QueueModel.java

import java.util.*;

public class QueueModel {

    public static void main(String[] args) {
        Queue<Message> queue = new LinkedList<>();
        QueueMessageProducer producer = new QueueMessageProducer(queue);

        List<QueueConsumer> consumers = new ArrayList<>();

        for (int i = 0; i < 10; i++ ) {
            QueueConsumer consumer = new QueueConsumer(
                    "Consumer"  + i,
                    new Random().nextBoolean() ? "group1" : "group2",
                    queue
            );
            consumer.start();

            consumers.add(consumer);
        }

        Scanner scanner = new Scanner(System.in);

        while(true) {
            String msgString = scanner.nextLine();
            String msgGroup = scanner.nextLine();
            Message message = new Message(
                    msgString,
                    msgGroup
            );

            producer.notify(message);
        }
    }

    static class QueueMessageProducer {

        private Queue<Message> queue;

        public QueueMessageProducer(Queue<Message> queue) {
            this.queue = queue;
        }

        public void notify(Message message) {
            synchronized (queue) {
                queue.add(message);
                queue.notify();
            }
        }

    }

    static class QueueConsumer extends Thread {

        private Queue<Message> queue;
        private String group;

        public QueueConsumer(String name, String group, Queue<Message> queue) {
            super(name);
            this.group = group;
            this.queue = queue;
        }

        @Override
        public void run() {
            try {
                while (true) {
                    synchronized (queue) {
                        queue.wait();
                    }

                    synchronized (queue) {
                        if (!queue.isEmpty()) {
                            Message message = queue.poll();

                            if (group.equals(message.getConsumerGroup())) {
                                System.out.printf(
                                        "%s: %s: Consuming message: %s%n", group, getName(), message
                                );
                            } else {
                                System.out.printf(
                                        "%s: %s: Skipping message, wrong group, message: %s%n", group, getName(), message
                                );

                                queue.add(message);
                                queue.notify();
                            }
                        }
                    }
                }
            } catch (Exception e) {
                System.out.printf(
                        "Exception occured: %s%n", e.toString()
                );
            }
        }

    }

    static class Message {

        private final String message;
        private final String consumerGroup;

        public Message(String message, String consumerGroup) {
            this.message = message;
            this.consumerGroup = consumerGroup;
        }

        public String getMessage() {
            return message;
        }

        public String getConsumerGroup() {
            return consumerGroup;
        }

        @Override
        public boolean equals(Object o) {
            if (this == o) return true;
            if (o == null || getClass() != o.getClass()) return false;
            Message message1 = (Message) o;
            return Objects.equals(message, message1.message) &&
                    Objects.equals(consumerGroup, message1.consumerGroup);
        }

        @Override
        public int hashCode() {
            return Objects.hash(message, consumerGroup);
        }

        @Override
        public String toString() {
            final StringBuilder sb = new StringBuilder("Message{");
            sb.append("message='").append(message).append('\'');
            sb.append(", consumerGroup='").append(consumerGroup).append('\'');
            sb.append('}');
            return sb.toString();
        }
    }
}