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From Merlin Beedell <MBeed...@cryoserver.com>
Subject RE: Getting console input with a timeout
Date Thu, 03 Sep 2015 09:11:28 GMT
Sorry for the long delay in replying.  I can confirm that the console Input with Timeout works
– excellent!  I now understand that the O/S buffers the keypresses, and only presents them
to the console input stream when the ‘Enter’ key is pressed – and thus no feedback is
provided when using this code until the enter key is pressed.

For the sort of requirements that I have (simple y/n answers – with a default option), this
may not be an issue.

But to take this to the next level, to be able to capture keypresses as they occur would be
even better.  I think this requires an understanding of CURSES – for which the ‘charva’
and similar efforts are available.  Just need to figure how they could be sensibly used with
groovy scripts.

Merlin Beedell

From: Paco Zarate [mailto:contacto@nazcasistemas.com]
Sent: 28 May 2015 05:54
To: users <users@groovy.incubator.apache.org>
Subject: Re: Getting console input with a timeout

Hello Merlin!
You should be able to compile the java classes that are shown in the example (http://www.javaspecialists.eu/archive/Issue153.html
f) and then use the generated jars in the groovy scripts (including the jars in the classpath).
Also you can use this code directly in groovy, i tried it with groovy 2.3.9 JVM 1.8.40.

This app is waits for the user to provide an input (characters + enter) for 10 seconds, it
the timeout is reached, it cancels the input:
File: readingConsoleWithTimeout.groovy
//-- Code starts here --//
import java.io.*;
import java.util.concurrent.*;

public class ConsoleInputReadTask implements Callable<String> {
  public String call() throws IOException {
    BufferedReader br = new BufferedReader(
        new InputStreamReader(System.in));
    System.out.println("ConsoleInputReadTask run() called.");
    String input;
    // replacing do .. while
    while (true) {
      System.out.println("Please type something: ");
      try {
        // wait until we have data to complete a readLine()
        while (!br.ready()) {
          Thread.sleep(200);
        }
        input = br.readLine();
      } catch (InterruptedException e) {
        System.out.println("ConsoleInputReadTask() cancelled");
        return null;
      }
      if (!("".equals(input))) break;
    }
    System.out.println("Thank You for providing input!");
    return input;
  }
}

public class ConsoleInput {
  private final int tries;
  private final int timeout;
  private final TimeUnit unit;

  public ConsoleInput(int tries, int timeout, TimeUnit unit) {
    this.tries = tries;
    this.timeout = timeout;
    this.unit = unit;
  }

  public String readLine() throws InterruptedException {
    ExecutorService ex = Executors.newSingleThreadExecutor();
    String input = null;
    try {
      // start working
      for (int i = 0; i < tries; i++) {
        System.out.println(String.valueOf(i + 1) + ". loop");
        Future<String> result = ex.submit(
            new ConsoleInputReadTask());
        try {
          input = result.get(timeout, unit);
          break;
        } catch (ExecutionException e) {
          e.getCause().printStackTrace();
        } catch (TimeoutException e) {
          System.out.println("Cancelling reading task");
          result.cancel(true);
          System.out.println("\nThread cancelled. input is null");
        }
      }
    } finally {
      ex.shutdownNow();
    }
    return input;
  }
}

ConsoleInput con = new ConsoleInput(
        1,
        10,
        TimeUnit.SECONDS
    );

    String input = con.readLine();
    System.out.println("Done. Your input was: " + input);
//-- Code ends here --//


On Mon, Apr 27, 2015 at 3:57 AM, Merlin Beedell <MBeedell@cryoserver.com<mailto:MBeedell@cryoserver.com>>
wrote:
I am trying to get Console Input when running simple scripts that stop with questions for
user input – but that a default response would be used after a short timeout.  Thus a script
could be run manually or run automatically.
  I found a handy example here http://www.javaspecialists.eu/archive/Issue153.html from Dr.
Heinz M. Kabutz.
However, I find that the keypresses are not echoed back to the user until the Enter key is
pressed.  This is a bit of a problem. It does this for both System.Console or System.in. 
I thought that adding thread “yield” calls might help, but they do not.  I don’t know
if this is a problem only when run under Groovy.

Anyway, I have tried to groovy-ize the Java version below. But I wonder if the System.in MetaClass
could be extended to provide the timeout functionality, rather than wrapping things on top
– and would that help?  Or perhaps to find a way to inject keypresses into the System.in
from a separate thread, to pop the Enter keypress after the timeout?


import java.util.concurrent.*;



    ConsoleInput con = new ConsoleInput();

    String input = con.readLine("What is your name? ", "Fred", 15);

    //def input = con.br.readLine() //this does echo keystrokes

    println("Done. Your input was: " + input);

    input = con.readLine("What is your age? ", "50", 5);

    println("Done. Your input was: " + input);



public class ConsoleInput {

  private final TimeUnit unit = TimeUnit.SECONDS;

       //Console cons = System.console()



  BufferedReader br = new BufferedReader(System.console().reader());

  //This is groovies weird syntax for implementing an interface.  Each map entry is a closure
implementing a method of that name.

  // it supports the usual class implementation syntax as well, of course.

  def myReader =  [

   call: {

      String input;

      try {

        // wait until we have data to complete a readLine()

        while (!br.ready()) {

          Thread.yield();

          Thread.sleep(200);

          Thread.yield();

        }

        input = br.readLine();

      } catch (InterruptedException e) {

        return null;

      }

      return input;

    }

  ] as Callable



  public String readLine(String sPrompt, String sDefault, int timeout) throws InterruptedException
{

    print "$sPrompt [$sDefault]: "

    ExecutorService ex = Executors.newSingleThreadExecutor();

    String input = null;

    //note: groovy does not support the do/while loop syntax.  Strange!

    try {

        Future<String> result = ex.submit(

            myReader);

        try {

          input = result.get(timeout, unit);

        } catch (ExecutionException e) {

          e.getCause().printStackTrace();

        } catch (TimeoutException e) {

          result.cancel(true);

          println ""  //user input always has a newline - so we must add one after timeout
case

        }

    } finally {

      ex.shutdownNow();

    }

    return input?:sDefault;

  }

}

Merlin Beedell


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