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,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,amount); 
 } 
  
 //----------------------------------------------------------------------- 
 /** 
  * Adds a number of months to a date returning a new object. 
  * The original date object is unchanged. 
  * 
  * @param date the date,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,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,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,amount); 
 } 
  
 //----------------------------------------------------------------------- 
 /** 
  * Adds a number of days to a date returning a new object. 
  * The original date object is unchanged. 
  * 
  * @param date the date,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,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,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,amount); 
 } 
  
 //----------------------------------------------------------------------- 
 /** 
  * Adds a number of minutes to a timestamp returning a new object. 
  * The original timestamp object is unchanged. 
  * 
  * @param timestamp the timestamp,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,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,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 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() { 
 } 
}