Looking for Java Telnet emulator

Question

I am writing a back end program that telnets into a server, runs some commands and saves all the output from those commands. Something just like Expect.

I would like to use an open source solution that is well supported and runs with JDK 6.

I have found 3 options so far and would like some help deciding which one (or a better suggestion) to use.

commons-net – This is very well supported but I having trouble getting a simple “Log in and do ‘ls’” command working. I would prefer to use this library, if anyone can provide a simple example (and not the example that comes with it that takes input from the user) I would like to go that route.

If I’m unable to use commons-net the next two options are:

JExpect – This is not that hard to use, does what I need but how well supported is it? Will it work with JDK 6, I think so.

Java Telnet Application (jta26) – This was easy to use but I’m not sure how versatile it is. I didn’t see any place to set a timeout value in the TelnetWrapper. I also was not sure if this code is being maintained since the last update to the site was in 2005. (http://www.javassh.org)

I know this is somewhat opinion oriented and hope SO is a good place to help me make a decision so I don’t start down one road and find out later it’s not what I’m looking for.

Thanks.

Answer 1

Have you looked at the Sadun utils library? I used it once to open a telnet session to a server and send some commands, read a response, and close the connection, it worked fine and it's LGPL

Answer 2

Try http://www.java2s.com/Code/Java/Network-Protocol/ExampleofuseofTelnetClient.htm.

Answer 3

Try these:

• http://www.davidjarvis.ca/dave/telnet.zip
• http://www.davidjarvis.ca/dave/jexpect.zip

Wrote them around 1997 and 2000, but they should do the trick.

Answer 4

Found what I was looking for here: http://twit88.com/blog/2007/12/22/java-writing-an-automated-telnet-client/

You will need to modify the prompt variable.

Copy of code:

import org.apache.commons.net.telnet.TelnetClient;

import java.io.InputStream;
import java.io.PrintStream;

public class AutomatedTelnetClient {
    private TelnetClient telnet = new TelnetClient();
    private InputStream in;
    private PrintStream out;
    private String prompt = "%";

    public AutomatedTelnetClient(String server, String user, String password) {
     try {
      // Connect to the specified server
      telnet.connect(server, 23);

      // Get input and output stream references
      in = telnet.getInputStream();
      out = new PrintStream(telnet.getOutputStream());

      // Log the user on
      readUntil("login: ");
      write(user);
      readUntil("Password: ");
      write(password);

      // Advance to a prompt
      readUntil(prompt + " ");
     } catch (Exception e) {
      e.printStackTrace();
     }
    }

    public void su(String password) {
     try {
      write("su");
      readUntil("Password: ");
      write(password);
      prompt = "#";
      readUntil(prompt + " ");
     } catch (Exception e) {
      e.printStackTrace();
     }
    }

    public String readUntil(String pattern) {
     try {
      char lastChar = pattern.charAt(pattern.length() - 1);
      StringBuffer sb = new StringBuffer();
      boolean found = false;
      char ch = (char) in.read();
      while (true) {
       System.out.print(ch);
       sb.append(ch);
       if (ch == lastChar) {
        if (sb.toString().endsWith(pattern)) {
         return sb.toString();
        }
       }
       ch = (char) in.read();
      }
     } catch (Exception e) {
      e.printStackTrace();
     }
     return null;
    }

    public void write(String value) {
     try {
      out.println(value);
      out.flush();
      System.out.println(value);
     } catch (Exception e) {
      e.printStackTrace();
     }
    }

    public String sendCommand(String command) {
     try {
      write(command);
      return readUntil(prompt + " ");
     } catch (Exception e) {
      e.printStackTrace();
     }
     return null;
    }

    public void disconnect() {
     try {
      telnet.disconnect();
     } catch (Exception e) {
      e.printStackTrace();
     }
    }

    public static void main(String[] args) {
     try {
      AutomatedTelnetClient telnet = new AutomatedTelnetClient(
        "myserver", "userId", "Password");
      System.out.println("Got Connection...");
      telnet.sendCommand("ps -ef ");
      System.out.println("run command");
      telnet.sendCommand("ls ");
      System.out.println("run command 2");
      telnet.disconnect();
      System.out.println("DONE");
     } catch (Exception e) {
      e.printStackTrace();
     }
    }
}