How to print Error logs of linux ping command uisng java

Question

i am trying to ping remote Linux server using java, whenever i will get an acknowledgment from server i am printing "connected", but whenever the Linux server is not connected with internet, it has to show "disconnected" I have tried to print disconnected, whenever i don't get any acknowledgment from Linux server. but i couldn't able to print it.

public class JavaLinuxConnection {

    public static void main(String[] args) {

        try {
            Properties config = new Properties();
            config.put(LinuxCredentials.STRICT_HOST_KEY_CHECKING, LinuxCredentials.HOST_KEY_VALUE);
            JSch jsch = new JSch();

            // Create a JSch session to connect to the server
            Session session = jsch.getSession(LinuxCredentials.USERNAME, LinuxCredentials.HOST, LinuxCredentials.PORT);
            session.setPassword(LinuxCredentials.PASS_WORD);
            session.setConfig(config);

            // Establish the connection
            session.connect();
            System.out.println("Connected...");

            ChannelExec channel = (ChannelExec) session.openChannel(LinuxCredentials.EXEC);
            channel.setCommand(LinuxCredentials.CMD);
            channel.setErrStream(System.err);

            InputStream in = channel.getInputStream();
            channel.connect();
            BufferedReader reader = new BufferedReader(new InputStreamReader(in));
            String line;

               while ((line = reader.readLine()) != null) {   // --> I am getting error from here as "ping: sendmsg: Network is unreachable", whenever network isnt there.
                    System.out.print(new Timestamp(new Date().getTime()) + "--");

                    if(line.equalsIgnoreCase("ping: sendmsg: Network is unreachable")) {
                        System.out.println("Disconnected");
                    }else {
                        System.out.println("Connected");
                    }
                    if (channel.isClosed()) {
                        System.out.println("Exit Status: " + channel.getExitStatus());
                        break;
                    }
                    Thread.sleep(1000);
                }

            channel.disconnect();
            session.disconnect();
            System.out.println("DONE!!!");

        } catch (Exception e) {
            e.getStackTrace();
        }
    }

}

 2019-09-06 19:19:38.063--Connected
    ping: sendmsg: Network is unreachable  // Instead of this it should be printed as disconnected

score 0 · Answer 1 · answered Sep 06 '19 at 14:46

In your code you never print the content of the variable line. But you see in your console the text you're looking for after printing "Connected". The reason is here:

channel.setErrStream(System.err);

The text ping: sendmsg: Network is unreachable is actually written to stderr but you don't read it.

Look here: How to read JSch command output? for an example of how to read both streams.

How to print Error logs of linux ping command uisng java

1 Answers1