How do I transfer a file from one directory to another using Java SFTP Library JSch?

Question

I need to program a file transfer using JSch library. I have a simple directory with two folders -

In the SFTP_1 folder, I have a bitmap image

Answer 1

Actually JSch is designed for remote work, and file system modification is one of the type such work. @Edwin Buck answer uses network for coping between local folders on remote host. There is better approach:

session.connect();
ChannelExec exec = (ChannelExec) session.openChannel("exec");
exec.setCommand("cp a.out b.out");
exec.connect();

I have no windows on the hand, as result my sample is for unix. But the idea is simple: execute copy command on the remote host.

Answer 2

Note that to copy between two folders, one doesn't need to use SFTP. One can copy from one folder to another without involving the SFTP protocol which is primarly used to copy files remotely, either from the local machine to a remote machine, or from a remote machine to (the same or a different) remote machine, or from the remote machine to the local machine.

That's because the FTP is a network based protocol. So using it (or any of it's related protocols) is going to use the network (or a simulated network).

The security that JSch provides is security designed to protect from certain kinds of attacks that occur on networks. It will not provide any extra security within the machine.

To copy files between folders on a single machine, the simplest way to do so is not to use JSch, like so

private static void copyFileUsingJava7Files(File source, File dest)
        throws IOException {
    Files.copy(source.toPath(), dest.toPath());
}

There are other techniques, and if you really want to use JSch, you need to realize that JSch must be provided a lot of "extra" information to connect to the machine you are on, because it will try to connect to this machine as if it were connecting from across the network

Session sessionRead = jsch.getSession("username", "127.0.0.1", 22);
sessionRead.connect();

Session sessionWrite = jsch.getSession("username", "127.0.0.1", 22);
sessionWrite.connect();

ChannelSftp channelRead = (ChannelSftp)sessionRead.openChannel("sftp");
channelRead.connect();

ChannelSftp channelWrite = (ChannelSftp)sessionWrite.openChannel("sftp");
channelWrite.connect();

PipedInputStream pin = new PipedInputStream(2048);
PipedOutputStream pout = new PipedOutputStream(pin);

channelRead.get("/path/to/your/file/including/filename.txt", pout);
channelWrite.put(pin, "/path/to/your/file/destination/including/filename.txt");

channelRead.disconnect();
channelWrite.disconnect();

sessionRead.disconnect();
sessionWrite.disconnect();

The above code lacks error checking, exception handling, and fall back routines for if files are missing, networks are not up, etc. But you should get the main idea.

It should also be obvious that using a network protocol where no network protocol needs to exist opens the door to a lot more failure scenarios. Only use the SFTP method if your program is soon meant to copy files that are not both located on your machine.

Answer 3

A core SFTP protocol does not support duplicating remote files.

There's a draft of copy-file extension to the protocol, but that's supported by only few SFTP servers (ProFTPD/mod_sftp and Bitvise SFTP server for example).

It's definitely not supported by the most widespread OpenSSH SFTP server.

And it's also not supported by the JSch library.

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See also my answer to How can I copy/duplicate a file to another directory using SFTP?

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So actually using the cp shell command over an "exec" channel (ChannelExec) is unfortunately the best available approach (assuming you connect to a *nix server and you have a shell access).

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If you do not have a shell access, then your only option is indeed to download the file to a local temporary folder and upload it back to the new location (or use streams, to avoid a temporary file). This is what the accepted answer by @Edwin Buck shows.

Answer 4

If the original poster is actually looking for a working example of JSch in action between two distinct FTP sites, here goes:

import com.jcraft.jsch.JSch;
import com.jcraft.jsch.Session;
import com.jcraft.jsch.Channel;
import com.jcraft.jsch.ChannelSftp;
...
JSch jsch = new JSch();
JSch session = null;
try {
  session = jsch.getSession(userid, sourceservername, sourceserverport);
  session.setPassword(sourceserverpassword);
  Properties props = new Properties();
  props.put("StrictHostKeyChecking", "no");
  session.setConfig(props);
  session.connect();
  Channel channel = session.openChannel("sftp");
  channel.connect();
  ChanelSftp channelsftp = (ChannelSftp) channel;
  channelsftp.cd(sourcefilepath);
  channelsftp.lcd(localfilepath);
  FileOutputStream fos = new FileOutputStream(new File(localfilepath + "/" + localfilename));
  channelsftp.get(sourcefilename, fos);
  fos.flush();
  fos.close();
  channelsftp.disconnect()
  session.disconnect();
} catch (Exception e) {
  e.printStackTrace();
}

In practice you might break up these actions into separate try{}catch(){} blocked statements so as to introduce more granular error reporting, as well as add any informational output lines to inform the user of status, etc. But this'll get you there. Admittedly while the JSch examples are better than most such examples from freeware libraries, even good ones like this one, there can be some omissions among them around details that can make or break your attempt to get the things to work. Hope this helps if not the original poster, then someone else looking for a working JSch example. Once you have it working, it does go like a charm, so it's worth the trouble.