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：
public static void main(String[] args) throws InterruptedException, ExecutionException {
final ExecutorService exec = Executors.newFixedThreadPool(1);
Callable<String> call = new Callable<String>() {
public String call() throws Exception {
Thread.sleep(1000 * 5);
return "线程执行完成.";
}
};
try {
Future<String> future = exec.submit(call);
String obj = future.get(4 * 1000, TimeUnit.MILLISECONDS); // 任务处理超时时间设置
System.out.println("任务成功返回:" + obj);
} catch (TimeoutException ex) {
System.out.println("处理超时啦....");
ex.printStackTrace();
} catch (Exception e) {
System.out.println("处理失败.");
e.printStackTrace();
}
// 关闭线程池
exec.shutdown();
System.out.println("完毕");
}
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.iyunv.com/wasp520/archive/2012/07/06/2580101.html
http://coolxing.iteye.com/blog/1476289
http://www.iyunv.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。
import org.apache.commons.net.ftp.FTP;
import org.apache.commons.net.ftp.FTPClient;
import org.apache.commons.net.ftp.FTPFile;
import org.apache.commons.net.ftp.FTPReply;
import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.UnknownHostException;
import java.util.ArrayList;
import java.util.List;
public class FtpUtil {
public static final String ANONYMOUS_LOGIN = "anonymous";
private FTPClient ftp;
private boolean is_connected;
public FtpUtil() {
ftp = new FTPClient();
is_connected = false;
}
public FtpUtil(int defaultTimeoutSecond, int connectTimeoutSecond, int dataTimeoutSecond){
ftp = new FTPClient();
is_connected = false;
ftp.setDefaultTimeout(defaultTimeoutSecond * 1000);
ftp.setConnectTimeout(connectTimeoutSecond * 1000);
ftp.setDataTimeout(dataTimeoutSecond * 1000);
}
/**
* Connects to FTP server.
*
* @param host
* FTP server address or name
* @param port
* FTP server port
* @param user
* user name
* @param password
* user password
* @param isTextMode
* text / binary mode switch
* @throws IOException
* on I/O errors
*/
public void connect(String host, int port, String user, String password, boolean isTextMode) throws IOException {
// Connect to server.
try {
ftp.connect(host, port);
} catch (UnknownHostException ex) {
throw new IOException("Can't find FTP server '" + host + "'");
}
// Check rsponse after connection attempt.
int reply = ftp.getReplyCode();
if (!FTPReply.isPositiveCompletion(reply)) {
disconnect();
throw new IOException("Can't connect to server '" + host + "'");
}
if (user == "") {
user = ANONYMOUS_LOGIN;
}
// Login.
if (!ftp.login(user, password)) {
is_connected = false;
disconnect();
throw new IOException("Can't login to server '" + host + "'");
} else {
is_connected = true;
}
// Set data transfer mode.
if (isTextMode) {
ftp.setFileType(FTP.ASCII_FILE_TYPE);
} else {
ftp.setFileType(FTP.BINARY_FILE_TYPE);
}
}
/**
* Uploads the file to the FTP server.
*
* @param ftpFileName
* server file name (with absolute path)
* @param localFile
* local file to upload
* @throws IOException
* on I/O errors
*/
public void upload(String ftpFileName, File localFile) throws IOException {
// File check.
if (!localFile.exists()) {
throw new IOException("Can't upload '" + localFile.getAbsolutePath() + "'. This file doesn't exist.");
}
// Upload.
InputStream in = null;
try {
// Use passive mode to pass firewalls.
ftp.enterLocalPassiveMode();
in = new BufferedInputStream(new FileInputStream(localFile));
if (!ftp.storeFile(ftpFileName, in)) {
throw new IOException("Can't upload file '" + ftpFileName + "' to FTP server. Check FTP permissions and path.");
}
} finally {
try {
in.close();
} catch (IOException ex) {
}
}
}
/**
* Downloads the file from the FTP server.
*
* @param ftpFileName
* server file name (with absolute path)
* @param localFile
* local file to download into
* @throws IOException
* on I/O errors
*/
public void download(String ftpFileName, File localFile) throws IOException {
// Download.
OutputStream out = null;
try {
// Use passive mode to pass firewalls.
ftp.enterLocalPassiveMode();
// Get file info.
FTPFile[] fileInfoArray = ftp.listFiles(ftpFileName);
if (fileInfoArray == null) {
throw new FileNotFoundException("File " + ftpFileName + " was not found on FTP server.");
}
// Check file size.
FTPFile fileInfo = fileInfoArray;
long size = fileInfo.getSize();
if (size > Integer.MAX_VALUE) {
throw new IOException("File " + ftpFileName + " is too large.");
}
// Download file.
out = new BufferedOutputStream(new FileOutputStream(localFile));
if (!ftp.retrieveFile(ftpFileName, out)) {
throw new IOException("Error loading file " + ftpFileName + " from FTP server. Check FTP permissions and path.");
}
out.flush();
} finally {
if (out != null) {
try {
out.close();
} catch (IOException ex) {
}
}
}
}
/**
* Removes the file from the FTP server.
*
* @param ftpFileName
* server file name (with absolute path)
* @throws IOException
* on I/O errors
*/
public void remove(String ftpFileName) throws IOException {
if (!ftp.deleteFile(ftpFileName)) {
throw new IOException("Can't remove file '" + ftpFileName + "' from FTP server.");
}
}
/**
* Lists the files in the given FTP directory.
*
* @param filePath
* absolute path on the server
* @return files relative names list
* @throws IOException
* on I/O errors
*/
public List<String> list(String filePath) throws IOException {
List<String> fileList = new ArrayList<String>();
// Use passive mode to pass firewalls.
ftp.enterLocalPassiveMode();
FTPFile[] ftpFiles = ftp.listFiles(filePath);
int size = (ftpFiles == null) ? 0 : ftpFiles.length;
for (int i = 0; i < size; i++) {
FTPFile ftpFile = ftpFiles;
if (ftpFile.isFile()) {
fileList.add(ftpFile.getName());
}
}
return fileList;
}
/**
* Sends an FTP Server site specific command
*
* @param args
* site command arguments
* @throws IOException
* on I/O errors
*/
public void sendSiteCommand(String args) throws IOException {
if (ftp.isConnected()) {
try {
ftp.sendSiteCommand(args);
} catch (IOException ex) {
}
}
}
/**
* Disconnects from the FTP server
*
* @throws IOException
* on I/O errors
*/
public void disconnect() throws IOException {
if (ftp.isConnected()) {
try {
ftp.logout();
ftp.disconnect();
is_connected = false;
} catch (IOException ex) {
}
}
}
/**
* Makes the full name of the file on the FTP server by joining its path and
* the local file name.
*
* @param ftpPath
* file path on the server
* @param localFile
* local file
* @return full name of the file on the FTP server
*/
public String makeFTPFileName(String ftpPath, File localFile) {
if (ftpPath == "") {
return localFile.getName();
} else {
String path = ftpPath.trim();
if (path.charAt(path.length() - 1) != '/') {
path = path + "/";
}
return path + localFile.getName();
}
}
/**
* Test coonection to ftp server
*
* @return true, if connected
*/
public boolean isConnected() {
return is_connected;
}
/**
* Get current directory on ftp server
*
* @return current directory
*/
public String getWorkingDirectory() {
if (!is_connected) {
return "";
}
try {
return ftp.printWorkingDirectory();
} catch (IOException e) {
}
return "";
}
/**
* Set working directory on ftp server
*
* @param dir
* new working directory
* @return true, if working directory changed
*/
public boolean setWorkingDirectory(String dir) {
if (!is_connected) {
return false;
}
try {
return ftp.changeWorkingDirectory(dir);
} catch (IOException e) {
}
return false;
}
/**
* Change working directory on ftp server to parent directory
*
* @return true, if working directory changed
*/
public boolean setParentDirectory() {
if (!is_connected) {
return false;
}
try {
return ftp.changeToParentDirectory();
} catch (IOException e) {
}
return false;
}
/**
* Get parent directory name on ftp server
*
* @return parent directory
*/
public String getParentDirectory() {
if (!is_connected) {
return "";
}
String w = getWorkingDirectory();
setParentDirectory();
String p = getWorkingDirectory();
setWorkingDirectory(w);
return p;
}
/**
* Get directory contents on ftp server
*
* @param filePath
* directory
* @return list of FTPFileInfo structures
* @throws IOException
*/
public List<FfpFileInfo> listFiles(String filePath) throws IOException {
List<FfpFileInfo> fileList = new ArrayList<FfpFileInfo>();
// Use passive mode to pass firewalls.
ftp.enterLocalPassiveMode();
FTPFile[] ftpFiles = ftp.listFiles(filePath);
int size = (ftpFiles == null) ? 0 : ftpFiles.length;
for (int i = 0; i < size; i++) {
FTPFile ftpFile = ftpFiles;
FfpFileInfo fi = new FfpFileInfo();
fi.setName(ftpFile.getName());
fi.setSize(ftpFile.getSize());
fi.setTimestamp(ftpFile.getTimestamp());
fi.setType(ftpFile.isDirectory());
fileList.add(fi);
}
return fileList;
}
/**
* Get file from ftp server into given output stream
*
* @param ftpFileName
* file name on ftp server
* @param out
* OutputStream
* @throws IOException
*/
public void getFile(String ftpFileName, OutputStream out) throws IOException {
try {
// Use passive mode to pass firewalls.
ftp.enterLocalPassiveMode();
// Get file info.
FTPFile[] fileInfoArray = ftp.listFiles(ftpFileName);
if (fileInfoArray == null) {
throw new FileNotFoundException("File '" + ftpFileName + "' was not found on FTP server.");
}
// Check file size.
FTPFile fileInfo = fileInfoArray;
long size = fileInfo.getSize();
if (size > Integer.MAX_VALUE) {
throw new IOException("File '" + ftpFileName + "' is too large.");
}
// Download file.
if (!ftp.retrieveFile(ftpFileName, out)) {
throw new IOException("Error loading file '" + ftpFileName + "' from FTP server. Check FTP permissions and path.");
}
out.flush();
} finally {
if (out != null) {
try {
out.close();
} catch (IOException ex) {
}
}
}
}
/**
* Put file on ftp server from given input stream
*
* @param ftpFileName
* file name on ftp server
* @param in
* InputStream
* @throws IOException
*/
public void putFile(String ftpFileName, InputStream in) throws IOException {
try {
// Use passive mode to pass firewalls.
ftp.enterLocalPassiveMode();
if (!ftp.storeFile(ftpFileName, in)) {
throw new IOException("Can't upload file '" + ftpFileName + "' to FTP server. Check FTP permissions and path.");
}
} finally {
try {
in.close();
} catch (IOException ex) {
}
}
}}
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