[英]How to solve exception with “org.apache.commons.net.ftp.FTPClient”
Im not sure if this is a similar problem as I faced since it doesn't state an Exception: Issue with org.apache.commons.net.ftp.FTPClient listFiles() 我不确定这是否是我遇到的类似问题,因为它没有指出异常: org.apache.commons.net.ftp.FTPClient listFiles()有问题
I'm trying to use this class FTPUtil
to download the root folder: https://www.codejava.net/java-se/ftp/how-to-download-a-complete-folder-from-a-ftp-server 我正在尝试使用此类
class FTPUtil
下载根文件夹: https : class FTPUtil
at the line FTPFile[] subFiles = ftpClient.listFiles(dirToList);
在
FTPFile[] subFiles = ftpClient.listFiles(dirToList);
行FTPFile[] subFiles = ftpClient.listFiles(dirToList);
I get this Exception: 我得到这个异常:
java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String java.net.InetAddress.getHostAddress()' on a null object reference
at org.apache.commons.net.ftp.FTPClient._openDataConnection_(FTPClient.java:938)
at org.apache.commons.net.ftp.FTPClient._openDataConnection_(FTPClient.java:785)
at org.apache.commons.net.ftp.FTPClient.initiateListParsing(FTPClient.java:3409)
at org.apache.commons.net.ftp.FTPClient.initiateListParsing(FTPClient.java:3339)
at org.apache.commons.net.ftp.FTPClient.listFiles(FTPClient.java:3016)
at com.censored.FTPUtil.downloadDirectory(FTPUtil.java:39)
I don't really understand which Object is null and why. 我不太了解哪个Object为null,为什么。 As
String parentDir
I tried ""
and "\\"
both with the same result I don't think the input is wrong. 作为
String parentDir
我以相同的结果尝试了""
和"\\"
,但我认为输入没有错。
The FTP server is running fine I see that my program logs in successful and file zilla can also access the folder. FTP服务器运行良好,我看到程序成功登录,并且文件zilla也可以访问该文件夹。
EDIT: 编辑:
Here is the class from the link I'm using: 这是我正在使用的链接中的类:
package com.censored;
import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import org.apache.commons.net.ftp.FTP;
import org.apache.commons.net.ftp.FTPClient;
import org.apache.commons.net.ftp.FTPFile;
/**
* This utility class implements a method that downloads a directory completely
* from a FTP server, using Apache Commons Net API.
*
* @author www.codejava.net
*
*/
public class FTPUtil {
/**
* Download a whole directory from a FTP server.
* @param ftpClient an instance of org.apache.commons.net.ftp.FTPClient class.
* @param parentDir Path of the parent directory of the current directory being
* downloaded.
* @param currentDir Path of the current directory being downloaded.
* @param saveDir path of directory where the whole remote directory will be
* downloaded and saved.
* @throws IOException if any network or IO error occurred.
*/
public static void downloadDirectory(FTPClient ftpClient, String parentDir,
String currentDir, String saveDir) throws IOException {
String dirToList = parentDir;
if (!currentDir.equals("")) {
dirToList += "/" + currentDir;
}
FTPFile[] subFiles = ftpClient.listFiles(dirToList); //This line gives the Exception
if (subFiles != null && subFiles.length > 0) {
for (FTPFile aFile : subFiles) {
String currentFileName = aFile.getName();
if (currentFileName.equals(".") || currentFileName.equals("..")) {
// skip parent directory and the directory itself
continue;
}
String filePath = parentDir + "/" + currentDir + "/"
+ currentFileName;
if (currentDir.equals("")) {
filePath = parentDir + "/" + currentFileName;
}
String newDirPath = saveDir + parentDir + File.separator
+ currentDir + File.separator + currentFileName;
if (currentDir.equals("")) {
newDirPath = saveDir + parentDir + File.separator
+ currentFileName;
}
if (aFile.isDirectory()) {
// create the directory in saveDir
File newDir = new File(newDirPath);
boolean created = newDir.mkdirs();
if (created) {
System.out.println("CREATED the directory: " + newDirPath);
} else {
System.out.println("COULD NOT create the directory: " + newDirPath);
}
// download the sub directory
downloadDirectory(ftpClient, dirToList, currentFileName,
saveDir);
} else {
// download the file
boolean success = downloadSingleFile(ftpClient, filePath,
newDirPath);
if (success) {
System.out.println("DOWNLOADED the file: " + filePath);
} else {
System.out.println("COULD NOT download the file: "
+ filePath);
}
}
}
}
}
/**
* Download a single file from the FTP server
* @param ftpClient an instance of org.apache.commons.net.ftp.FTPClient class.
* @param remoteFilePath path of the file on the server
* @param savePath path of directory where the file will be stored
* @return true if the file was downloaded successfully, false otherwise
* @throws IOException if any network or IO error occurred.
*/
public static boolean downloadSingleFile(FTPClient ftpClient,
String remoteFilePath, String savePath) throws IOException {
File downloadFile = new File(savePath);
File parentDir = downloadFile.getParentFile();
if (!parentDir.exists()) {
parentDir.mkdir();
}
OutputStream outputStream = new BufferedOutputStream(
new FileOutputStream(downloadFile));
try {
ftpClient.setFileType(FTP.BINARY_FILE_TYPE);
return ftpClient.retrieveFile(remoteFilePath, outputStream);
} catch (IOException ex) {
throw ex;
} finally {
if (outputStream != null) {
outputStream.close();
}
}
}
}
And this my code calling it (censored the unrelevant stuff I dont have the permission to show the full class): 这就是我的代码调用它(检查了我没有权限显示完整课程的无关内容):
val server = "10.0.2.2" // Because of Emulator
val port = 8080 //yeah I know not standard port, this will change
val user = "censored"
val pass = "censored"
val remoteDirPath = "" //also tried "/"
val saveDirPath = File(myFilesDir, "fromFTP/").absolutePath //ignore myFilesDir the Debuger shows that its set correct and it isnt relevant before the Exception
val ftpClient = FTPClient()
try {
// connect and login to the server
ftpClient.connect(server, port)
ftpClient.login(user, pass)
// use local passive mode to pass firewall
ftpClient.enterLocalPassiveMode()
println("Connected")
FTPUtil.downloadDirectory(ftpClient, remoteDirPath, "", saveDirPath) //this line is the one giving the exception
// log out and disconnect from the server
ftpClient.logout()
ftpClient.disconnect()
println("Disconnected")
} catch (ex: IOException) {
ex.printStackTrace()
}
Update: During Debuging I found that this if
in class FTPClient extends FTP
is true: 更新:在调试过程中,我发现
if
在类FTPClient extends FTP
,这是真的:
if (__remoteVerificationEnabled && !verifyRemote(socket))
{
socket.close();
throw new IOException(
"Host attempting data connection " + socket.getInetAddress().getHostAddress() +
" is not same as server " + getRemoteAddress().getHostAddress());
}
return socket;
I think socket.getInetAddress()
causes an exception (inside of the outer exception) because the Socket is already closed? 我认为
socket.getInetAddress()
导致异常(在外部异常内部),因为Socket已关闭? This would mean that the FTPClient
itself contains a bug? 这是否意味着
FTPClient
本身包含错误? However I think the solution for my problem is that the if (__remoteVerificationEnabled && !verifyRemote(socket))
is true, so somehow this if must become false. 但是,我认为解决我的问题的方法是
if (__remoteVerificationEnabled && !verifyRemote(socket))
为true,因此,如果if必须变为false。 Why is it true? 为什么会这样呢? What kind of verification is this?
这是什么样的验证?
Ok I think it is just a workaround but the solution seams to be to ad this line: ftpClient.setRemoteVerificationEnabled(false);
好的,我认为这只是一种解决方法,但是解决方案似乎是在广告这行:
ftpClient.setRemoteVerificationEnabled(false);
Read the Update part in the question to see how I found this solution. 阅读问题中的“更新”部分,以了解如何找到此解决方案。
I think you're correct. 我认为你是对的。 This is a bug in FTPClient.
这是FTPClient中的错误。
socket.getInetAddress() is documented to throw NullPointerException if the socket is not open. 如果套接字未打开,则记录socket.getInetAddress()引发NullPointerException。 This is called right after we call socket.close().
在调用socket.close()之后立即调用此方法。
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