JAVA计算2个日期之间的相差天数

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;
import java.util.Locale;

/**
 * 计算2个日期之间的相差天数
 */
public class CountTimeDiff {
	public static void main(String[] args) {
		try {
			// 日期格式 
			SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
			Date smallDate = sdf.parse("2013-04-30");
			Date bigDate = sdf.parse("2013-05-01");
			System.out.println(daysBetween(smallDate, bigDate));

			// 字符串格式
			System.out.println(daysBetween("2012-02-09", "2013-05-09")); 
		} catch (ParseException e) {
			e.printStackTrace();
		}
	}

	/**
	 * 计算2个日期之间相差的天数
	 * 
	 * @param smallDate
	 *            较小的日期
	 * @param bigDate
	 *            较大的日期
	 * @return 相差天数
	 * @throws ParseException
	 */
	public static int daysBetween(Date smallDate, Date bigDate)
			throws ParseException {
		SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");

		smallDate = sdf.parse(sdf.format(smallDate));
		bigDate = sdf.parse(sdf.format(bigDate));

		Calendar calendar = Calendar.getInstance(Locale.CHINA);

		calendar.setTime(smallDate);
		long smallDateTime = calendar.getTimeInMillis();

		calendar.setTime(bigDate);
		long bigDateTime = calendar.getTimeInMillis();

		long betweenDays = (bigDateTime - smallDateTime) / (1000 * 3600 * 24);
		return Integer.parseInt(String.valueOf(betweenDays));
	}

	/**
	 * 
	 * @param smallDate
	 *            较小的日期
	 * @param bigDate
	 *            较大的日期
	 * @return 相差天数
	 * @throws ParseException
	 */
	public static int daysBetween(String smallDate, String bigDate)
			throws ParseException {
		SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");

		Calendar calendar = Calendar.getInstance(Locale.CHINA);

		calendar.setTime(sdf.parse(smallDate));
		long smallDateTime = calendar.getTimeInMillis();

		calendar.setTime(sdf.parse(bigDate));
		long bigDateTime = calendar.getTimeInMillis();

		long betweenDays = (bigDateTime - smallDateTime) / (1000 * 3600 * 24);
		return Integer.parseInt(String.valueOf(betweenDays));
	}
}