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我正在用java制作一个简单的FTP服务器。当我在本地测试它（在我自己的机器上运行服务器和客户端）时，我一切正常。但是，当我在两台不同的远程计算机上运行服务器和客户端时，客户端在收到来自服务器的“150 文件状态正常”消息后不久就会挂起。我不明白为什么它在一个地方工作得很好，而在另一个地方却不行。以下是相关代码：

服务器（发送文件）：

FileInputStream input = null;
                            try {
                                input = new FileInputStream(filePath);
                            } catch (FileNotFoundException e) {
                                out.writeBytes("550 File not found or access denied.\r\n");
                            }
                            out.writeBytes("150 File status okay.\r\n");

                            // TCP CONNECT
                            DataOutputStream outToClient_d = null;
                            Socket clientSocket1 = null;

                            try {
                                ipAddress = ipAddress.substring(0,
                                        ipAddress.length() - 1);
                                clientSocket1 = new Socket(ipAddress,
                                        portNumber);
                                outToClient_d = new DataOutputStream(
                                        clientSocket1.getOutputStream());
                            }

                            catch (UnknownHostException e) {
                                out.writeBytes("425 Can not open data connection.\r\n");
                            }

                            byte[] buf = new byte[2048];
                            int len;
                            while ((len = input.read(buf)) > 0) {
                                outToClient_d.write(buf, 0, len);
                            }
                            input.close();

                            out.writeBytes("250 Requested file action completed.\r\n");
                            clientSocket1.close();
                            outToClient_d.close();

客户端（将文件保存到 /retr_files）：

InputStream inFromServer_d = null;

    if (welcomeSocket != null) {
        if (!welcomeSocket.isClosed()) {
            welcomeSocket.close();
        }
    }

    try {
        welcomeSocket = new ServerSocket(port);
        System.out.print("PORT " + myIP + "," + num1 + "," + num2 + "\r\n");
        out.writeBytes("PORT " + myIP + "," + num1 + "," + num2 + "\r\n");
        System.out.print(parseReply(getResponse()));
        System.out.print("RETR " + pathname + "\r\n");
        out.writeBytes("RETR " + pathname + "\r\n");
        String reply = parseReply(getResponse());
        if (reply.charAt(10) == '1') {
            System.out.print(reply);
            System.out.print(parseReply(getResponse()));

            try {
                clientSocket_d = welcomeSocket.accept();
            } catch (IOException e) {
                System.out
                        .print("GET failed, FTP-data port not allocated.\r\n");
                System.exit(-1);
            }

            inFromServer_d = clientSocket_d.getInputStream();

            // READ
            InputStream input = inFromServer_d;
            OutputStream output = new FileOutputStream("retr_files/file"
                    + retrCnt);

            byte[] buf = new byte[2048];
            int len;
            while ((len = input.read(buf)) > 0) {
                output.write(buf, 0, len);
            }

            input.close();
            output.close();
            clientSocket_d.close();

        } else {
            System.out.print(reply);
        }
    } catch (IOException e) {
        System.out.print("GET failed, FTP-data port not allocated.\r\n");
        System.exit(-1);
    }

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1 回答 1

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我猜客户端和服务器之间有防火墙阻止从服务器到客户端的反向连接。这个问题是人们现在通常使用“被动”转账而不是“主动”转账的原因。

于 2013-03-27T22:44:01.680 回答