工作中常用代码--DateUtils

工作中经常遇到处理日期的问题， 当然有一些优秀开源的库（例如 joda-time, 功能十分强大）， 不过个人还是比较偏好自写一点常用的代码， 毕竟开源库中我们实际使用到的功能并不多，如果引入库，个人感觉造成一些资源浪费（纯属个人观点）。下面就是我常用一个工具类，DateUtils,  仅仅就封装了一些本人工作中常用到的方法，这儿贴出来，代码如有不当之处，麻烦指出（不胜感激）：

/**
 * @author ying.dong
 * DateUtils
 */
public class DateUtils {

    private static final ThreadLocal<SimpleDateFormat> threadLocal = new ThreadLocal<SimpleDateFormat>();

    /**
     * define datePattern
     * @author ying.dong
     *
     */
    public enum DatePattern {

        DATE_TIME_PATTERN("yyyy-MM-dd HH:mm:ss"), DATE_PATTERN("yyyy-MM-dd"), DATE_NO_SYMBOL_PATTERN("yyyyMMdd");

        private String datePattern;

        private DatePattern(String pattern) {
            this.datePattern = pattern;
        }
        public String getDatePattern() {
            return this.datePattern;
        }
    }

    /**
     * define operation unit
     * @author ying.dong
     *
     */
    public enum OperationUnit {
        YEAR, MONTH, DAY, HOUR, MINUTE, SECOND;
    }

    /**
     * get SimpleDateFormat instance by ThreadLocal
     * @return
     */
    private static SimpleDateFormat getSimpleDateFormat() {
        SimpleDateFormat formatter = threadLocal.get();
        if (formatter == null) {
            formatter = new SimpleDateFormat();
            threadLocal.set(formatter);
        }
        return formatter;
    }

    /**
     * config DateFomatter
     * @param datePattern
     */
    private static SimpleDateFormat configFormatterPattern(DatePattern datePattern) {
        SimpleDateFormat formatter = getSimpleDateFormat();
        formatter.applyPattern(datePattern.getDatePattern());
        return formatter;
    }

    /**
     * parse calendar to String
     * @param calendar
     * @return
     */
    public static String parseDate2Str(Calendar calendar) {
        return parseDate2Str(DatePattern.DATE_TIME_PATTERN, calendar.getTime());
    }

    /**
     * parse date to String
     * @param date
     * @return
     */
    public static String parseDate2Str(Date date) {
        return parseDate2Str(DatePattern.DATE_TIME_PATTERN, date);
    }

    /**
     * parse calendar to String
     * @param datePattern
     * @param calendar
     * @return String
     */
    public static String parseDate2Str(DatePattern datePattern, Calendar calendar) {
        return parseDate2Str(datePattern, calendar.getTime());
    }

    /**
     * parse Date to String
     * @param datePattern
     * @param date
     * @return String
     */
    public static String parseDate2Str(DatePattern datePattern, Date date) {
        SimpleDateFormat formatter = configFormatterPattern(datePattern);
        return formatter.format(date);
    }

    /**
     * parse String to Date
     * @param datePattern
     * @param dateStr
     * @return Date
     * @throws ParseException
     */
    public static Date parseStr2Date(DatePattern datePattern, String dateStr) throws ParseException {
        SimpleDateFormat formatter = configFormatterPattern(datePattern);
        return formatter.parse(dateStr);
    }

    /**
     * parse timestamp String to date
     * @param timestampStr
     * @return
     */
    public static Date parseTimestampStr2Date(String timestampStr) {
        long timestamp = Long.parseLong(timestampStr) * 1000;
        return parseTimestampStr2Date(timestamp);
    }

    /**
     * parse timestamp to date
     * @param timestamp
     * @return
     */
    public static Date parseTimestampStr2Date(long timestamp) {
        Calendar calendar = Calendar.getInstance();
        calendar.setTimeInMillis(timestamp * 1000);
        return calendar.getTime();
    }

    /**
     * calendar plus operation
     * @param unit
     * @param amount
     * @param calendar
     * @return
     */
    public static Calendar plus(OperationUnit unit, int amount, Calendar calendar) {
        switch (unit) {
        case YEAR:
            calendar.add(Calendar.YEAR, amount);
            break;

        case MONTH:
                calendar.add(Calendar.MONTH, amount);
                break;

        case DAY:
            calendar.add(Calendar.DAY_OF_YEAR, amount);
            break;

        case HOUR:
            calendar.add(Calendar.HOUR_OF_DAY, amount);
            break;

        case MINUTE:
            calendar.add(Calendar.MINUTE, amount);
            break;

        case SECOND:
            calendar.add(Calendar.SECOND, amount);
            break;

        default:
            break;
        }
        return calendar;
    }

    /**
     * date plus operation
     * @param unit
     * @param amount
     * @param date
     * @return
     */
    public static Date plus(OperationUnit unit, int amount, Date date) {
        Calendar calendar = Calendar.getInstance();
        calendar.setTime(date);
        calendar = plus(unit, amount, calendar);
        return calendar.getTime();
    }

    /**
     * date plus operation with timestamp
     * @param date
     * @param timestamp
     * @return
     */
    public static Date plus(Date date, long timestamp) {
        timestamp = date.getTime() + timestamp * 1000;
        date.setTime(timestamp);
        return date;
    }

    /**
     * calendar minus operation
     * @param unit
     * @param amount
     * @param calendar
     * @return
     */
    public static Calendar minus(OperationUnit unit, int amount, Calendar calendar) {
        return plus(unit, -amount, calendar);
    }

    /**
     * date minus operation
     * @param unit
     * @param amount
     * @param date
     * @return
     */
    public static Date minus(OperationUnit unit, int amount, Date date) {
        return plus(unit, -amount, date);
    }

    /**
     * date minus operation with timestamp
     * @param date
     * @param timestamp
     * @return
     */
    public static Date minus(Date date, long timestamp) {
        return plus(date, -timestamp);
    }

    /**
     * whether the date is before when
     * @param date
     * @param when
     * @return
     * @throws ParseException
     */
    public static boolean isBefore(Date date, String when) throws ParseException {
        Date whenDate = parseStr2Date(DatePattern.DATE_TIME_PATTERN, when);
        return isBefore(date, whenDate);
    }

    /**
     * whether the date is before when
     * @param date
     * @param when
     * @param datePattern
     * @return
     * @throws ParseException
     */
    public static boolean isBefore(Date date, String when, DatePattern datePattern) throws ParseException {
        Date whenDate = parseStr2Date(datePattern, when);
        return isBefore(date, whenDate);
    }

    /**
     * whether the date is before when
     * @param date
     * @param when
     * @return
     */
    public static boolean isBefore(Date date, Date when) {
        return date.before(when);
    }

    /**
     * whether the date is after when
     * @param date
     * @param when
     * @return
     * @throws ParseException
     */
    public static boolean isAfter(Date date, String when) throws ParseException {
        Date whenDate = parseStr2Date(DatePattern.DATE_TIME_PATTERN, when);
        return isAfter(date, whenDate);
    }

    /**
     * whether the date is after when
     * @param date
     * @param when
     * @param datePattern
     * @return
     * @throws ParseException
     */
    public static boolean isAfter(Date date, String when, DatePattern datePattern) throws ParseException {
        Date whenDate = parseStr2Date(datePattern, when);
        return isAfter(date, whenDate);
    }

    /**
     * whether the date is after when
     * @param date
     * @param when
     * @return
     */
    public static boolean isAfter(Date date, Date when) {
        return date.after(when);
    }

}

目前，自知bug一处： parseStr2Date 方法没去校验传入的dataPattern的格式（此处需用正则，人比较懒，没写）。