我的简单 Java URL FTP 连接的本地测试设置有一个奇怪的问题。 以下代码片段(删除了 try/catches):

URL url = new URL("ftp://127.0.0.1/subOne/subTwo/subThree/subFour");
URLConnection conn = url.openConnection();
conn.setConnectTimeout(30000);
conn.setReadTimeout(30000);

InputStream is = conn.getInputStream(); /// And here flies the IOException!

...实际的 IOException-Cause 是“subOne/subTwo/subThree/subFour”，但有趣的事情发生在服务器端:

(000012)23.02.2011 13:01:05 - (not logged in) (127.0.0.1)> Connected, sending welcome message...
(000012)23.02.2011 13:01:05 - (not logged in) (127.0.0.1)> 220 Blabla
(000012)23.02.2011 13:01:05 - (not logged in) (127.0.0.1)> USER anonymous
(000012)23.02.2011 13:01:05 - (not logged in) (127.0.0.1)> 331 Password required for anonymous
(000012)23.02.2011 13:01:05 - (not logged in) (127.0.0.1)> PASS *************
(000012)23.02.2011 13:01:05 - anonymous (127.0.0.1)> 230 Logged on
(000012)23.02.2011 13:01:05 - anonymous (127.0.0.1)> TYPE I
(000012)23.02.2011 13:01:05 - anonymous (127.0.0.1)> 200 Type set to I
(000012)23.02.2011 13:01:05 - anonymous (127.0.0.1)> CWD das
(000012)23.02.2011 13:01:05 - anonymous (127.0.0.1)> 250 CWD successful. "/subOne" is current directory.
(000012)23.02.2011 13:01:05 - anonymous (127.0.0.1)> CWD 2011
(000012)23.02.2011 13:01:05 - anonymous (127.0.0.1)> 250 CWD successful. "/subOne/subTwo" is current directory.
(000012)23.02.2011 13:01:05 - anonymous (127.0.0.1)> CWD 02
(000012)23.02.2011 13:01:05 - anonymous (127.0.0.1)> 250 CWD successful. "/subOne/subTwo/subThree" is current directory.
(000012)23.02.2011 13:01:05 - anonymous (127.0.0.1)> EPSV ALL
(000012)23.02.2011 13:01:05 - anonymous (127.0.0.1)> 229 Entering Extended Passive Mode (|||3881|)
(000012)23.02.2011 13:01:05 - anonymous (127.0.0.1)> EPSV
(000012)23.02.2011 13:01:05 - anonymous (127.0.0.1)> 229 Entering Extended Passive Mode (|||3882|)
(000012)23.02.2011 13:01:05 - anonymous (127.0.0.1)> RETR subFour
(000012)23.02.2011 13:01:05 - anonymous (127.0.0.1)> 550 File not found
(000012)23.02.2011 13:01:05 - anonymous (127.0.0.1)> CWD subOne
(000012)23.02.2011 13:01:05 - anonymous (127.0.0.1)> 550 CWD failed. "/subOne/subTwo/subThree/subOne": directory not found.
(000012)23.02.2011 13:03:06 - anonymous (127.0.0.1)> 421 Connection timed out.
(000012)23.02.2011 13:03:06 - anonymous (127.0.0.1)> disconnected.

我完全不明白，为什么 Tester 试图进入扩展被动模式 以及为什么在它无法检索后添加 subOne subFour。

我刚刚安装了 FileZilla Server 并设置了匿名用户和共享驱动器。我通过浏览器和 FileZilla-Client 检查了 FTP-Dir 是否可以访问(当然是相同的登录)，仅此而已。 一切都在同一台机器上安装和运行!

不知道...

感谢您的帮助!

最佳答案

这种连接到 FTP 的方式非常有限，而且文档也很模糊。我可以先给你EPSV的答案。连接由内部实现建立，在我的 JDK 中恰好是 sun.net.www.protocol.ftp.FtpURLConnection。

当首先连接到服务器时 EPSV 和 PASV 将被尝试(默认是被动模式)然后它会回退到主动模式 - PORT - 如果无法建立被动模式。您可以查看 here 的实现细节。

解释您的一个问题的基本评论是:

 /**
  * Here is the idea:
  *
  * - First we want to try the new (and IPv6 compatible) EPSV command
  *   But since we want to be nice with NAT software, we'll issue the
  *   EPSV ALL cmd first.
  *   EPSV is documented in RFC2428
  * - If EPSV fails, then we fall back to the older, yet OK PASV command
  * - If PASV fails as well, then we throw an exception and the calling method
  *   will have to try the EPRT or PORT command
  */

至于你的第二个问题......subFour 的检索失败......好吧，乍一看它似乎表现得那样，因为它有错误。但我现在无法真正安装适当的环境来验证这一点。此外，你有异常(exception)。我猜问题是在第 455 行尝试再次导航到完整路径时启动的。 FTP 连接的完整来源是 here。

373       public InputStream getInputStream() throws IOException {
  ...
  390           try {
  391               decodePath(url.getPath());
  392               if (filename == null || type == DIR) {
  ...
  399               } else {
  400                   if (type == ASCII)
  401                       ftp.ascii();
  402                   else
  403                       ftp.binary();
  404                   cd(pathname);
  405                   is = new FtpInputStream(ftp, ftp.get(filename));
  406               }
  407   
  408
  ...
  453           } catch (FileNotFoundException e) {
  454               try {
  455                   cd(fullpath);
  456                   /* if that worked, then make a directory listing
  457                      and build an html stream with all the files in
  458                      the directory */
  459                   ftp.ascii();
  460   
  461                   is = new FtpInputStream(ftp, ftp.list());
  462                   msgh.add("content-type", "text/plain");
  463               } catch (IOException ex) {
  464                   throw new FileNotFoundException(fullpath);
  465               }
  466           }
  ...
  469       }

我建议您使用 Apache Commons Net 库进行 FTP 操作。它更先进，更易于使用。

如果您愿意，干杯并快乐调试!

关于FileZilla 的 Java FTP 连接问题，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/5090800/