Question

java如何转换日期格式？

比如我有一个date对象 格式是yy-mm-dd
我如何把它转换成yyyy-mm-dd

Answer 1

import java.util.*;
import java.text.*;
import java.util.Calendar;

public class VeDate {
/**
* 获取现在时间
*
* @return 返回时间类型 yyyy-MM-dd HH:mm:ss
*/
public static Date getNowDate() {
Date currentTime = new Date();
SimpleDateFormat formatter = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
String dateString = formatter.format(currentTime);
ParsePosition pos = new ParsePosition(8);
Date currentTime_2 = formatter.parse(dateString, pos);
return currentTime_2;
}

/**
* 获取现在时间
*
* @return返回短时间格式 yyyy-MM-dd
*/
public static Date getNowDateShort() {
Date currentTime = new Date();
SimpleDateFormat formatter = new SimpleDateFormat("yyyy-MM-dd");
String dateString = formatter.format(currentTime);
ParsePosition pos = new ParsePosition(8);
Date currentTime_2 = formatter.parse(dateString, pos);
return currentTime_2;
}

/**
* 获取现在时间
*
* @return返回字符串格式 yyyy-MM-dd HH:mm:ss
*/
public static String getStringDate() {
Date currentTime = new Date();
SimpleDateFormat formatter = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
String dateString = formatter.format(currentTime);
return dateString;
}

/**
* 获取现在时间
*
* @return 返回短时间字符串格式yyyy-MM-dd
*/
public static String getStringDateShort() {
Date currentTime = new Date();
SimpleDateFormat formatter = new SimpleDateFormat("yyyy-MM-dd");
String dateString = formatter.format(currentTime);
return dateString;
}

/**
* 获取时间 小时:分;秒 HH:mm:ss
*
* @return
*/
public static String getTimeShort() {
SimpleDateFormat formatter = new SimpleDateFormat("HH:mm:ss");
Date currentTime = new Date();
String dateString = formatter.format(currentTime);
return dateString;
}

/**
* 将长时间格式字符串转换为时间 yyyy-MM-dd HH:mm:ss
*
* @param strDate
* @return
*/
public static Date strToDateLong(String strDate) {
SimpleDateFormat formatter = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
ParsePosition pos = new ParsePosition(0);
Date strtodate = formatter.parse(strDate, pos);
return strtodate;
}

/**
* 将长时间格式时间转换为字符串 yyyy-MM-dd HH:mm:ss
*
* @param dateDate
* @return
*/
public static String dateToStrLong(java.util.Date dateDate) {
SimpleDateFormat formatter = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
String dateString = formatter.format(dateDate);
return dateString;
}

/**
* 将短时间格式时间转换为字符串 yyyy-MM-dd
*
* @param dateDate
* @param k
* @return
*/
public static String dateToStr(java.util.Date dateDate) {
SimpleDateFormat formatter = new SimpleDateFormat("yyyy-MM-dd");
String dateString = formatter.format(dateDate);
return dateString;
}

/**
* 将短时间格式字符串转换为时间 yyyy-MM-dd
*
* @param strDate
* @return
*/
public static Date strToDate(String strDate) {
SimpleDateFormat formatter = new SimpleDateFormat("yyyy-MM-dd");
ParsePosition pos = new ParsePosition(0);
Date strtodate = formatter.parse(strDate, pos);
return strtodate;
}

/**
* 得到现在时间
*
* @return
*/
public static Date getNow() {
Date currentTime = new Date();
return currentTime;
}

/**
* 提取一个月中的最后一天
*
* @param day
* @return
*/
public static Date getLastDate(long day) {
Date date = new Date();
long date_3_hm = date.getTime() - 3600000 * 34 * day;
Date date_3_hm_date = new Date(date_3_hm);
return date_3_hm_date;
}

/**
* 得到现在时间
*
* @return 字符串 yyyyMMdd HHmmss
*/
public static String getStringToday() {
Date currentTime = new Date();
SimpleDateFormat formatter = new SimpleDateFormat("yyyyMMdd HHmmss");
String dateString = formatter.format(currentTime);
return dateString;
}

/**
* 得到现在小时
*/
public static String getHour() {
Date currentTime = new Date();
SimpleDateFormat formatter = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
String dateString = formatter.format(currentTime);
String hour;
hour = dateString.substring(11, 13);
return hour;
}

/**
* 得到现在分钟
*
* @return
*/
public static String getTime() {
Date currentTime = new Date();
SimpleDateFormat formatter = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
String dateString = formatter.format(currentTime);
String min;
min = dateString.substring(14, 16);
return min;
}

/**
* 根据用户传入的时间表示格式，返回当前时间的格式 如果是yyyyMMdd，注意字母y不能大写。
*
* @param sformat
* yyyyMMddhhmmss
* @return
*/
public static String getUserDate(String sformat) {
Date currentTime = new Date();
SimpleDateFormat formatter = new SimpleDateFormat(sformat);
String dateString = formatter.format(currentTime);
return dateString;
}

/**
* 二个小时时间间的差值,必须保证二个时间都是"HH:MM"的格式，返回字符型的分钟
*/
public static String getTwoHour(String st1, String st2) {
String[] kk = null;
String[] jj = null;
kk = st1.split(":");
jj = st2.split(":");
if (Integer.parseInt(kk[0]) < Integer.parseInt(jj[0]))
return "0";
else {
double y = Double.parseDouble(kk[0]) + Double.parseDouble(kk[1]) / 60;
double u = Double.parseDouble(jj[0]) + Double.parseDouble(jj[1]) / 60;
if ((y - u) > 0)
return y - u + "";
else
return "0";
}
}

/**
* 得到二个日期间的间隔天数
*/
public static String getTwoDay(String sj1, String sj2) {
SimpleDateFormat myFormatter = new SimpleDateFormat("yyyy-MM-dd");
long day = 0;
try {
java.util.Date date = myFormatter.parse(sj1);
java.util.Date mydate = myFormatter.parse(sj2);
day = (date.getTime() - mydate.getTime()) / (24 * 60 * 60 * 1000);
} catch (Exception e) {
return "";
}
return day + "";
}

/**
* 时间前推或后推分钟,其中JJ表示分钟.
*/
public static String getPreTime(String sj1, String jj) {
SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
String mydate1 = "";
try {
Date date1 = format.parse(sj1);
long Time = (date1.getTime() / 1000) + Integer.parseInt(jj) * 60;
date1.setTime(Time * 1000);
mydate1 = format.format(date1);
} catch (Exception e) {
}
return mydate1;
}

Answer 2

使用SimpleDateFormat格式化日期

import java.text.SimpleDateFormat;
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd"); //yyyy-MM-dd为格式化的格式
sdf.format(new Date());//传入日期即可，我传入的是当前日期

Answer 3

public static Date strToDateTime(String arg0) {
Date resultDate = null;
SimpleDateFormat simpleDateFormat = new SimpleDateFormat(
"yy-MM-dd");
try {
resultDate = simpleDateFormat.parse(arg0);
return resultDate;
} catch (Exception e) {
return resultDate;
}
}

public static String dateTimeToStr(Date arg0) {
String resultStr;
SimpleDateFormat simpleDateFormat = new SimpleDateFormat(
"yyyy-MM-dd");
resultStr = simpleDateFormat.format(arg0);
return resultStr;
}

如果说原来的日期是

String datestr=“12-11-08”;

想转成yyyy-mm-dd格式的字符串吧？
那就可以 dateTimeToStr(strToDateTime(datestr))

Answer 4

用SimpleDateFormat类
java.text.SimpleDateFormat fmt = new java.text.SimpleDateFormat("yyyy-MM-dd");
oldDate=fmt.format(oldDate);
在日期时间格式中小写的m代表分钟，大写的M代表的是月份

Answer 5

Date 本身并没格式。要显示出来，才有格式。

java.text.SimpleDateFormat 看这个API说明

Letter Date or Time Component Presentation Examples

G Era designator Text AD
y Year Year 1996; 96
M Month in year Month July; Jul; 07
w Week in year Number 27
W Week in month Number 2
D Day in year Number 189
d Day in month Number 10
F Day of week in month Number 2
E Day in week Text Tuesday; Tue
a Am/pm marker Text PM
H Hour in day (0-23) Number 0
k Hour in day (1-24) Number 24
K Hour in am/pm (0-11) Number 0
h Hour in am/pm (1-12) Number 12
m Minute in hour Number 30
s Second in minute Number 55
S Millisecond Number 978
z Time zone General time zone Pacific Standard Time; PST; GMT-08:00
Z Time zone RFC 822 time zone -0800

java.text.SimpleDateFormat fmt = new java.text.SimpleDateFormat("yyyy-MM-dd");
fmt.format(new Date());