取没有date的邮件发送时间

public String getHeader(){
        Enumeration temp;
        String ReceivedDate="";
        Date date=null;
        String[] lines = new String[]{"Received"};//获取Received的信息
        try {
            temp=mimeMessage.getMatchingHeaderLines(lines);
                String Received=(String) temp.nextElement();
                if(Received.split(";").length>1){
                    SimpleDateFormat format = new SimpleDateFormat(dateformat);
                    SimpleDateFormat sdf = new SimpleDateFormat(" EEE, dd MMM yyyy HH:mm:ss Z",Locale.US);//根据Received里提取的时间信息格式决定（ps:必须保持一致）
                        ReceivedDate=Received.split(";")[1];
                         try {
                            date=sdf.parse(ReceivedDate);//将提取的时间转成date
                        } catch (ParseException e) {
                            // TODO Auto-generated catch block
                            e.printStackTrace();
                        }
                        
                     ReceivedDate=format.format(date);//转成自己想要的时间格式
                }
        } catch (MessagingException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        return ReceivedDate;
    }