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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 Runtime.exec(String) 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 Runtime.exec(String) 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());
    this.read(br);
    System.out.println("Sending username");
    pw.println("username");
    this.read(br);  // Always blocks here
    System.out.println("Sending password");
    pw.println("password");
    this.read(br);
    pw.close();
    br.close();
    sock.close();
  catch(IOException e)
    e.printStackTrace();
void read(BufferedReader br) throws IOException
  char[] ca = new char[1024];
  int rc = br.read(ca);
  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);
        try {
            pingSocket = new Socket("servername", 23);
            out = new PrintWriter(pingSocket.getOutputStream(), true);
            in = new BufferedReader(new InputStreamReader(pingSocket.getInputStream()));
        } catch (IOException e) {
            return;
        out.println("ping");
        System.out.println(in.readLine());
        out.close();
        in.close();
        pingSocket.close();
                Tried but readLine() locks up.  I put the readLine() inside a loop to read all the received lines but it locks up almost immediately.  What I see is:
– BigMac66
                Sep 21, 2010 at 20:14
                Damn return key! What I see is Vendor's name\n blank line \n username:\n  And it freezes at that point.  I know that readLine() blocks so I suspect it is waiting for an EOF to unblock but never gets one so I can never send my username etc.  This is precisely the low level of detail I want to avoid.  Sure I could look for username: and simply not read the next line but I want to avoid writing my own telnet app :)
– BigMac66
                Sep 21, 2010 at 20:18
                One way or another you'll have to wait for the username to be asked before sending the username, so basically you'll still need to write your own "telnet app". But for your current problem you should use two threads, one for reading, and another one for sending answers at the right time.
– Colin Hebert
                Sep 21, 2010 at 20:36
                I tried different variations of read - all lock up right after I send the username.  The very next read blocks - I don't even get the password: prompt.
– BigMac66
                Sep 21, 2010 at 20:47
                Ha, found it. You forgot to flush data. Try new PrintWriter(sock.getOutputStream(), true) to enable autoflush, or you can call flush() manually after each println()
– Colin Hebert
                Sep 21, 2010 at 21:13
The problem with doing it down at the socket level is that you suddenly need to be a protocol expert, when all you want to do is a few telnet commands.
I wrote a driver on top of de.mud.jta, but it leaves threads open, and I don't know where, and how to fix those.  Seems to me that there must be something better out there than coding at the protocol level or this old JTA stuff.
telnet is almost bare tcp. you can probably make a socket connection, write commands, read responses.
well - telnet does have some control commands that can be mixed with data stream. you can probably program to ignore them. or, to be perfectly protocol aware, use a java telnet client package.
Try Checking Netty Java Library. they have a good set of Telnet , SSH and other very useful network library
https://netty.io