How to retrieve a file from a server via SFTP?

Question

I'm trying to retrieve a file from a server using SFTP (as opposed to FTPS) using Java. How can I do this?

Solution 1

Another option is to consider looking at the JSch library. JSch seems to be the preferred library for a few large open source projects, including Eclipse, Ant and Apache Commons HttpClient, amongst others.

It supports both user/pass and certificate-based logins nicely, as well as all a whole host of other yummy SSH2 features.

Here's a simple remote file retrieve over SFTP. Error handling is left as an exercise for the reader :-)

JSch jsch = new JSch();

String knownHostsFilename = "/home/username/.ssh/known_hosts";
jsch.setKnownHosts( knownHostsFilename );

Session session = jsch.getSession( "remote-username", "remote-host" );    
{
  // "interactive" version
  // can selectively update specified known_hosts file 
  // need to implement UserInfo interface
  // MyUserInfo is a swing implementation provided in 
  //  examples/Sftp.java in the JSch dist
  UserInfo ui = new MyUserInfo();
  session.setUserInfo(ui);

  // OR non-interactive version. Relies in host key being in known-hosts file
  session.setPassword( "remote-password" );
}

session.connect();

Channel channel = session.openChannel( "sftp" );
channel.connect();

ChannelSftp sftpChannel = (ChannelSftp) channel;

sftpChannel.get("remote-file", "local-file" );
// OR
InputStream in = sftpChannel.get( "remote-file" );
  // process inputstream as needed

sftpChannel.exit();
session.disconnect();

Solution 2

Here is the complete source code of an example using JSch without having to worry about the ssh key checking.

import com.jcraft.jsch.*;

public class TestJSch {
    public static void main(String args[]) {
        JSch jsch = new JSch();
        Session session = null;
        try {
            session = jsch.getSession("username", "127.0.0.1", 22);
            session.setConfig("StrictHostKeyChecking", "no");
            session.setPassword("password");
            session.connect();

            Channel channel = session.openChannel("sftp");
            channel.connect();
            ChannelSftp sftpChannel = (ChannelSftp) channel;
            sftpChannel.get("remotefile.txt", "localfile.txt");
            sftpChannel.exit();
            session.disconnect();
        } catch (JSchException e) {
            e.printStackTrace();  
        } catch (SftpException e) {
            e.printStackTrace();
        }
    }
}

Solution 3

Below is an example using Apache Common VFS:

FileSystemOptions fsOptions = new FileSystemOptions();
SftpFileSystemConfigBuilder.getInstance().setStrictHostKeyChecking(fsOptions, "no");
FileSystemManager fsManager = VFS.getManager();
String uri = "sftp://user:password@host:port/absolute-path";
FileObject fo = fsManager.resolveFile(uri, fsOptions);

Solution 4

A nice abstraction on top of Jsch is Apache commons-vfs which offers a virtual filesystem API that makes accessing and writing SFTP files almost transparent. Worked well for us.

Solution 5

This was the solution I came up with http://sourceforge.net/projects/sshtools/ (most error handling omitted for clarity). This is an excerpt from my blog

SshClient ssh = new SshClient();
ssh.connect(host, port);
//Authenticate
PasswordAuthenticationClient passwordAuthenticationClient = new PasswordAuthenticationClient();
passwordAuthenticationClient.setUsername(userName);
passwordAuthenticationClient.setPassword(password);
int result = ssh.authenticate(passwordAuthenticationClient);
if(result != AuthenticationProtocolState.COMPLETE){
     throw new SFTPException("Login to " + host + ":" + port + " " + userName + "/" + password + " failed");
}
//Open the SFTP channel
SftpClient client = ssh.openSftpClient();
//Send the file
client.put(filePath);
//disconnect
client.quit();
ssh.disconnect();

View more solutions

Comments

[Benedikt Waldvogel]

is it possible to use pre-shared keys in combination with commons-vfs?

[Russ Hayward]

Yes it is. If you need non-standard identities you can call SftpFileSystemConfigBuilder.getInstance().setIdentities(...)‌​.

[David Hayes]

I agree (belatedly), it worked fine for the original site/download I required but it refuesed to work for the new one. I'm in the process of switching to JSch

[Cheekysoft]

Sorry, it is not something i work with at the moment. (Please try and leave these sort of responses as comments -- like this message -- and not as a new answer to the original question)

[Admin]

Cheekysoft, I noticed - while using Jsch - removing files on the sftp-server does not work. Also renaming files does not work too. Any ideas please??? Andy

[Scott Jones]

Another nice thing to do is to set the timeout, so that if the remote system is offline, you don't hang there forever. You can do this just like was done for the host key check disable: SftpFileSystemConfigBuilder.getInstance().setTimeout(fsOptio‌​ns, 5000);

[KrzyH]

You can use pre-shared keys. But this keys have to be without password. OtrosLogViewer is using SSH key authorization with VFS but requires to remove passphrase from key (code.google.com/p/otroslogviewer/wiki/SftpAuthPubKey)

[AZ_]

Source: mysamplecode.com/2013/06/sftp-apache-commons-file-download.h‌​tml

[hotshot309]

A finally block should be used to include the channel clean-up code, to ensure that it always runs.

[Michael Peterson]

What is that code block after the assignment of session? Is that some fancy Java syntax I've never seen? If so - what does it accomplish being written that way?

[Cheekysoft]

@p1x3l5 standard java syntax allows a block to be inserted anywhere; it can be used to provide finer control over variable scope, if you wish. However, in this case, it is just a visual aid to help indicate the two implementation choices: either use the interactive version which requests a password from the user, or use a hardcoded password requiring no user intervention but arguably an additional security risk.

[OhadR]

nice job!! an example in the main page could be helpful though.

[M S Parmar]

how to configure while having ssh-key (public key) to copy files on server. Because i need to make ssh_trust between my server and remote server.

[rü-]

Zehon seems dead. And where's the source? What 'license' is behind 'free'?

[rü-]

github.com/terencehonles/jaramiko is abandoned in favor of JSch (see notice on github).

[rü-]

JFileUpload is an applet, not a lib. License is commercial. Doesn't look active, either.

[fIwJlxSzApHEZIl]

I'm getting this exception now: com.jcraft.jsch.JSchException: Session.connect: java.security.InvalidAlgorithmParameterException: Prime size must be multiple of 64, and can only range from 512 to 2048 (inclusive)

[2Big2BeSmall]

How would you advise close this connection when using multiple SFTP clients at the same time ?

[User3]

What if my password contains @ symbol?

[Johan]

Is there a way to get the file as an InputStream?

[Maxence]

sshj in 2019 is still well maintained and is used by Alpakka (Akka) project

[englebart]

I found JSCH to have 0 or 1 extra dependencies. You can ignore the JZLIB dependency if you disable compression. // disable compression session.setConfig("compression.s2c", "none"); session.setConfig("compression.c2s", "none");

[rustyx]

Without strict host checking you're susceptible to a man-in-the-middle attack.

[Itay wazana]

I must say, that library is reallt overhead for the question requirements. the part that handles sftp is something like 10% of the library or even less...

[Raymond Chenon]

Another example relying on JSch library : baeldung.com/java-file-sftp