为什么FTPClient listFiles() 返回的总是0,该怎么解决

为什么FTPClient listFiles() 返回的总是0
我已经添加了commons-net-1.4.1和jakarta-oro-2.0.8包。
测试过不同的ftp地址，有的listFiles()返回0有的没反映，谁知道为什么呀
谢谢！
以下程序：

import   org.apache.commons.net.*;
import   org.apache.commons.net.ftp.*;

public   class   ConnectServer  
{
        public   ConnectServer(String   server,String   username,   String   password)  
        {
try  
{
        this.ftp   =   new   FTPClient();
        FTPClientConfig   conf   =   new   FTPClientConfig(FTPClientConfig.SYST_UNIX);
        this.ftp.configure(conf);
        //   Connect   and   logon   to   FTP   Server
        this.ftp.connect(server);
        System.out.println( "Connected   to   "   +   server   +   ". ");
        this.ftp.login(username,   password);
        System.out.print(this.ftp.getReplyString());
        //this.ftp.setFileType(FTP.BINARY_FILE_TYPE);
        //this.ftp.changeWorkingDirectory( "/ ");   不起任何作用
        FTPFile[]   files   =   this.ftp.listFiles();
        System.out.println(   "Number   of   files   in   dir:   "   +   files.length   );
        this.ftp.logout();
        System.out.print(this.ftp.getReplyString());
        this.ftp.disconnect();
       
}
catch   (Exception   e)
{
        System.out.println(e);
}
        }

        public   static   void   main   (String   args[])
        {
new   ConnectServer( "ftp.microsoft.com ", "anonymous ",   "anonymous ");
        }
        private   FTPClient   ftp;
}

运行结果：

init:
deps-jar:
compile:
run-single:
Connected   to   ftp.microsoft.com.
230-Welcome   to   FTP.MICROSOFT.COM.   Also   visit   http://www.microsoft.com/downloads.
230   Anonymous   user   logged   in.
Number   of   files   in   dir:   0
221   Thank   you   for   using   Microsoft   products.
BUILD   SUCCESSFUL   (total   time:   4   seconds)


[解决办法]
下面是我寫過關於FTPClient，看對你有沒有一點幫助

package com.XXXX;

import org.apache.commons.net.ftp.FTPClient;
import org.apache.commons.net.ftp.FTPFile;
import org.apache.commons.net.ftp.FTPReply;

import java.io.*;
import java.net.SocketException;

public class myFtpClient {
protected FTPClient FTP_;
protected String host;
protected int port = 21;
protected String userID;
protected String password;

public myFtpClient() {
FTP_ = new FTPClient();
}

public myFtpClient(String host, String userID, String password) {
this.host = host;
this.userID = userID;

this.password = password;
FTP_ = new FTPClient();
}

public myFtpClient(String host, int port, String userID, String password) {
this.host = host;
this.port = port;
this.userID = userID;
this.password = password;
FTP_ = new FTPClient();
}

/**
* set Info
*
* @param host
* @param port
* @param userID
* @param password
*/
public void setInfo(String host, int port, String userID, String password) {
this.host = host;
this.port = port;
this.userID = userID;
this.password = password;
}

/**
* open connection
*
* @return boolean
* @throws java.io.IOException
* @throws SocketException
*/
public boolean connect() throws Exception {
FTP_.setDefaultPort(this.port);
FTP_.setDataTimeout(120000); //timeout為120秒
FTP_.connect(this.host);
if (!FTP_.isConnected()) {
throw new Exception( "NOT CONNECT FTP ");
}
if (!FTPReply.isPositiveCompletion(FTP_.getReplyCode())) {
FTP_.disconnect();
System.out.println( "Connection refused. ");
return false;
}
if (FTP_.login(this.userID, this.password)) {
return true;
} else {
throw new Exception( "NOT LOGIN ");
}
}

/**
* open connection by info
*
* @param host
* @param userID
* @param password
* @return boolean
* @throws IOException
* @throws SocketException
*/
public boolean connect(String host, String userID, String password)
throws IOException, SocketException {
try {
FTP_.connect(host);
if (!FTPReply.isPositiveCompletion(FTP_.getReplyCode())) {
FTP_.disconnect();
System.out.println( "Connection refused. ");
return false;
}
FTP_.login(userID, password);
return true;
} catch (SocketException e) {
throw e;
} catch (IOException e) {
throw e;
}
}