时间工具类

package date.util;


import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;


public class DateUtils {

static final String formatPattern = "yyyy-MM-dd";

static final String formatPattern_Short = "yyyyMMdd";


/**
* 获取当前日期
* @return
*/
public static String getCurrentDate(){
SimpleDateFormat format = new SimpleDateFormat(formatPattern);
return format.format(new Date());
}

/**
* 获取制定毫秒数之前的日期
* @param timeDiff
* @return
*/
public static String getDesignatedDate(long timeDiff){
SimpleDateFormat format = new SimpleDateFormat(formatPattern);
long nowTime = System.currentTimeMillis();
long designTime = nowTime - timeDiff;
return format.format(designTime);
}

/**
* 
* 获取前几天的日期
*/
public static String getPrefixDate(String count){
Calendar cal = Calendar.getInstance();
int day = 0-Integer.parseInt(count);
cal.add(Calendar.DATE,day);   // int amount   代表天数
Date datNew = cal.getTime(); 
SimpleDateFormat format = new SimpleDateFormat(formatPattern);
return format.format(datNew);
}
/**
* 日期转换成字符串
* @param date
* @return
*/
public static String dateToString(Date date){
SimpleDateFormat format = new SimpleDateFormat(formatPattern);
return format.format(date);
}
/**
* 字符串转换日期
* @param str
* @return
*/
public static Date stringToDate(String str){
//str =  " 2008-07-10 19:20:00 " 格式
SimpleDateFormat format = new SimpleDateFormat(formatPattern);
if(!str.equals("")&&str!=null){
try {
return format.parse(str);
} catch (ParseException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
return null;
}

//java中怎样计算两个时间如：“21:57”和“08:20”相差的分钟数、小时数 java计算两个时间差小时 分钟 秒 .
public void timeSubtract(){
SimpleDateFormat dfs = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"); 
Date begin = null; 
Date end = null; 
try { 
begin = dfs.parse("2004-01-02 11:30:24"); 
end = dfs.parse("2004-03-26 13:31:40"); 
} catch (ParseException e) { 
e.printStackTrace(); 
} 


long between = (end.getTime() - begin.getTime()) / 1000;// 除以1000是为了转换成秒 


long day1 = between / (24 * 3600); 
long hour1 = between % (24 * 3600) / 3600; 
long minute1 = between % 3600 / 60; 
long second1 = between % 60; 
System.out.println("" + day1 + "天" + hour1 + "小时" + minute1 + "分" 
+ second1 + "秒"); 
}


}