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<?xml version="1.0"?>
<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
"http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd"
[
<!ENTITY % entities SYSTEM "commonEntities.xml">
%entities;
]>
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<chapter id="JMS-Client-0-8-Examples">
<title>Examples</title>
<para>The following programs shows how to send and receive messages using the Qpid JMS client.
The first program illustrates a <emphasis>point to point</emphasis> example, the second, a
pubish/subscribe example. </para>
<para>Both examples show the use JNDI to obtain connection factory and destination objects which
the application needs. In this way the configuration is kept separate from the application
code itself.</para>
<para>The example code will be straightforward for anyone familiar with Java JMS. Readers in
need of an introduction are directed towards <ulink url="&oracleJmsTutorial;">Oracle's JMS
tutorial</ulink>.</para>
<section id="JMS-Client-0-8-Examples-PTP">
<title>Point to point example</title>
<para>In this example, we illustrate point to point messaging. We create a JNDI context
using a properties file, use the context to lookup a connection factory, create and
start a connection, create a session, and lookup a destination (a queue) from the JNDI
context. Then we create a producer and a consumer, send a message with the producer and
receive it with the consumer.</para>
<example id="JMS-Client-0-8-Examples-PTP-Java">
<title>JMS Example - Point to Point Messaging</title>
<programlisting language="java">
import javax.jms.*;
import javax.naming.Context;
import javax.naming.InitialContext;
import java.util.Properties;
public class Hello {
public Hello() {
}
public static void main(String[] args) throws Exception {
Hello hello = new Hello();
hello.runTest();
}
private void runTest() throws Exception {
Properties properties = new Properties();
properties.load(this.getClass().getResourceAsStream("helloworld.properties")); <co id="ptp-java-properties" linkends="callout-ptp-properties"/>
Context context = new InitialContext(properties); <co id="ptp-java-context" linkends="callout-ptp-context"/>
ConnectionFactory connectionFactory
= (ConnectionFactory) context.lookup("qpidConnectionFactory"); <co id="ptp-java-connection-factory" linkends="callout-ptp-connection-factory"/>
Connection connection = connectionFactory.createConnection(); <co id="ptp-java-connection" linkends="callout-ptp-connection"/>
connection.start(); <co id="ptp-java-start" linkends="callout-ptp-start"/>
Session session = connection.createSession(true, Session.SESSION_TRANSACTED); <co id="ptp-java-session" linkends="callout-ptp-session"/>
Queue queue = (Queue) context.lookup("myqueue"); <co id="ptp-java-destination" linkends="callout-ptp-destination"/>
MessageConsumer messageConsumer = session.createConsumer(queue); <co id="ptp-java-consumer" linkends="callout-ptp-consumer"/>
MessageProducer messageProducer = session.createProducer(queue); <co id="ptp-java-producer" linkends="callout-ptp-producer"/>
TextMessage message = session.createTextMessage("Hello world!"); <co id="ptp-java-send" linkends="callout-ptp-send"/>
messageProducer.send(message);
session.commit();
message = (TextMessage)messageConsumer.receive(); <co id="ptp-java-receive" linkends="callout-ptp-receive"/>
session.commit();
System.out.println(message.getText());
connection.close(); <co id="ptp-java-close" linkends="callout-ptp-close"/>
context.close(); <co id="ptp-java-jndi-close" linkends="callout-ptp-jndi-close"/>
}
}
</programlisting>
</example>
<calloutlist>
<callout id="callout-ptp-properties" arearefs="ptp-java-properties">
<para>Loads the JNDI properties file, which specifies the connection factory, queues
and topics. See <xref linkend="JMS-Client-0-8-JNDI-Properties-Format"/> for
details.</para>
</callout>
<callout id="callout-ptp-context" arearefs="ptp-java-context">
<para>Creates the JNDI initial context.</para>
</callout>
<callout id="callout-ptp-connection-factory" arearefs="ptp-java-connection-factory">
<para>Looks up a JMS connection factory for Qpid.</para>
</callout>
<callout id="callout-ptp-connection" arearefs="ptp-java-connection">
<para>Creates a JMS connection. Creating the JMS connections establishes the
connection to the Broker.</para>
</callout>
<callout id="callout-ptp-start" arearefs="ptp-java-start">
<para>Starts the connection, required for the consumption of messages.</para>
</callout>
<callout id="callout-ptp-session" arearefs="ptp-java-session">
<para>Creates a transactional session.</para>
</callout>
<callout id="callout-ptp-destination" arearefs="ptp-java-destination">
<para>Looks up a destination for the queue with JNDI name <emphasis>myqueue</emphasis>.</para>
</callout>
<callout id="callout-ptp-consumer" arearefs="ptp-java-consumer">
<para>Creates a consumer that reads messages from the queue<footnote>
<para>Creating consumer will automatically create the queue on the Broker
and bind it to an exchange. Specifically, in this case as the
<literal>queue.</literal> form is used in the JNDI properties the
effect will be to create a queue called <literal>queue1</literal> on the
Broker, and create a binding between the <literal>amq.direct</literal>
exchange and this queue using the queue's name. This process is
described in detail in <xref
linkend="JMS-Client-0-8-Client-Understanding-MessageConsumer-ConsumerSideEffect"
/></para>
</footnote>.</para>
</callout>
<callout id="callout-ptp-producer" arearefs="ptp-java-producer">
<para>Creates a producer that sends messages to the queue.</para>
</callout>
<callout id="callout-ptp-send" arearefs="ptp-java-send">
<para>Creates a new message of type <emphasis>javax.jms.TextMessage</emphasis>, publishes the message and commits the
session.</para>
</callout>
<callout id="callout-ptp-receive" arearefs="ptp-java-receive">
<para>Reads the next available message (awaiting indefinitely if necessary) and
commits the session.</para>
</callout>
<callout id="callout-ptp-close" arearefs="ptp-java-close">
<para>Closes the Connection. All sessions owned by the Connection along with their
MessageConsumers and MessageProducers are automatically closed. The connection
to the Broker is closed as this point.</para>
</callout>
<callout id="callout-ptp-jndi-close" arearefs="ptp-java-jndi-close">
<para>Closes the JNDI context.</para>
</callout>
</calloutlist>
<para>The contents of the <literal>helloworld.properties</literal> file are shown
below.</para>
<example id="JMS-Client-0-8-Examples-PTP-PropertiesFile">
<title>JMS Example - Point to Point Messaging - JNDI Properties</title>
<programlisting language="properties">
java.naming.factory.initial = org.apache.qpid.jndi.PropertiesFileInitialContextFactory
connectionfactory.qpidConnectionFactory = amqp://guest:guest@clientid/?brokerlist='tcp://localhost:5672' <co id="ptp-properties-connectionfactory" linkends="callout-ptp-properties-connectionfactory"/>
queue.myqueue = queue1 <co id="ptp-properties-destination" linkends="callout-ptp-properties-destination"/>
</programlisting>
</example>
<calloutlist>
<callout id="callout-ptp-properties-connectionfactory"
arearefs="ptp-properties-connectionfactory">
<para>Defines a connection factory from which Connections can be created. The syntax
of a ConnectionURL is given in <xref
linkend="JMS-Client-0-8-Connection-URL"/>.</para>
</callout>
<callout id="callout-ptp-properties-destination" arearefs="ptp-properties-destination">
<para>Defines a queue for which MessageProducers and/or MessageConsumers send and
receive messages. The format of these entries is described in <xref
linkend="JMS-Client-0-8-JNDI-Properties-Format-Queue"/>.</para>
</callout>
</calloutlist>
</section>
<section id="JMS-Client-0-8-Examples-PubSub">
<title>Publish/subscribe example</title>
<para>In this second example, we illustrate publish/subscribe messaging. Again, we create a
JNDI context using a properties file, use the context to lookup a connection factory,
create and start a connection, create a session, and lookup a destination (a topic) from
the JNDI context. Then we create a producer and two durable subscribers , send a message
with the producer. Both subscribers receive the same message.</para>
<example id="JMS-Client-0-8-Examples-PubSub-Java">
<title>JMS Example - Publish/subscribe Messaging</title>
<programlisting language="java">
import javax.jms.*;
import javax.naming.Context;
import javax.naming.InitialContext;
import java.util.Properties;
public class StocksExample {
public StocksExample() {
}
public static void main(String[] args) throws Exception {
StocksExample stocks = new StocksExample();
stocks.runTest();
}
private void runTest() throws Exception {
Properties properties = new Properties();
properties.load(this.getClass().getResourceAsStream("stocks.properties"));
Context context = new InitialContext(properties);
ConnectionFactory connectionFactory
= (ConnectionFactory) context.lookup("qpidConnectionFactory");
Connection connection = connectionFactory.createConnection();
connection.start();
Session session = connection.createSession(true, Session.SESSION_TRANSACTED);
Topic priceTopic = (Topic) context.lookup("myprices"); <co id="pubsub-java-destination" linkends="callout-pubsub-destination"/>
MessageConsumer subscriber1 = session.createDurableSubscriber(priceTopic, "sub1"); <co id="pubsub-java-subscribers" linkends="callout-pubsub-subscribers"/>
MessageConsumer subscriber2 = session.createDurableSubscriber(priceTopic, "sub2" /*, "price > 150", false*/ );
MessageProducer messageProducer = session.createProducer(priceTopic);
Message message = session.createMessage();
message.setStringProperty("instrument", "IBM");
message.setIntProperty("price", 100);
messageProducer.send(message);
session.commit();
message = subscriber1.receive(1000);
session.commit();
System.out.println("Subscriber 1 received : " + message);
message = subscriber2.receive(1000);
session.commit();
System.out.println("Subscriber 2 received : " + message);
session.unsubscribe("sub1"); <co id="pubsub-java-unsubscribe" linkends="callout-pubsub-unsubscribe"/>
session.unsubscribe("sub2");
connection.close();
context.close();
}
}
</programlisting>
</example>
<calloutlist>
<callout id="callout-pubsub-destination" arearefs="pubsub-java-destination">
<para>Looks up a destination for the topic with JNDI name myprices.</para>
</callout>
<callout id="callout-pubsub-subscribers" arearefs="pubsub-java-subscribers">
<para>Creates two durable subscribers, <literal>sub1</literal> and
<literal>sub2</literal>. Durable subscriptions retain messages for the
client even when the client is disconnected, until the subscription is
unsubscribed. Subscription 2 has a (commented out) message selector argument so
you can conveniently experiement with the effect of those. <footnote>
<para>Each durable subscription is implemented as a queue on the Broker. See
<xref
linkend="JMS-Client-0-8-Client-Understanding-MessageConsumer-TopicSubscriptions"
/> for details.</para>
</footnote></para>
</callout>
<callout id="callout-pubsub-unsubscribe" arearefs="pubsub-java-unsubscribe">
<para>Unsubscribes the two durable subscribers, permanently removing the knowledge
of the subscriptions from the system. An application would normally
<emphasis>NOT</emphasis> do this. The typical use-case for durable
subsciption is one where the subscription exists over an extended period of
time.</para>
</callout>
</calloutlist>
<para>The contents of the <literal>stocks.properties</literal> file are shown below.</para>
<example id="JMS-Client-0-8-Examples-PubSub-PropertiesFile">
<title>JMS Example - Publish/subscribe Messaging - JNDI Properties</title>
<programlisting>
java.naming.factory.initial = org.apache.qpid.jndi.PropertiesFileInitialContextFactory
connectionfactory.qpidConnectionFactory = amqp://guest:guest@clientid/?brokerlist='tcp://localhost:5672'
topic.myprices = prices <co id="pubsub-properties-destination" linkends="callout-pubsub-properties-destination"/>
</programlisting>
</example>
<calloutlist>
<callout id="callout-pubsub-properties-destination"
arearefs="pubsub-properties-destination">
<para>Defines a topic for which MessageProducers and/or MessageConsumers send and
receive messages. The format of this entry is described in <xref
linkend="JMS-Client-0-8-JNDI-Properties-Format-Topic"/>.</para>
</callout>
</calloutlist>
</section>
</chapter>
|
