多线程查询FTP Server上的文件

import java.io.IOException;

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

public class FTPUtil extends Thread {
    private FTPClient ftpClient = new FTPClient();
    private String ftpdict = ".";
    private boolean flag;
    private static boolean find = false;
    private static long timeslot = 10000;

    public boolean connect(String host, int port, String username,
            String password) throws IOException {
        ftpClient.connect(host, port);
        if (FTPReply.isPositiveCompletion(ftpClient.getReplyCode())) {
            if (ftpClient.login(username, password)) {
                return true;
            }
        }
        ftpClient.disconnect();
        return false;
    }

    public boolean fileExist(String dict, String filename) {
        String pattren = "\\.{1,}";
        ftpdict = ftpdict + "/" + dict;
        try {
            FTPFile[] files = ftpClient.listFiles(ftpdict);
            for (int i = 0; i < files.length; i++) {
                if (files[i].getName().equalsIgnoreCase(filename)) {
                    flag = true;
                }
                if (files[i].isDirectory()
                        && !files[i].getName().matches(pattren)) {
                    fileExist(files[i].getName(), filename);
                }
            }
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        return flag;
    }

    public void disconnect() throws IOException {
        if (ftpClient.isConnected()) {
            ftpClient.disconnect();
        }
    }

    public void run() {
        System.out.println(getName() + " thread started!");
        FTPUtil ftp = new FTPUtil();
        try {
            ftp.connect("127.0.0.1", 21, "admin", "admin");
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        boolean b = ftp.fileExist(ftp.ftpdict, "3.txt");
        System.err.println(b);
        if (b) {
            find = true;
        }
        try {
            ftp.disconnect();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        System.out.println(getName() + " thread ended!");
    }

    @SuppressWarnings("static-access")
    public static void main(String[] args) throws Exception {
        // TODO Auto-generated method stub
        int index = 0;
        while (!find) {
            new FTPUtil().start();
            Thread.currentThread().sleep(timeslot);
            if (index == 4) {
                return;
            }
            index++;
        }
    }
}