Failover Consumer Example
The following code sample, FailoverConsumer, illustrates good coding practices for handling exceptions during a failover. The transacted session is able to receive messages forever. The program sets the auto reconnect property to true, requiring the Message Queue runtime to automatically perform a reconnect when the connected broker fails or is killed. It is designed to work with the dura.example.FailoverProducer, shown in the previous section.
To run this program enter the following command.
java dura.example.FailoverConsumer
/*
* @(#)FailoverConsumer.java 1.1 06/06/09
* Copyright 2006 Sun Microsystems, Inc. All Rights Reserved
* SUN PROPRIETARY/CONFIDENTIAL
* Use is subject to license terms.
*
*/
package dura.example;
import java.util.Date;
import javax.jms.Destination;
import javax.jms.ExceptionListener;
import javax.jms.JMSException;
import javax.jms.Message;
import javax.jms.Connection;
import javax.jms.MessageConsumer;
import javax.jms.Session;
import javax.jms.Topic;
import javax.jms.TransactionRolledBackException;
import com.sun.messaging.ConnectionConfiguration;
public class FailoverConsumer implements ExceptionListener, Runnable {
//JMS connection
private Connection conn = null;
//JMS session
private Session session = null;
//JMS Message consumer
private MessageConsumer messageConsumer = null;
//JMS destination.
private Destination destination = null;
//flag indicates whether this program should continue running.
private boolean isConnected = false;
//destination name.
private static final String DURA_TEST_TOPIC = "DuraTestTopic";
//the commit counter, for information only.
private long commitCounter = 0;
/**
* message counter property set by the producer.
*/
public static final String MESSAGE_COUNTER = "MESSAGE_COUNTER";
/**
* Message in doubt bit set by the producer
*/
public static final String MESSAGE_IN_DOUBT = "MESSAGE_IN_DOUBT";
/**
* receive time out
*/
public static final long RECEIVE_TIMEOUT = 0;
/**
* Default constructor -
* Set up JMS Environment.
*/
public FailoverConsumer() {
setup();
}
/* Connection Exception listener. This is called when connection
* breaks and no reconnect attempts are performed by MQ client runtime.
*/
public void onException (JMSException e) {
print ("Reconnect failed. Shutting down the connection ...");
/**
* Set this flag to false so that the run() method will exit.
*/
this.isConnected = false;
e.printStackTrace();
}
/**
* Best effort to roll back a jms session. When a broker crashes, an
* open-transaction should be rolled back. But the re-started broker
* may not have the uncommitted tranaction information due to system
* failure. In a situation like this, an application can just quit
* calling rollback after retrying a few times The uncommitted
* transaction (resources) will eventually be removed by the broker.
*/
private void rollBackJMS() {
//rollback fail count
int failCount = 0;
boolean keepTrying = true;
while ( keepTrying ) {
try {
print ("<<< rolling back JMS ...., consumer commit counter:
" + this.commitCounter);
session.rollback();
print("<<< JMS rolled back ...., consumer commit counter:
" + this.commitCounter);
keepTrying = false;
} catch (JMSException jmse) {
failCount ++;
jmse.printStackTrace();
sleep (3000); //3 secs
if ( failCount == 1 ) {
print ("<<< rollback failed : total count" + failCount);
keepTrying = false;
}
}
}
}
/**
* Close the JMS connection and exit the program.
*
*/
private void close() {
try {
if ( conn != null ) {
conn.close();
}
} catch (Exception e) {
e.printStackTrace();
} finally {
this.isConnected = false;
}
}
/*Receive messages in a loop until closed.*/
public void run () {
while (isConnected) {
try {
/*receive message with specified timeout.*/
Message m = messageConsumer.receive(RECEIVE_TIMEOUT);
/* process the message. */
processMessage(m);
/* commit JMS transaction. */
this.commit();
/*increase the commit counter.*/
this.commitCounter ++;
} catch (TransactionRolledBackException trbe) {
/**
* the transaction is rolled back
* a new transaction is automatically started.
*/
trbe.printStackTrace();
} catch (JMSException jmse) {
/* The transaction is in unknown state.
* We need to roll back the transaction.*/
jmse.printStackTrace();
/* roll back if not closed.
*/
if ( this.isConnected == true ) {
this.rollBackJMS();
}
} catch (Exception e) {
e.printStackTrace();
/* Exit if this is an unexpected Exception.
*/
this.close();
} finally {
;//do nothing
}
}
print(" <<< consumer exit ...");
}
/*Set up connection, destination, etc*/
/
protected void setup() {
try {
//create connection factory
com.sun.messaging.ConnectionFactory factory =
new com.sun.messaging.ConnectionFactory();
//set auto reconnect to true.
factory.setProperty(ConnectionConfiguration.imqReconnectEnabled, "true");
//A value of -1 will retry forever if connection is broken.
factory.setProperty(ConnectionConfiguration.imqReconnectAttempts, "-1");
//retry interval - every 10 seconds
factory.setProperty(ConnectionConfiguration.imqReconnectInterval, "10000");
//create connection
conn = factory.createConnection();
//set client ID
conn.setClientID(DURA_TEST_TOPIC);
//set exception listener
conn.setExceptionListener(this);
//create a transacted session
session = conn.createSession(true, -1);
//get destination
destination = session.createTopic(DURA_TEST_TOPIC);
//message consumer
messageConsumer = session.createDurableSubscriber((Topic)destination,
DURA_TEST_TOPIC);
//set flag to true
this.isConnected = true;
//we are ready, start the connection
conn.start();
print("<<< Ready to receive on destination: " + DURA_TEST_TOPIC);
} catch (JMSException jmse) {
this.isConnected = false;
jmse.printStackTrace();
this.close();
}
}
/**
* Process the received message message.
* This prints received message counter.
* @param m the message to be processed.
*/
private synchronized void processMessage(Message m) {
try {
//in this example, we do not expect a timeout, etc.
if ( m == null ) {
throw new RuntimeException ("<<< Received null message.
Maybe reached max time out. ");
}
//get message counter property
long msgCtr = m.getLongProperty (MESSAGE_COUNTER);
//get message in-doubt bit
boolean indoubt = m.getBooleanProperty(MESSAGE_IN_DOUBT);
if ( indoubt) {
print("<<< received message: " + msgCtr + ", indoubt bit is true");
} else {
print("<<< received message: " + msgCtr);
}
} catch (JMSException jmse) {
jmse.printStackTrace();
}
}
/**
* Commit a JMS transaction.
* @throws JMSException
*/
private void commit() throws JMSException {
session.commit();
}
/**
* Sleep for the specified time.
* @param millis sleep time in milli-seconds.
*/
private void sleep (long millis) {
try {
Thread.sleep(millis);
} catch (java.lang.InterruptedException inte) {
print (inte);
}
}
/**
* Print the specified message.
* @param msg the message to be printed.
*/
private static void print (String msg) {
System.out.println(new Date() + ": " + msg);
}
/**
* Print Exception stack trace.
* @param e the exception to be printed.
*/
private static void print (Exception e) {
System.out.print(e.getMessage());
e.printStackTrace();
}
/**
* Start this example program.
*/
public static void main (String args[]) {
FailoverConsumer fc = new FailoverConsumer();
fc.run();
}
}
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