importjava.text.SimpleDateFormat;importjava.util.Calendar;importjava.util.Date;importjava.util.GregorianCalendar;importorg.junit.Test;public classTestDateUtil {//1、获取当月第一天
@Testpublic voidtestForDate(){//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 voidtestForDatelast(){//获取Calendar
Calendar 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 voidtestt(){
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()throwsException{
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()throwsException{
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 staticString 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-2
Date dateFrom =cl.getTime();returnsdf.format(dateFrom);
}
@Testpublic voidtestStartDate(){
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
}
}