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RabbitMQ Cookbook

RabbitMQ Cookbook

By : Sigismondo Boschi, Gabriele Santomaggio
4.1 (9)
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RabbitMQ Cookbook

RabbitMQ Cookbook

4.1 (9)
By: Sigismondo Boschi, Gabriele Santomaggio

Overview of this book

RabbitMQ is an open source message broker software (sometimes called message-oriented middleware) that implements the Advanced Message Queuing Protocol (AMQP). The RabbitMQ server is written in the Erlang programming language and is built on the Open Telecom Platform framework for clustering and failover. Messaging enables software applications to connect and scale. Applications can connect to each other as components of a larger application or to user devices and data. RabbitMQ Cookbook touches on all the aspects of RabbitMQ messaging. You will learn how to use this enabling technology for the solution of highly scalable problems dictated by the dynamic requirements of Web and mobile architectures, based for example on cloud computing platforms. This is a practical guide with several examples that will help you to understand the usefulness and the power of RabbitMQ. This book helps you learn the basic functionalities of RabbitMQ with simple examples which describe the use of RabbitMQ client APIs and how a RabbitMQ server works. You will find examples of RabbitMQ deployed in real-life use-cases, where its functionalities will be exploited combined with other technologies. This book helps you understand the advanced features of RabbitMQ that are useful for even the most demanding programmer. Over the course of the book, you will learn about the usage of basic AMQP functionalities and use RabbitMQ to let decoupled applications exchange messages as per enterprise integration applications. The same building blocks are used to implement the architecture of highly scalable applications like today's social networks, and they are presented in the book with some examples. You will also learn how to extend RabbitMQ functionalities by implementing Erlang plugins. This book combines information with detailed examples coupled with screenshots and diagrams to help you create a messaging application with ease.
Table of Contents (19 chapters)
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RabbitMQ Cookbook
Credits
About the Authors
About the Reviewers
www.PacktPub.com
Preface
1
Index

Handling unroutable messages

In this example we are showing how to manage unroutable messages. An unroutable message is a message without a destination. For example, a message sent to an exchange without any bound queue.

Unroutable messages are not similar to dead letter messages; the first are messages sent to an exchange without any suitable queue destination. The latter, on the other hand, reach a queue but are rejected because of an explicit consumer decision, expired TTL, or exceeded queue length limit. You can find the source at Chapter01/Recipe13/Java_13/.

Getting ready

To use this recipe you will need to set up the Java development environment as indicated in the Introduction section.

How to do it…

In order to handle unroutable messages, you need to perform the following steps:

  1. First of all we need to implement the class ReturnListener and its interface:
    public class HandlingReturnListener implements ReturnListener
    @Override
      public void handleReturn…
  2. Add the HandlingReturnListener class to the channel ReturnListener:
    channel.addReturnListener(new HandlingReturnListener());
  3. Then create an exchange:
    channel.exchangeDeclare(myExchange, "direct", false, false, null);
  4. And finally publish a mandatory message to the exchange:
    boolean isMandatory = true; 
    channel.basicPublish(myExchange, "",isMandatory, null, message.getBytes()); 

How it works…

When we execute the publisher, the messages sent to myExchange won't reach any destination since it has no bound queues. However, these messages aren't, they are redirected to an internal queue. The HandlingReturnListener class will handle such messages using handleReturn().

The ReturnListener class is bound to a publisher channel, and it will trap only its own unroutable messages.

You can also find a consumer in the source code example. Try also to execute the publisher and the consumer together, and then stop the consumer.

There's more…

If you don't set the channel ReturnListener, the unroutable messages are silently dropped by the broker. In case you want to be notified about the unroutable messages, it's important to set the mandatory flag to true; if false, the unroutable messages are dropped as well.

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RabbitMQ Cookbook
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