java之获取时间

一：获取当前时间，一小时前，一小时后，一月前，一月后的时间

GregorianCalendar a = new GregorianCalendar();
SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");

System.out.println("当前时间："+format.format(a.getTime()));

a.add(Calendar.HOUR_OF_DAY, -1);
System.out.println("一小时前："+format.format(a.getTime()));

a = new GregorianCalendar();
a.add(Calendar.DAY_OF_MONTH, -1);
System.out.println("一 天 前："+format.format(a.getTime()));

a = new GregorianCalendar();
a.add(Calendar.MONTH, -1);
System.out.println("一 月 前："+format.format(a.getTime()));

a = new GregorianCalendar();
a.add(Calendar.MONTH, 1);
System.out.println("一 月 后："+format.format(a.getTime()));

a = new GregorianCalendar();
a.add(Calendar.HOUR_OF_DAY,5);
System.out.print("5 小 时 后："+format.format(a.getTime()));

 二 ：获取当前月最大天数

Calendar cal = Calendar.getInstance();
int day=cal.getActualMaximum(Calendar.DAY_OF_MONTH);
System.out.println(“当前月最大天数：”+day);

三：格式化日期

public static Date parseDate(String dateStr, String format) {
Date date = null;
try {
SimpleDateFormat format2 = new SimpleDateFormat(format);
date = format2.parse(dateStr);
} catch (Exception e) {
}
return date;
}

四：date转String

public static String format(Date date, String format) {
String result = "";
try {
if (date != null) {
SimpleDateFormat dateFormat = new SimpleDateFormat(format);
result = dateFormat.format(date);
}
} catch (Exception e) {
}
return result;
}

五：返回这个时间是本年第多少周

public static int getYearOfWeek(Date date) {
Calendar calendar = Calendar.getInstance();
calendar.setTime(date);
return calendar.get(Calendar.WEEK_OF_YEAR);
}

六：判断两个日期是不是一个周

public static boolean weekOfYeak(Date date1, Date date2) {
String dates1 = getMondayOfThisWeek(date1);
String dates2 = getMondayOfThisWeek(date2);
if (dates1.equals(dates2)) {
return true;
}
return false;
}

七：返回这个时间是本年第多少天

public static int getYearOfDay(Date date) {
Calendar calendar = Calendar.getInstance();
calendar.setTime(date);
return calendar.get(Calendar.DAY_OF_YEAR);
}