Java tutorial
/** * Licensed to the Apache Software Foundation (ASF) under one or more * contributor license agreements. See the NOTICE file distributed with * this work for additional information regarding copyright ownership. * The ASF licenses this file to You under the Apache License, Version 2.0 * (the "License"); you may not use this file except in compliance with * the License. You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ /* DurableChat application A basic JMS Application that uses: - Publish and Subscribe - Durable Subsciptions - Persistent Messages This sample publishes and subscribes to a specified topic. Text you enter is published to the topic with the user name. The message will persist for ten minutes if the subscriber is not available. If the subscriber reconnects within that time, the message is delivered. Usage: java DurableChat -b <broker:port> -u <username> -p <password> -b broker:port points to your message broker Default: tcp://localhost:61616 -u username must be unique (but is not checked) -p password password for user (not checked) Suggested demonstration: - In separate console windows, start instances of the application under unique user names.For example: java DurableChat -b tcp://localhost:61616 -u ACCOUNTING java DurableChat -b tcp://localhost:61616 -u LEGAL - Enter text and then press Enter to publish the message. - See messages appear under the various user names as you enter messages in each console window. - Stop a session by pressing CTRL+C in its console window. - Keep sending messages in other sessions. - Restart the subscriber username session that was stopped. - Note that the "missed" messages are still available if the restart is within thirty minutes. */ import org.apache.activemq.*; public class DurableChat implements javax.jms.MessageListener // to handle message subscriptions { private static final String APP_TOPIC = "jms.samples.durablechat"; private static final String DEFAULT_BROKER_NAME = "tcp://localhost:61616"; private static final String DEFAULT_PASSWORD = "password"; private static final long MESSAGE_LIFESPAN = 1800000; //30 minutes private javax.jms.Connection connection = null; private javax.jms.Session pubSession = null; private javax.jms.Session subSession = null; public void DurableChatter(String broker, String username, String password) { javax.jms.MessageProducer publisher = null; javax.jms.MessageConsumer subscriber = null; javax.jms.Topic topic = null; //Create a connection: try { javax.jms.ConnectionFactory factory; factory = new ActiveMQConnectionFactory(username, password, broker); connection = factory.createConnection(username, password); //Durable Subscriptions are indexed by username, clientID and subscription name //It is a good practice to set the clientID: connection.setClientID(username); pubSession = connection.createSession(false, javax.jms.Session.AUTO_ACKNOWLEDGE); subSession = connection.createSession(false, javax.jms.Session.AUTO_ACKNOWLEDGE); } catch (javax.jms.JMSException jmse) { System.err.println("Error: Cannot connect to Broker - " + broker); jmse.printStackTrace(); System.exit(1); } //Create Publisher and Durable Subscriber: try { topic = pubSession.createTopic(APP_TOPIC); subscriber = subSession.createDurableSubscriber(topic, username); subscriber.setMessageListener(this); publisher = pubSession.createProducer(topic); connection.start(); } catch (javax.jms.JMSException jmse) { System.out.println("Error: connection not started."); jmse.printStackTrace(); System.exit(1); } //Wait for user input try { System.out.println("\nDurableChat application:\n" + "========================\n" + "The user " + username + " connects to the broker at " + DEFAULT_BROKER_NAME + ".\n" + "The application will publish messages to the " + APP_TOPIC + " topic.\n" + "The application also creates a durable subscription to that topic to consume any messages published there.\n\n" + "Type some text, and then press Enter to publish it as a TextMesssage from " + username + ".\n"); java.io.BufferedReader stdin = new java.io.BufferedReader(new java.io.InputStreamReader(System.in)); while (true) { String s = stdin.readLine(); if (s == null) { exit(); } else if (s.length() > 0) { try { javax.jms.TextMessage msg = pubSession.createTextMessage(); msg.setText(username + ": " + s); //Publish the message persistantly: publisher.send(msg, //message javax.jms.DeliveryMode.PERSISTENT, //publish persistently javax.jms.Message.DEFAULT_PRIORITY, //priority MESSAGE_LIFESPAN); //Time to Live } catch (javax.jms.JMSException jmse) { System.err.println("Error publishing message:" + jmse.getMessage()); } } } } catch (java.io.IOException ioe) { ioe.printStackTrace(); } } /** Message Handler**/ public void onMessage(javax.jms.Message aMessage) { try { // Cast the message as a text message. javax.jms.TextMessage textMessage = (javax.jms.TextMessage) aMessage; // This handler reads a single String from the // message and prints it to the standard output. try { String string = textMessage.getText(); System.out.println(string); } catch (javax.jms.JMSException jmse) { jmse.printStackTrace(); } } catch (java.lang.RuntimeException rte) { rte.printStackTrace(); } } /** Cleanup resources cleanly and exit. */ private void exit() { try { connection.close(); } catch (javax.jms.JMSException jmse) { jmse.printStackTrace(); } System.exit(0); } // // NOTE: the remainder of this sample deals with reading arguments // and does not utilize any JMS classes or code. // /** Main program entry point. */ public static void main(String argv[]) { // Is there anything to do? if (argv.length == 0) { printUsage(); System.exit(1); } // Values to be read from parameters String broker = DEFAULT_BROKER_NAME; String username = null; String password = DEFAULT_PASSWORD; // Check parameters for (int i = 0; i < argv.length; i++) { String arg = argv[i]; if (arg.equals("-b")) { if (i == argv.length - 1 || argv[i + 1].startsWith("-")) { System.err.println("error: missing broker name:port"); System.exit(1); } broker = argv[++i]; continue; } if (arg.equals("-u")) { if (i == argv.length - 1 || argv[i + 1].startsWith("-")) { System.err.println("error: missing user name"); System.exit(1); } username = argv[++i]; continue; } if (arg.equals("-p")) { if (i == argv.length - 1 || argv[i + 1].startsWith("-")) { System.err.println("error: missing password"); System.exit(1); } password = argv[++i]; continue; } if (arg.equals("-h")) { printUsage(); System.exit(1); } // Invalid argument System.err.println("error: unexpected argument: " + arg); printUsage(); System.exit(1); } // Check values read in. if (username == null) { System.err.println("error: user name must be supplied"); printUsage(); } // Start the JMS client for the "chat". DurableChat durableChat = new DurableChat(); durableChat.DurableChatter(broker, username, password); } /** Prints the usage. */ private static void printUsage() { StringBuffer use = new StringBuffer(); use.append("usage: java DurableChat (options) ...\n\n"); use.append("options:\n"); use.append(" -b name:port Specify name:port of broker.\n"); use.append(" Default broker: " + DEFAULT_BROKER_NAME + "\n"); use.append(" -u username Specify unique user name. (Required)\n"); use.append(" -p password Specify password for user.\n"); use.append(" Default password: " + DEFAULT_PASSWORD + "\n"); use.append(" -h This help screen.\n"); System.err.println(use); } }