Stream the output from SSHJ or JScH

Question

I went through the Java APIs like SSHJ and JScH for executing commands over a remote machine. I explored Java Expect API's like ExpectIt and Expect4j . But I could not find a way to stream the output line by line from the machine to my java process. Let say I am doing a grep on a huge file in my remote machine and I want to stream the huge output, line by line , to my process instead of waiting for the whole command to complete. Is it possible ? if so , how to do it ?

Answer 1

I hope we can do this once you set the output stream to a file. In the below code my output stream is directed to "outs.txt" file in your system. While it is filling you can create a new thread start processing the contents of file. Below snippet shows how to set output stream can be set. After this code snippet you have to start a thread in order to process the output from "outs.txt" file. Happy Coding!!!

                    ss=new StringBuilder("grep aa.txt");
                    ss.append("\n");
                    FileWriter fw = new FileWriter("comm.txt");
                    BufferedWriter bw = new BufferedWriter(fw);
                    bw.write(ss.toString());
                    bw.flush();
                    fw.close();
                    bw.close();
                    InputStream is=new FileInputStream("comm.txt");
                    OutputStream os=new FileOutputStream("outs.txt");   
                    channel.setInputStream(is);
                    channel.setOutputStream(os);
                    Thread.sleep(1000);
                    channel.connect();

Answer 2

For opening and reading an input stream from a remote host with SSHJ and a String filename :

try (final RemoteFile handle = sftp.open(filename, EnumSet.of(OpenMode.READ));
    final InputStream in = handle.new RemoteFileInputStream();
    final InputStreamReader isr = new InputStreamReader(in);
    final BufferedReader reader = new BufferedReader(isr)) {
    // Do stuff, for example:
    String line;
    while ((line = reader.readLine()) != null) {
        // more stuff
    }
} catch (IOException e) {
    logger.error("Couldn't open SFTP input stream for file: {}", filename, e);
}

If you're looking to stream the output of a command, it's largely identical.

try (Session session = sshClient.startSession();
    final Command command = session.exec("grep temp.txt");
    final InputStreamReader isr = new InputStreamReader(command.getInputStream());
    final BufferedReader reader = new BufferedReader(isr)) {
    // Do stuff, for example:
    String line;
    while ((line = reader.readLine()) != null) {
        // more stuff
    }
} catch (IOException e) {
    logger.error("Couldn't open SFTP input stream for file: {}", filename, e);
}

This should work for Java 8 and any recent version of SSHJ (currently, 0.32.0).