java中的一些日期操作

特定string to date:

 		String pattern = "yyyyMMdd";
		SimpleDateFormat sdf = new SimpleDateFormat(pattern);
		Date startTime = null;
		Date endTime = null;
		try {
			startTime = sdf.parse("20090420");
			endTime = sdf.parse("20090426");
		} catch (ParseException e) {
			e.printStackTrace();
		}

将data to 特定string.new SimpleDateFormat("yyyy/MM/dd").format(c.getTime());
还有c.roll(Calendar.DATE, -7)不进行更大单位的滚动，这个在跨月份的时候会出现问题，可以采用c.add()代替。

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

public class GetTime {

	/**
	 * @param args
	 */
	public static void main(String[] args) {

		Date date = new Date(System.currentTimeMillis());
//		System.out.println(date);
		
		String firstDayOfCurrentWeek = getFirstDayOfCurrentWeek(date);
		System.out.println(firstDayOfCurrentWeek);
		
		String firstDayOfLastWeek = getFirstDayOfLastWeek(date);
		System.out.println(firstDayOfLastWeek);
	}

	// 获得周一的日期
	public static String getFirstDayOfCurrentWeek(Date date){
		Calendar c = Calendar.getInstance();
		c.setTime(date);
		c.set(Calendar.DAY_OF_WEEK,Calendar.MONDAY);
		return new SimpleDateFormat("yyyy/MM/dd").format(c.getTime());
	}
	
	public static String getFirstDayOfLastWeek(Date date){
		Calendar c = Calendar.getInstance();
		c.setTime(date);
		c.set(Calendar.DAY_OF_WEEK,Calendar.MONDAY);
		c.roll(Calendar.DATE, -7);
		return new SimpleDateFormat("yyyy/MM/dd").format(c.getTime());
	}
}