when ssh with a low-privileged user, how to switch user with "su root" and execute command?

[1780spark]

hi !
I want to use ExpectIt to achieve the following functions:
When using ssh remote linux service, log in with a low-privileged user, and then switch to a high-privileged user to execute related commands.

But the following code does not return relevant results:
JSch jSch = new JSch();
Session session = jSch.getSession("u1", "h1");
Properties config = new Properties();
config.put("StrictHostKeyChecking", "no");
session.setConfig(config);
session.setPassword("u1pdw");
session.connect();
Channel channel = session.openChannel("shell");
channel.connect();

    Expect expect = new ExpectBuilder()
            .withOutput(channel.getOutputStream())
            .withInputs(channel.getInputStream(), channel.getExtInputStream())
            .build();
    try {
        expect.expect(contains("$"));
        System.out.println("login in with u1 and execute pwd command..");
        expect.sendLine("pwd");
        System.out.println(
                "pwd1:" + expect.expect(times(2, contains("\n")))
                        .getResults()
                        .get(1)
                        .getBefore());
        System.out.println("su to root.");
        expect.sendLine("su - root");
        System.out.println("su root:" + expect.expect(contains("(.+:)|(.+：)")).group(1));
        System.out.println("send password：");
        expect.sendLine("rootpwd");
        System.out.println(expect.expect(times(2, contains("#"))).getResults().get(1).getBefore());
        System.out.println("execute pwd wtih root...");
        expect.sendLine("pwd");
        // a regexp which captures the output of pwd
        System.out.println("pwd2:" + expect.expect(regexp("(?m)\\n([^\\n]*)\\n")).group(1));
        System.out.println("ls...");
        expect.expect(contains("$"));
        expect.sendLine("ls -l");
        // skipping the echo command
        expect.expect(times(2, contains("\n")));
        // getting the output of ls
        System.out.println("list ===== "+expect.expect(regexp(".*\\$")).getBefore().trim());
        expect.sendLine("exit");
    } finally {
        expect.close();
        channel.disconnect();
        session.disconnect();
    }