用Java写一个ftp分片上传与合并的代码

以下是一个用Java实现FTP分片上传和合并的示例代码：

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.ArrayList;
import java.util.List;

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

public class FtpUpload {

    public static void main(String[] args) {
        String server = "ftp.example.com";
        int port = 21;
        String user = "username";
        String password = "password";
        String remotePath = "/upload/";
        String localPath = "/path/to/local/file";
        String fileName = "example.txt";
        int bufferSize = 1024 * 1024;
        int chunkSize = 1024 * 1024 * 10; // 10MB

        try {
            FTPClient ftp = new FTPClient();
            ftp.connect(server, port);
            int reply = ftp.getReplyCode();
            if (!FTPReply.isPositiveCompletion(reply)) {
                ftp.disconnect();
                throw new IOException("FTP server refused connection.");
            }
            ftp.login(user, password);
            ftp.setFileType(FTP.BINARY_FILE_TYPE);
            ftp.enterLocalPassiveMode();
            ftp.changeWorkingDirectory(remotePath);

            File file = new File(localPath, fileName);
            long fileSize = file.length();
            int chunks = (int) Math.ceil((double) fileSize / chunkSize);
            System.out.println("File size: " + fileSize + " bytes");
            System.out.println("Chunk size: " + chunkSize + " bytes");
            System.out.println("Number of chunks: " + chunks);

            List<String> chunkFiles = new ArrayList<String>();
            InputStream input = new FileInputStream(file);
            byte[] buffer = new byte[bufferSize];
            int bytesRead = 0;
            int chunkNumber = 1;
            while ((bytesRead = input.read(buffer)) != -1) {
                String chunkFileName = fileName + ".part" + chunkNumber;
                OutputStream output = new FileOutputStream(new File(localPath, chunkFileName));
                output.write(buffer, 0, bytesRead);
                output.close();
                chunkFiles.add(chunkFileName);
                chunkNumber++;
            }
            input.close();

            for (int i = 0; i < chunks; i++) {
                String chunkFileName = chunkFiles.get(i);
                File chunkFile = new File(localPath, chunkFileName);
                input = new FileInputStream(chunkFile);
                ftp.storeFile(chunkFileName, input);
                input.close();
                chunkFile.delete();
                System.out.println("Uploaded chunk " + (i + 1) + "/" + chunks);
            }

            ftp.disconnect();

            System.out.println("All chunks uploaded.");

            // merge chunks
            OutputStream output = new FileOutputStream(new File(localPath, fileName));
            for (int i = 0; i < chunks; i++) {
                String chunkFileName = fileName + ".part" + (i + 1);
                input = new FileInputStream(new File(localPath, chunkFileName));
                buffer = new byte[bufferSize];
                while ((bytesRead = input.read(buffer)) != -1) {
                    output.write(buffer, 0, bytesRead);
                }
                input.close();
            }
            output.close();

            System.out.println("File merged.");

        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

该代码通过Apache Commons Net库实现FTP客户端连接和文件上传，将大文件分割成多个小文件进行上传，并在上传完成后将它们合并成一个完整的文件。