Launching telnet using java program fails with Win 7 OS

[Sham Phadtale]

I have sample program which launches telnet on Windows XP OS.

import java.io.IOException;

public class TestTelnet {
    public static void main(String[] args) {
        try {
            Runtime.getRuntime().exec(
                    "cmd.exe /c start " + "telnet");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

In Win 07 we need to manually turned on telnet option. I did it. I able to launch telnet from cmd but above java program fail to launch telnet on Win 7.

What I need to do to launch telnet using Java on Win 7?

[Brian Burress]

Is there an exception / stack trace that can be shared?

[William Brogden]

Where are you consuming std out and std err and providing std in streams? Read the javadocs for java.lang.Process

Bill

[Campbell Ritchie]

. . . and the classic article which you can find by Googling for Michael Daconta when Runtime.exec() won't.

[Sham Phadtale]

Thanks all for your quick replies.
I read the classic article. I updated the code as given in article as -

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;

class StreamGobbler extends Thread {
    InputStream is;

    String type;

    StreamGobbler(InputStream is, String type) {
        this.is = is;
        this.type = type;
    }

    public void run() {
        try {
            InputStreamReader isr = new InputStreamReader(is);
            BufferedReader br = new BufferedReader(isr);
            String line = null;
            while ((line = br.readLine()) != null)
                System.out.println(type + ">" + line);
        } catch (IOException ioe) {
            ioe.printStackTrace();
        }
    }
}

public class TestTelnet {
    public static void main(String args[]) {
        try {
            String osName = System.getProperty("os.name");
            String[] cmd = new String[3];
            cmd[0] = "cmd.exe";
            cmd[1] = "/C";
            cmd[2] = "telnet";
            Runtime rt = Runtime.getRuntime();
            System.out.println("Execing " + cmd[0] + " " + cmd[1] + " "
                    + cmd[2]);
            Process proc = rt.exec(cmd);
            StreamGobbler errorGobbler = new StreamGobbler(
                    proc.getErrorStream(), "ERROR");
            StreamGobbler outputGobbler = new StreamGobbler(
                    proc.getInputStream(), "OUTPUT");
            errorGobbler.start();
            outputGobbler.start();
            int exitVal = proc.waitFor();
            System.out.println("ExitValue: " + exitVal);
        } catch (Throwable t) {
            t.printStackTrace();
        }
    }
}

I am getting following out put

Execing cmd.exe /C telnet
ERROR>'telnet' is not recognized as an internal or external command,
ERROR>operable program or batch file.
ExitValue: 1

I can run telnet by opening Start--->cmd---->telnet but not through java program.
What I need to do to run telnet from Java program?

[John Jai]

You might consider using the Apache Commons Net package. It lists Telnet in the supported protocol. This examples guide can help you start.

Note that while executing telnet you fork a sub-process from the cmd.exe. Try giving the dir command in your code and check if it works first with the cmd.

[Sham Phadtale]

dir works from my Java program, it opens command prompt and shows directories.

I will check Apache Commons Net package.

[Rob Spoor]

Are you using a 32-bit JVM?

I've tried it on my system as well without Java. I opened CMD from the start menu which will then open a 64-bit CMD window. Telnet works in it. I then opened CMD from Total Commander. Since Total Commander is 32-bit, it launches a 32-bit CMD. Telnet does not work in that. Apparently, on a 64-bit Windows 7 system, telnet only works when launched from a 64-bit application.

[Sham Phadtale]

Telnet works with CMD but does not work when launch from java program.

[John Jai]

I guess Rob tells that telnet does not launch from a 32-bit JVM and only on a 64-bit JVM (in case of Win7 i believe). What is the bit version of the JVM that executes your java program and that invokes the cmd.exe?

Which one listed here is that you have - x86 or x64?

[Sham Phadtale]

OK.. My JVM is 32 bit. I will try by installing 64 bit JVM and check the result.