1. Message-Driven Bean(MDB)

2. Goals Be able to produce messages from the EJB server
Be able to consume messages within the EJB server
Be able to define timers within EJB server
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3. Objectives EJB JMS Producers
EJB JMS Consumers (Message Driven Beans; MDBs)
Asynchronous Methods
EJB Timers
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4. EJB JMS Producers Obtain Resources Create Session Publish Message
ConnectionFactory
Destination
Create Session
integrate with JTA transaction
Publish Message
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5. Obtaining a ConnectionFactory
Using annotations
@Stateless
public class SellerEJB ... {
@Resource(mappedName=“java:/JmsXA")
private ConnectionFactory connFactory;
mappedName points to global JNDI name
benefits
concise & simple
drawbacks
mixes deployment concepts with Java code
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6. Obtaining a ConnectionFactory (cont.)
Using ejb-jar.xml
<ejb-name>SellerEJB</ejb-name>
<resource-ref>
<res-ref-name>jms/ConnectionFactory</res-ref-name>
<res-type>javax.jms.ConnectionFactory</res-type>
<mapped-name>java:/JmsXA</mapped-name>
<injection-target>
<injection-target-class>
ejava.examples.asyncmarket.ejb.SellerEJB
</injection-target-class>
<injection-target-name>
connFactory
</injection-target-name>
</injection-target>
</resource-ref>
...
mappedName moved away from code to DD
factory injected into EJB
ejb-jar.xml is no longer vendor/deployment-neutral
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7. Obtaining a ConnectionFactory (cont.)
Using jboss-ejb3.xml
<session>
<ejb-name>SellerEJB</ejb-name>
<resource-ref>
<res-ref-name>jms/ConnectionFactory</res-ref-name>
<jndi-name>java:/JmsXA</jndi-name>
</resource-ref>
</session>
mappedName is now removed
replaced with vendor/deployment specific reference
Required 3 files to complete
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8. Obtaining a Destination
Using annotations
@Stateless
public class SellerEJB implements SellerLocal, SellerRemote {
...
@Resource(mappedName="java:/topic/ejava/examples/asyncMarket/topic1",
type=Topic.class)
private Destination sellTopic;
mappedName points to global JNDI entry
benefits
concise and simple
drawbacks
mixes deployment properties with implementation
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9. Obtaining a Destination (cont.)
Using ejb-jar.xml
<resource-env-ref>
<resource-env-ref-name>jms/sellTopic</resource-env-ref-name>
<resource-env-ref-type>javax.jms.Topic</resource-env-ref-type>
<mapped-name>topic/ejava/examples/asyncMarket/topic</mapped-name>
<injection-target>
<injection-target-class>
ejava.examples.asyncmarket.ejb.SellerEJB
</injection-target-class>
<injection-target-name>sellTopic</injection-target-name>
</injection-target>
</resource-env-ref>
mappedName moved away from Java and to DD
note resource-env-ref used for Destinations
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10. Getting a Session v131202 Asynchronous EJB 10
@TransactionAttribute(TransactionAttributeType.REQUIRED)
public long sellProduct(String sellerId, AuctionItem item)
throws MarketException {
Connection connection = null;
Session session = null;
try {
connection = connFactory.createConnection();
session = connection.createSession(false,
Session.AUTO_ACKNOWLEDGE);
... }
catch (JMSException ex) {
log.error("error publishing sell", ex);
ctx.setRollbackOnly();
throw new EJBException("error publishing sell:" + ex);
finally {
if (session != null) { session.close(); }
if (connection != null) { connection.close(); }
} catch (JMSException ex) {
log.error("unable to close resources", ex);
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11. Integrating JMS into the Transaction
Person seller = sellerDAO.getPersonByUserId(sellerId);
seller.getItems().add(item);
item.setOwner(seller);
auctionItemDAO.createItem(item);
publishForSale(session, item);
return item.getId();
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12. Publishing the Message
protected void publishForSale(Session session, AuctionItem item)
throws JMSException {
MessageProducer producer = null;
try {
producer = session.createProducer(sellTopic);
MapMessage message = session.createMapMessage();
message.setJMSType("forSale");
message.setLong("id", item.getId());
message.setString("name", item.getName());
message.setString("seller", item.getOwner().getUserId());
message.setLong("startDate", item.getStartDate().getTime());
message.setLong("endDate", item.getEndDate().getTime());
message.setDouble("minBid", item.getMinBid());
message.setDouble("bids", item.getBids().size());
message.setDouble("highestBid",
(item.getHighestBid() == null ? 0.00 :
item.getHighestBid().getAmount()));
producer.send(message); }
finally {
if (producer != null) { producer.close(); }
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13. EJB JMS Consumers; MDBs
“Message Driven Bean”
Introduced in EJB 2.0 to support JMS providers
Extended in EJB 2.1 to support non-JMS message providers
using the Java EE Connector API
commonly called JCA
EJB 3.0 support for configuration
Java EE Providers
must support a JMS provider
must support external providers through JCA
Session and Entity Beans cannot be a MessageListener
can poll for messages with MessageConsumer.receive()
can be wrapped by an MDB to be called asynchronously
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14. MessageDriven Bean Configuration
Destination Type
Destination
Selector
Message Acknowledgement
...
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15. MDB Configuration Using annotations v131202 Asynchronous EJB
@MessageDriven(name="BuyerMDB", activationConfig={
@ActivationConfigProperty(
propertyName="destinationType",
propertyValue="javax.jms.Topic"),
propertyName="destination",
propertyValue="topic/ejava/.../topic1"),
propertyName="messageSelector",
propertyValue=
"JMSType in ('forSale', 'saleUpdate')"),
propertyName="acknowledgeMode",
propertyValue="Auto-acknowledge") })
public class BuyerMDB implements MessageListener {
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16. MDB Configuration (cont.)
Using ejb-jar.xml
<message-driven>
<ejb-name>BuyerMDB</ejb-name>
<ejb-class>ejava.examples.asyncmarket.ejb.BuyerMDB</ejb-class>
<message-destination-type>
javax.jms.Topic
</message-destination-type>
<activation-config>
<activation-config-property>
<activation-config-property-name>
...
</activation-config-property-name>
<activation-config-property-value>
</activation-config-property-value>
</activation-config-property>
</activation-config>
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17. MDB Configuration (cont.)
Using jboss.xml
<message-driven>
<ejb-name>BuyerMDB</ejb-name>
<destination-jndi-name>
topic/ejava/examples/asyncMarket/topic1
</destination-jndi-name>
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18. MDB Structure
@MessageDriven(name="BuyerMDB", activationConfig={ ... })
public class BuyerMDB implements MessageListener {
@PostConstruct
public void init() { ... }
public void onMessage(Message message) {
try {
log.debug("onMessage:" + message.getJMSMessageID());
MapMessage auctionMsg = (MapMessage)message;
long itemId = auctionMsg.getLong("id");
processAuctionItem(itemId); }
catch (Exception ex) {
log.error("error processing message", ex);

19. MDB and Transactions SUPPORTED NOT_SUPPORTED
message receipt/acknowledgement integrated with overall transaction
NOT_SUPPORTED
message receipt/acknowledgement independent of transactions within processing
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20. Asynchronous Methods Scenario @javax.ejb.Asynchronous null return type
Task(s) may take considerable time to complete
Client need not wait for them to complete
@javax.ejb.Asynchronous
Return control to the client before EJB is invoked
Any session bean business method may be (*see Serialization note below)
null return type
Client and issued task fully decoupled from one another
java.util.concurrent.Future return type
Allows task and client to coordinate a future return value
Client returns instance of javax.ejb.AsyncResult
Not Serializable (i.e., cannot use directly with RMI client)

21. Synchronous Example: Client EJB
@Stateless public class AuctionMgmtEJB implements AuctionMgmtRemote, AuctionMgmtLocal { AuctionMgmtActionEJB actions; public void workSync(int count, long delay) { DateFormat df = new SimpleDateFormat("HH:mm:ss.SSS"); long startTime = System.currentTimeMillis(); for (int i=0; i<count; i++) { log.info(String.format("%s issuing sync request, delay=%d", df.format(new Date()), delay)); Date date= actions.doWorkSync(delay); log.info(String.format("sync waitTime=%d msecs", System.currentTimeMillis()-startTime)); } long syncTime = System.currentTimeMillis() - startTime; log.info(String.format("workSync time=%d msecs", syncTime));

22. Synchronous Example: Helper EJB
@Stateless public class AuctionMgmtActionEJB { public Date doWorkSync(long delay) { DateFormat df = new SimpleDateFormat("HH:mm:ss.SSS"); log.debug(String.format("sync method %d starting %d delay at %s", Thread.currentThread().getId(), delay, df.format(new Date()))); try { Thread.sleep(delay); } catch (Exception ex) { ... } Date now = new Date(); log.debug(String.format("sync method %d completed %d delay at %s", Thread.currentThread().getId(), delay, df.format(now))); return now; }

23. Synchronous Example: Results
11:06:44,624 INFO [AuctionMgmtEJB:306] 11:06: issuing sync request, delay= :06:44,626 DEBUG [AuctionMgmtActionEJB:24] sync method 163 starting 3000 delay at 11:06: :06:47,628 DEBUG [AuctionMgmtActionEJB:30] sync method 163 completed 3000 delay at 11:06:47,630 INFO [AuctionMgmtEJB:309] sync waitTime=3018 msecs 11:06:47,631 INFO [AuctionMgmtEJB:306] 11:06: issuing sync request, delay= :06:47,634 DEBUG [AuctionMgmtActionEJB:24] sync method 163 starting 3000 delay at 11:06: :06:50,636 DEBUG [AuctionMgmtActionEJB:30] sync method 163 completed 3000 delay at 11:06:50,637 INFO [AuctionMgmtEJB:309] sync waitTime=6025 msecs 11:06:50,637 INFO [AuctionMgmtEJB:306] 11:06: issuing sync request, delay= :06:50,638 DEBUG [AuctionMgmtActionEJB:24] sync method 163 starting 3000 delay at 11:06: :06:53,640 DEBUG [AuctionMgmtActionEJB:30] sync method 163 completed 3000 delay at 11:06: :06:53,641 INFO [AuctionMgmtEJB:309] sync waitTime=9029 msecs 11:06:53,642 INFO [AuctionMgmtEJB:312] workSync time=9030 msecs

24. Asynchronous Example: Client EJB
@Stateless public class AuctionMgmtEJB implements AuctionMgmtRemote, AuctionMgmtLocal { public void workAsync(int count, long delay) { DateFormat df = new SimpleDateFormat("HH:mm:ss.SSS"); long startTime = System.currentTimeMillis(); List<Future<Date>> results = new ArrayList<Future<Date>>(); for (int i=0; i<count; i++) { log.info(String.format("%s issuing async request, delay=%d", df.format(new Date()), delay)); Future<Date> date = actions.doWorkAsync(delay); results.add(date); log.info(String.format("async waitTime=%d msecs", System.currentTimeMillis()-startTime)); } for (Future<Date> f: results) { log.info(String.format("%s getting async response", df.format(new Date()))); try { Date date = f.get(); } catch (Exception ex) { throw new EJBException("unexpected error in future.get():"+ex);} log.info(String.format("%s got async response", df.format(new Date()))); long asyncTime = System.currentTimeMillis() - startTime; log.info(String.format("workAsync time=%d msecs", asyncTime));

25. Asynchronous Example: Helper EJB
@Stateless public class AuctionMgmtActionEJB public java.util.concurrent.Future<Date> doWorkAsync(long delay) { DateFormat df = new SimpleDateFormat("HH:mm:ss.SSS"); log.debug(String.format("async method %d starting %d delay at %s", Thread.currentThread().getId(), delay, df.format(new Date()))); try { Thread.sleep(delay); } catch (Exception ex) { ... } Date now = new Date(); log.debug(String.format("async method %d completed %d delay at %s", Thread.currentThread().getId(), delay, df.format(now))); return new javax.ejb.AsyncResult<Date>(now); }

26. Asynchronous Example: Results
11:06:53,650 INFO [AuctionMgmtEJB:325] 11:06: issuing async request, delay= :06:53,658 INFO [AuctionMgmtEJB:328] async waitTime=8 msecs 11:06:53,659 INFO [AuctionMgmtEJB:325] 11:06: issuing async request, delay= :06:53,659 DEBUG [AuctionMgmtActionEJB:41] async method 166 starting 3000 delay at 11:06: :06:53,668 DEBUG [AuctionMgmtActionEJB:41] async method 167 starting 3000 delay at 11:06: :06:53,668 INFO [AuctionMgmtEJB:328] async waitTime=18 msecs 11:06:53,669 INFO [AuctionMgmtEJB:325] 11:06: issuing async request, delay= :06:53,670 INFO [AuctionMgmtEJB:328] async waitTime=20 msecs 11:06:53,670 DEBUG [AuctionMgmtActionEJB:41] async method 168 starting 3000 delay at 11:06: :06:53,671 INFO [AuctionMgmtEJB:331] 11:06: getting async response 11:06:56,667 DEBUG [AuctionMgmtActionEJB:47] async method 166 completed 3000 delay at 11:06:56,669 DEBUG [AuctionMgmtActionEJB:47] async method 167 completed 3000 delay at 11:06:56,669 INFO [AuctionMgmtEJB:339] 11:06: got async response 11:06:56,670 INFO [AuctionMgmtEJB:331] 11:06: getting async response 11:06:56,671 INFO [AuctionMgmtEJB:339] 11:06: got async response 11:06:56,672 DEBUG [AuctionMgmtActionEJB:47] async method 168 completed 3000 delay at 11:06:56,673 INFO [AuctionMgmtEJB:331] 11:06: getting async response 11:06:56,673 INFO [AuctionMgmtEJB:339] 11:06: got async response 11:06:56,674 INFO [AuctionMgmtEJB:342] workAsync time=3024 msecs

27. EJB Timers Performs similar role of job schedulers Two types v131202
“cron”
Two types
Single-action
createTimer(Date expiration, Serializable info)
fires once at or after a specific time in the future
createTimer(long duration, Serializable info)
fires once after a specific delay period
Interval-timer
createTimer(Date intialExpiration, long intervalDuration, Serializable info)
continually fires every intervalDuration after the initialExpiration time
createTimer(long initialDuration, long intervalDuration, Serializable info)
continually fires every intervalDuration after the initialDuration delay
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28. EJB Timers Original EJB Timer Service part of EJB 2.1
EJB 3.0 added annotation-based extensions that eliminated inheritance-based solution requirements
EJB 3.1 provided an overhaul of the overall service
Added declarative scheduling
@javax.ejb.ScheduleExpression
@javax.ejb.Schedule

29. Declarative Calendar Timer
@Schedule(second="*/10", minute ="*", hour="*", dayOfMonth="*", month="*", year="*”, persistent=false) public void execute(Timer timer) { log.info("timer fired:" + timer); try { checkAuction(); } catch (Exception ex) { log.error("error checking auction", ex);

30. Programmatic Calendar Timer
ScheduleExpression schedule = new ScheduleExpression(); schedule.second("*/10"); schedule.minute("*"); schedule.hour("*"); schedule.dayOfMonth("*"); schedule.month("*"); schedule.year("*"); auctionMgmt.initTimers(schedule); public void initTimers(ScheduleExpression schedule) { cancelTimers(); log.debug("initializing timers, schedule="+schedule); timerService.createCalendarTimer(schedule); public void execute(Timer timer) { log.info("timer fired:" + timer); try { checkAuction(); catch (Exception ex) { log.error("error checking auction", ex);

31. Programmatic Interval Timer
auctionMgmt.initTimers(10*1000);
public void initTimers(long delay) {
cancelTimers();
log.debug("initializing timers, checkItemInterval="+delay);
timerService.createTimer(0,delay, "checkAuctionTimer"); }
@Timeout
public void execute(Timer timer) {
log.info("timer fired:" + timer);
try {
checkAuction();
catch (Exception ex) {
log.error("error checking auction", ex);

32. EJB Timers Accessing TimerService Getting Timers Cancelling Timers
Using Annotations
@Resource private TimerService timerService;
Getting Timers
timerService.getTimers()
Cancelling Timers
for (Timer timer :
(Collection<Timer>)timerService.getTimers()) {
timer.cancel(); }
Timers
associated with the EJB that created them
are automatically integrated into JTA transaction

33. EJB Timer Callbacks Using annotations Using interfaces
public class AuctionMgmtEJB ...
@Timeout
public void execute(Timer timer) {
try {
checkAuction(); }
catch (Exception ex) {
log.error("error checking auction", ex);
Using interfaces
public class AuctionMgmtEJB implements TimedObject, ...
public void ejbTimeout(Timer timer) {
...

34. javax.ejb.TimerService
public interface javax.ejb.TimerService{ javax.ejb.Timer createTimer(long, java.io.Serializable) throws ...; javax.ejb.Timer createSingleActionTimer(long, javax.ejb.TimerConfig) throws ...; javax.ejb.Timer createTimer(long, long, java.io.Serializable) throws ...; javax.ejb.Timer createIntervalTimer(long, long, javax.ejb.TimerConfig) javax.ejb.Timer createTimer(java.util.Date, java.io.Serializable) throws ...; javax.ejb.Timer createSingleActionTimer(java.util.Date, javax.ejb.TimerConfig) javax.ejb.Timer createTimer(java.util.Date, long, java.io.Serializable) javax.ejb.Timer createIntervalTimer(java.util.Date, long,javax.ejb.TimerConfig) javax.ejb.Timer createCalendarTimer(javax.ejb.ScheduleExpression) throws ...; javax.ejb.Timer createCalendarTimer(javax.ejb.ScheduleExpression, javax.ejb.TimerConfig) throws ...; java.util.Collection getTimers() throws ...; }

35. Summary EJB JMS Publishers EJB JMS Subscriber Asynchronous Methods
integrates into Session and MDB processing
EJB JMS Subscriber
implemented using MDB
MDBs support more than JMS using JCA
Asynchronous Methods
EJB Timers
schedule re-activation of Session Bean
Single-action and interval
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36. References Java Messaging Service API
“Enterprise JavaBeans 3.0, 5th Edition”; Burke & Monsen-Haefel; ISBN X; O'Reilly