java - 在 Java 中使用 FTP 并检测断开连接

Question

我用过 org.apache.commons.net.ftp.FtpClient创建一个可靠的 FTP 类，它应该并行下载多个文件，并在失败时重试。

奇怪的是，我似乎无法获得识别失败的代码。例如，如果我在传输过程中拉我的以太网电缆，代码似乎会继续阻塞在:

client.retrieveFile(nextFile, ftpOutputStream);

行。有人能告诉我为什么它会阻塞在这一行而不是返回 false 或抛出异常吗？我是否错过了设置超时或类似的东西？

try {
    OutputStream ftpOutputStream = new FileOutputStream(fileName);

    System.out.println("Attempting to retrieve file [" + nextFile + "].");
    success = iclient.retrieveFile(nextFile, ftpOutputStream);
    System.out.println("Returned from retrieving file [" + nextFile + "].");

    ftpOutputStream.close();
}

//Can fail due to FTPConnectionClosedException, CopyStreamException, or IOException.  In any case, best course
//of action is to simply create a new connection, log in again, and change back to target directory.
catch(Exception ex) {

    try {
        System.out.println("Error occurred during download, deleting file and restarting.");
        Thread.sleep(1000);

        //Delete the failed file assuming any of it got written to the local drive.
        File f = new File(fileName);                        
        if(f.exists()) {
            System.out.println("Deleting file...");
            f.delete();
        }             

        Thread.sleep(5000);
    }
    catch (InterruptedException iex) {
        System.out.println("Interrupted exceptoin while respoding to failed FTP attempt.");
    }
}

Answer 1

“解决此问题的方法是实现您自己的 SocketFactory 并使用 SocketClient.setSocketFactory 设置它(FTPClient 是 SocketClient 的子类)。当您实现 SocketFactory 时，添加 setConnectTimeout 方法或类似方法。在 createSocket 方法内部, 使用带超时的 J2SE 1.4 连接方法。”

请参阅“如何设置连接超时？”关于 Commons Net FAQ 的问题为什么会这样。