利用java如何实现判断ftp目录是否存在

package com.soft4j.log4j;import java.io.IOException; import sun.net.ftp.FtpClient; public class FtpTest{ static String middle_ftpServer = "10.103.2.250"; static String middle_user = "ora9iftp"; static String middle_password = "ftp"; static String middle_dir = "/image/NWKPHOTO/Middle/2009/3";  public static void main(String[] args) { FtpClient ftpClient = new FtpClient(); try { ftpClient.openServer(middle_ftpServer); ftpClient.login(middle_user, middle_password); FtpTest ft = new FtpTest(); ft.isDirExist(ftpClient, middle_dir); } catch (IOException e) { e.printStackTrace(); }  }   public boolean isDirExist(FtpClient ftpClient, String dir) { try { ftpClient.cd(dir);  } catch (IOException e1) {  reurn false; } return true; }}