ActiveMQ supports the Stomp protocol and the Stomp - JMS mapping. This makes it easy to write a client in pure Ruby, Perl, Python or PHP for working with ActiveMQ.

Please see the Stomp site for more details

Enabling the ActiveMQ Broker for Stomp

To enable STOMP protocol support in the broker add a transport connector definition whose URI scheme is stomp.

Example:

<transportConnectors>
   <transportConnector name="stomp" uri="stomp://localhost:61613"/>
</transportConnectors>

To see a full example, try this XML. If you save that XML as foo.xml then you can run stomp via the command line as

activemq xbean:foo.xml

For more help see Run Broker.

The Stomp Wire Format

Stomp uses a text based wire format that can be configured with the following options.  All options can be configured on a Brokers transport bind URI.

Example:

<transportConnector name="stomp+ssl" uri="stomp+ssl://localhost:61612?wireFormat.maxFrameSize=1000000"/>

Security

From ActiveMQ 5.1: Stomp fully supports ActiveMQ's security mechanism. This means that the CONNECT command will return an ERROR STOMP frame on unsuccessful authentication. Also, the authorization policies will be applied when you try to access (read/write) certain destinations. If you use synchronous operations (by using receipts), you can expect an ERROR frame in case of unauthorized access attempt. In other case, operations will be discarded but the client will not be informed of errors. This applies to all errors that can occur broker-side.

Enabling Stomp over NIO

From ActiveMQ 5.3: for better scalability and performance the Stomp protocol can be configured to be run over the NIO transport. The NIO transport will use far fewer threads than the corresponding TCP connector. This can help when support for a large number of queues is required. To use NIO change the URI scheme of the transport connector to stomp+nio.

Example:

<transportConnector name="stomp+nio" uri="stomp+nio://localhost:61612"/>

Enabling Stomp over SSL

To configure ActiveMQ to use Stomp over an SSL connection change the URI scheme to stomp+ssl.

Example:

<transportConnector name="stomp+ssl" uri="stomp+ssl://localhost:61612"/>

For more details on using SSL with ActiveMQ see the following article (How do I use SSL). An example of using Stomp over SSL on the client side can be found in the PHP Stomp client example.

Heart-Beat Grace Period

The STOMP protocol (version 1.1 or greater) defines the concept of heart beats as a method by which a client and broker can determine the health of the underlying TCP connection between them. ActiveMQ supports STOMP heart beating provided the client is using version 1.1 (or greater) of the protocol.

Before ActiveMQ 5.9.0: enforcement of the 'read' heart-beat timeout (that is, a heart-beat sent from the client to the broker) was strict. In other words, the broker was intolerant of late arriving read heart-beats from the client. This resulted in the broker concluding that the client was no longer present causing it to close its side of the client's connection when the client failed to honor it's configured heart-beat settings.

From ActiveMQ 5.9.0: the timeout enforcement for read heart-beats is now configurable via a new transport option transport.hbGracePeriodMultiplier:

<transportConnectors>
   <transportConnector name="stomp" uri="stomp://localhost:61613?transport.hbGracePeriodMultiplier=1.5"/>
</transportConnectors>

This multiplier is used to calculate the effective read heart-beat timeout the broker will enforce for each client's connection. The multiplier is applied to the read-timeout interval the client specifies in its CONNECT frame:

  <client specified read heart-beat interval> * <grace periodmultiplier> == <broker enforced read heart-beat timeout interval>

For backward compatibility, if the grace period multiplier is not configured the default enforcement mode remains strict, e.g., transport.hbGracePeriodMultiplier=1.0. Attempts to configure the grace period multiplier to a value less than, or equal to 1.0 will be silently ignored.

STOMP clients that wish to be tolerant of late arriving heart-beats from the broker must implement their own solution for doing so.

• Please check the STOMP specification for the details on heart-beating

• The JIRA that implemented this: ActiveMQ 5.x does not support the notion of a grace-period for heart beats as supported by the STOMP protocol

Working with Destinations with Stomp

Note that the prefix in stomp /queue/ or /topic/ is removed from the string before passing it to ActiveMQ as a JMS destination. Also note that the default separator in MOM systems is . (dot). Whilst FOO.BAR is the normal syntax to identify a queue type destination the Stomp equivalent is /queue/FOO.BAR

Working with JMS Text/Bytes Messages and Stomp

Stomp is a very simple protocol - that's part of the beauty of it! As such, it does not have knowledge of JMS messages such as TextMessage's or BytesMessage's. The protocol does however support a content-length header. To provide more robust interaction between STOMP and JMS clients, ActiveMQ keys off of the inclusion of this header to determine what message type to create when sending from Stomp to JMS. The logic is simple:

This same logic can be followed when going from JMS to Stomp, as well. A Stomp client could be written to key off of the inclusion of the content-length header to determine what type of message structure to provide to the user.

Message Transformations

The transformation message header on SEND and SUBSCRIBE messages could be used to instruct ActiveMQ to transform messages from text to the format of your desire. Currently, ActiveMQ comes with a transformer that can transform XML/JSON text to Java objects, but you can add your own transformers as well.

Here's a quick example of how to use built-in transformer (taken from test cases)

    private String xmlObject = "<pojo>\n" 
            + "  <name>Dejan</name>\n"
            + "  <city>Belgrade</city>\n" 
            + "</pojo>";

    public void testTransformationReceiveXMLObject() throws Exception {
    	
        MessageProducer producer = session.createProducer(new ActiveMQQueue("USERS." + getQueueName()));
        ObjectMessage message = session.createObjectMessage(new SamplePojo("Dejan", "Belgrade"));
        producer.send(message);
    	
        String frame = "CONNECT\n" + "login: system\n" + "passcode: manager\n\n" + Stomp.NULL;
        stompConnection.sendFrame(frame);

        frame = stompConnection.receiveFrame();
        assertTrue(frame.startsWith("CONNECTED"));

        frame = "SUBSCRIBE\n" + "destination:/queue/USERS." + getQueueName() + "\n" + "ack:auto" + "\n" + "transformation:jms-object-xml\n\n" + Stomp.NULL;
        stompConnection.sendFrame(frame);
        
        frame = stompConnection.receiveFrame();

        assertTrue(frame.trim().endsWith(xmlObject));
        
        frame = "DISCONNECT\n" + "\n\n" + Stomp.NULL;
        stompConnection.sendFrame(frame);
    }     

In order to create your own transformer, you have to do the following:

1. Build your transformer by implementing a FrameTranslator interface

2. Associate it with the appropriate header value by creating a file named as a value you want to use in the META-INF/services/org/apache/activemq/transport/frametranslator/ folder of your JAR which will contain the value class=fully qualified classname of your transformer

For example the built-in transformer contains the following value:

class=org.apache.activemq.transport.stomp.XStreamFrameTranslator

in the META-INF/services/org/apache/activemq/transport/frametranslator/jms-xml file.

Debugging

In case you want to debug Stomp communication between broker and clients you should configure the Stomp connector with the trace parameter, like this:

<transportConnectors>
   <transportConnector name="stomp" uri="stomp://localhost:61613?trace=true"/>
</transportConnectors>

This will instruct the broker to trace all packets it sends and receives.

Furthermore, you have to enable tracing for the appropriate log. You can achieve that by adding the following to your conf/log4j.properties

log4j.logger.org.apache.activemq.transport.stomp=TRACE

Finally, you will probably want to keep these messages in the separate file instead of polluting the standard broker's log. You can achieve that with the following log4j configuration:

log4j.appender.stomp=org.apache.log4j.RollingFileAppender
log4j.appender.stomp.file=${activemq.base}/data/stomp.log
log4j.appender.stomp.maxFileSize=1024KB
log4j.appender.stomp.maxBackupIndex=5
log4j.appender.stomp.append=true
log4j.appender.stomp.layout=org.apache.log4j.PatternLayout
log4j.appender.stomp.layout.ConversionPattern=%d [%-15.15t] %-5p %-30.30c{1} - %m%n

log4j.logger.org.apache.activemq.transport.stomp=TRACE, stomp
log4j.additivity.org.apache.activemq.transport.stomp=false

# Enable these two lines and disable the above two if you want the frame IO ONLY (e.g., no heart beat messages, inactivity monitor etc).
#log4j.logger.org.apache.activemq.transport.stomp.StompIO=TRACE, stomp
#log4j.additivity.org.apache.activemq.transport.stomp.StompIO=false

After this, all your Stomp packets will be logged to the data/stomp.log

Java API

From ActiveMQ 5.2: there is a simple Java Stomp API distributed with ActiveMQ. Note that this API is provided purely for testing purposes and you should always consider using standard JMS API from Java instead of this one. The following code snippet provides a simple example of using this API:

StompConnection connection = new StompConnection();
connection.open("localhost", 61613);
		
connection.connect("system", "manager");
StompFrame connect = connection.receive();

if(!connect.getAction().equals(Stomp.Responses.CONNECTED)) {
	throw new Exception ("Not connected");
}
		
connection.begin("tx1");
connection.send("/queue/test", "message1", "tx1", null);
connection.send("/queue/test", "message2", "tx1", null);
connection.commit("tx1");
	
connection.subscribe("/queue/test", Subscribe.AckModeValues.CLIENT);
	
connection.begin("tx2");
	
StompFrame message = connection.receive();
System.out.println(message.getBody());
connection.ack(message, "tx2");
	
message = connection.receive();
System.out.println(message.getBody());
connection.ack(message, "tx2");
	
connection.commit("tx2");
		
connection.disconnect();

This example is part of the standard ActiveMQ distribution. You can run it from the ./example folder with:

ant stomp

Stomp Extensions for JMS Message Semantics

Note that STOMP is designed to be as simple as possible - so any scripting language/platform can message any other with minimal effort. STOMP allows pluggable headers on each request such as sending & receiving messages. ActiveMQ has several extensions to the Stomp protocol, so that JMS semantics can be supported by Stomp clients. An OpenWire JMS producer can send messages to a Stomp consumer, and a Stomp producer can send messages to an OpenWire JMS consumer. And Stomp to Stomp configurations, can use the richer JMS message control.

STOMP supports the following standard JMS properties on SENT messages:

ActiveMQ Extensions to STOMP

You can add custom headers to STOMP commands to configure the ActiveMQ protocol. Here are some examples: