java时间类Calander，Date等的问题

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<num;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));
}
}