java 实现FTP协议多个文件的上传

FTP 协议是文件传输协议，用于在网络上传输文件。Java 通过 FTPClient 类提供了 FTP 客户端的实现，可以使用该类实现 FTP 文件上传。

下面是一个实现 FTP 协议多个文件上传的示例代码：

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

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;

public class FTPUploader {

    private String server;
    private int port;
    private String user;
    private String password;
    private FTPClient ftpClient;

    public FTPUploader(String server, int port, String user, String password) {
        this.server = server;
        this.port = port;
        this.user = user;
        this.password = password;
    }

    public void connect() throws IOException {
        ftpClient = new FTPClient();
        ftpClient.connect(server, port);
        int replyCode = ftpClient.getReplyCode();
        if (!FTPReply.isPositiveCompletion(replyCode)) {
            throw new IOException("FTP server refused connection.");
        }
        boolean success = ftpClient.login(user, password);
        if (!success) {
            throw new IOException("Could not login to the FTP server.");
        }
        ftpClient.enterLocalPassiveMode();
        ftpClient.setFileType(FTP.BINARY_FILE_TYPE);
    }

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

    public void uploadFiles(String directory, File[] files) throws IOException {
        if (!ftpClient.changeWorkingDirectory(directory)) {
            throw new IOException("Could not change working directory to " + directory);
        }
        for (File file : files) {
            String filename = file.getName();
            try (FileInputStream inputStream = new FileInputStream(file)) {
                boolean success = ftpClient.storeFile(filename, inputStream);
                if (!success) {
                    throw new IOException("Could not upload file " + filename);
                }
            }
        }
    }

}

使用该类的示例代码如下：

public static void main(String[] args) throws IOException {
    String server = "ftp.example.com";
    int port = 21;
    String user = "username";
    String password = "password";
    String directory = "/upload";
    File[] files = new File[] {new File("file1.txt"), new File("file2.txt"), new File("file3.txt")};

    FTPUploader uploader = new FTPUploader(server, port, user, password);
    uploader.connect();
    uploader.uploadFiles(directory, files);
    uploader.disconnect();
}

以上代码实现了连接到 FTP 服务器，切换到指定目录，然后上传多个文件的操作。其中，`FTPClient` 类提供了很多与 FTP 协议相关的方法，可以根据需要进行调用。