Using the AMQ OpenWire JMS Client

AMQ OpenWire JMS supports the following industry-recognized standards and network protocols:

Refer to Red Hat AMQ 7 Supported Configurations on the Red Hat Customer Portal for current information regarding AMQ OpenWire JMS supported configurations.

This section introduces the core API entities and describes how they operate together.

AMQ OpenWire JMS sends and receives messages. Messages are transferred between connected peers using message producers and consumers. Producers and consumers are established over sessions. Sessions are established over connections. Connections are created by connection factories.

A sending peer creates a producer to send messages. The producer has a destination that identifies a target queue or topic at the remote peer. A receiving peer creates a consumer to receive messages. Like the producer, the consumer has a destination that identifies a source queue or topic at the remote peer.

A destination is either a queue or a topic. In JMS, queues and topics are client-side representations of named broker entities that hold messages.

A queue implements point-to-point semantics. Each message is seen by only one consumer, and the message is removed from the queue after it is read. A topic implements publish-subscribe semantics. Each message is seen by multiple consumers, and the message remains available to other consumers after it is read.

See the JMS tutorial for more information.

The sudo command

In this document, sudo is used for any command that requires root privileges. Exercise caution when using sudo because any changes can affect the entire system. For more information about sudo, see Using the sudo command.

File paths

In this document, all file paths are valid for Linux, UNIX, and similar operating systems (for example, /home/andrea). On Microsoft Windows, you must use the equivalent Windows paths (for example, C:\Users\andrea).

Variable text

This document contains code blocks with variables that you must replace with values specific to your environment. Variable text is enclosed in arrow braces and styled as italic monospace. For example, in the following command, replace <project-dir> with the value for your environment:

$ cd <project-dir>

Configure your Maven environment to download the client library from the Red Hat Maven repository.

The client is now available in your Maven project.

As an alternative to the online repository, AMQ OpenWire JMS can be installed to your local filesystem as a file-based Maven repository.

The example creates a consumer and producer for a queue named exampleQueue. It sends a text message and then receives it back, printing the received message to the console.

Running it on Linux results in the following output:

$ java -cp "target/classes:target/dependency/*" org.apache.activemq.artemis.jms.example.QueueExample
Sent message: This is a text message
Received message: This is a text message

The source code for the example is in the <install-dir>/examples/protocols/openwire/queue/src directory. Additional examples are available in the <install-dir>/examples/protocols/openwire directory.

JMS applications use a JNDI InitialContext object obtained from an InitialContextFactory to look up JMS objects such as the connection factory. AMQ OpenWire JMS provides an implementation of the InitialContextFactory in the org.apache.activemq.jndi.ActiveMQInitialContextFactory class.

The InitialContextFactory implementation is discovered when the InitialContext object is instantiated:

javax.naming.Context context = new javax.naming.InitialContext();

To find an implementation, JNDI must be configured in your environment. There are three ways of achieving this: using a jndi.properties file, using a system property, or using the initial context API.

Using a jndi.properties file

Create a file named jndi.properties and place it on the Java classpath. Add a property with the key java.naming.factory.initial.

java.naming.factory.initial = org.apache.activemq.jndi.ActiveMQInitialContextFactory

In Maven-based projects, the jndi.properties file is placed in the <project-dir>/src/main/resources directory.

Using a system property

Set the java.naming.factory.initial system property.

$ java -Djava.naming.factory.initial=org.apache.activemq.jndi.ActiveMQInitialContextFactory ...

Using the initial context API

Use the JNDI initial context API to set properties programatically.

Hashtable<Object, Object> env = new Hashtable<>();

env.put("java.naming.factory.initial", "org.apache.activemq.jndi.ActiveMQInitialContextFactory");

InitialContext context = new InitialContext(env);

Note that you can use the same API to set the JNDI properties for connection factories, queues, and topics.

The JMS connection factory is the entry point for creating connections. It uses a connection URI that encodes your application-specific configuration settings.

To set the factory name and connection URI, create a property in the format below. You can store this configuration in a jndi.properties file or set the corresponding system property.

connectionFactory.<lookup-name> = <connection-uri>

For example, this is how you might configure a factory named app1:

connectionFactory.app1 = tcp://example.net:61616?jms.clientID=backend

You can then use the JNDI context to look up your configured connection factory using the name app1:

ConnectionFactory factory = (ConnectionFactory) context.lookup("app1");

Connections are configured using a connection URI. The connection URI specifies the remote host, port, and a set of configuration options, which are set as query parameters. For more information about the available options, see Chapter 5, Configuration options.

<scheme>://<host>:<port>[?<option>=<value>[&<option>=<value>...]]

The scheme is tcp for unencrypted connections and ssl for SSL/TLS connections.

For example, the following is a connection URI that connects to host example.net at port 61616 and sets the client ID to backend:

tcp://example.net:61616?jms.clientID=backend

Failover URIs

URIs used for reconnect and failover can contain multiple connection URIs. They take the following form:

failover:(<connection-uri>[,<connection-uri>])[?<option>=<value>[&<option>=<value>...]]

Transport options prefixed with nested. are applied to each connection URI in the list.

JMS provides the option of using JNDI to look up deployment-specific queue and topic resources.

To set queue and topic names in JNDI, create properties in the following format. Either place this configuration in a jndi.properties file or set corresponding system properties.

queue.<lookup-name> = <queue-name>
topic.<lookup-name> = <topic-name>

For example, the following properties define the names jobs and notifications for two deployment-specific resources:

queue.jobs = app1/work-items
topic.notifications = app1/updates

You can then look up the resources by their JNDI names:

Queue queue = (Queue) context.lookup("jobs");
Topic topic = (Topic) context.lookup("notifications");

Prefetch policy options

Prefetch policy determines how many messages each MessageConsumer fetches from the remote peer and holds in a local "prefetch" buffer.

The value of prefetch can affect the distribution of messages to multiple consumers on a queue. A higher value can result in larger batches sent at once to each consumer. To achieve more even round-robin distribution when consumers operate at different rates, use a lower value.

Redelivery policy options

Redelivery policy controls how redelivered messages are handled on the client.

To write to a large message, use the BytesMessage.writeBytes() method. The following example reads bytes from a file and writes them to a message:

BytesMessage message = session.createBytesMessage();
File inputFile = new File(inputFilePath);
InputStream inputStream = new FileInputStream(inputFile);

int numRead;
byte[] buffer = new byte[1024];

while ((numRead = inputStream.read(buffer, 0, buffer.length)) != -1) {
    message.writeBytes(buffer, 0, numRead);
}

To read from a large message, use the BytesMessage.readBytes() method. The following example reads bytes from a message and writes them to a file:

BytesMessage message = (BytesMessage) consumer.receive();
File outputFile = new File(outputFilePath);
OutputStream outputStream = new FileOutputStream(outputFile);

int numRead;
byte buffer[] = new byte[1024];

for (int pos = 0; pos < message.getBodyLength(); pos += buffer.length) {
    numRead = message.readBytes(buffer);
    outputStream.write(buffer, 0, numRead);
}