Java中怎么对日期类进行处理

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;
public class FormatTime {
  private final static SimpleDateFormat sdf=new SimpleDateFormat("yyyyMMdd");
  private final static SimpleDateFormat sdfymdhm = new SimpleDateFormat("yyyyMMddHHmmss");
  private final static SimpleDateFormat sdfymdhms =  new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
  /**
   *
  * @Title: getCurrentDay
  * @Description: TODO 获取当天时间(20161109)
  * @return
   */
  public static String getCurrentDay(){
    return sdf.format(new Date());
  }
  /**
   *
  * @Title: fTime2
  * @Description: TODO 获取time这个日期以前dayAgo天的日期
  * @return
   */
  public static String fTime(String time,int dayAgo){
    Date date = null;
    try {
      date = sdf.parse(time);
    } catch (ParseException e) {
        throw new RuntimeException(e);
    }
    Calendar calendar = Calendar.getInstance();
    calendar.setTime(date);
    if(dayAgo>0){
      calendar.add(Calendar.DAY_OF_MONTH, -dayAgo);//前15天数据
      date = calendar.getTime();
      calendar.setTime(date);
    }
    int year=calendar.get(Calendar.YEAR);
    int month=calendar.get(Calendar.MONTH) + 1;
    int day = calendar.get(Calendar.DAY_OF_MONTH);
    String mon="";
    String d="";
    if(month<10){
      mon="0"+month;
    }else{
      mon=month+"";
    }
    if(day<10){
      d="0"+day;
    }else{
      d=""+day;
    }
    String ret=year+""+mon+""+d;
    return ret;
  }
  /**
   *
  * @Title: fTime2
  * @Description: TODO 获取time这个日期以后dayAfter天的日期
  * @return
   */
  public static String fTime2(String time,int dayAfter){
    Date date = null;
    try {
      date = sdf.parse(time);
    } catch (ParseException e) {
        throw new RuntimeException(e);
    }
    Calendar calendar = Calendar.getInstance();
    calendar.setTime(date);
    if(dayAfter>0){
      calendar.add(Calendar.DAY_OF_MONTH, +dayAfter);//后15天数据
      date = calendar.getTime();
      calendar.setTime(date);
    }
    int year=calendar.get(Calendar.YEAR);
    int month=calendar.get(Calendar.MONTH) + 1;
    int day = calendar.get(Calendar.DAY_OF_MONTH);
    String mon="";
    String d="";
    if(month<10){
      mon="0"+month;
    }else{
      mon=month+"";
    }
    if(day<10){
      d="0"+day;
    }else{
      d=""+day;
    }
    String ret=year+""+mon+""+d;
    return ret;
  }
  /**
   *
  * @Title: getDefaultTime
  * @Description: TODO 获取昨天的日期
  * @return
   */
  public static String getDefaultTime(){
    Calendar calendar = Calendar.getInstance();
    calendar.add(Calendar.DAY_OF_MONTH, -1);//前1天
    Date date = calendar.getTime();
    String time=sdf.format(date);
    return time;
  }
  /**
   *
  * @Title: getSunday
  * @Description: TODO 获取最近一个星期天
  * @return
   */
  public static String getSunday(){
    SimpleDateFormat f = new SimpleDateFormat("yyyyMMdd");
    Calendar c = Calendar.getInstance();
    c.set(Calendar.DAY_OF_WEEK, Calendar.SUNDAY);
    return f.format(c.getTime());
  }
  /**
   *
  * @Title: getMonthFirstDay
  * @Description: TODO 获取本月第一天
  * @return
   */
  public static String getCurrentMonthFirstDay(){
    Calendar  cal_1=Calendar.getInstance();//获取当前日期
    cal_1.add(Calendar.MONTH, 0);
    cal_1.set(Calendar.DAY_OF_MONTH,1);//设置为1号,当前日期既为本月第一天
    String firstDay = sdf.format(cal_1.getTime());
    return firstDay;
  }
  /**
   *
  * @Title: getMonthFirstDay
  * @Description: TODO 获取上月第一天
  * @return
   */
  public static String getPreviousMonthFirstDay(){
   //获取当前月第一天：
  Calendar c = Calendar.getInstance();
  c.add(Calendar.MONTH, -1);
  c.set(Calendar.DAY_OF_MONTH,1);//设置为1号,当前日期既为本月第一天
  String first = sdf.format(c.getTime());
  return first;
  }
  /**
   *
  * @Title: getMonthFirstDay
  * @Description: TODO 获取上月最后一天
  * @return
   */
  public static String getPreviousMonthLastDay(){
  //获取当前月最后一天
  Calendar ca = Calendar.getInstance();
  ca.set(Calendar.DAY_OF_MONTH,0);//
  String lastDay = sdf.format(ca.getTime());
  return lastDay;
  }
  /**
   *
  * @Title: getCurrentMonthLastDay
  * @Description: TODO 获取指定时间最后一天
  * @return
   */
  public static String getCurrentMonthLastDay(String time){
    Date date =null;
   try {
    date= sdf.parse(time);
  } catch (ParseException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
  }
  //获取当前月最后一天
  Calendar ca = Calendar.getInstance();
  ca.setTime(date);
  ca.set(Calendar.DAY_OF_MONTH,
      ca.getActualMaximum(Calendar.DAY_OF_MONTH)); //
  String lastDay = sdf.format(ca.getTime());
  return lastDay;
  }
  /***
   *
  * @Title: getCurrentWeekDay
  * @Description: TODO 获取本周周一
   */
  public static String getCurrentMonday(){
     Calendar cal = Calendar.getInstance();
     cal.setFirstDayOfWeek(Calendar.MONDAY);//将每周第一天设为星期一，默认是星期天
     cal.add(Calendar.DATE, 0);
     cal.set(Calendar.DAY_OF_WEEK,Calendar.MONDAY);
     String monday = sdf.format(cal.getTime());
     return monday;
  }
  /***
   *
  * @Title: getPreviousSunday
  * @Description: TODO 获取上周周日
   */
  public static String getPreviousSunday(){
     Calendar cal = Calendar.getInstance();
     cal.setFirstDayOfWeek(Calendar.MONDAY);//将每周第一天设为星期一，默认是星期天
     cal.add(Calendar.DATE, -1*7);
     cal.set(Calendar.DAY_OF_WEEK, Calendar.SUNDAY);
     String sunday =sdf.format(cal.getTime());
     return sunday;
  }
  /**
   *
  * @Title: getMiniSencond
  * @Description: TODO 将日期转换为毫秒数
  * @param str
  * @return
   */
  public static String getMiniSencond(String str){
    long millionSeconds=0;
    try {
      millionSeconds = sdfymdhm.parse(str).getTime();//毫秒
    } catch (ParseException e) {
      // TODO Auto-generated catch block
      e.printStackTrace();
    }
    return millionSeconds+"";
  }
   /**
   *
  * @Title: getDateSencond
  * @Description: TODO 将日期转换为毫秒数
  * @param str
  * @return
   */
  public static long getDateSencond(String str){
    long millionSeconds=0;
    try {
      millionSeconds = sdfymdhms.parse(str).getTime();//毫秒
    } catch (ParseException e) {
      // TODO Auto-generated catch block
      e.printStackTrace();
    }
    return millionSeconds;
  }
  /**
   * 计算日期相差天数
   * @param str1
   * @param str2
   * @return
   */
  public static int getDistanceOfTwoDate(String str1,String str2){
    int result=0;
    try{
      Date date1 = sdf.parse(str1);
      Date date2 =sdf.parse(str2);
      Calendar aCalendar = Calendar.getInstance();
        aCalendar.setTime(date1);
        int day1 = aCalendar.get(Calendar.DAY_OF_YEAR);
        aCalendar.setTime(date2);
        int day2 = aCalendar.get(Calendar.DAY_OF_YEAR);
        result = day1-day2;
    }catch(Exception e){
      e.printStackTrace();
    }
    return result;
  }
  /**
   *
  * @Title: long2Date
  * @Description: TODO long 转日期(年-月-日 时-分-秒)
  * @param timestamp
  * @return
   */
  public static String longToDate(Long msecond){
    Date date = new Date(msecond);
    return sdfymdhms.format(date);
  }
}