Sun Java System Message Queue 4.3 Technical Overview

Message Queue: Elements and Features

So far we have described the elements of message-oriented middleware and the use of JMS as a way of adding portability to MOM applications. It now remains to describe how Message Queue implements the JMS specification and to introduce the features and tools it uses to provide reliable, secure, and scalable messaging services.

First, like many JMS providers, Message Queue can be used as a stand-alone product or it can be used as an enabling technology, embedded in a Java EE application server to provide asynchronous messaging. Chapter 5, Message Queue and Java EE describes the role Message Queue plays in Java EE in greater detail. Unlike other JMS providers, Message Queue has been designated as the JMS reference implementation. This designation attests to the fact that Message Queue is a correct and complete JMS implementation. It also guarantees that the Message Queue product will remain current with any future JMS revisions and extensions.

This section covers the following topics:

The Message Queue Service

As a JMS provider, Message Queue offers a message service that implements the JMS interfaces and that also provides administrative management and control. So far, in illustrating JMS providers, the focus has been mainly on the role of a broker in delivering messages. But in fact, a JMS provider must include many additional elements to provide reliable, secure, and scalable messaging. Figure 1–6 shows the elements that make up the Message Queue message service (the shaded elements in the figure).

Figure 1–6 Message Queue Service

Figure shows components of the Message Queue service.
Figure explained in text.

As you can see, a full-featured JMS provider is more complex than the basic JMS model might lead one to suspect. The following sections introduce the elements of the Message Queue service shown in Figure 1–6:

The Broker

At the heart of the message service is the broker, which routes and delivers messages reliably, authenticates users, and gathers data for monitoring performance.

The Message Queue service provides a variety of administrative tools that the administrator can use to configure broker support. For more information, see Built-in Administration Tools.

Client Runtime Support

Client runtime support is provided in libraries that you use when building and running Message Queue clients. You can think of the client runtime as the part of the Message Queue service that enables the client. For example, when client code makes an API call to send a message, code in these libraries is invoked that packages the message bits appropriately for the protocol that will be used to relay the message to a physical destination on the broker.

Java and C Client Support

A JMS provider is only required to support Java clients; however, as Figure 1–6 shows, a Message Queue client can use either the Java API or a proprietary C API to send or receive a message. These interfaces are implemented in Java or C runtime libraries, which do the actual work of creating connections to the broker and packaging the bits appropriately for the connection service being used.

There are a number of differences in the functionality provided by these two APIs; these are documented in Java and C Clients.

It is important to remember that the JMS specification is a standard for Java clients only. C support is specific to the Message Queue provider and should not be used in client applications that you plan to port to other providers.

Support for SOAP Messages

SOAP (Simple Object Access Protocol) allows the exchange of structured data between two peers in a distributed environment. The data exchanged is specified by an XML schema. SOAP message delivery is limited to using the point-to-point domain and does not by itself guarantee reliability.

However, Message Queue Java clients are able to send and receive SOAP messages, encapsulated as JMS messages. By encapsulating a SOAP message in a JMS message and delivering it using the broker, you can take advantage of full featured Message Queue messaging, which guarantees reliable delivery and also allows you to use the publish/subscribe domain. Message Queue provides utility routines that a message producer can use to encapsulate a SOAP message as a JMS message and that a message consumer can use to extract a SOAP message from the JMS message. Message Queue also provides XML schema validation of the encapsulated XML message.

Working with SOAP Messages gives you a more detailed view of SOAP message processing.

Universal Message Service (UMS)

The Universal Messaging Service (UMS) and its messaging API provides access to Message Queue from any http-enabled device. As a result, almost any application can communicate with any other application and benefit from the reliability and guaranteed delivery of the Message Queue service.

The UMS, which runs in a web server, is language neutral and platform independent. The UMS serves as a gateway between any non-JMS client application and Message Queue. It receives messages sent using the UMS API, transforms them into JMS messages, and produces them to destinations in the Message Queue broker by way of the broker's connection services. Similarly, it retrieves messages from destinations in the broker, transforms them into text or SOAP messages, and sends the messages to non-JMS clients as requested by the clients through the UMS API.

The simple, language-independent, protocol-based UMS API supports both Web-based and non-Web-based applications, and can be used with both scripting and programming languages. The API is offered in two styles: a simple messaging API that uses a Representational State Transfer (REST)-style protocol, and an XML messaging API that embeds the protocol in a SOAP message header. In both cases, however, the API requires only a single http request to send or receive a message.

The simplicity and flexibility of the UMS API means that AJAX, .NET, Python, Ruby, C, Java, and many other applications can send text message and/or SOAP (with attachment) messages to JMS destinations or receive messages from JMS destinations. For example, Python applications can communicate with .NET applications, iPhone can communicate with Java applications, and so forth.


The Message Queue service offers command line tools that you can use to do the following:

You can also use a GUI-based administration console to perform the following command-line functions:

In addition, to these built-in administration tools, Message Queue also supports the Java Management Extensions (JMX) specification for configuring and monitoring brokers, destinations, connection services, and so forth. Using the JMX Administration API, you can perform these administration functions programmatically from within a Java application.

Broker Clusters: Scalability and Availability

Message Queue brokers can be connected into a broker cluster: a set of brokers that work collectively to perform message delivery between message producers and consumers. Broker clusters add scalability and availability to the Message Queue service, as described briefly in the following sections:

For additional information on broker clusters, see Chapter 4, Broker Clusters

Message Service Scalability

As the number of clients or the number of connections grows, you might need to scale a message service to eliminate bottlenecks or to improve performance. In general, you can scale a message service both vertically (increasing the number of client applications that are supported by a single broker) and horizontally (distributing client applications among a number of interconnected brokers).

Vertical scaling usually requires adding more processing power for a broker and by expanding available resources. You can do this by adding more processors or memory, by switching to a shared thread model, or by running the Java VM in 64 bit mode.

Horizontal scaling is generally achieved using a broker cluster. While it is possible to scale horizontally by simply redistributing clients among additional brokers that are not in a cluster, this approach is appropriate only if your messaging operations can be divided into independent work groups. However, if producer clients must produce messages to be consumed by consumer clients connected to remote brokers, then brokers must work collectively, as part of a broker cluster, to achieve horizontal scaling.

In a broker cluster, each broker is connected to every other broker in the cluster. Brokers can reside on the same host, but more often are distributed across a network. Each broker can route messages from producers to which it is directly connected to consumers that are connected to remote brokers in the cluster.

Note –

If you are using the point-to-point domain, you can scale the consumer side by allowing multiple consumers to access a queue. This is a Message Queue feature (the JMS specification defines messaging behavior in the case of only one consumer accessing a queue). When multiple consumers access a queue, the load-balancing among them takes into account each consumer’s capacity and message processing rate.

Message Service Availability

In addition to providing for message service scalability, broker clusters also provide for message service availability. If one broker in a cluster fails, then other brokers in the cluster are available to continue to provide messaging services to client applications.

Message Queue supports two clustering models that provide different degrees of availability:

Note –

You can also achieve data availability in a conventional cluster by using Sun Cluster software. Sun Cluster software replicates broker data and provides for a hot standby broker to take over the pending work of a failed broker. For details, see the documentation for Sun Cluster Data Service Agent for Message Queue.

Message Queue as an Enabling Technology

The Java Platform, Enterprise Edition (Java EE) is a specification for a distributed component model in a Java programming environment. One of the requirements of the Java EE platform is that distributed components be able to interact with one another through reliable, asynchronous message exchange. This capacity is furnished by a JMS provider, which can play two roles: it can be used to provide a service and it can support message-driven beans (MDB), a specialized type of Enterprise Java Bean (EJB) component that can consume JMS message.

A Java EE-compliant application server must use a resource adapter furnished by a given JMS provider to use the functionality of that provider. Message Queue provides such a resource adapter. Using the support of a plugged in JMS provider, Java EE components, including MDBs, deployed and running in the application server environment can exchange JMS messages among themselves and with external JMS components. This provides a powerful integration capability for distributed components.

For information on the Message Queue resource adapter, see Chapter 5, Message Queue and Java EE

Message Queue Feature Summary

Message Queue has capabilities and features that far exceed the requirements of the JMS specification and JMS API. These features enable Message Queue to integrate systems consisting of large numbers of distributed components exchanging many thousands of messages in round-the-clock, mission-critical operations.

The following enterprise-strength features, which are listed alphabetically in Appendix B, Message Queue Features, can be divided into the quality-of-service categories below:

Integration Support