Question

Is it possible to do file/directory sync in Java using JSch ? I need to sync directory from a remote linux machine to my local windows machine. Is this possible ?

-Tivakar

Answer 1

The easiest way to download files from SCP server is using Commons VFS along with JSch:

import java.io.*;
import org.apache.commons.io.FileUtils;
import org.apache.commons.vfs2.*;

public class CopyRemoteFile {
    public static void copyRemoteFiles(String host, String user, String remotePath, String localPath) throws IOException {
        FileSystemOptions fsOptions = new FileSystemOptions();
        SftpFileSystemConfigBuilder.getInstance().setStrictHostKeyChecking(fsOptions, "no");
        SftpFileSystemConfigBuilder.getInstance().setIdentities(fsOptions,
                new File[] { new File(FileUtils.getUserDirectoryPath() + "/.ssh/id_dsa") });
        DefaultFileSystemManager fsManager = (DefaultFileSystemManager) VFS.getManager();
        String uri = "sftp://" + user + "@" + host + "/" + remotePath;

        FileObject fo = fsManager.resolveFile(uri, fsOptions);

        FileObject[] files = fo.getChildren();
        for (FileObject file : files) {
                    // We will be dealing with the files here only
            if (file.getType() == FileType.FILE) {
                FileUtils.copyInputStreamToFile(file.getContent().getInputStream(),
                        new File(localPath + "/" + file.getName().getBaseName()));
            }
            file.close();
        }

        fo.close();

        fsManager.close();
    }
}

It’s just an example I got in my Wiki, so nothing fancy. But do keep in mind that if you’ll close fsManager, you will not be able to open it again in the same VM. I got this issue while testing this solution…

Although the example above does not import any JSch classes, you need to put it in the classpath anyway.

The above example is using private key to authenticate with the remote host. You can easily change that by providing password and modifying the uri to include that.

If you need to sync files, you can compare dates of the files on the local file system (or DB, or any other source of the information) and the remote files:

import java.io.*;
import org.apache.commons.io.*;
import org.apache.commons.vfs2.*;
import org.apache.commons.vfs2.impl.*;
import org.apache.commons.vfs2.provider.sftp.*;

public class CopyRemoteFile {
    public static void copyRemoteFiles(final String host, final String user, final String remotePath, final String localPath)
            throws IOException {
        FileSystemOptions fsOptions = new FileSystemOptions();
        SftpFileSystemConfigBuilder.getInstance().setStrictHostKeyChecking(fsOptions, "no");
        SftpFileSystemConfigBuilder.getInstance().setIdentities(fsOptions,
                new File[] { new File(FileUtils.getUserDirectoryPath() + "/.ssh/id_dsa") });
        DefaultFileSystemManager fsManager = (DefaultFileSystemManager) VFS.getManager();
        String uri = "sftp://" + user + "@" + host + "/" + remotePath;

        FileObject fo = fsManager.resolveFile(uri, fsOptions);

        FileObject[] files = fo.getChildren();
        for (FileObject file : files) {
            // We will be dealing with the files here only
            File newFile = new File(localPath + "/" + file.getName().getBaseName());
            if (file.getType() == FileType.FILE && newFile.lastModified() != file.getContent().getLastModifiedTime()) {
                FileUtils.copyInputStreamToFile(file.getContent().getInputStream(), newFile);
                newFile.setLastModified(file.getContent().getLastModifiedTime());
            } 
            file.close();
        }

        fo.close();

        fsManager.close();
    }
}