java获取时间段、时间点

java获取本月开始时间和结束时间、上个月第一天和最后一天的时间以及当前日期往前推一周、一个月

import java.text.SimpleDateFormat;import java.util.Calendar;import java.util.Date;import java.util.GregorianCalendar;import org.junit.Test;public class TestDateUtil {//1、获取当月第一天@Testpublic void testForDate(){//规定返回日期格式SimpleDateFormat sf=new SimpleDateFormat("yyyy-MM-dd");Calendar calendar=Calendar.getInstance();Date theDate=calendar.getTime();GregorianCalendar gcLast=(GregorianCalendar)Calendar.getInstance();gcLast.setTime(theDate);//设置为第一天gcLast.set(Calendar.DAY_OF_MONTH, 1);String day_first=sf.format(gcLast.getTime());//打印本月第一天System.out.println(day_first);}//2、获取当月最后一天@Testpublic void testForDatelast(){//获取CalendarCalendar calendar=Calendar.getInstance();//设置日期为本月最大日期calendar.set(Calendar.DATE, calendar.getActualMaximum(calendar.DATE));//设置日期格式SimpleDateFormat sf=new SimpleDateFormat("yyyy-MM-dd");String ss=sf.format(calendar.getTime());System.out.println(ss+" 23:59:59");}//3、非常简单和实用的获取本月第一天和最后一天@Testpublic void testt(){SimpleDateFormat format=new SimpleDateFormat("yyyy-MM-dd");Calendar c = Calendar.getInstance();           c.add(Calendar.MONTH, 0);       c.set(Calendar.DAY_OF_MONTH,1);//设置为1号,当前日期既为本月第一天        String first = format.format(c.getTime());       System.out.println("===============本月first day:"+first);              //获取当前月最后一天       Calendar ca = Calendar.getInstance();           ca.set(Calendar.DAY_OF_MONTH, ca.getActualMaximum(Calendar.DAY_OF_MONTH));         String last = format.format(ca.getTime());       System.out.println("===============本月last day:"+last);}//4、获取上个月的第一天@Testpublic void getBeforeFirstMonthdate()throws Exception{SimpleDateFormat format=new SimpleDateFormat("yyyy-MM-dd");Calendar calendar=Calendar.getInstance();calendar.add(Calendar.MONTH, -1);calendar.set(Calendar.DAY_OF_MONTH, 1);System.out.println("上个月第一天："+format.format(calendar.getTime()));}//5、获取上个月的最后一天@Testpublic void getBeforeLastMonthdate()throws Exception{SimpleDateFormat sf=new SimpleDateFormat("yyyy-MM-dd");Calendar calendar=Calendar.getInstance();int month=calendar.get(Calendar.MONTH);calendar.set(Calendar.MONTH, month-1);calendar.set(Calendar.DAY_OF_MONTH, calendar.getActualMaximum(Calendar.DAY_OF_MONTH));System.out.println("上个月最后一天："+sf.format(calendar.getTime()));}6、获取当前日期的前一周或者前一个月时间 public static String getFirstDate(){SimpleDateFormat  sdf = new SimpleDateFormat("yyyyMMdd");Calendar cl = Calendar.getInstance();// cl.setTime(dateNow);// cl.add(Calendar.DAY_OF_YEAR, -1);//一天// cl.add(Calendar.WEEK_OF_YEAR, -1);//一周cl.add(Calendar.MONTH, -1);//从现在算，之前一个月,如果是2个月，那么-1-----》改为-2Date dateFrom = cl.getTime();return sdf.format(dateFrom); } @Test public void testStartDate(){ System.out.println("当前日期往前推一个月是："+getFirstDate()); //如果当前日期是2015.11.08,那么打印日期是:20151008 }}