Date，DateTime，String等日期格式的相互转化

日期之间的转化关系：
        
1，获取当前系统时间
   Date date = new Date();

2，Date转为DateTime
   DateTime dateTime = new DateTime(date.getTime());

3，DateTime转为Date
   Date date = dateTime.toDate();

4，获取日期格式,
   DateFormat df = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");

5，Date转换为String类型格式
   String dateStr = df.format(new Date());

工具类
/**
 * 返回当前日期时间字符串

 * 默认格式:yyyy-mm-dd hh:mm:ss
 *
 * @return String 返回当前字符串型日期时间
 */
public static String getCurrentTime() {
        String returnStr = null;
        SimpleDateFormat f = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        Date date = new Date();
        returnStr = f.format(date);
        return returnStr;
        }

/**
 * 返回当前日期时间字符串

 * 默认格式:yyyymmddhhmmss
 *
 * @return String 返回当前字符串型日期时间
 */
public static BigDecimal getCurrentTimeAsNumber() {
        String returnStr = null;
        SimpleDateFormat f = new SimpleDateFormat("yyyyMMddHHmmss");
        Date date = new Date();
        returnStr = f.format(date);
        return new BigDecimal(returnStr);
        }


/**
 * 返回自定义格式的当前日期时间字符串
 *
 * @param format
 *            格式规则
 * @return String 返回当前字符串型日期时间
 */
public static String getCurrentTime(String format) {
        String returnStr = null;
        SimpleDateFormat f = new SimpleDateFormat(format);
        Date date = new Date();
        returnStr = f.format(date);
        return returnStr;
        }

/**
 * 返回当前字符串型日期
 *
 * @return String 返回的字符串型日期
 */
public static String getCurDate() {
        Calendar calendar = Calendar.getInstance();
        SimpleDateFormat simpledateformat = new SimpleDateFormat("yyyy-MM-dd");
        String strDate = simpledateformat.format(calendar.getTime());
        return strDate;
        }

/**
 * 返回指定格式的字符型日期
 * @param date
 * @param formatString
 * @return
 */
public static String Date2String(Date date, String formatString) {
        if (G4Utils.isEmpty(date)) {
        return null;
        }
        SimpleDateFormat simpledateformat = new SimpleDateFormat(formatString);
        String strDate = simpledateformat.format(date);
        return strDate;
        }

/**
 * 返回当前字符串型日期
 *
 * @param format
 *            格式规则
 *
 * @return String 返回的字符串型日期
 */
public static String getCurDate(String format) {
        Calendar calendar = Calendar.getInstance();
        SimpleDateFormat simpledateformat = new SimpleDateFormat(format);
        String strDate = simpledateformat.format(calendar.getTime());
        return strDate;
        }

/**
 * 返回TimeStamp对象
 *
 * @return
 */
public static Timestamp getCurrentTimestamp() {
        Object obj = TypeCaseHelper.convert(getCurrentTime(), "Timestamp", "yyyy-MM-dd HH:mm:ss");
        if (obj != null)
        return (Timestamp) obj;
        else
        return null;
        }

/**
 * 将字符串型日期转换为日期型
 *
 * @param strDate
 *            字符串型日期
 * @param srcDateFormat
 *            源日期格式
 * @param dstDateFormat
 *            目标日期格式
 * @return Date 返回的util.Date型日期
 */
public static Date stringToDate(String strDate, String srcDateFormat, String dstDateFormat) {
        Date rtDate = null;
        Date tmpDate = (new SimpleDateFormat(srcDateFormat)).parse(strDate, new ParsePosition(0));
        String tmpString = null;
        if (tmpDate != null)
        tmpString = (new SimpleDateFormat(dstDateFormat)).format(tmpDate);
        if (tmpString != null)
        rtDate = (new SimpleDateFormat(dstDateFormat)).parse(tmpString, new ParsePosition(0));
        return rtDate;
        }

/**
 * dp转px
 *
 * @param context
 * @param
 * @return
 */
public static float dp2px(Context context, int dpVal) {
        return TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP,
        dpVal, context.getResources().getDisplayMetrics());
        }

/**
 * sp转px
 *
 * @param context
 * @param spVal
 * @return
 */
public static float sp2px(Context context, float spVal) {
        return TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_SP,
        spVal, context.getResources().getDisplayMetrics());
        }
/**
 * 屏幕宽度
 *
 * @param context
 * @return
 */
public static int getDisplayWidth(Context context) {
        return context.getResources().getDisplayMetrics().widthPixels;
        }
/**
 * 屏幕高度
 *
 * @param context
 * @return
 */
public static int getDisplayHeight(Context context) {
        return context.getResources().getDisplayMetrics().heightPixels;
        }

//是否同月
public static boolean isEqualsMonth(DateTime dateTime1, DateTime dateTime2) {
        return dateTime1.getMonthOfYear() == dateTime2.getMonthOfYear();
        }
/**
 * 第一个是不是第二个的上一个月,只在此处有效
 *
 * @param dateTime1
 * @param dateTime2
 * @return
 */
public static boolean isLastMonth(DateTime dateTime1, DateTime dateTime2) {
        DateTime dateTime = dateTime2.plusMonths(-1);
        return dateTime1.getMonthOfYear() == dateTime.getMonthOfYear();
        }
/**
 * 第一个是不是第二个的下一个月，只在此处有效
 * @param dateTime1
 * @param dateTime2
 * @return
 */
public static boolean isNextMonth(DateTime dateTime1, DateTime dateTime2) {
        DateTime dateTime = dateTime2.plusMonths(1);
        return dateTime1.getMonthOfYear() == dateTime.getMonthOfYear();
        }
/**
 * 获得两个日期距离几个月
 * @return
 */
public static int getIntervalMonths(DateTime dateTime1, DateTime dateTime2) {
        return (dateTime2.getYear() - dateTime1.getYear()) * 12 + (dateTime2.getMonthOfYear() - dateTime1.getMonthOfYear());
        }
/**
 * 获得两个日期距离几周
 *
 * @param dateTime1
 * @param dateTime2
 * @return
 */
public static int getIntervalWeek(DateTime dateTime1, DateTime dateTime2) {
        DateTime sunFirstDayOfWeek1 = getSunFirstDayOfWeek(dateTime1);
        DateTime sunFirstDayOfWeek2 = getSunFirstDayOfWeek(dateTime2);
        int days = Days.daysBetween(sunFirstDayOfWeek1, sunFirstDayOfWeek2).getDays();
        if (days > 0) {
        return (days + 1) / 7;
        } else if (days < 0) {
        return (days - 1) / 7;
        } else {
        return days;
        }
        }
/**
 * 是否是今天
 * @param dateTime
 * @return
 */
public static boolean isToday(DateTime dateTime) {
        return new DateTime().toLocalDate().equals(dateTime.toLocalDate());
        }
/**
 * 某月第一天是周几
 *
 * @return
 */
public static int getFirstDayOfWeekOfMonth(int year, int month) {
        int dayOfWeek = new DateTime(year, month, 1, 0, 0, 0).getDayOfWeek();
        if (dayOfWeek == 7) {
        return 0;
        }
        return dayOfWeek;
        }
//转化一周从周日开始
public static DateTime getSunFirstDayOfWeek(DateTime dateTime) {
        if (dateTime.dayOfWeek().get() == 7) {
        return dateTime;
        } else {
        return dateTime.minusWeeks(1).withDayOfWeek(7);
        }
        }
/**
 * 通过年份和月份 得到当月的日子
 *
 * @param year
 * @param month
 * @return
 */
public static int getMonthDays(int year, int month) {
        month++;
        switch (month) {
        case 1:
        case 3:
        case 5:
        case 7:
        case 8:
        case 10:
        case 12:
        return 31;
        case 4:
        case 6:
        case 9:
        case 11:
        return 30;
        case 2:
        if (((year % 4 == 0) && (year % 100 != 0)) || (year % 400 == 0)) {
        return 29;
        } else {
        return 28;
        }
default:
        return -1;
        }
        }
/**
 * 获取这个月有几行
 *
 * @param year
 * @param month
 * @return
 */
public static int getMonthRows(int year, int month) {
        int size = getFirstDayOfWeekOfMonth(year, month) + getMonthDays(year, month) - 1;
        return size % 7 == 0 ? size / 7 : (size / 7) + 1;
        }

/**
 * 返回当前月份1号位于周几
 *
 * @param year  年份
 * @param month 月份，传入系统获取的，不需要正常的
 * @return 日：1    一：2       二：3       三：4       四：5       五：6       六：7
 */
public static int getFirstDayWeek(int year, int month) {
        Calendar calendar = Calendar.getInstance();
        calendar.set(year, month, 1);
        return calendar.get(Calendar.DAY_OF_WEEK);
        }

public static int getYearByTimeStamp(long timeStamp) {
        String date = timeStampToDate(timeStamp);
        String year = date.substring(0, 4);
        return Integer.parseInt(year);
        }

public static String timeStampToDate(long timeStamp) {
        Date date = new Date(timeStamp);
        SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        String dateStr = simpleDateFormat.format(date);
        return dateStr;
        }

/**
 * 获取当前日期是星期几

 *
 * @param dt
 * @return 当前日期是星期几
 */
public static Integer getWeekOfDate(DateTime dt) {
//        String[] weekDays = {"星期日", "星期一", "星期二", "星期三", "星期四", "星期五", "星期六"};
        Integer[] weekDays = {0, 1, 2, 3, 4, 5, 6};
        Calendar cal = Calendar.getInstance();
        cal.setTime(dt.toDate());
        int w = cal.get(Calendar.DAY_OF_WEEK) - 1;
        if (w < 0)
        w = 0;
        return weekDays[w];
        }

/**
 * 获取一个日期加上天数得到最后的日期
 *
 * @param d   日期
 * @param day 加的天数 如果天数是负数，即是减
 * @return 当前日期是星期几
 */
public static Date addDate(Date d, long day) {
        long time = d.getTime();
        day = day * 24 * 60 * 60 * 1000;
        time += day;
        return new Date(time);
        }