：Apache FTPClient操作“卡死”问题的分析和解决

    最近在和一个第三方的合作中不得已需要使用FTP文件接口。由于FTP Server由对方提供，而且双方背后各自的网络环境都很不单纯等等原因，造成测试环境无法模拟实际情况。测试环境中程序一切正常，但是在部署到生产环境之后发现FTP操作不规律性出现“卡死”现象：程序捕获不到任何异常一直卡着，导致轮巡无法正常工作（由于担心在轮巡时间间隔内处理不能完成，我没有采用类似quartz或者crontab的定时任务，而是采用while-true然后sleep的方式）。

    为了解决这个问题，我首先考虑的是对于FTPClient的使用上没有设置超时时间，于是设置了ConnectTimeout、DataTimeout、DefaultTimeout后在生产环境上继续观察，但是问题依旧没有解决。后来我有些怀疑FTPClient api本身是不是有什么问题，想实在不行自己实现一个超时机制吧，不过还是不甘心，还是想从FTPClient api本身去解决问题。又经过一翻研究之后发现：需要使用被动模式，以下摘抄别人的一段简单描述：
在项目中使用commons-net-3.0.1.jar实现FTP文件的下载，在windows xp上运行正常，但是放到linux上，却出现问题，程序运行到 FTPClient.listFiles()或者FTPClient.retrieveFile()方法时，就停止在那里，什么反应都没有，出现假死状态。google一把，发现很多人也出现了此类问题，最终在一个帖子里找到了解决办法。在调用这两个方法之前，调用FTPClient.enterLocalPassiveMode();这个方法的意思就是每次数据连接之前，ftp client告诉ftp server开通一个端口来传输数据。为什么要这样做呢，因为ftp server可能每次开启不同的端口来传输数据，但是在linux上，由于安全限制，可能某些端口没有开启，所以就出现阻塞。OK，问题解决。

    于是我回滚了之前的修改，改为被动模式（关于FTP主动/被动模式的解释，这里我不多说了，关注的朋友可以自己查阅）。但是问题依旧。于是能想到的就是最有的绝招：实在不行自己实现一个超时机制吧。经过一翻研究最简单的方式就是使用：Future解决：

 1 public static void main(String[] args) throws InterruptedException, ExecutionException {
 2         final ExecutorService exec = Executors.newFixedThreadPool(1);
 3 
 4         Callable<String> call = new Callable<String>() {
 5             public String call() throws Exception {
 6                 Thread.sleep(1000 * 5);
 7                 return "线程执行完成.";
 8             }
 9         };
10 
11         try {
12             Future<String> future = exec.submit(call);
13             String obj = future.get(4 * 1000, TimeUnit.MILLISECONDS); // 任务处理超时时间设置
14             System.out.println("任务成功返回:" + obj);
15         } catch (TimeoutException ex) {
16             System.out.println("处理超时啦....");
17             ex.printStackTrace();
18         } catch (Exception e) {
19             System.out.println("处理失败.");
20             e.printStackTrace();
21         }
22         // 关闭线程池
23         exec.shutdown();
24         
25         System.out.println("完毕");
26     }

当然了还有很多其他方式：
http://tech.sina.com.cn/s/2008-07-04/1051720260.shtml
http://itindex.net/blog/2010/08/11/1281486125717.html
http://darkmasky.iteye.com/blog/1115047
http://www.cnblogs.com/wasp520/archive/2012/07/06/2580101.html
http://coolxing.iteye.com/blog/1476289
http://www.cnblogs.com/chenying99/archive/2012/10/24/2737924.html

    虽然找到了终极的“必杀技”，但是此时我还是不甘心，还是想从FTPClient api本身去解决问题，但此时看来也别无它他法。只能试试：即设置被动模式又设置超时时间。经过实际测试，发现问题得以解决。下面把我的FTP工具类贴给大家分享，希望能帮到遇到同样问题的人。

  1 import org.apache.commons.net.ftp.FTP;
  2 import org.apache.commons.net.ftp.FTPClient;
  3 import org.apache.commons.net.ftp.FTPFile;
  4 import org.apache.commons.net.ftp.FTPReply;
  5 
  6 import java.io.BufferedInputStream;
  7 import java.io.BufferedOutputStream;
  8 import java.io.File;
  9 import java.io.FileInputStream;
 10 import java.io.FileNotFoundException;
 11 import java.io.FileOutputStream;
 12 import java.io.IOException;
 13 import java.io.InputStream;
 14 import java.io.OutputStream;
 15 import java.net.UnknownHostException;
 16 import java.util.ArrayList;
 17 import java.util.List;
 18 
 19 public class FtpUtil {
 20     public static final String ANONYMOUS_LOGIN = "anonymous";
 21     private FTPClient ftp;
 22     private boolean is_connected;
 23 
 24     public FtpUtil() {
 25         ftp = new FTPClient();
 26         is_connected = false;
 27     }
 28     
 29     public FtpUtil(int defaultTimeoutSecond, int connectTimeoutSecond, int dataTimeoutSecond){
 30         ftp = new FTPClient();
 31         is_connected = false;
 32         
 33         ftp.setDefaultTimeout(defaultTimeoutSecond * 1000);
 34         ftp.setConnectTimeout(connectTimeoutSecond * 1000);
 35         ftp.setDataTimeout(dataTimeoutSecond * 1000);
 36     }
 37 
 38     /**
 39      * Connects to FTP server.
 40      * 
 41      * @param host
 42      *            FTP server address or name
 43      * @param port
 44      *            FTP server port
 45      * @param user
 46      *            user name
 47      * @param password
 48      *            user password
 49      * @param isTextMode
 50      *            text / binary mode switch
 51      * @throws IOException
 52      *             on I/O errors
 53      */
 54     public void connect(String host, int port, String user, String password, boolean isTextMode) throws IOException {
 55         // Connect to server.
 56         try {
 57             ftp.connect(host, port);
 58         } catch (UnknownHostException ex) {
 59             throw new IOException("Can't find FTP server '" + host + "'");
 60         }
 61 
 62         // Check rsponse after connection attempt.
 63         int reply = ftp.getReplyCode();
 64         if (!FTPReply.isPositiveCompletion(reply)) {
 65             disconnect();
 66             throw new IOException("Can't connect to server '" + host + "'");
 67         }
 68 
 69         if (user == "") {
 70             user = ANONYMOUS_LOGIN;
 71         }
 72 
 73         // Login.
 74         if (!ftp.login(user, password)) {
 75             is_connected = false;
 76             disconnect();
 77             throw new IOException("Can't login to server '" + host + "'");
 78         } else {
 79             is_connected = true;
 80         }
 81 
 82         // Set data transfer mode.
 83         if (isTextMode) {
 84             ftp.setFileType(FTP.ASCII_FILE_TYPE);
 85         } else {
 86             ftp.setFileType(FTP.BINARY_FILE_TYPE);
 87         }
 88     }
 89 
 90     /**
 91      * Uploads the file to the FTP server.
 92      * 
 93      * @param ftpFileName
 94      *            server file name (with absolute path)
 95      * @param localFile
 96      *            local file to upload
 97      * @throws IOException
 98      *             on I/O errors
 99      */
100     public void upload(String ftpFileName, File localFile) throws IOException {
101         // File check.
102         if (!localFile.exists()) {
103             throw new IOException("Can't upload '" + localFile.getAbsolutePath() + "'. This file doesn't exist.");
104         }
105 
106         // Upload.
107         InputStream in = null;
108         try {
109 
110             // Use passive mode to pass firewalls.
111             ftp.enterLocalPassiveMode();
112 
113             in = new BufferedInputStream(new FileInputStream(localFile));
114             if (!ftp.storeFile(ftpFileName, in)) {
115                 throw new IOException("Can't upload file '" + ftpFileName + "' to FTP server. Check FTP permissions and path.");
116             }
117 
118         } finally {
119             try {
120                 in.close();
121             } catch (IOException ex) {
122             }
123         }
124     }
125 
126     /**
127      * Downloads the file from the FTP server.
128      * 
129      * @param ftpFileName
130      *            server file name (with absolute path)
131      * @param localFile
132      *            local file to download into
133      * @throws IOException
134      *             on I/O errors
135      */
136     public void download(String ftpFileName, File localFile) throws IOException {
137         // Download.
138         OutputStream out = null;
139         try {
140             // Use passive mode to pass firewalls.
141             ftp.enterLocalPassiveMode();
142 
143             // Get file info.
144             FTPFile[] fileInfoArray = ftp.listFiles(ftpFileName);
145             if (fileInfoArray == null) {
146                 throw new FileNotFoundException("File " + ftpFileName + " was not found on FTP server.");
147             }
148 
149             // Check file size.
150             FTPFile fileInfo = fileInfoArray[0];
151             long size = fileInfo.getSize();
152             if (size > Integer.MAX_VALUE) {
153                 throw new IOException("File " + ftpFileName + " is too large.");
154             }
155 
156             // Download file.
157             out = new BufferedOutputStream(new FileOutputStream(localFile));
158             if (!ftp.retrieveFile(ftpFileName, out)) {
159                 throw new IOException("Error loading file " + ftpFileName + " from FTP server. Check FTP permissions and path.");
160             }
161 
162             out.flush();
163         } finally {
164             if (out != null) {
165                 try {
166                     out.close();
167                 } catch (IOException ex) {
168                 }
169             }
170         }
171     }
172 
173     /**
174      * Removes the file from the FTP server.
175      * 
176      * @param ftpFileName
177      *            server file name (with absolute path)
178      * @throws IOException
179      *             on I/O errors
180      */
181     public void remove(String ftpFileName) throws IOException {
182         if (!ftp.deleteFile(ftpFileName)) {
183             throw new IOException("Can't remove file '" + ftpFileName + "' from FTP server.");
184         }
185     }
186 
187     /**
188      * Lists the files in the given FTP directory.
189      * 
190      * @param filePath
191      *            absolute path on the server
192      * @return files relative names list
193      * @throws IOException
194      *             on I/O errors
195      */
196     public List<String> list(String filePath) throws IOException {
197         List<String> fileList = new ArrayList<String>();
198         
199         // Use passive mode to pass firewalls.
200         ftp.enterLocalPassiveMode();
201         
202         FTPFile[] ftpFiles = ftp.listFiles(filePath);
203         int size = (ftpFiles == null) ? 0 : ftpFiles.length;
204         for (int i = 0; i < size; i++) {
205             FTPFile ftpFile = ftpFiles[i];
206             if (ftpFile.isFile()) {
207                 fileList.add(ftpFile.getName());
208             }
209         }
210         
211         return fileList;
212     }
213 
214     /**
215      * Sends an FTP Server site specific command
216      * 
217      * @param args
218      *            site command arguments
219      * @throws IOException
220      *             on I/O errors
221      */
222     public void sendSiteCommand(String args) throws IOException {
223         if (ftp.isConnected()) {
224             try {
225                 ftp.sendSiteCommand(args);
226             } catch (IOException ex) {
227             }
228         }
229     }
230 
231     /**
232      * Disconnects from the FTP server
233      * 
234      * @throws IOException
235      *             on I/O errors
236      */
237     public void disconnect() throws IOException {
238 
239         if (ftp.isConnected()) {
240             try {
241                 ftp.logout();
242                 ftp.disconnect();
243                 is_connected = false;
244             } catch (IOException ex) {
245             }
246         }
247     }
248 
249     /**
250      * Makes the full name of the file on the FTP server by joining its path and
251      * the local file name.
252      * 
253      * @param ftpPath
254      *            file path on the server
255      * @param localFile
256      *            local file
257      * @return full name of the file on the FTP server
258      */
259     public String makeFTPFileName(String ftpPath, File localFile) {
260         if (ftpPath == "") {
261             return localFile.getName();
262         } else {
263             String path = ftpPath.trim();
264             if (path.charAt(path.length() - 1) != '/') {
265                 path = path + "/";
266             }
267 
268             return path + localFile.getName();
269         }
270     }
271 
272     /**
273      * Test coonection to ftp server
274      * 
275      * @return true, if connected
276      */
277     public boolean isConnected() {
278         return is_connected;
279     }
280 
281     /**
282      * Get current directory on ftp server
283      * 
284      * @return current directory
285      */
286     public String getWorkingDirectory() {
287         if (!is_connected) {
288             return "";
289         }
290 
291         try {
292             return ftp.printWorkingDirectory();
293         } catch (IOException e) {
294         }
295 
296         return "";
297     }
298 
299     /**
300      * Set working directory on ftp server
301      * 
302      * @param dir
303      *            new working directory
304      * @return true, if working directory changed
305      */
306     public boolean setWorkingDirectory(String dir) {
307         if (!is_connected) {
308             return false;
309         }
310 
311         try {
312             return ftp.changeWorkingDirectory(dir);
313         } catch (IOException e) {
314         }
315 
316         return false;
317     }
318 
319     /**
320      * Change working directory on ftp server to parent directory
321      * 
322      * @return true, if working directory changed
323      */
324     public boolean setParentDirectory() {
325         if (!is_connected) {
326             return false;
327         }
328 
329         try {
330             return ftp.changeToParentDirectory();
331         } catch (IOException e) {
332         }
333 
334         return false;
335     }
336 
337     /**
338      * Get parent directory name on ftp server
339      * 
340      * @return parent directory
341      */
342     public String getParentDirectory() {
343         if (!is_connected) {
344             return "";
345         }
346 
347         String w = getWorkingDirectory();
348         setParentDirectory();
349         String p = getWorkingDirectory();
350         setWorkingDirectory(w);
351 
352         return p;
353     }
354 
355     /**
356      * Get directory contents on ftp server
357      * 
358      * @param filePath
359      *            directory
360      * @return list of FTPFileInfo structures
361      * @throws IOException
362      */
363     public List<FfpFileInfo> listFiles(String filePath) throws IOException {
364         List<FfpFileInfo> fileList = new ArrayList<FfpFileInfo>();
365         
366         // Use passive mode to pass firewalls.
367         ftp.enterLocalPassiveMode();
368         FTPFile[] ftpFiles = ftp.listFiles(filePath);
369         int size = (ftpFiles == null) ? 0 : ftpFiles.length;
370         for (int i = 0; i < size; i++) {
371             FTPFile ftpFile = ftpFiles[i];
372             FfpFileInfo fi = new FfpFileInfo();
373             fi.setName(ftpFile.getName());
374             fi.setSize(ftpFile.getSize());
375             fi.setTimestamp(ftpFile.getTimestamp());
376             fi.setType(ftpFile.isDirectory());
377             fileList.add(fi);
378         }
379 
380         return fileList;
381     }
382 
383     /**
384      * Get file from ftp server into given output stream
385      * 
386      * @param ftpFileName
387      *            file name on ftp server
388      * @param out
389      *            OutputStream
390      * @throws IOException
391      */
392     public void getFile(String ftpFileName, OutputStream out) throws IOException {
393         try {
394             // Use passive mode to pass firewalls.
395             ftp.enterLocalPassiveMode();
396             
397             // Get file info.
398             FTPFile[] fileInfoArray = ftp.listFiles(ftpFileName);
399             if (fileInfoArray == null) {
400                 throw new FileNotFoundException("File '" + ftpFileName + "' was not found on FTP server.");
401             }
402 
403             // Check file size.
404             FTPFile fileInfo = fileInfoArray[0];
405             long size = fileInfo.getSize();
406             if (size > Integer.MAX_VALUE) {
407                 throw new IOException("File '" + ftpFileName + "' is too large.");
408             }
409 
410             // Download file.
411             if (!ftp.retrieveFile(ftpFileName, out)) {
412                 throw new IOException("Error loading file '" + ftpFileName + "' from FTP server. Check FTP permissions and path.");
413             }
414 
415             out.flush();
416 
417         } finally {
418             if (out != null) {
419                 try {
420                     out.close();
421                 } catch (IOException ex) {
422                 }
423             }
424         }
425     }
426 
427     /**
428      * Put file on ftp server from given input stream
429      * 
430      * @param ftpFileName
431      *            file name on ftp server
432      * @param in
433      *            InputStream
434      * @throws IOException
435      */
436     public void putFile(String ftpFileName, InputStream in) throws IOException {
437         try {
438             // Use passive mode to pass firewalls.
439             ftp.enterLocalPassiveMode();
440             
441             if (!ftp.storeFile(ftpFileName, in)) {
442                 throw new IOException("Can't upload file '" + ftpFileName + "' to FTP server. Check FTP permissions and path.");
443             }
444         } finally {
445             try {
446                 in.close();
447             } catch (IOException ex) {
448             }
449         }
450     }
451 }