Develop Reference

FTP LOGIN Issue in Java

I am trying to connect to FTP client using java. My code is here
FTPClient ftpClient = new FTPClient();
ftpClient.connect(url);
boolean login = ftpClient.login(user, pwd);
ftpClient.setFileType(FTP.BINARY_FILE_TYPE);
It is working on my local, but when I run on AWS server is throws following issue.
org.apache.commons.net.ftp.FTPConnectionClosedException: Connection closed without indication.
at org.apache.commons.net.ftp.FTP.__getReply(FTP.java:317)
at org.apache.commons.net.ftp.FTP.__getReply(FTP.java:294)
at org.apache.commons.net.ftp.FTP.sendCommand(FTP.java:483)
at org.apache.commons.net.ftp.FTP.sendCommand(FTP.java:608)
at org.apache.commons.net.ftp.FTP.sendCommand(FTP.java:582)
at org.apache.commons.net.ftp.FTP.quit(FTP.java:864)
at org.apache.commons.net.ftp.FTPClient.logout(FTPClient.java:1109)
at dashboard.utils.DownloadDataFeed.cjAutomation(DownloadDataFeed.java:441)

Upgrading apache.commons dependencies might solve this

FTPSClient failing to connect

I have been trying to change a working FTP connection FTPClient to a FTPSClient provided by apache. The only changes made were changing the class and indicating what port the application is going to connect.
The server connects to another server within the same network. For external servers, a proxy is required.
I already tried setting up the constructor to true, it shows the following message:
Unrecognized SSL message, plaintext connection?
final FTPSClient ftp = new FTPSClient( true );
//same results
//final FTPSClient ftp = new FTPSClient("SSL", true );
//final FTPSClient ftp = new FTPSClient("TLS", true );
ftp.setDefaultPort(22);
When I set it up to false, the connection hangs up for a lot of time. It shows the following message:
Could not parse response code. Server Reply: SSH-2.0-OpenSSH_4.1
and tomcat shows the following page:
Proxy Error
The proxy server received an invalid response from an upstream server.
The proxy server could not handle the request POST /myapppath/APage.htm.
Reason: Error reading from remote server
final FTPSClient ftp = new FTPSClient( false );
ftp.setDefaultPort(22);
I tried connecting manually with WinSCP via SFTP and the connection is successful.

FTPS (FTP over SSL/TLS) is not the same as SFTP (SSH file transfer); these are two completely different protocols. The reason you are getting the error Unrecognized SSL message, plaintext connection? is because you are not connecting to a FTPS server.
You can read more about the difference here. If you want to make an SFTP connection rather than an FTPS connection, I would recommend using the JSch library.

Connect to FTPS through proxy

The initial problem we encountered was that a regular FTPs download started failing due to an untrusted server certificate. This prompted us to wonder whether the certificate had been updated without the counterparty notifying us so we wanted to download the current certificate and compare it to the one we have in our keystore.
This seems to be a trickier problem than we had anticipated. The usual suspects (firefox, filezilla, ...) did not seem up to the task of connecting to an FTPs server through an FTP proxy so out of curiosity I started playing around with a more low level java approach. I can not for the life of me get it to work though.
First (overly simplistic) java attempt:
// create proxy connection
SocketFactory plainFactory = SocketFactory.getDefault();
Socket proxy = plainFactory.createSocket(proxyServer, proxyPort);
// create ssl connection on top of it?
SSLSocketFactory sslFactory = getSocketFactory();
SSLSocket socket = (SSLSocket) sslFactory.createSocket(proxy, server, port, true);
This approach obviously does not work.
Next I started playing around with ftp4j (http://www.sauronsoftware.it/projects/ftp4j/) it seems to have a clean and accessible codebase:
FTPClient client = new FTPClient();
client.setConnector(new FTPProxyConnector(proxyHost, proxyPort));
client.getConnector().setConnectionTimeout(0);
client.getConnector().setReadTimeout(0);
client.setSSLSocketFactory(getSocketFactory());
// also tried SECURITY_FTPS
client.setSecurity(FTPClient.SECURITY_FTPES);
client.connect(server, port);
This outputs:
REPLY: 220 Blue Coat FTP Service
SEND: USER anonymous
REPLY: 530-User Access denied.
REPLY: 530-
REPLY: 530-Usage: USER username#hostname
REPLY: 331 PASS userpassword
Exception in thread "main" java.io.IOException: Invalid proxy response
The proxy server has optional authentication and on our development servers we generally use "user#host" without proxy authentication. As such I assume the username, hostname and password are those of the remote server?
So I tried adding the remote parameters, this does not work:
REPLY: 220 Blue Coat FTP Service
SEND: USER test#ftps.example.com
Exception in thread "main" java.io.IOException: FTPConnection closed
Adding the proxy user to match the bluecoat format does not seem to work either:
USER %u#%h %s
PASS %p
ACCT %w
Any help with either of these two problems would be most welcome:
how to retrieve the server certificate from an ftps server through an ftp proxy
how to connect to an ftps server through an ftp proxy in java

You might want to try Apache Net commons libs.
Here is a similar thread that uses that Net Commons library
Net commons also has a fully functional FTP Client Example so you can test with something you know works.

Upload file using java in ftp

I want to upload file from my system to remote server as ftp.how i am to resolve this.I am using FTPClient client = new FTPClient(); and client.connect("sftp://something.com");But i am unable to connect it how i am check weather problem with my code or url.like ping command

I haven't used FTPClient (assume you mean Apache Commons FTPClient but a quick browse of apidocs shows two errors in your use:
The parameter to connect is server name, not url: client.connect("sftp://something.com") should be client.connect("something.com")
If you are using sftp you have to use FTPSClient

If you're connecting to an Sftp you might need to add the appropriate certificates (public/private keys) to the JVM where the code is running. Try your code on a regular FTP connection first, if that works, but not the sftp connections, it's almost sure is because of that.

Should retrieveFile of commons FTPClient remove file from remote server

We are using Commons FTPClient to retrieve files from an ftp server. Our code is similar to:
FTPClient ftpClient= new FTPClient();
ftpClient.connect(server);
ftpClient.login(username, password);
FileOutputStream out = new FileOutputStream(localFile);
ftpClient.retrieveFile(remoteFile, out)
When we run this code the file is moved from the FTP Server instead of copied. Just wondering is this expected behavior?
If this is expected behavior what is the best approach to retrieve a copy of the file from the server but leave a copy of the file on the server? (We do not have access to write to the FTP Server so we cannot write the file back to the server)
Any help appreciated,
Thanks

It is very strange behavior. I have just examined the code of FTPClient and did not see something that may remove the remote file. I believe that this is a configuration of your FTP server.
To check it I'd recommend you to try other FTP client. For example unix command line utility ftp or fget or regular web browser.
I wish you good luck.