SSH using Java

Overview

This article will demonstrate how using the SSH classes in SSH Factory or Secure iNet Factory components you can develop a console based interactive SSH shell.

To see what else these components have to offer please download a FREE 30 day evaluation here: SSH Factory Evaluation and Secure iNet Factory Evaluation.

Prerequisites

• An SSH server
• JDK 1.4 or above
• SSH Factory or Secure iNet Factory 

Using Ssh Class to Connect to an SSH Server

The Ssh class provides an easy to use programming interface for communicating with SSH (Secure SHell) servers. This tutorial focuses on using the class by itself to communicate with an SSH server like a regular interactive SSH client. To see it used as an underlying object for SSH scripting see Scripting SSH sessions using Java and JSCAPE Components

Please note that the Ssh Class is present in both SSH Factory and Secure iNet Factory.

There are two ways to define a class that make use of the Ssh class. If you want to listen to events fired by the SSH instance you could have your class implement the SshListener interface or extend the SshAdapater class, which already implements SshListener and provide a default implementation.

//import the necessary interface/class
import com.jscape.inet.ssh.SshListener;

public class SshTutorial implements SshListener {
   …
}

Or if not interested on listening to SSH events then a plain Java class will do.

public class SshTutorial {
   …
}

Below is a code snippet that uses Ssh class to connect an SSH server. Once a connection with an SSH server is established the user will then be able to issue interactive commands within the session.

//import the necessary classes
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.OutputStream;

import com.jscape.inet.ssh.Ssh;
import com.jscape.inet.ssh.util.SshParameters;

…

   // state of SSH connection
   private boolean connected = false;

   public void connectSsh(String hostname, String username, String password) {
      Ssh ssh = null;

      try {
         // create/initialize new Ssh instance
         SshParameters params = new SshParameters(hostname, username, password);
         ssh = new Ssh(params);

         // register to capture events if applicable (if your class extends
         // SshAdapter or implements SshListener)
         ssh.addSshListener(this);

         System.out.println("Connecting please wait...");

         // connect
         ssh.connect();

         // get output stream for writing data to SSH server
         OutputStream out = ssh.getOutputStream();

         // holds line entered at console
         String line = null;

         // read session commands from user via standard input
         BufferedReader bin =
            new BufferedReader(new InputStreamReader(System.in));

         // read data from console
         while (connected && (line = bin.readLine()) != null) {
            // send line with LF to SSH server
            line += "\n";
            try {
               out.write(line.getBytes());
               out.flush();
            } catch(Exception ioe) {
               // set this flag to false to exit this loop when exception occurs
               connected = false;
            }       
         }                    
      } catch (Exception e) {
         e.printStackTrace();                   
      } finally {
         try {
            if(connected) {
               ssh.disconnect();     
            }
         } catch(Exception e) {

         }                    
      }
   }
…

Download the complete Java code for this tutorial here: SshTutorial.java

Summary

There are maybe few rare cases that an application will require an interactive SSH client. The power of the Ssh class lies in its ability to be used in a non-interactive (batch mode) and automate commands issued on an SSH server.

References

Ssh Class Overview
Ssh Class Javadoc
Secure Shell