帮我用Java写一份ftp分片上传文件的代码

好的，以下是一份Java实现的FTP分片上传文件的代码：

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

import java.io.*;

public class FtpUploader {

    private static final int BUFFER_SIZE = 1024 * 1024;  // 每个分片的大小
    private static final int RETRY_TIMES = 3;  // 上传失败重试次数

    private String hostname;
    private int port;
    private String username;
    private String password;

    public FtpUploader(String hostname, int port, String username, String password) {
        this.hostname = hostname;
        this.port = port;
        this.username = username;
        this.password = password;
    }

    public void upload(File file, String remotePath) throws IOException {
        FTPClient ftpClient = new FTPClient();
        ftpClient.connect(hostname, port);
        ftpClient.login(username, password);

        int replyCode = ftpClient.getReplyCode();
        if (!FTPReply.isPositiveCompletion(replyCode)) {
            ftpClient.disconnect();
            throw new IOException("FTP server refused connection.");
        }

        ftpClient.enterLocalPassiveMode();
        ftpClient.setFileType(FTP.BINARY_FILE_TYPE);

        // 将文件分成若干个分片
        int partNumber = 0;
        long fileSize = file.length();
        long remainingSize = fileSize;
        while (remainingSize > 0) {
            partNumber++;

            // 计算当前分片的大小
            long partSize = Math.min(BUFFER_SIZE, remainingSize);

            // 从文件中读取该分片的数据
            byte[] buffer = new byte[(int) partSize];
            try (FileInputStream fis = new FileInputStream(file)) {
                fis.skip(fileSize - remainingSize);
                int bytesRead = fis.read(buffer);
                if (bytesRead != buffer.length) {
                    throw new IOException("Failed to read file.");
                }
            }

            // 上传该分片
            boolean success = false;
            for (int i = 0; i < RETRY_TIMES && !success; i++) {
                success = ftpClient.storeFile(remotePath + ".part" + partNumber, new ByteArrayInputStream(buffer));
            }
            if (!success) {
                throw new IOException("Failed to upload file part " + partNumber);
            }

            remainingSize -= partSize;
        }

        // 合并所有分片
        boolean success = false;
        for (int i = 0; i < RETRY_TIMES && !success; i++) {
            success = combineParts(ftpClient, remotePath, partNumber);
        }
        if (!success) {
            throw new IOException("Failed to combine file parts.");
        }

        ftpClient.logout();
        ftpClient.disconnect();
    }

    private boolean combineParts(FTPClient ftpClient, String remotePath, int partNumber) throws IOException {
        // 创建目标文件
        if (!ftpClient.storeFile(remotePath + ".tmp", new ByteArrayInputStream(new byte[0]))) {
            return false;
        }

        // 将所有分片合并到目标文件中
        try (OutputStream os = ftpClient.appendFileStream(remotePath + ".tmp")) {
            for (int i = 1; i <= partNumber; i++) {
                try (InputStream is = ftpClient.retrieveFileStream(remotePath + ".part" + i)) {
                    byte[] buffer = new byte[BUFFER_SIZE];
                    int bytesRead;
                    while ((bytesRead = is.read(buffer)) != -1) {
                        os.write(buffer, 0, bytesRead);
                    }
                    ftpClient.completePendingCommand();
                }
            }
        }

        // 重命名目标文件
        return ftpClient.rename(remotePath + ".tmp", remotePath);
    }
}

使用方法：

FtpUploader uploader = new FtpUploader("hostname", 21, "username", "password");
File file = new File("/path/to/local/file");
uploader.upload(file, "/path/to/remote/file");

其中，`hostname`、`username` 和 `password` 分别是 FTP 服务器的主机名、用户名和密码，`/path/to/local/file` 是本地文件的路径，`/path/to/remote/file` 是远程文件的路径。该方法会自动将文件分成若干个分片，每个分片的大小为 `BUFFER_SIZE`，并在上传完成后将所有分片合并成一个文件。如果上传失败，则会进行 `RETRY_TIMES` 次重试。