BigMac66 BigMac66 - 2 years ago 267
Java Question

Sending telnet commands and reading the response with Java

I work for a large organization that supports many different sites on a nation wide network. Our vendor supplies diagnostic tools for the hardware we use at each site. The diagnostics and reports are accessed via Telnet.

The problem is we want to monitor all sites simultaneously and currently we can only check them one at a time (via telnet).

I have already built something that will use

to send ping commands to each IP address. But now I want to be able to send specific commands automatically using the vendor's diagnostic and reporting tools. Any ideas on the best way to do this? NOTE we have a hybrid system - some of the sites are behind a firewall some are not. A complete solution would be ideal but I will settle for a partial one as well.

Could it be as simple as getting the input and output streams of the Process object returned by the
and send my commands to the input and reading the response on the output? Or should I be connecting to port 23 (the usual telnet port) and then behave as any other client-server system. Or something else completely different?

I am continuing to try things out, just brainstorming at this point...

CODE: (sensitive information removed)

void exec(String ip)
Socket sock = null;
BufferedReader br = null;
PrintWriter pw = null;

sock = new Socket(ip, 23);

br = new BufferedReader(new InputStreamReader(sock.getInputStream()));
pw = new PrintWriter(sock.getOutputStream());;
System.out.println("Sending username");
pw.println("username");; // Always blocks here
System.out.println("Sending password");

catch(IOException e)

void read(BufferedReader br) throws IOException
char[] ca = new char[1024];
int rc =;
String s = new String(ca).trim();

Arrays.fill(ca, (char)0);

System.out.println("RC=" + rc + ":" + s);

//String s = br.readLine();
//while(s != null)
// if(s.equalsIgnoreCase("username:"))
// break;
// s = br.readLine();
// System.out.println(s);

Answer Source

Why don't you simply use the Socket system ?

Open a socket to the chosen server on port 23 and send your own commands from here.

Here is a quick example :

public class EchoClient {
    public static void main(String[] args) throws IOException {

        Socket pingSocket = null;
        PrintWriter out = null;
        BufferedReader in = null;

        try {
            pingSocket = new Socket("servername", 23);
            out = new PrintWriter(pingSocket.getOutputStream(), true);
            in = new BufferedReader(new InputStreamReader(pingSocket.getInputStream()));
        } catch (IOException e) {


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