM)

{

now.roll(Calendar.YEAR,-1);

}

return df.format(now.getTime());

}

即获取日期后，如果回卷完发现月份更大了，这个时候，年是需要更换的，判断一下再回卷一下年，OK

附上所有的时间源代码

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package cn.yicha.util;

import java.text.ParseException;

import java.text.SimpleDateFormat;

import java.util.Calendar;

import java.util.Date;

import org.apache.log4j.Logger;

public class AdDateUtil {

private static Logger logger = Logger.getLogger(AdDateUtil.class);

static public String getNowStr(String format) {

SimpleDateFormat sdf = new SimpleDateFormat(format);

String now = sdf.format(new Date());

return now;

}

static public Date getFormatDate(String date, String format) {

SimpleDateFormat sdf = new SimpleDateFormat(format);

Date d = new Date();

try {

d = sdf.parse(date);

} catch (ParseException e) {

logger.error(e);

}

return d;

}

static public String getDateStr(Date date, String format) {

SimpleDateFormat sdf = new SimpleDateFormat(format);

String d = sdf.format(date);

return d;

}

static public String getPadZeroString(String s, int size) {

StringBuffer sb = new StringBuffer();

for (int i = 0; i < size - s.length(); i++) {

sb.append("0");

}

sb.append(s);

return sb.toString();

}

/**

* 得到某月的天数

*

* @param year

* @param month

* @return

*/

static public int getDayCountOfMonth(String year, String month) {

Calendar cal = Calendar.getInstance();

// 年

cal.set(Calendar.YEAR, Integer.parseInt(year));

// 月，因为Calendar里的月是从0开始，所以要-1

cal.set(Calendar.MONTH, Integer.parseInt(month) - 1);

return cal.getActualMaximum(Calendar.DAY_OF_MONTH);

}

static public String getYesterday(String format) {

SimpleDateFormat df=new SimpleDateFormat(format);

Calendar now = Calendar.getInstance();

now.roll(Calendar.DAY_OF_YEAR,-1);//昨天

return df.format(now.getTime());

}

/**

* 获取和今天附近的某天

* @param format

* @param diff

* @return

*/

static public String getADay(String format,int diff) {

SimpleDateFormat df=new SimpleDateFormat(format);

Calendar now = Calendar.getInstance();

int beforeM=now.get(Calendar.MONTH);

now.roll(Calendar.DAY_OF_YEAR,diff);//

int nowM=now.get(Calendar.MONTH);

//必须进行日期处理，否则2009-01-04日前七天是2009-12-28

if(nowM>beforeM)

{

now.roll(Calendar.YEAR,-1);

}

return df.format(now.getTime());

}

static public String getTomorrow(String format) {

SimpleDateFormat df=new SimpleDateFormat(format);

Calendar now = Calendar.getInstance();

now.roll(Calendar.DAY_OF_YEAR, 1);//明天

return df.format(now.getTime());

}

/**

* 得到最近num天的全部日期

* 说明:

* 1.日期是从昨天开始算的.

* 2.如果num=2 , 日期是2008-03-14 ,则返回的结果为 2008-03-12、2008-03-13

* @param num

* @return

*/

public static String[] getDaysByNum(int num,String date){

SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");

String[] result = {} ;

Calendar cal = Calendar.getInstance() ;

cal.setTime(getDateFromString(date, "yyyy-MM-dd"));

//最近一周

result = new String[num];

for(int i=num;i>0;i--){

cal.add(Calendar.DAY_OF_YEAR, -1);

result[i-1] = sdf.format(new Date(cal.getTimeInMillis()));

}

return result;

}

public static Date getDateFromString(String dateStr, String format) {

if (dateStr == null || format == null) {

try {

throw new Exception("数据类型异常" + dateStr + "|" + format);

} catch (Exception e) {

logger.error("数据类型异常:" + e);

}

}

SimpleDateFormat df = new SimpleDateFormat(format);

Date date;

try {

date = df.parse(dateStr);

return date;

} catch (Exception ex) {

logger.error(ex);

return new Date();

}

}

static public int getNowYear(){

Calendar cal = Calendar.getInstance();

return cal.get(Calendar.YEAR);

}

static public int getNowMonth(){

Calendar cal = Calendar.getInstance();

return cal.get(Calendar.MONTH)+1;

}

public static String[] getMonthRang(String year,String month){

String beginDate = year + "-" + month + "-01";

String endDate = year + "-" + month + "-" + getDayCountOfMonth(year,month);

return getDaysByRang(beginDate,endDate);

}

public static String[] getDaysByRang(String beginDate,String endDate){

SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");

//得到两个日期间相差多少天

int num = dateDiff(beginDate,endDate);

if(num<0){

//颠倒一下日期

String tmp = beginDate;

beginDate = endDate;

endDate = tmp;

num = 0-num;

}

String[] result = {} ;

Calendar cal = Calendar.getInstance() ;

try {

cal.setTime(sdf.parse(beginDate));

} catch (ParseException e) {

e.printStackTrace();

}

num = num + 1; //把开始和结束日期都包含进去

result = new String[num];

for(int i=0;i

if(i>0) cal.add(Calendar.DAY_OF_YEAR, 1);

result[i] = sdf.format(new Date(cal.getTimeInMillis()));

}

return result;

}

public static int dateDiff(String beginDate,String endDate){

SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");

Date date = null;

try {

date = sdf.parse(endDate);

} catch (ParseException e) {

date = new Date();

e.printStackTrace();

}

long end = date.getTime();

try {

date = sdf.parse(beginDate);

} catch (ParseException e) {

date = new Date();

e.printStackTrace();

}

long begin = date.getTime();

long day = (end-begin)/(1000*3600*24); //除1000是把毫秒变成秒

return Integer.parseInt(Long.toString(day));

}

public static void main(String[] args)

{

System.out.println(AdDateUtil.getADay("yyyy-MM-dd",-7));

}

}