You've got to find what you love.

package sunshiny.util;

import java.util.Date;
import java.util.GregorianCalendar;
import java.text.*;

public class Utils {

 /**
  * Comment  : 1. 입력받은 값 만큼의 날자를 더하기, 빼기 연산을 처리한다.
  *            2. plus : 입력받은 수 만큼 더한 날자를 반환.
  *            3. minus : 입력받은 수 만큼 뺀 날자를 반환.
  * @version : 1.0
  * @tags    : @param value
  * @tags    : @return
  * @date    : 2009. 8. 17.
  */
 public static String setOperationDate(String mode, int value){
  SimpleDateFormat fmt = new SimpleDateFormat("yyyyMMdd");
  GregorianCalendar cal = new GregorianCalendar();

  if(mode.equals("plus")){
   cal.add(cal.DATE,value); //현재날짜에 value 값을 더한다.
  }else if(mode.equals("minus")){
   cal.add(cal.DATE,-value); //현재날짜에 value 값을 뺀다.
  }

  Date date = cal.getTime(); //연산된 날자를 생성.
  String setDate = fmt.format(date);

  return setDate;
 }
}

public void gregorianCalendar(){
     // get the supported ids for GMT-08:00 (Pacific Standard Time)
     String[] ids = TimeZone.getAvailableIDs(-8 * 60 * 60 * 1000);
     // if no ids were returned, something is wrong. get out.
     if (ids.length == 0)
         System.exit(0);

      // begin output
     System.out.println("Current Time");

     // create a Pacific Standard Time time zone
     SimpleTimeZone pdt = new SimpleTimeZone(-8 * 60 * 60 * 1000, ids[0]);

     // set up rules for daylight savings time
     pdt.setStartRule(Calendar.APRIL, 1, Calendar.SUNDAY, 2 * 60 * 60 * 1000);
     pdt.setEndRule(Calendar.OCTOBER, -1, Calendar.SUNDAY, 2 * 60 * 60 * 1000);

     // create a GregorianCalendar with the Pacific Daylight time zone
     // and the current date and time
     Calendar calendar = new GregorianCalendar(pdt);
     Date trialTime = new Date();
     calendar.setTime(trialTime);

     // print out a bunch of interesting things
     System.out.println("ERA: " + calendar.get(Calendar.ERA));
     System.out.println("YEAR: " + calendar.get(Calendar.YEAR));
     System.out.println("MONTH: " + calendar.get(Calendar.MONTH));
     System.out.println("현재 월의 마지막 날자: " + calendar.getMaximum(Calendar.DAY_OF_MONTH));
     System.out.println("WEEK_OF_YEAR: " + calendar.get(Calendar.WEEK_OF_YEAR));
     System.out.println("WEEK_OF_MONTH: " + calendar.get(Calendar.WEEK_OF_MONTH));
     System.out.println("DATE: " + calendar.get(Calendar.DATE));
     System.out.println("DAY_OF_MONTH: " + calendar.get(Calendar.DAY_OF_MONTH));
     System.out.println("DAY_OF_YEAR: " + calendar.get(Calendar.DAY_OF_YEAR));
     System.out.println("DAY_OF_WEEK: " + calendar.get(Calendar.DAY_OF_WEEK));
     System.out.println("DAY_OF_WEEK_IN_MONTH: "
                        + calendar.get(Calendar.DAY_OF_WEEK_IN_MONTH));
     System.out.println("AM_PM: " + calendar.get(Calendar.AM_PM));
     System.out.println("HOUR: " + calendar.get(Calendar.HOUR));
     System.out.println("HOUR_OF_DAY: " + calendar.get(Calendar.HOUR_OF_DAY));
     System.out.println("MINUTE: " + calendar.get(Calendar.MINUTE));
     System.out.println("SECOND: " + calendar.get(Calendar.SECOND));
     System.out.println("MILLISECOND: " + calendar.get(Calendar.MILLISECOND));
     System.out.println("ZONE_OFFSET: "
                        + (calendar.get(Calendar.ZONE_OFFSET)/(60*60*1000)));
     System.out.println("DST_OFFSET: "
                        + (calendar.get(Calendar.DST_OFFSET)/(60*60*1000)));

     System.out.println("Current Time, with hour reset to 3");
     calendar.clear(Calendar.HOUR_OF_DAY); // so doesn't override
     calendar.set(Calendar.HOUR, 3);
     System.out.println("ERA: " + calendar.get(Calendar.ERA));
     System.out.println("YEAR: " + calendar.get(Calendar.YEAR));
     System.out.println("MONTH: " + calendar.get(Calendar.MONTH));
     System.out.println("WEEK_OF_YEAR: " + calendar.get(Calendar.WEEK_OF_YEAR));
     System.out.println("WEEK_OF_MONTH: " + calendar.get(Calendar.WEEK_OF_MONTH));
     System.out.println("DATE: " + calendar.get(Calendar.DATE));
     System.out.println("DAY_OF_MONTH: " + calendar.get(Calendar.DAY_OF_MONTH));
     System.out.println("DAY_OF_YEAR: " + calendar.get(Calendar.DAY_OF_YEAR));
     System.out.println("DAY_OF_WEEK: " + calendar.get(Calendar.DAY_OF_WEEK));
     System.out.println("DAY_OF_WEEK_IN_MONTH: "
                        + calendar.get(Calendar.DAY_OF_WEEK_IN_MONTH));
     System.out.println("AM_PM: " + calendar.get(Calendar.AM_PM));
     System.out.println("HOUR: " + calendar.get(Calendar.HOUR));
     System.out.println("HOUR_OF_DAY: " + calendar.get(Calendar.HOUR_OF_DAY));
     System.out.println("MINUTE: " + calendar.get(Calendar.MINUTE));
     System.out.println("SECOND: " + calendar.get(Calendar.SECOND));
     System.out.println("MILLISECOND: " + calendar.get(Calendar.MILLISECOND));
     System.out.println("ZONE_OFFSET: "
            + (calendar.get(Calendar.ZONE_OFFSET)/(60*60*1000))); // in hours
     System.out.println("DST_OFFSET: "
            + (calendar.get(Calendar.DST_OFFSET)/(60*60*1000))); // in hours

     calendar.add(Calendar.DATE, -1); // 하루전
     calendar.add(Calendar.MONTH, 5); // 5개월 뒤
     calendar.add(Calendar.WEEK_OF_YEAR, -5); // 5 주전
     System.out.println("calendar.getTime() : " + calendar.getTime()); //설정 내용 반영된 값 출력    

    }

/**
 * Comment  : 입력받은 수만큼 날자 더하기.
 * @version : 1.0
 * @tags    : @param iDay
 * @tags    : @return
 * @date    : 2010. 10. 29.
 */
 public static String getDate(int iDay){
  Calendar temp = Calendar.getInstance();
  StringBuffer sbDate = new StringBuffer();

  temp.add(Calendar.DAY_OF_MONTH, iDay);

  int nYear = temp.get(Calendar.YEAR);
  int nMonth = temp.get(Calendar.MONTH)+1;
  int nDay = temp.get(Calendar.DAY_OF_MONTH);

  sbDate.append(nYear);
  if(nMonth < 10)
   sbDate.append("0");
  sbDate.append(nMonth);
  if(nDay < 10)
   sbDate.append("0");
  sbDate.append(nDay);

  return sbDate.toString();
 }

 /**
 * Comment  : 등록된 날자와 현재날자를 비교하여 설정한 기간까지 New 이미지를 보여준다.
 * @version : 1.0
 * @tags    : @return
 * @date    : 2010. 10. 29.
 */
 public String getIsNewImage(){
  if(logger.isDebugEnabled()){
   logger.debug("######### StatusReturnTag.getIsNewImage()~! #########");
  }
  String setImg = "";
  SimpleDateFormat fmt = new SimpleDateFormat("yyyyMMdd");
  Calendar cal = Calendar.getInstance();
  cal.add(Calendar.DATE, -this.dateValueEnd);
 
 
  int createDate = Integer.parseInt(fmt.format(this.dateValue));
  int nowDate = Integer.parseInt(fmt.format(cal.getTime()));
 
  if(nowDate < createDate){
   setImg = "<img src='${contextPath}/img/img_b_04.gif' border='0' />";
  }
  return setImg;
 }