Java SFTP | File Transfer Using SFTP in Java JSCH

In digital word transferring file client to server and vice-versa is a typical process because the size of file may be large or may be un authorize access. So, it become necessary to protect the file and data from authorization. The SFTP ensures the security while transferring the file over the network. In this section, we will discuss how to transfer file from a remote server to the local system and vice versa using SSH File Transfer Protocol (SFTP) in Java.

SFTP

SFTP stands for SSH File Transfer Protocol. It has replaced the legacy FTP protocol. It runs over the SSH protocol. It supports the full security and authentication functionality of SSH. In couple of years, it will also take over the FTPS protocol. There is no dedicated SFTP port; SFTP uses the normal SSH port i.e. 22.

Features of SFTP

It protects against password sniffing.
It avoids man-in-the-middle attack.
Protects the integrity of data using encryption and cryptographic hash function.
It authenticates both server and user.

Many SSH clients support SFTP:

Tectia SSH Client
WinSCP
FileZilla
PuTTY
Cyberduck

SFTP Libraries for Java Developers

JCraft JSch
SSHJ

Using JSch Library

JSch library provides the get() and put() method to transfer file between server and client. The put() method is used to transfer files from a local system to a remote server.

Add the jsch dependency to the pom.xml file.

  <dependency>
      <groupId>com.jcraft</groupId>
      <artifactId>jsch</artifactId>
      <version>0.1.55</version>
  </dependency>

It automatically downloads the jsch-0.1.55.jar file to the project directory.

We use put() method to transfer files from a local host to the server.

We use get() to download files from server to the local host.

Authenticate Password

  JSch jsch = new JSch();
  jsch.setKnownHosts("/home/mkyong/.ssh/known_hosts");
  jschSession = jsch.getSession(USERNAME, REMOTE_HOST, REMOTE_PORT);
  jschSession.setPassword(PASSWORD);

Public and private keys authentication use Public Key Authentication with SSH

Local private key: /home/javatpoint/.ssh/id_rsa
Remote public key: ~/.ssh/authorized_keys

Let's see how to use keys in program.

JSch jsch = new JSch();
jsch.setKnownHosts("/home/ javatpoint/.ssh/known_hosts");
jschSession = jsch.getSession(USERNAME, REMOTE_HOST, REMOTE_PORT);
jsch.addIdentity("/home/ javatpoint/.ssh/id_rsa");

let's see the following JSch example to transfer a file from the local system to a remote server 1.2.3.4, authenticate using an SSH password.

SFTPFileTransfer.java

import com.jcraft.jsch.*;
public class SFTPFileTransfer 
{
private static final String REMOTE_HOST = "1.2.3.4";
//variable for user name
private static final String USERNAME = "";
//variable for password
private static final String PASSWORD = "";
//port number for SFTP
private static final int REMOTE_PORT = 22;
private static final int SESSION_TIMEOUT = 10000;
private static final int CHANNEL_TIMEOUT = 5000;
public static void main(String args[]) 
{
String localFile = "/home/javatpoint/local/random.txt";
String remoteFile = "/home/javatpoint/remote/afile.txt";
Session jschSession = null;
try 
{
JSch jsch = new JSch();
jsch.setKnownHosts("/home/javatpoint/.ssh/known_hosts");
jschSession = jsch.getSession(USERNAME, REMOTE_HOST, REMOTE_PORT);
// authenticate using private key
// jsch.addIdentity("/home/javatpoint/.ssh/id_rsa");
// authenticate using password
jschSession.setPassword(PASSWORD);
// 10 seconds session timeout
jschSession.connect(SESSION_TIMEOUT);
Channel sftp = jschSession.openChannel("sftp");
// 5 seconds timeout
sftp.connect(CHANNEL_TIMEOUT);
ChannelSftp channelSftp = (ChannelSftp) sftp;
// transfer file from local to remote server
channelSftp.put(localFile, remoteFile);
// download file from remote server to local
// channelSftp.get(remoteFile, localFile);
channelSftp.exit();
} 
catch (JSchException | SftpException e) 
{
e.printStackTrace();
} 
finally 
{
if (jschSession != null) 
{
jschSession.disconnect();
}
}
System.out.println("Done");
}
}

Output: