日期工具类

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

/***
 * 日期工具类
 *
 */
public class DateUtil {
	public static final String ENG_DATE_FROMAT = "EEE, d MMM yyyy HH:mm:ss z";  
    public static final String YYYY_MM_DD_HH_MM_SS = "yyyy-MM-dd HH:mm:ss";  
    public static final String YYYY_MM_DD_HH_MM = "yyyy-MM-dd HH:mm";  
    public static final String YYYY_MM_DD = "yyyy-MM-dd";  
    public static final String YYYY = "yyyy";  
    public static final String MM = "MM";  
    public static final String DD = "dd";
	
    /**
     * 时间对象转换成字符串
     * @param date
     * @param formatStr
     * @return
     */
    public static String dateToString(Date date, String formatStr) {  
        String strDate = "";  
        SimpleDateFormat sdf = new SimpleDateFormat(formatStr);  
        strDate = sdf.format(date);  
        return strDate;  
    }  
    
    /**
	 * 得到系统当前时间
	 * @return
	 */
	public static Date getCurrentDate(){
		return new Date();
	}
	
	/**
	 * 比较两个日期相差天数
	 * @param startDate  开始日期
	 * @param endDate	结束日期
	 * @return
	 */
	public static int daysOfDate(Date startDate, Date endDate) {
		if (startDate == null)
			throw new RuntimeException(
					"input parametars beginDate can't be null!");
		if (endDate == null)
			throw new RuntimeException(
					"input parametars endDate can't be null!");
		Calendar calBegin = Calendar.getInstance();
		Calendar calEnd = Calendar.getInstance();
		Calendar cal = Calendar.getInstance();

		cal.setTime(startDate);
		calBegin.clear();
		calBegin.set(cal.get(Calendar.YEAR), cal.get(Calendar.MONTH),
				cal.get(Calendar.DAY_OF_MONTH));

		cal.setTime(endDate);
		calEnd.clear();
		calEnd.set(cal.get(Calendar.YEAR), cal.get(Calendar.MONTH),
				cal.get(Calendar.DAY_OF_MONTH));

		long times = calEnd.getTimeInMillis() - calBegin.getTimeInMillis();
		Long days = new Long(times / (24 * 60 * 60 * 1000));
		return days.intValue();
	}
	
	
	/**
	 * 获取某年的第几周的开始日期
	 * @param year
	 * @param week
	 * @return
	 */
    public static Date getFirstDayOfWeek(int year, int week) {
        Calendar c = new GregorianCalendar();
        c.set(Calendar.YEAR, year);
        c.set(Calendar.MONTH, Calendar.JANUARY);
        c.set(Calendar.DATE, 1);

        Calendar cal = (GregorianCalendar) c.clone();
        cal.add(Calendar.DATE, week * 7);

        return getFirstDayOfWeek(cal.getTime());
    }

    /**
     * 获取某年的第几周的结束日期
     * @param year
     * @param week
     * @return
     */
    public static Date getLastDayOfWeek(int year, int week) {
        Calendar c = new GregorianCalendar();
        c.set(Calendar.YEAR, year);
        c.set(Calendar.MONTH, Calendar.JANUARY);
        c.set(Calendar.DATE, 1);

        Calendar cal = (GregorianCalendar) c.clone();
        cal.add(Calendar.DATE, week * 7);

        return getLastDayOfWeek(cal.getTime());
    }
	
    /**
     * 获取当前时间所在周的开始日期
     * @param date
     * @return
     */
    public static Date getFirstDayOfWeek(Date date) {
        Calendar c = new GregorianCalendar();
        c.setFirstDayOfWeek(Calendar.MONDAY);
        c.setTime(date);
        c.set(Calendar.DAY_OF_WEEK, c.getFirstDayOfWeek()); // Monday
        return c.getTime();
    }

    /**
     * 获取当前时间所在周的结束日期
     * @param date
     * @return
     */
    public static Date getLastDayOfWeek(Date date) {
        Calendar c = new GregorianCalendar();
        c.setFirstDayOfWeek(Calendar.MONDAY);
        c.setTime(date);
        c.set(Calendar.DAY_OF_WEEK, c.getFirstDayOfWeek() + 6); // Sunday
        return c.getTime();
    }
    
}