In Java: Write a program that is a publisher/subscriber program. There should be

Question

In Java: Write a program that is a publisher/subscriber program. There should be at least one student class with one student with info (generic email and phone number for text and email class), email class, text class which calls to the students info and the message (type of disaster), and a disaster class with different disasters that can happen(such as active shooter, earthquake, flood warning). Program can be completed using whatever methods make most sense but should be modifiable and not too complicated. The program actually does not have to send out emails or texts, just the classes have to store the information and call to the student or disaster class (whichever makes more sense). For example: if a certain disaster is chosen, then the program will call to the students info and send a message (something like :email/text John Doe "Flood Warning".) on the println. If it doesn't make sense to have different classes for text and email, then that is sufficient.

Explanation / Answer

import javax.jms.*; /** * The SynchTopicExample class demonstrates the simplest form of the * publish/subscribe model: the producer publishes a message, and the * consumer reads it using a synchronous receive. *

* The program contains a SimpleProducer class, a SynchConsumer class, a * main method, and a method that runs the consumer and producer * threads. *

* Specify a topic name on the command line when you run the program. *

* The program calls methods in the SampleUtilities class. * * @author Kim Haase * @version 1.7, 08/18/00 */ public class SynchTopicExample { String topicName = null; int exitResult = 0; /** * The SynchConsumer class fetches a single message from a topic using * synchronous message delivery. * * @author Kim Haase * @version 1.7, 08/18/00 */ public class SynchConsumer extends Thread { /** * Runs the thread. */ public void run() { ConnectionFactory connectionFactory = null; Connection connection = null; Session session = null; Topic topic = null; MessageConsumer msgConsumer = null; final boolean NOLOCAL = true; TextMessage inMessage = null; TextMessage outMessage = null; MessageProducer msgProducer = null; /* * Obtain connection factory. * Create connection. * Create session from connection; false means session is not * transacted. * Obtain topic name. */ try { connectionFactory = SampleUtilities.getConnectionFactory(); connection = connectionFactory.createConnection(); session = connection.createSession(false, Session.AUTO_ACKNOWLEDGE); topic = SampleUtilities.getTopic(topicName, session); } catch (Exception e) { System.out.println("Connection problem: " + e.toString()); if (connection != null) { try { connection.close(); } catch (JMSException ee) {} } System.exit(1); } /* * Create consumer, then start message delivery. Consumer is * non-local so that it won't receive the message we publish. * Wait for text message to arrive, then display its contents. * Close connection and exit. */ try { msgConsumer = session.createConsumer(topic, null, NOLOCAL); connection.start(); inMessage = (TextMessage) msgConsumer.receive(); System.out.println("CONSUMER THREAD: Reading message: " + inMessage.getText()); /* * Notify producer that we received a message and it * can stop broadcasting. */ msgProducer = session.createProducer(topic); outMessage = session.createTextMessage(); outMessage.setText("Done"); msgProducer.send(outMessage); } catch (JMSException e) { System.out.println("Exception occurred: " + e.toString()); exitResult = 1; } finally { if (connection != null) { try { connection.close(); } catch (JMSException e) { exitResult = 1; } } } } } /** * The SimpleProducer class publishes a single message to a topic. * * @author Kim Haase * @version 1.7, 08/18/00 */ public class SimpleProducer extends Thread { /** * Runs the thread. */ public void run() { ConnectionFactory connectionFactory = null; Connection connection = null; Session session = null; Topic topic = null; MessageConsumer producerControlConsumer = null; final boolean NOLOCAL = true; MessageProducer msgProducer = null; TextMessage sentMessage = null; final String MSG_TEXT = new String("Here is a message "); Message receivedMessage = null; /* * Obtain connection factory. * Create connection. * Create session from connection; false means session is not * transacted. * Obtain topic name. */ try { connectionFactory = SampleUtilities.getConnectionFactory(); connection = connectionFactory.createConnection(); session = connection.createSession(false, Session.AUTO_ACKNOWLEDGE); topic = SampleUtilities.getTopic(topicName, session); } catch (Exception e) { System.out.println("Connection problem: " + e.toString()); if (connection != null) { try { connection.close(); } catch (JMSException ee) {} } System.exit(1); } /* * Create non-local consumer to receive "Done" message from * another connection; start delivery. * Create producer and text message. * Set message text, display it, and publish message. * Close connection and exit. */ try { producerControlConsumer = session.createConsumer(topic, null, NOLOCAL); connection.start(); /* * Publish a message once per second until consumer * reports that it has finished receiving messages. */ msgProducer = session.createProducer(topic); sentMessage = session.createTextMessage(); for (int i = 1; receivedMessage == null; i++) { sentMessage.setText(MSG_TEXT + i); System.out.println("PRODUCER THREAD: Publishing message: " + sentMessage.getText()); msgProducer.send(sentMessage); try { Thread.sleep(1000); } catch (InterruptedException ie){} receivedMessage = producerControlConsumer.receiveNoWait(); } } catch (JMSException e) { System.out.println("Exception occurred: " + e.toString()); exitResult = 1; } finally { if (connection != null) { try { connection.close(); } catch (JMSException e) { exitResult = 1; } } } } } /** * Instantiates the consumer and producer classes and starts their * threads. * Calls the join method to wait for the threads to die. *

* It is essential to start the consumer before starting the producer. * In the publish/subscribe model, a consumer can ordinarily receive only * messages published while it is active. */ public void run_threads() { SynchConsumer synchConsumer = new SynchConsumer(); SimpleProducer simpleProducer = new SimpleProducer(); synchConsumer.start(); simpleProducer.start(); try { synchConsumer.join(); simpleProducer.join(); } catch (InterruptedException e) {} } /** * Reads the topic name from the command line and displays it. The * topic must have been created by the jmsadmin tool. * Calls the run_threads method to execute the program threads. * Exits program. * * @param args the topic used by the example */ public static void main(String[] args) { SynchTopicExample ste = new SynchTopicExample(); if (args.length != 1) { System.out.println("Usage: java SynchTopicExample "); System.exit(1); } ste.topicName = new String(args[0]); System.out.println("Topic name is " + ste.topicName); ste.run_threads(); SampleUtilities.exit(ste.exitResult); } }

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