Java日期处理工具类DateUtils详解

import java.sql.Timestamp; import java.text.ParseException; import java.text.SimpleDateFormat; import java.util.Calendar; import java.util.Date;  /**  * <日期时间处理工具类>  */ public class DateUtils {    /**   * Date format pattern this is often used.   */  public static final String PATTERN_YMD = "yyyy-MM-dd";    /**   * Date format pattern this is often used.   */  public static final String PATTERN_YMDHMS="yyyy-MM-dd HH:mm:ss";    /**   * Formats the given date according to the YMD pattern.   *   * @param date The date to format.   * @return An YMD formatted date string.   *   * @see #PATTERN_YMD   */  public static String formatDate(Date date) {   return formatDate(date, PATTERN_YMD);  }    /**   * Formats the given date according to the specified pattern. The pattern   * must conform to that used by the {@link SimpleDateFormat simple date   * format} class.   *   * @param date The date to format.   * @param pattern The pattern to use for formatting the date.   * @return A formatted date string.   *   * @throws IllegalArgumentException If the given date pattern is invalid.   *   * @see SimpleDateFormat   */  public static String formatDate(Date date, String pattern) {   if (date == null)    throw new IllegalArgumentException("date is null");   if (pattern == null)    throw new IllegalArgumentException("pattern is null");      SimpleDateFormat formatter = new SimpleDateFormat(pattern);   return formatter.format(date);  }    /**   * Parses a date value. The format used for parsing the date value are retrieved from   * the default PATTERN_YMD.   *   * @param dateValue the date value to parse   *   * @return the parsed date   *   * @throws IllegalArgumentException If the given dateValue is invalid.   */  public static Date parseDate(String dateValue) {   return parseDate(dateValue, null);  }    /**   * Parses the date value using the given date format.   *   * @param dateValue the date value to parse   * @param dateFormat the date format to use   *   * @return the parsed date. if parse is failed , return null   *   * @throws IllegalArgumentException If the given dateValue is invalid.   */  public static Date parseDate(String dateValue, String dateFormat) {   if (dateValue == null) {    throw new IllegalArgumentException("dateValue is null");   }   if (dateFormat == null) {    dateFormat = PATTERN_YMD;   }      SimpleDateFormat df = new SimpleDateFormat(dateFormat);   Date result = null;   try {    result = df.parse(dateValue);   }   catch (ParseException pe) {    pe.printStackTrace();// 日期型字符串格式错误   }   return result;  }    /**   * Adds a number of years to a date returning a new object.   * The original date object is unchanged.   *   * @param date the date, not null   * @param amount the amount to add, may be negative   * @return the new date object with the amount added   * @throws IllegalArgumentException if the date is null   */  public static Date addYears(Date date, int amount) {   return add(date, Calendar.YEAR, amount);  }    /**   * Adds a number of years to a timestamp returning a new object.   * The original timestamp object is unchanged.   *   * @param timestamp the timestamp, not null   * @param amount the amount to add, may be negative   * @return the new timestamp object with the amount added   * @throws IllegalArgumentException if the timestamp is null   */  public static Timestamp addYears(Timestamp timestamp, int amount) {   return add(timestamp, Calendar.YEAR, amount);  }    //-----------------------------------------------------------------------  /**   * Adds a number of months to a date returning a new object.   * The original date object is unchanged.   *   * @param date the date, not null   * @param amount the amount to add, may be negative   * @return the new date object with the amount added   * @throws IllegalArgumentException if the date is null   */  public static Date addMonths(Date date, int amount) {   return add(date, Calendar.MONTH, amount);  }    /**   * Adds a number of months to a timestamp returning a new object.   * The original timestamp object is unchanged.   *   * @param timestamp the timestamp, not null   * @param amount the amount to add, may be negative   * @return the new timestamp object with the amount added   * @throws IllegalArgumentException if the timestamp is null   */  public static Timestamp addMonths(Timestamp timestamp, int amount) {   return add(timestamp, Calendar.MONTH, amount);  }    //-----------------------------------------------------------------------  /**   * Adds a number of days to a date returning a new object.   * The original date object is unchanged.   *   * @param date the date, not null   * @param amount the amount to add, may be negative   * @return the new date object with the amount added   * @throws IllegalArgumentException if the date is null   */  public static Date addDays(Date date, int amount) {   return add(date, Calendar.DATE, amount);  }    /**   * Adds a number of days to a timestamp returning a new object.   * The original timestamp object is unchanged.   *   * @param timestamp the timestamp, not null   * @param amount the amount to add, may be negative   * @return the new timestamp object with the amount added   * @throws IllegalArgumentException if the timestamp is null   */  public static Timestamp addDays(Timestamp timestamp, int amount) {   return add(timestamp, Calendar.DATE, amount);  }    //-----------------------------------------------------------------------  /**   * Adds a number of minutes to a timestamp returning a new object.   * The original timestamp object is unchanged.   *   * @param timestamp the timestamp, not null   * @param amount the amount to add, may be negative   * @return the new timestamp object with the amount added   * @throws IllegalArgumentException if the timestamp is null   */  public static Timestamp addMinutes(Timestamp timestamp, int amount) {   return add(timestamp, Calendar.MINUTE, amount);  }    /**   * Adds a number of days to current time returning a new object.   *   * @param amount the amount to add, may be negative   * @return the new timestamp object with the amount added   */  public static Timestamp addDays(int amount) {   Calendar c = Calendar.getInstance();   c.add(Calendar.DATE, amount);   return new Timestamp(c.getTimeInMillis());  }    //-----------------------------------------------------------------------  /**   * Adds to a date returning a new object.   * The original date object is unchanged.   *   * @param date the date, not null   * @param calendarField the calendar field to add to   * @param amount the amount to add, may be negative   * @return the new date object with the amount added   * @throws IllegalArgumentException if the date is null   */  private static Date add(Date date, int calendarField, int amount) {   if (date == null) {    throw new IllegalArgumentException("The date must not be null");   }   Calendar c = Calendar.getInstance();   c.setTime(date);   c.add(calendarField, amount);   return c.getTime();  }    /**   * Adds to a timestamp returning a new object.   * The original timestamp object is unchanged.   *   * @param timestamp the timestamp, not null   * @param calendarField the calendar field to add to   * @param amount the amount to add, may be negative   * @return the new timestamp object with the amount added   * @throws IllegalArgumentException if the timestamp is null   */  private static Timestamp add(Timestamp timestamp, int calendarField, int amount) {   if (timestamp == null) {    throw new IllegalArgumentException("The timestamp must not be null");   }   Calendar c = Calendar.getInstance();   c.setTime(timestamp);   c.add(calendarField, amount);   return new Timestamp(c.getTimeInMillis());  }    /**   * <生成最小的当天日期值>   * @return 最小的当天日期值   */  public static Timestamp now() {   Calendar c = Calendar.getInstance();   c.set(Calendar.HOUR_OF_DAY, 0);   c.set(Calendar.MINUTE, 0);   c.set(Calendar.SECOND, 0);   c.set(Calendar.MILLISECOND, 0);   return new Timestamp(c.getTimeInMillis());  }        /** This class should not be instantiated. */  private DateUtils() {  } }