java日期的比较 计算

做财务 erp之类的系统会经常用到很多时间上的比较和计算，这里我总结了一下我用过的东西

public static Date StringToDate2(String str){
if(str==null||str.trim().equals("")) return null;
Date date = new Date();
SimpleDateFormat sf = new SimpleDateFormat("yyyy-MM-dd");
try {
date = sf.parse(str);
} catch (ParseException e) {
e.printStackTrace();
date = null;
}
return date;
}

/*
* 获取该周
*/
public static Date[] getWeekDays(Date date) {

Calendar cale = Calendar.getInstance();
cale.setTime(date);
cale.setFirstDayOfWeek(Calendar.SUNDAY);

int days = 7;
int today = cale.get(Calendar.DAY_OF_WEEK);
long millis = cale.getTimeInMillis();

Date dates[] = new Date[days];
for (int i = 1; i <= days; i++) {
long sub = (today - i) * 24 * 60 * 60 * 1000L;
dates[i - 1] = new Date(millis - sub);
}

cale = null;
return dates;
}
/*
* 获取该月
*/
public static Date[] getMonthDays(Date date) {

Calendar cale = Calendar.getInstance();
cale.setTime(date);

int today = cale.get(Calendar.DAY_OF_MONTH);
int days = cale.getActualMaximum(Calendar.DAY_OF_MONTH);
long millis = cale.getTimeInMillis();

Date dates[] = new Date[days];
for (int i = 1; i <= days; i++) {
long sub = (today - i) * 24 * 60 * 60 * 1000L;
dates[i - 1] = new Date(millis - sub);
}

cale = null;
return dates;
}

public static Date getMonthStartDays() {
return getMonthDays(new Date())[0];
}

public static Date getMonthEndDays() {
return getMonthDays(new Date())[(getMonthDays(new Date()).length)-1];
}

/*
* 获取该年
*/
public static Date[] getYearDays(Date date) {

Calendar cale = Calendar.getInstance();
cale.setTime(date);

int today = cale.get(Calendar.DAY_OF_YEAR);
int days = cale.getActualMaximum(Calendar.DAY_OF_YEAR);
long millis = cale.getTimeInMillis();

Date dates[] = new Date[days];
for (int i = 1; i <= days; i++) {
long sub = (today - i) * 24 * 60 * 60 * 1000L;
dates[i - 1] = new Date(millis - sub);
}

cale = null;
return dates;
}

/**
* 比较两个日期之间的大小
*
* @param d1
* @param d2
* @return 前者大于后者返回true 反之false
*/
public static boolean compareDate(Date d1, Date d2) {
Calendar c1 = Calendar.getInstance();
Calendar c2 = Calendar.getInstance();
c1.setTime(d1);
c2.setTime(d2);

int result = c1.compareTo(c2);
if (result >= 0)
return true;
else
return false;
}
/**
* 返回指定年月的月的最后一天
*
* @param year
* @param month
* @return
*/
public static Date getLastDayOfMonth(Integer year, Integer month) {
Calendar calendar = Calendar.getInstance();
if (year == null) {
year = calendar.get(Calendar.YEAR);
}
if (month == null) {
month = calendar.get(Calendar.MONTH);
}
calendar.set(year, month,-1);
calendar.roll(Calendar.DAY_OF_MONTH, -1);
return calendar.getTime();
}
/**
* 返回指定年月的月的第一天
*
* @param year
* @param month
* @return
*/
public static Date getFirstDayOfMonth(Integer year, Integer month) {
Calendar calendar = Calendar.getInstance();
if (year == null) {
year = calendar.get(Calendar.YEAR);
}
if (month == null) {
month = calendar.get(Calendar.MONTH);
}
calendar.set(year, month, 1);
return calendar.getTime();
}