Question

I am using Jcraft library to connect with SSH, I have done the code successfully. but when i try to get password the null pointer exception occur. i need password for future uses
Can anybody help me how to solve it ?

public class UserAuthKI {
    public static void main(String[] arg) {

        try {
            JSch jsch = new JSch();

            String host = null;
            if (arg.length > 0) {
                host = arg[0];
            } else {
                host = JOptionPane.showInputDialog("Enter username@hostname",
                        System.getProperty("user.name") + "@localhost");
            }
            String user = host.substring(0, host.indexOf('@'));
            host = host.substring(host.indexOf('@') + 1);

            Session session = jsch.getSession(user, host, 22);

            // username and passphrase will be given via UserInfo interface.
            UserInfo ui = new MyUserInfo();
            session.setUserInfo(ui);

            session.connect();
            String newPass = session.getUserInfo().getPassword();//here I got      null value thats why Null pointer Exception occur in below
            System.out.print(newPass);
            Channel channel = session.openChannel("shell");
            InputStream is = new ByteArrayInputStream(newPass.getBytes());

            channel.setInputStream(is);

            channel.setOutputStream(System.out);

            channel.connect();

        } catch (Exception e) {
            System.out.println(e);
        }
    }

    public static class MyUserInfo implements UserInfo, UIKeyboardInteractive {
        String passwd;
        JTextField passwordField = (JTextField) new JPasswordField(20);

        final GridBagConstraints gbc = new GridBagConstraints(0, 0, 1, 1, 1, 1,
                GridBagConstraints.NORTHWEST, GridBagConstraints.NONE,
                new Insets(0, 0, 0, 0), 0, 0);
        private Container panel;

        @Override
        public String[] promptKeyboardInteractive(String destination,
                String name, String instruction, String[] prompt, boolean[] echo) {
            // TODO Auto-generated method stub
            panel = new JPanel();
            panel.setLayout(new GridBagLayout());

            gbc.weightx = 1.0;
            gbc.gridwidth = GridBagConstraints.REMAINDER;
            gbc.gridx = 0;
            panel.add(new JLabel(instruction), gbc);
            gbc.gridy++;

            gbc.gridwidth = GridBagConstraints.RELATIVE;

            JTextField[] texts = new JTextField[prompt.length];
            for (int i = 0; i < prompt.length; i++) {
                gbc.fill = GridBagConstraints.NONE;
                gbc.gridx = 0;
                gbc.weightx = 1;
                panel.add(new JLabel(prompt[i]), gbc);

                gbc.gridx = 1;
                gbc.fill = GridBagConstraints.HORIZONTAL;
                gbc.weighty = 1;
                if (echo[i]) {
                    texts[i] = new JTextField(20);
                } else {
                    texts[i] = new JPasswordField(20);
                }
                panel.add(texts[i], gbc);
                gbc.gridy++;
            }

            if (JOptionPane.showConfirmDialog(null, panel, destination + ": "
                    + name, JOptionPane.OK_CANCEL_OPTION,
                    JOptionPane.QUESTION_MESSAGE) == JOptionPane.OK_OPTION) {
                String[] response = new String[prompt.length];
                for (int i = 0; i < prompt.length; i++) {
                    response[i] = texts[i].getText();
                }
                return response;
            } else {
                return null; // cancel
            }
        }

        @Override
        public String getPassphrase() {
            // TODO Auto-generated method stub
            return null;
        }

        @Override
        public String getPassword() {
            // TODO Auto-generated method stub
                return passwd;
        }

        @Override
        public boolean promptPassphrase(String arg0) {
            // TODO Auto-generated method stub
            return false;
        }

        @Override
        public boolean promptPassword(String message) {
            // TODO Auto-generated method stub
            Object[] ob = { passwordField };
            int result = JOptionPane.showConfirmDialog(null, ob, message,
                    JOptionPane.OK_CANCEL_OPTION);
            if (result == JOptionPane.OK_OPTION) {
                passwd = passwordField.getText();
                return true;
            } else {
                return false;
            }
        }

        @Override
        public boolean promptYesNo(String str) {
            // TODO Auto-generated method stub
            Object[] options = { "yes", "no" };
            int foo = JOptionPane.showOptionDialog(null, str, "Warning",
                    JOptionPane.DEFAULT_OPTION, JOptionPane.WARNING_MESSAGE,
                    null, options, options[0]);
            return foo == 0;
        }

        @Override
        public void showMessage(String message) {
            JOptionPane.showMessageDialog(null, message);
            // TODO Auto-generated method stub

        }
    }
}

Answer 1

Yoh have use shell to get channel but you can use sftp to perform all shell command. Its working with code on window system to connect unix system.

    try
    {
        JSch jsch = new JSch();
        session = jsch.getSession(username, host, port);
        Properties config = new Properties();
        config.put("StrictHostKeyChecking", "no");
        session.setConfig(config);
        session.setPassword(password);
        session.connect();
        channel = session.openChannel("sftp");
        channel.connect();
        channelSftp = (ChannelSftp) channel;
    }
    catch (Throwable t)
    {
        System.out.println(t);            
    }