1 JMS as XML and Object-Based Messaging Integration Infrastructure Michael Wynholds Founder Carbon Five mike@carbonfive.com.

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JMS as XML and Object-Based Messaging Integration Infrastructure

Michael WynholdsFounderCarbon Fivemike@carbonfive.com

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THIS PRESENTATION

• Basics of JMS – 10%• Types of integration – 50%

– Integrate system components– Integrate dependent objects in EJBs

• Message payloads – 20%– Java objects– XML

• Q & A – 20%

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WHAT IS JMS?

• Java Messaging Service• Java API for enterprise messaging

– Non-Java implementations available• Multiple messaging paradigms

– Point-to-point– Publish/Subscribe

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REAL WORLD EXAMPLE #1

Major Components

vs.

Sub-Components

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INTEGRATING SYSTEM COMPONENTS

• Major components– Crucial serial functionality– Affects user experience– Example: shopping basket

• Sub-components– Possibly crucial functionality– Slight delays acceptable– Example: Email notification engine

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THE WRONG WAYProcesses happening serially:

– User does something in major component– Waits for sub-component to finish before

continuing on through the application

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THE WRONG WAYTwo things wrong:

– Why should the user wait?– What if we decide later we want to perform other

non-crucial actions at this time?

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THE RIGHT WAY:ASYNCHRONOUS

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ASYNCHRONOUS

• Fire and continue• Can still have guaranteed delivery• Sub-components can be moved to other

machines

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THE RIGHT WAY:LOOSE COUPLING

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LOOSE COUPLING• Determine significant events• Major components publish• Sub-components subscribe• Addition or modification of sub-component

requires no change to major component

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EXAMPLE:EMAIL NOTIFICATION

• Pet Store• What are significant events?

– User logs in– User status is changed– User purchases pet– Shipment is delayed (from another publisher)

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SIGNIFICANT EVENT XML<event type="user-status-change"> <context> <timestamp>2001-03-17 12:42:06 PST</timestamp> <user> <first-name>Guy</first-name> <last-name>Incognito</last-name> <email>guy@coolpets.com</email> <status>ADMINISTRATOR</status> </user> </context>

<user> <first-name>Michael</first-name> <last-name>Wynholds</last-name> <email>mike@carbonfive.com</email> <status>REGULAR</status> </user>

<new-status>PREFERRED</new-status></event>

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SIGNIFICANT EVENT OBJECTS

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NOTIFICATION ENGINE CODEprivate void init() throws NamingException, JMSException{ Context ctx = JNDIUtil.getContext(); String selector = new StringBuffer() .append("type = ").append(MessageTypes.CARBONFIVE_EVENT) .toString();

tconFactory = (TopicConnectionFactory) ctx.lookup(JMS_FACTORY); tcon = tconFactory.createTopicConnection(); tsession = tcon.createTopicSession(false, javax.jms.Session.AUTO_ACKNOWLEDGE); try { topic = (Topic) ctx.lookup(TOPIC_NAME); } catch (NamingException ne) { topic = tsession.createTopic(TOPIC_NAME); ctx.bind(TOPIC_NAME, topic); } tsubscriber = tsession.createSubscriber(topic, selector, false); tsubscriber.setMessageListener(this); tcon.start();}

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public void onMessage(javax.jms.Message msg){ synchronized (this) { int type = msg.getIntProperty("type"); Event event = (Event) ((ObjectMessage) msg).getObject(); switch (msg.getIntProperty("type")) { case MessageTypes.USER_STATUS_CHANGE: Email email = generateEmail((UserStatusChangeEvent) event); email.send(); break;

default: break; } }}

NOTIFICATION ENGINE CODE

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private Email generateEmail(UserStatusChangeEvent event){ Email email = new Email(); email.setTo(event.getUser().getEmail()); email.setFrom("administrator@carbonfive.com"); email.setSubject("Your status has changed"); email.setBody(getBody()); return email;}

NOTIFICATION ENGINE CODE

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MESSAGE SENDER CODE

private void init() throws NamingException, JMSException{ Context ctx = JNDIUtil.getContext();

tconFactory = (TopicConnectionFactory) ctx.lookup(JMS_FACTORY); tcon = tconFactory.createTopicConnection(); tsession = tcon.createTopicSession(false, Session.AUTO_ACKNOWLEDGE); try { topic = (Topic) ctx.lookup(TOPIC_NAME); } catch (NamingException ne) { topic = tsession.createTopic(TOPIC_NAME); ctx.bind(TOPIC_NAME, topic); } tpublisher = tsession.createPublisher(topic);}

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public void send(Serializable obj, int type) throws JMSException{ if (obj == null) { throw new NullPointerException("obj is null"); } ObjectMessage msg = tsession.createObjectMessage(); msg.setObject(obj); msg.setIntProperty("type", type); tpublisher.publish(msg); msg = null; // gc}

MESSAGE SENDER CODE

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USER STATUS CHANGE CODE

private void handleStatusChange(ServletRequest request){ HttpSession session = request.getSession(true);

User user = UserManager.getUserById(request.getParameter("user_id")); User me = session.getCurrentUser();

UserStatusChangeEvent event = new UserStatusChangeEvent(); EventContext ctx = new EventContext(); ctx.setUser(me); ctx.setTimestamp(new Date()); event.setContext(ctx); event.setUser(user); event.setNewStatus(request.getParameter("new_status")); MessageSender.send(event, MessageTypes.USER_STATUS_CHANGE_EVENT);

user.setStatus(request.getParameter("new_status"));}

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Entity EJB persistence optimization

REAL WORLD EXAMPLE #2

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ENTITY EJB PERSISTENCE• Entity EJB guarantees synchronization

with persistent store• Overhead in EJB container• Coarse-grained Entity Beans are better• isModified() method often used to optimize

• So what’s the problem?

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THE PROBLEM

• Multiple beans modify same dependent object• Bean instance may be on separate machines

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SOLUTION #1• Make dependent object an EJB• No longer coarse-grained

– EJB overhead takes toll

• Multiple machine problem not fixed

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• Don’t use isModified()• Slooooooowwwwwww….• Every getter hits the database

– Something may have changed– But most of the time, nothing has changed

SOLUTION #2

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• JMS-based isModified()• Dependent object publishes to topic when

a setter is called• Entity Beans subscribe to events

corresponding to their dependent objects• Efficient• Spans multiple machines

SOLUTION #3

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DEPENDENT OBJECT CODEpublic class Thing{ private String name;

public void setName(String name) { this.name = name; fireModificationEvent(this.getClass().getName(), this.hashCode()); }}

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EJB isModified()private void init() throws NamingException, JMSException{ Context ctx = JNDIUtil.getContext(); String selector = new StringBuffer() .append(“class = ”) .append(Thing.class.getName()) .toString();

tconFactory = (TopicConnectionFactory) ctx.lookup(JMS_FACTORY); tcon = tconFactory.createTopicConnection(); tsession = tcon.createTopicSession(false, javax.jms.Session.AUTO_ACKNOWLEDGE); try { topic = (Topic) ctx.lookup(TOPIC_NAME); } catch (NamingException ne) { topic = tsession.createTopic(TOPIC_NAME); ctx.bind(TOPIC_NAME, topic); } tsubscriber = tsession.createSubscriber(topic, selector, false); tsubscriber.setMessageListener(this); tcon.start();}

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EJB isModified()public void onMessage(javax.jms.Message msg){ synchronized (this) { ModEvent event = (ModEvent) ((ObjectMessage) msg).getObject(); if (Thing.class.getName().equals(event.getClassName())) { if (this.thing.hashCode == event.getHashCode()) { this.setModified(true); } } }}

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ISSUES• Class-based, not object-based events

– May receive many messages when using common objects

• hashCode() method not always unique– Just means you do a database hit

• Must implement hashCode() in objects to work across machines

• Can use hash code in selector– Which is more efficient?– I don’t know.

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MESSAGE PAYLOADS

• Objects– Rule of thumb: Use objects when you can

use objects.

• XML– Rule of thumb: Use XML when you need to

use XML.

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OBJECT MESSAGES• Easy to create / use• Little processing overhead• No need for XML tools• Better within same JVM or when JVM is

guaranteed• Full functionality of Java inside message

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XML MESSAGES• Can be much smaller size

– Better for high-traffic distributed systems

• Potential direct interaction with receiving systems

• Producer or consumer may be non-Java JMS client

• No class sync needed

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REFERENCES

• http://www.carbonfive.com/oreilly

Contains links to this and other Carbon Five presentations.