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:

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

Be careful about starting destinations with /

If in Stomp world you use /queue/foo/bar then in a JMS world the queue would be called foo/bar not /foo/bar.

Persistent Messaging in STOMP

STOMP messages are non-persistent by default. To use persistent messaging add the following STOMP header to all SEND requests: persistent:true. This default is the opposite of that for JMS messages.

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:

Inclusion of content-length header

Resulting Message

yes

BytesMessage

no

TextMessage

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);
}     

Dependencies

ActiveMQ uses XStream for its transformation needs. Since it's the optional dependency you have to add it to broker's classpath by putting the appropriate JAR into the lib/ folder. Additionally, if you plan to use JSON transformations you have to add Jettison JSON parser to the classpath.

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:

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:

STOMP Header

JMS Header

Description

correlation-id

JMSCorrelationID

Good consumers will add this header to any responses they send.

expires

JMSExpiration

Expiration time of the message.

JMSXGroupID

JMSXGroupID

Specifies the Message Groups.

JMSXGroupSeq

JMSXGroupSeq

Optional header that specifies the sequence number in the Message Groups.

persistent

JMSDeliveryMode

Whether or not the message is persistent.

priority

JMSPriority

Priority on the message.

reply-to

JMSReplyTo

Destination you should send replies to.

type

JMSType

Type of the message.

ActiveMQ Extensions to STOMP

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

Verb

Header

Type

Description

CONNECT

client-id

string

Specifies the JMS clientID which is used in combination with the activemq.subcriptionName to denote a durable subscriber.

SUBSCRIBE

activemq.dispatchAsync

boolean

Should messages be dispatched synchronously or asynchronously from the producer thread for non-durable topics in the broker?

For fast consumers set this to false.

For slow consumers set it to true so that dispatching will not block fast consumers.

SUBSCRIBE

activemq.exclusive

boolean

I would like to be an Exclusive Consumer on the queue.

SUBSCRIBE

activemq.maximumPendingMessageLimit

int

For Slow Consumer Handling on non-durable topics by dropping old messages - we can set a maximum-pending limit, such that once a slow consumer backs up to this high water mark we begin to discard old messages.

SUBSCRIBE

activemq.noLocal

boolean

Specifies whether or not locally sent messages should be ignored for subscriptions.

Set to true to filter out locally sent messages.

SUBSCRIBE

activemq.prefetchSize

int

Specifies the maximum number of pending messages that will be dispatched to the client. Once this maximum is reached no more messages are dispatched until the client acknowledges a message.

Set to a low value > 1 for fair distribution of messages across consumers when processing messages can be slow

Note: if your STOMP client is implemented using a dynamic scripting language like Ruby, say, then this parameter must be set to 1 as there is no notion of a client-side message size to be sized.

STOMP does not support a value of 0.

SUBSCRIBE

activemq.priority

byte

Sets the priority of the consumer so that dispatching can be weighted in priority order.

SUBSCRIBE

activemq.retroactive

boolean

For non-durable topics make this subscription retroactive.

SUBSCRIBE

activemq.subscriptionName

string

For durable topic subscriptions you must specify the same activemq.client-id on the connection and activemq.subcriptionName on the subscribe prior to v5.7.0.

Note: the spelling subcriptionName NOT subscriptionName. This is not intuitive, but it is how it is implemented in ActiveMQ 4.x.

For the 5.0 release of ActiveMQ, both subcriptionName and subscriptionName will be supported (subcriptionName was removed as of v5.6.0).

SUBSCRIBE

selector

string

Specifies a JMS Selector using SQL 92 syntax as specified in the JMS 1.1 specification. This allows a filter to be applied to each message as part of the subscription.