Run local/remote terminal commands with java using ssh

Sometimes you need to use some CLI-Tools before you want to create or search for a native JNI Binding.
So there is a common way, using the Java Process-Class. But then you might meet two problems i had to face in the past during several problems:

  1. There are (a really small) number of CLI-Tools, that giving no constant output over the STD-OUT (the standard output the Process-Class uses for output)
  2. There is no “elegant” way to implement a process call into your project.

To solve this Problem I created a basic HelperClass, that calls the System over SSH (with the Convenience to work remote and the side-effect to always get STD-compatible output).
I am primarely using it for a fun project SAM i started some months ago to try to create a Management-Tool for Unices and Windows with a very low client-side footprint.

The first Class is used to capsulate the basic SSH Calls:

 
// some imports... 
 public class SystemHelper {
    private Runtime r;
    private String sshPrefix = "";

    // call with $user and 127.0.0.1 to run local command.     
    public SystemHelper(String user, String ip) {
        r = Runtime.getRuntime();
        sshPrefix = " ssh -o UserKnownHostsFile=/dev/null -o StrictHostKeyChecking=no " + user + "@" + ip;
    }

    public void runCommand(String command, ProcessParser pp) {
        try {
            Logger.info("running: " + this.sshPrefix + " " + command);
            Process p = r.exec(this.sshPrefix + " " + command);
            InputStream in = p.getInputStream();
            BufferedInputStream buf = new BufferedInputStream(in);
            InputStreamReader inread = new InputStreamReader(buf);
            BufferedReader bufferedreader = new BufferedReader(inread);
            pp.parse(bufferedreader);
            try {
                if (p.waitFor() != 0) {
                    Logger.info("exit value = " + p.exitValue());
                }
            } catch (InterruptedException e) {
                System.err.println(e);
            } finally {
                // Close the InputStream                 
                bufferedreader.close();
                inread.close();
                buf.close();
                in.close();
            }
        } catch (IOException ex) {
            Logger.error(ex.getLocalizedMessage());
        }
    }
}

ProcessParser is an interface that defines the methode parse, accepting a BufferedReader for parsing the output of the Process. Unfortunately there is no timeout ATM to kill a hanging SSH-Call.

 public interface ProcessParser { 
     public void parse(BufferedReader bufferedreader); 
 } 

The most basic (Output-)Parser looks like this:

 
    public String getPublicSSHKey() {
        SimpeOutputPP so = new SimpeOutputPP();
        String command = "cat ~/.ssh/id_rsa.pub";
        runCommand(command, so);
        if (!so.getOutput().isEmpty()) {
            return so.getOutput().get(0);
        }
        return "";
    }

This returns just the public SSH-Key of the current user. I implemented some more parsers for the output of apt (dpkg), rpm and pacman. You can find them in the github project here.

3 Replies to “Run local/remote terminal commands with java using ssh”

  1. To prevent ssh to prompt for a password you can use the following command to check if a password is necessary before you run the command (and then forces the java-app to hang)

    ssh -o UserKnownHostsFile=/dev/null -o StrictHostKeyChecking=no user@host -qo PasswordAuthentication=no echo 0 || echo 1
    

    example here: https://github.com/phaus/sam/blob/master/app/helper/sam/SamHelper.java

    Then you can use a BooleanParser (i just created for that purpose) to check the output (see it here: https://github.com/phaus/sam/blob/master/app/helper/parser/BooleanPP.java ). But i have to admit, that the whole SAM Source needs some rewrite and is currently just WiP.

  2. Logger.info(“running: ” + this.sshPrefix + ” ” + command);

    info is a non static method.

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