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 } }}