Question

I wrote a program and now I am expected to convert it to a daemon. Since I am a noob and dont know anything about it, can you please tell me how can I do it or can you please give me basic tutorials or readings about it ? I really want to learn how I can do it ?

Thank you all

Answer 1

Java class:

package example;

import java.util.Date;
import java.util.Timer;
import java.util.TimerTask;
import org.apache.commons.daemon.*;

class EchoTask extends TimerTask {
    @Override
    public void run() {
        System.out.println(new Date() + " running ...");
    }
}

public class Main implements Daemon {

    private static Timer timer = null;

    public static void main(String[] args) {
        timer = new Timer();
        timer.schedule(new EchoTask(), 0, 1000);
    }

    @Override
    public void init(DaemonContext dc) throws DaemonInitException, Exception {
        System.out.println("initializing ...");
    }

    @Override
    public void start() throws Exception {
        System.out.println("starting ...");
        main(null);
    }

    @Override
    public void stop() throws Exception {
        System.out.println("stopping ...");
        if (timer != null) {
            timer.cancel();
        }
    }

    @Override
    public void destroy() {
        System.out.println("done.");
    }

 }

Shell start/stop script:

#!/bin/sh

# Setup variables
EXEC=/usr/bin/jsvc
JAVA_HOME=/usr/lib/jvm/java-6-sun
CLASS_PATH="/usr/share/java/commons-daemon.jar":"/path/to/your.jar"
CLASS=example.Main
USER=foo
PID=/tmp/example.pid
LOG_OUT=/tmp/example.out
LOG_ERR=/tmp/example.err

do_exec()
{
    $EXEC -home "$JAVA_HOME" -cp $CLASS_PATH -user $USER -outfile $LOG_OUT -errfile $LOG_ERR -pidfile $PID $1 $CLASS
}

case "$1" in
    start)
        do_exec
            ;;
    stop)
        do_exec "-stop"
            ;;
    restart)
        if [ -f "$PID" ]; then
            do_exec "-stop"
            do_exec
        else
            echo "service not running, will do nothing"
            exit 1
        fi
            ;;
    *)
            echo "usage: daemon {start|stop|restart}" >&2
            exit 3
            ;;
esac

And the effect:

$ ./service start && sleep 5 && ./service stop
$ cat /tmp/example.out
initializing ...
starting ...
Fri Oct 07 16:26:54 EEST 2011 running ...
Fri Oct 07 16:26:55 EEST 2011 running ...
Fri Oct 07 16:26:56 EEST 2011 running ...
Fri Oct 07 16:26:57 EEST 2011 running ...
Fri Oct 07 16:26:58 EEST 2011 running ...
stopping ...
done.