Send an SFTP command by using runtime.exec

Question

I would like to download a file from an sftp server by using the class Runtime of Java. I can't use a library like Jsch or SSHJ because i need to use the -B option to increase the buffer size. I've tried with this code so far:

public void download(String source, String destination,String port, String user, String host ){
    Runtime runtime = Runtime.getRuntime();
    String cmd = "sftp -oPort=" + port + " -B 150000 "+ user + "@" + host + ":" + source + " " + destination;

    String[] args = { "/bin/sh", "-c", cmd };
    try {
        long startTime = System.currentTimeMillis();
        log.info("cmd: "+ cmd);
        final Process process = runtime.exec(args);
        process.waitFor();
        long stopTime = System.currentTimeMillis();
        long elapsedTime = stopTime - startTime;
        System.out.println("Time: "+elapsedTime);

        BufferedReader bre = new BufferedReader(new InputStreamReader(process.getErrorStream()));
        StringBuffer sbe = new StringBuffer();
        String lineError;
        while ((lineError = bre.readLine()) != null) {   
          sbe.append(lineError).append("\n");
        }   
        String answerError = sbe.toString();
        if(answerError.length()>0)log.error("Error:"+answerError);
    } catch (IOException e) {
        e.printStackTrace();
    } catch (InterruptedException e) {
        e.printStackTrace();
    }
}

I get the error message : Connecting to xxxxxxx... with the name of the host instead of the "xxxxxx"

I've tried the command directly in putty and it works great but when i use it in java it doesn't work at all. I've also tried an scp command with runtime.exec() for downloading instead of an sftp and that work.

Does someone have a clue why it's not working? I can't find an exemple with this method. Or does someone know a library for sftp transfer that allows to set the -B option? i've maybe missed a method in Jsch and Sshj.

Thanks in advance

Answer 1

I do this using psftp on windows. I expect your results using sftp on *nix should be the same.

 static java.io.File downloadFileViaSftp(String file) {
    String string = null;

    try {
        String c = "psftp -l user -P 22 -v -pw password hostname";
        Process p = Runtime.getRuntime().exec(c);

        OutputStream out = p.getOutputStream();

        Writer out2 = new BufferedWriter(new OutputStreamWriter(out));

        out2.write("get " + file + "\n");
        out2.flush();
        out2.write("close\n");
        out2.flush();
        out2.write("quit\n");
        out2.flush();
        out2.close();

        InputStream in = p.getInputStream();
        InputStream err = p.getErrorStream();

        BufferedReader bufferedreader1 = new BufferedReader(new InputStreamReader(in), 999999);
        BufferedReader bufferedreader2 = new BufferedReader(new InputStreamReader(err), 999999);

        while ((string = bufferedreader2.readLine()) != null) {
            System.out.println("2=" + string);
            System.out.flush();
        }
        bufferedreader2.close();

        while ((string = bufferedreader1.readLine()) != null) {
            System.out.println("1=" + string);
            System.out.flush();
        }
        bufferedreader1.close();

        int x = p.waitFor();
        p.destroy();

    } catch (Exception e) {
        e.printStackTrace();
        return null;
    }

    return new java.io.File(file);

}