ftp客户端程序java

可以使用Apache Commons Net库来开发FTP客户端程序。您可以使用FTPClient类来连接FTP服务器并执行各种FTP操作，例如上传，下载，删除等。以下是一个简单的FTP客户端java程序示例：

import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

import org.apache.commons.net.ftp.FTP;
import org.apache.commons.net.ftp.FTPClient;

public class FTPClientExample {

    public static void main(String[] args) {

        String server = "ftp.example.com";
        int port = 21;
        String user = "username";
        String pass = "password";
        String remoteFile = "/path/to/remote/file.txt";
        String localFile = "local_file.txt";

        FTPClient ftpClient = new FTPClient();

        try {

            ftpClient.connect(server, port);
            ftpClient.login(user, pass);
            ftpClient.enterLocalPassiveMode();
            ftpClient.setFileType(FTP.BINARY_FILE_TYPE);

            OutputStream outputStream = new FileOutputStream(localFile);
            InputStream inputStream = ftpClient.retrieveFileStream(remoteFile);

            byte[] bytesArray = new byte[4096];
            int bytesRead = -1;
            while ((bytesRead = inputStream.read(bytesArray)) != -1) {
                outputStream.write(bytesArray, 0, bytesRead);
            }

            boolean success = ftpClient.completePendingCommand();
            if (success) {
                System.out.println("File has been downloaded successfully.");
            }

            inputStream.close();
            outputStream.close();

        } catch (IOException ex) {
            System.out.println("Error: " + ex.getMessage());
            ex.printStackTrace();
        } finally {
            try {
                if (ftpClient.isConnected()) {
                    ftpClient.logout();
                    ftpClient.disconnect();
                }
            } catch (IOException ex) {
                ex.printStackTrace();
            }
        }
    }
}

此程序将连接到FTP服务器，下载remote_file.txt文件，并将其保存在本地文件local_file.txt中。您可以根据需要修改此代码以执行其他FTP操作。