在以root用户身份连接后执行su <user>时，它会在JSCH中挂起

Question

我正在尝试按特定顺序执行命令。

（1）连接到远程节点  ssh -i path-to-key root @ some-remote-node

（2）su user

使用JSCH做同样的事情时，我能够连接到远程节点。但是在执行下一个命令时，它会挂起。但是当我从终端做的时候，情况并没有发生。

代码，

private void execute(String command, Session session, long sleepTime,
            boolean isCloseSession) throws JSchException, IOException {

        System.out.println("Command \"" + command + "\" executed on HOST : "
                + session.getHost());

        Channel channel = session.openChannel("exec");
        ((ChannelExec) channel).setCommand(command.trim());
        String str = null;

        channel.setInputStream(null);
        ((ChannelExec) channel).setErrStream(System.err);
        InputStream in = channel.getInputStream();
        channel.connect();
        StringBuilder sb = new StringBuilder();
        byte[] tmp = new byte[1024];
        while (true) {
            while (in.available() > 0) {
                int i = in.read(tmp, 0, 1024);
                if (i <= 0) {
                    break;
                }
                try {
                    Thread.sleep(sleepTime);
                    str = new String(tmp, 0, i);
                    sb.append(str);
                    channel.disconnect();
                    if (isCloseSession) {
                        closeSession();
                    }

                } catch (Exception e) {
                    System.out.println(e.getClass()
                            + " occured while calling execute(" + command
                            + ", Session, " + sleepTime + ")");
                }
            }

            exitCode = channel.getExitStatus();
            if (channel.isClosed()) {
                break;
            }
        }
        response = sb.toString();
        if (isCloseSession) {
            closeSession();
        }
    }

 public void executeCommand(String command, boolean isCloseSession) {
    executeCommand(command, 0, isCloseSession);
 }

 public void executeCommand(String command, long sleepTime,
        boolean isCloseSession) {

    try {
        session = createSession(basicInfo);
        if (session != null) {
            if(!session.isConnected()) {
               session.connect();
            }
            execute(command, session, sleepTime);
        } else {
            System.out.println("Session is NULL!");
        }
    } catch (JSchException ex) {
        System.out.println("Connection to HOST \"" + basicInfo.getHostName() + "\" failed"
                + ex.getStackTrace());
    } catch (IOException ex) {
        System.out.println("Unable to execute the command \"" + command
                + "\" on the HOST \"" + this.basicInfo.getHostName()
                + "\" : " + ex.getStackTrace());
    }
}

 public static void main(String[] args) {
    SSHUtil util = new SSHUtil(hostName, userName, keyFile);
    util.executeCommand("ls", false); // For this I'm getting response
    System.out.println(util.getResponse());
    util.executeCommand("su hdfs", false); // For this, its going into while(true) {} and breaking no where.
    System.out.println(util.getResponse());
}