Java FTP：上传到FTP后无法删除本地文件

Question

我成功上传到FTP后无法删除本地文件（因此我的目标是在上传完成后立即删除本地文件）。我怀疑FileInputStream会阻止本地文件，但我不确定。也许还有其他我无法看到的东西。任何帮助都没问题。我正在使用org.apache.commons.net.ftp.FTP。这是我的代码的一部分：

public class FtpConnection {
  String FTP_SERVER;
  String FTP_USER;
  String FTP_PASSWORD;
  int FTP_PORT;
  public FTPClient ftpClient;
  int attempts = 3;
  long FILE_SIZE;


  public FtpConnection(String ftp_server, String ftp_user, String ftp_password, int ftp_port) {
    FTP_SERVER = ftp_server;
    FTP_USER = ftp_user;
    FTP_PASSWORD = ftp_password;
    FTP_PORT = ftp_port;

    ftpClient = new FTPClient();
    ftpClient.enterLocalPassiveMode();

    ftpClient.setBufferSize(1024 * 1024 * 1024);
    ftpClient.setConnectTimeout(120000);
    ftpClient.setDataTimeout(60000);
    try {
      ftpClient.connect(FTP_SERVER, FTP_PORT);

      int replyCode = ftpClient.getReplyCode();
      if (!FTPReply.isPositiveCompletion(replyCode)) {
        System.out.println("Operation failed. Server reply code: " + replyCode);
        return;
      }
      boolean success = ftpClient.login(FTP_USER, FTP_PASSWORD);
      ftpClient.setFileType(FTP.BINARY_FILE_TYPE);

      if (!success) {
        System.out.println("Could not login to the server");
      }
    } catch (IOException ex) {
      System.out.println("Oops! Something wrong happened");
      ex.printStackTrace();
    }
  }


  public boolean copyFile(File source, String destination) {

    try {
      FILE_SIZE = source.length();

      for(int i=0;i<attempts;i++) {
        FileInputStream file = new FileInputStream(source);

        ftpClient.storeFile(destination, file);

        for(FTPFile f : ftpClient.listFiles()) {
          if(f.getName().equals(destination) && f.getSize() == source.length()) {
            file.close();
            return true;
          }
        }
      }

      ftpClient.deleteFile(destination + "/" + source.getName());
      return false;
    } catch (IOException ex) {
      Logger.getLogger(FtpConnection.class.getName()).log(Level.SEVERE, null, ex);
      this.closeConnection();
      return false;
    }
  }


}

在这里我调用copyFile方法：

File f = new File("myfile.txt");
boolean b = FTP.copyFile(ORIG,filename);
if(b) {
  System.out.println(f.exists()); //true
  System.out.println(f.canWrite()); //true
  System.out.println(f.delete()); //false
}