只要格式正确，直接比较字符串就可以了呀，精确到秒的也一样
String s1 = "2003-12-12 11:30:24"; String s2 = "2004-04-01 13:31:40"; int res = s1.compareTo(s2);
求日期差
SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"); Date begin=df.parse("2004-01-02 11:30:24"); Date end = df.parse("2004-03-26 13:31:40"); long between=(end.getTime()-begin.getTime())/1000;//除以1000是为了转换成秒 int day=between/(24*3600); int hour=between%(24*3600)/3600; int minute=between%3600/60; int second=between%60; 经常用到时间日期类，所以就将常用的日期方法和属性都归纳总结如下，方便大家查找
1.计算某一月份的最大天数
Calendar time=Calendar.getInstance(); time.clear(); time.set(Calendar.YEAR,year); time.set(Calendar.MONTH,i-1);//注意,Calendar对象默认一月为0 int day=time.getActualMaximum(Calendar.DAY_OF_MONTH);//本月份的天数
注：在使用set方法之前，最好先clear一下，否则很多信息会继承自系统当前时间
2.Calendar和Date的转化
(1) Calendar转化为Date
Calendar cal=Calendar.getInstance(); Date date=cal.getTime();
(2) Date转化为Calendar
Date date=new Date(); Calendar cal=Calendar.getInstance(); cal.setTime(date);
3.格式化输出日期时间
Date date=new Date(); SimpleDateFormat df=new SimpleDateFormat("yyyy-MM-dd hh:mm:ss"); System.out.println(df.format(date)); 4.计算一年中的第几星期
(1)计算某一天是一年中的第几星期
Calendar cal=Calendar.getInstance(); cal.set(Calendar.YEAR, 2006); cal.set(Calendar.MONTH, 9); cal.set(Calendar.DAY_OF_MONTH, 3); int weekno=cal.get(Calendar.WEEK_OF_YEAR);
(2)计算一年中的第几星期是几号
SimpleDateFormat df=new SimpleDateFormat("yyyy-MM-dd"); Calendar cal=Calendar.getInstance(); cal.set(Calendar.YEAR, 2006); cal.set(Calendar.WEEK_OF_YEAR, 1); cal.set(Calendar.DAY_OF_WEEK, Calendar.MONDAY); System.out.println(df.format(cal.getTime())); 输出:
2006-01-02
5.add()和roll()的用法
(1)add()方法
SimpleDateFormat df=new SimpleDateFormat("yyyy-MM-dd"); Calendar cal=Calendar.getInstance(); cal.set(Calendar.YEAR, 2006); cal.set(Calendar.MONTH, 9); cal.set(Calendar.DAY_OF_MONTH, 3); cal.add(Calendar.DATE, -4); Date date=cal.getTime(); System.out.println(df.format(date)); cal.add(Calendar.DATE, 4); date=cal.getTime(); System.out.println(df.format(date)); 输出：
2006-08-30
2006-10-03
(2)roll方法
cal.set(Calendar.YEAR, 2006); cal.set(Calendar.MONTH, 9); cal.set(Calendar.DAY_OF_MONTH, 3); cal.roll(Calendar.DATE, -4); date=cal.getTime(); System.out.println(df.format(date)); cal.roll(Calendar.DATE, 4); date=cal.getTime(); System.out.println(df.format(date));
输出：
2006-10-29
2006-10-03
可见，roll()方法在本月内循环，一般使用add()方法；
6.计算两个任意时间中间的间隔天数
(1)传进Calendar对象
/** *//**计算两个时间之间相隔天数 * @param startday 开始时间 * @param endday 结束时间 * @return */public int getIntervalDays(Calendar startday,Calendar endday)...{//确保startday在endday之前 if(startday.after(endday))...{Calendar cal=startday;startday=endday;endday=cal;}//分别得到两个时间的毫秒数 long sl=startday.getTimeInMillis();long el=endday.getTimeInMillis();long ei=el-sl;//根据毫秒数计算间隔天数 return (int)(ei/(1000*60*60*24));}(2)传进Date对象
/** *//**计算两个时间之间相隔天数 * @param startday 开始时间 * @param endday 结束时间 * @return */public int getIntervalDays(Date startday,Date endday)...{//确保startday在endday之前 if(startday.after(endday))...{Date cal=startday;startday=endday;endday=cal;}//分别得到两个时间的毫秒数 long sl=startday.getTime();long el=endday.getTime();long ei=el-sl;//根据毫秒数计算间隔天数 return (int)(ei/(1000*60*60*24));}同理，可以用相同的方法计算出任意两个时间相隔的小时数，分钟数，秒钟数等
注：以上方法是完全按时间计算，有时并不能令人满意，如：
startday="2006-10-11 20:00:00" endday="2006-10-12 8:00:00"
计算结果为0，但是我们也许相让计算结果变为1，此时可以用如下方法实现：
在传参之前，先设定endday的时间，如：
endday.set(Calendar.HOUR_OF_DAY, 23); endday.set(Calendar.MINUTE, 59); endday.set(Calendar.SECOND, 59); endday.set(Calendar.MILLISECOND, 59);
这样再传进去startday,endday，则结果就如我们所愿了。不过，如果嫌以上方法麻烦，可以参考以下方法：
(3)改进精确计算相隔天数的方法
public int getDaysBetween (Calendar d1, Calendar d2) ...{if (d1.after(d2)) ...{// swap dates so that d1 is start and d2 is end java.util.Calendar swap = d1;d1 = d2;d2 = swap;}int days = d2.get(Calendar.DAY_OF_YEAR) - d1.get(Calendar.DAY_OF_YEAR);int y2 = d2.get(Calendar.YEAR);if (d1.get(Calendar.YEAR) != y2) ...{d1 = (Calendar) d1.clone();do ...{days += d1.getActualMaximum(Calendar.DAY_OF_YEAR);//得到当年的实际天数 d1.add(Calendar.YEAR, 1);}while (d1.get(Calendar.YEAR) != y2);}return days;}获取系统当前时间：
public static String getSystemTime(){Date date=new Date();SimpleDateFormat df=new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");return df.format(date);}//字符串转化成时间类型（字符串可以是任意类型，只要和SimpleDateFormat中的格式一致即可） java.text.SimpleDateFormat sdf = new java.text.SimpleDateFormat("M/dd/yyyy hh:mm:ss a",java.util.Locale.US);java.util.Date d = sdf.parse("5/13/2003 10:31:37 AM");SimpleDateFormat formatter = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");String mDateTime1=formatter.format(d);//当前时间 Calendar cal = Calendar.getInstance();// SimpleDateFormat formatter = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"); SimpleDateFormat formatter = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss G E D F w W a E F");String mDateTime=formatter.format(cal.getTime());//1年前日期 java.util.Date myDate=new java.util.Date();long myTime=(myDate.getTime()/1000)-60*60*24*365;myDate.setTime(myTime*1000);String mDate=formatter.format(myDate);//明天日期 myDate=new java.util.Date();myTime=(myDate.getTime()/1000)+60*60*24;myDate.setTime(myTime*1000);mDate=formatter.format(myDate);//两个时间之间的天数 SimpleDateFormat myFormatter = new SimpleDateFormat("yyyy-MM-dd");java.util.Date date= myFormatter.parse("2003-05-1");java.util.Date mydate= myFormatter.parse("1899-12-30");long day=(date.getTime()-mydate.getTime())/(24*60*60*1000);//加半小时 SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss");java.util.Date date1 = format.parse("2002-02-28 23:16:00");long Time=(date1.getTime()/1000)+60*30;date1.setTime(Time*1000);String mydate1=formatter.format(date1);//年月周求日期 SimpleDateFormat formatter2 = new SimpleDateFormat("yyyy-MM F E");java.util.Date date2= formatter2.parse("2003-05 5 星期五");SimpleDateFormat formatter3 = new SimpleDateFormat("yyyy-MM-dd");String mydate2=formatter3.format(date2);//求是星期几 mydate= myFormatter.parse("2001-1-1");SimpleDateFormat formatter4 = new SimpleDateFormat("E");String mydate3=formatter4.format(mydate);在开发web应用中，针对不同的数据库日期类型，我们需要在我们的程序中对日期类型做各种不同的转换。若对应数据库数据是oracle的Date类型，即只需要年月日的，可以选择使用java.sql.Date类型，若对应的是MSsqlserver数据库的DateTime类型，即需要年月日时分秒的，选择java.sql.Timestamp类型
你可以使用dateFormat定义时间日期的格式，转一个字符串即可
package personal.jessica;import java.util.Date;import java.util.Calendar;import java.sql.Timestamp;import java.text.DateFormat;import java.text.SimpleDateFormat;import java.util.Locale;class Datetest{/** *method 将字符串类型的日期转换为一个timestamp（时间戳记java.sql.Timestamp） *@param dateString 需要转换为timestamp的字符串 *@return dataTime timestamp */public final static java.sql.Timestamp string2Time(String dateString) throws java.text.ParseException {DateFormat dateFormat;dateFormat = new SimpleDateFormat("yyyy-MM-dd kk:mm:ss.SSS", Locale.ENGLISH);//设定格式 //dateFormat = new SimpleDateFormat("yyyy-MM-dd kk:mm:ss", Locale.ENGLISH); dateFormat.setLenient(false);java.util.Date timeDate = dateFormat.parse(dateString);//util类型 java.sql.Timestamp dateTime = new java.sql.Timestamp(timeDate.getTime());//Timestamp类型,timeDate.getTime()返回一个long型 return dateTime;}/** *method 将字符串类型的日期转换为一个Date（java.sql.Date） *@param dateString 需要转换为Date的字符串 *@return dataTime Date */public final static java.sql.Date string2Date(String dateString) throws java.lang.Exception {DateFormat dateFormat;dateFormat = new SimpleDateFormat("yyyy-MM-dd", Locale.ENGLISH);dateFormat.setLenient(false);java.util.Date timeDate = dateFormat.parse(dateString);//util类型 java.sql.Date dateTime = new java.sql.Date(timeDate.getTime());//sql类型 return dateTime;}public static void main(String[] args){Date da = new Date();//注意：这个地方da.getTime()得到的是一个long型的值 System.out.println(da.getTime());//由日期date转换为timestamp //第一种方法：使用new Timestamp(long) Timestamp t = new Timestamp(new Date().getTime());System.out.println(t);//第二种方法：使用Timestamp(int year,int month,int date,int hour,int minute,int second,int nano) Timestamp tt = new Timestamp(Calendar.getInstance().get( Calendar.YEAR) - 1900, Calendar.getInstance().get( Calendar.MONTH), Calendar.getInstance().get( Calendar.DATE), Calendar.getInstance().get( Calendar.HOUR), Calendar.getInstance().get( Calendar.MINUTE), Calendar.getInstance().get( Calendar.SECOND), 0);System.out.println(tt);try {String sToDate = "2005-8-18";//用于转换成java.sql.Date的字符串 String sToTimestamp = "2005-8-18 14:21:12.123";//用于转换成java.sql.Timestamp的字符串 Date date1 = string2Date(sToDate);Timestamp date2 = string2Time(sToTimestamp);System.out.println("Date:"+date1.toString());//结果显示 System.out.println("Timestamp:"+date2.toString());//结果显示}catch(Exception e) {e.printStackTrace();}}}下面是例子：
Java代码
package test;import java.text.DateFormat;import java.text.ParseException;import java.text.SimpleDateFormat;import java.util.Calendar;import java.util.Date;import java.util.Hashtable;import javax.swing.JOptionPane;public class Test2{public static Boolean isdate(String s){String a[]=s.split("-");Boolean flg=true;if(!(Integer.parseint(a[0])>=1950 && Integer.parseint(a[0])<=2050)){flg=false;}return flg;}public static Boolean checkDate(String s){Boolean ret = true;try{DateFormat df = new SimpleDateFormat("yyyy-MM-dd");ret = df.format(df.parse(s)).equals(s);}catch(ParseException e){ret = false;}return ret;}public Object dateinfo(String s){String a[]=s.split("-",2);Hashtable fest =new Hashtable();fest.put("01-01","元旦节");fest.put("02-14","情人节");fest.put("03-12","植树节");fest.put("03-15","消费者节");fest.put("04-01","愚人节");fest.put("04-05","清明节");fest.put("05-01","劳动节");fest.put("06-01","儿童节");fest.put("07-01","建党节");fest.put("08-01","建军节");fest.put("09-10","教师节");fest.put("10-01","国庆节");fest.put("12-25","圣诞节");if(fest.containsKey(a[1])){return fest.get(a[1]);} else{return "无节日";}}public String xingzuo(Date s){Calendar cal = Calendar.getInstance();cal.setTime(s);String xingzuo="无";int day=cal.get(Calendar.DAY_OF_YEAR);if((cal.get(Calendar.YEAR)%4==0)&&(cal.get(Calendar.YEAR)%100!=0)||(cal.get(Calendar.YEAR)%400==0)){if((day>=1 &&day<=19)||(day>=357&&day<=366)){xingzuo= "魔蝎座";} else if(day>=20 &&day<=49){xingzuo= "水瓶座";} else if(day>=50 &&day<=80){xingzuo= "双鱼座";} else if(day>=81 &&day<=110){xingzuo= "白羊座";} else if(day>=111 &&day<=141){xingzuo= "金牛座";} else if(day>=142 &&day<=173){xingzuo= "双子座";} else if(day>=174 &&day<=203){xingzuo= "巨蟹座";} else if(day>=204 &&day<=235){xingzuo= "狮子座";} else if(day>=236 &&day<=266){xingzuo= "处女座";} else if(day>=267 &&day<=296){xingzuo= "天秤座";} else if(day>=297 &&day<=326){xingzuo= "天蝎座";} else if(day>=327 &&day<=356){xingzuo= "射手座";}} else{if((day>=1 &&day<=19)||(day>=357&&day<=366)){xingzuo= "魔蝎座";} else if(day>=20 &&day<=48){xingzuo= "水瓶座";} else if(day>=49 &&day<=79){xingzuo= "双鱼座";} else if(day>=80 &&day<=109){xingzuo= "白羊座";} else if(day>=110 &&day<=140){xingzuo= "金牛座";} else if(day>=141 &&day<=172){xingzuo= "双子座";} else if(day>=173 &&day<=202){xingzuo= "巨蟹座";} else if(day>=203 &&day<=234){xingzuo= "狮子座";} else if(day>=235 &&day<=265){xingzuo= "处女座";} else if(day>=266 &&day<=295){xingzuo= "天秤座";} else if(day>=296 &&day<=325){xingzuo= "天蝎座";} else if(day>=326 &&day<=355){xingzuo= "射手座";}}return xingzuo;}public Date parseDate(String s){SimpleDateFormat bartDateFormat = new SimpleDateFormat("yyyy-MM-dd");try {Date date3 = bartDateFormat.parse(s);date3=bartDateFormat.parse(s);return date3;}catch (Exception ex) {return null;}}public static void main(String[] args) {Calendar cal = Calendar.getInstance();Test2 test2=new Test2();String date1=JOptionPane.showInputDialog("请你输入日期，格式如2000-10-15");while(!(Test2.checkDate(date1)&&Test2.isdate(date1))){date1=JOptionPane.showInputDialog("请你输入日期，格式如2000-10-15");}SimpleDateFormat bartDateFormat1 = new SimpleDateFormat("yyyy,MM,dd,EEEE");SimpleDateFormat bartDateFormat2 = new SimpleDateFormat("yyyy-MM-dd");Date date2=test2.parseDate(date1);String festinfo=(String)test2.dateinfo(date1);System.out.println(bartDateFormat1.format(date2) +","+ festinfo+","+ test2.xingzuo(date2));String day=JOptionPane.showInputDialog("请你输入要查询N天后的日期信息");cal.setTime(date2);cal.add(Calendar.DATE, Integer.parseint(day));String date5=bartDateFormat2.format(cal.getTime());festinfo=(String)test2.dateinfo(date5);System.out.println(bartDateFormat1.format(cal.getTime())+","+ festinfo+","+ test2.xingzuo(cal.getTime()));}}总结
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