java监听ftp目录

在Java中监听FTP目录可以使用Apache Commons Net库中的FTPClient类和FTPFile类。

首先，创建FTP连接并登录到FTP服务器：

FTPClient ftpClient = new FTPClient();
ftpClient.connect(server, port);
ftpClient.login(username, password);

然后进入要监听的目录并设置FTP文件过滤器：

ftpClient.changeWorkingDirectory(directory);
ftpClient.setFileType(FTP.BINARY_FILE_TYPE);
FTPFileFilter filter = new FTPFileFilter() {
    public boolean accept(FTPFile ftpFile) {
        return ftpFile.isFile();
    }
};

接下来可以使用Apache Commons Net库中的FTPFileObserver类实现FTP文件监听。FTPFileObserver类是一个抽象类，需要自定义一个继承自该类的监听器类，并重写其中的方法。

以下是一个简单的FTP文件监听器实现：

public class FtpFileListener extends FTPFileObserver {
    public FtpFileListener(FTPClient ftpClient, FTPFileFilter filter) {
        super(ftpClient, filter);
    }

    public void onFileCreate(FTPFile ftpFile) {
        System.out.println("New file created: " + ftpFile.getName());
    }

    public void onFileDelete(FTPFile ftpFile) {
        System.out.println("File deleted: " + ftpFile.getName());
    }

    public void onFileChange(FTPFile ftpFile) {
        System.out.println("File changed: " + ftpFile.getName());
    }

    public void onDirectoryCreate(FTPFile ftpFile) {
        System.out.println("New directory created: " + ftpFile.getName());
    }

    public void onDirectoryDelete(FTPFile ftpFile) {
        System.out.println("Directory deleted: " + ftpFile.getName());
    }

    public void onError(Exception e) {
        e.printStackTrace();
    }
}

最后，将监听器添加到FTPFileObserver对象中并启动监听：

FTPFileObserver observer = new FtpFileListener(ftpClient, filter);
observer.start();

完整的代码示例：

import org.apache.commons.net.ftp.FTP;
import org.apache.commons.net.ftp.FTPClient;
import org.apache.commons.net.ftp.FTPFile;
import org.apache.commons.net.ftp.FTPFileFilter;
import org.apache.commons.net.ftp.FTPFileObserver;

public class FtpDirectoryListener {
    public static void main(String[] args) throws Exception {
        String server = "ftp.example.com";
        int port = 21;
        String username = "username";
        String password = "password";
        String directory = "/ftp/directory/to/listen";
        
        FTPClient ftpClient = new FTPClient();
        ftpClient.connect(server, port);
        ftpClient.login(username, password);
        
        ftpClient.changeWorkingDirectory(directory);
        ftpClient.setFileType(FTP.BINARY_FILE_TYPE);
        FTPFileFilter filter = new FTPFileFilter() {
            public boolean accept(FTPFile ftpFile) {
                return ftpFile.isFile();
            }
        };
        
        FTPFileObserver observer = new FtpFileListener(ftpClient, filter);
        observer.start();
    }
    
    public static class FtpFileListener extends FTPFileObserver {
        public FtpFileListener(FTPClient ftpClient, FTPFileFilter filter) {
            super(ftpClient, filter);
        }

        public void onFileCreate(FTPFile ftpFile) {
            System.out.println("New file created: " + ftpFile.getName());
        }

        public void onFileDelete(FTPFile ftpFile) {
            System.out.println("File deleted: " + ftpFile.getName());
        }

        public void onFileChange(FTPFile ftpFile) {
            System.out.println("File changed: " + ftpFile.getName());
        }

        public void onDirectoryCreate(FTPFile ftpFile) {
            System.out.println("New directory created: " + ftpFile.getName());
        }

        public void onDirectoryDelete(FTPFile ftpFile) {
            System.out.println("Directory deleted: " + ftpFile.getName());
        }

        public void onError(Exception e) {
            e.printStackTrace();
        }
    }
}