DateUtil 日期常用工具

/**
 * 日期处理工具类
 * @author BIANDONGYU850
 * @date 2012-7-26 下午07:38:46
 * @path com.pingan.saims.scms.common.util
 * @description
 */
public class DateUtil {
    /**
     * 默认日期格式化字符串:yyyy-MM-dd
     */
    public static final String DEFAULT_DATE_FORMAT = "yyyy-MM-dd";
    //日期格式化对象
    private static SimpleDateFormat sdf = new SimpleDateFormat();
    /**
     * 将日期对象按照指定的格式转换成字符串
     *@description  
     *@date 2012-7-26 
     *@author BIANDONGYU850
     *@param date
     *@param formatStr
     *@return}
     */
    public static String formatDateToString(Date date,String formatStr){
        synchronized (sdf) {
            sdf = new SimpleDateFormat(formatStr);
            return sdf.format(date);
        }
    }
     
    /**
     * 将字符串对象按照指定的格式转换成日期
     *@description  
     *@date 2012-7-26 
     *@author BIANDONGYU850
     *@param date
     *@param formatStr
     *@return}
     * @throws ParseException 
     */
    public static Date formatDateToString(String dateString,String formatStr) throws ParseException{
        synchronized (sdf) {
            sdf = new SimpleDateFormat(formatStr);
            return sdf.parse(dateString);
        }
    }
    /**
     * 将日期对象按照默认的格式转换成字符串
     *@description  
     *@date 2012-7-26 
     *@author BIANDONGYU850
     *@param date
     *@return}
     */
    public static String formatDateToString(Date date){
        return formatDateToString(date,DEFAULT_DATE_FORMAT);
    }
     
    /**
     * 将字符串对象按照默认的格式转换成日期类型
     *@description  
     *@date 2012-8-9 
     *@author EX-ZHANGWEI001
     *@param date
     *@return}
     * @throws ParseException 
     */
    public static Date formatStringToDate(String date) throws ParseException
    {
        if(date != null)
        {
            synchronized (sdf) {
                sdf = new SimpleDateFormat(DEFAULT_DATE_FORMAT);
                return sdf.parse(date);
            }
        }
        else{
            return null;
        }
         
    }
     
    /**
     * 获取当天年，月，日
     *@description  
     *@date 2012-8-2 
     *@author EX-ZHANGWEI001
     *@param dateFlag
     *@return}
     */
    public static String getYearOrMonthOrDay(String dateFlag)
    {
        // 设置年、月、日
        dateFlag = dateFlag.toLowerCase();
        String date = formatDateToString(new Date());
        String year = date.substring(0, 4);
        String month = date.substring(5, 7);
        String day = date.substring(8, 10);
        if("yyyy".equals(dateFlag))
        {
            return year;
        }
        else if("mm".equals(dateFlag))
        {
            return month;
        }
        else
        {
            return day;
        }
    }
     
    /**获取日期
     * 
     * @param date 带时分秒的日期 2010-10 10:10:10
     * @return 不带时分秒的日期 2010-10-10
     * @throws ParseException 
     */
    public static Date getDateToDate(Date date) throws ParseException
    {
        sdf = new SimpleDateFormat("yyyy-MM-dd");
        synchronized(sdf)
        {
        String dateString = sdf.format(date);
         
        return sdf.parse(dateString);
        }
    }
     
    /**加减日期时间
     * 
     * @param date 计算的日期时间
     * @param daynum 秒数(负数表示几天前，正数表示几天后)
     * @return 计算后的日期
     */
    public static Date apDatetime(Date date, int secondnum) throws ParseException
    {
        Calendar calendar = Calendar.getInstance();
        calendar.setTime(date);
        calendar.add(Calendar.SECOND, secondnum);  
        return calendar.getTime();
    }
     
    /**加减日期
     * 
     * @param date 计算的日期
     * @param daynum 天数(负数表示几天前，正数表示几天后)
     * @return 计算后的日期
     */
    public static Date apDate(Date date, int daynum)
    {
        Calendar calendar = Calendar.getInstance();
        calendar.setTime(date);
        calendar.add(Calendar.DATE, daynum);  
        return calendar.getTime();
    }
}