java 格式化日期字符串

1. 字符串转换为日期

public static Date parseDate(String strDate,String pattern){
                            if(strDate==null || pattren==null ||        "".equals(strDate.trim()) ||"".equals(pattern.trim()) )){
    throw new IllegalArgumentException("字符串或日期格式为空");
    }
    Date date = null;
    try{
    SimpleDateFormat parser = new SimpleDateFormat(pattern);
            date=parser.parse(str);
    }catch (ParseException e) {
            System.out.println("格式化失败" + e.getMessage());
        }
    return date;
}
           

2. 日期格式化为字符串

public static String format(Date date, String pattern) {
        if(date==null)
        {
            return "";
        }
        if (date == null || pattern == null || "".equals(pattern.trim()))
            throw new IllegalArgumentException("日期或字符串格式为空");
        String str = null;
        try {
            SimpleDateFormat parser = new SimpleDateFormat(pattern);
            str = parser.format(date);
        } catch (Exception e) {
            System.out.println("不能转换" + e.getMessage());
        }
        return str;
    }
           

3. 把一种格式的日期字符串格式化成另一种格式的日期字符串

public static String format  (String str, String oldP, String newP) {
        if (str == null || "".equals(str.trim()) || oldP == null
                || "".equals(oldP.trim()) || newP == null
                || "".equals(newP.trim()))
            throw new IllegalArgumentException("不能为空");
        return format(parseDate(str,oldP),newP);
    }