Archive for the ‘Camel’ Category

Camel Cookbook Launch at LJC, March 5th

After all the hard work comes the fun. On Wednesday 5th of March, I will be giving a presentation entitled “Effective System Integrations with Apache Camel” at Skillsmatter, in London; hosted by the good folks from the London Java Community. The evening will kick off at 6:15, and I’ll be headlining 😉 at 6:45.

The premise for the talk is going to be a touch different from most of the “Intro to X” talks you may have watched – I will be discussing why most integrations you encounter tend to be half-baked and brittle, and what Apache Camel brings to the table that allows you to address the reasons behind this. The technical ones at least (there are other, non-technical ones too).

The evening is going to be the official London launch of the Apache Camel Developer’s Cookbook. I will be giving away a few copies, and there will also be a chance to buy a copy at the end of the talk for yourself, your workmates, family, friends, pets, etc. All proceeds on the night will be going to Shelter, the housing and homelessness charity. So bring your hard earned cash, grab yourself over 100 recipes for rock-solid integration, and do some good at the same time. Donate an extra £5, and I won’t deface your book with my signature 😉

Apache Camel Developer’s Cookbook

I am pleased to finally announce the reason that I have fallen off the face of the Earth over the past year – myself and Scott Cranton have just finished writing the Apache Camel Developer’s Cookbook. The book will be published by Packt Publishing later this month. It is available for pre-order on the Packt website, and also on Amazon (where it’s currently listed by its working title – Camel Enterprise Integration Cookbook). After 12 months of hard work and late nights (as well as early mornings) at home, in planes, trains, automobiles, hotel rooms, and airport lounges we’re very excited. And relieved – it has been a huge job writing about the ins-and-outs of this incredibly rich integration toolset.

Apache Camel Developer's Cookbook Our intention when writing the book was to develop something that complemented Claus Ibsen’s and Jon Anstey’s awesome Camel in Action. After 3 years Camel in Action continues to be an outstanding reference and a great text for learning Apache Camel inside-out, and has aged incredibly well – a testament to Camel’s solid underlying design. One of the comments that we heard frequently when out on site with clients was that they had bought it, and were going to get around to reading it… eventually.

Our main driver, therefore, was to write a book for the busy system integration developer who just needed to Get Stuff Done. All without requiring them to read a whole book and learn the entire framework, while at the same time not glossing over any of the key issues that they needed to consider in order to build a complete production-ready integration with Apache Camel – you know, with good performance, error handling, transactions etc. The result is a book with over 100 how-to recipes, each written in both of Camel’s Java and XML DSL variants, put together in such a way that people can jump around and get just the info that they need in order to get the job done.

There is a lot of good content there across all difficulty levels. Developers new to Apache Camel will find useful information on how to set up Camel in both regular Java and Spring-based applications, through to the ins-and-outs of the various Enterprise Integration Patterns (EIPs) (how they are affected by multithreading, transactions etc.), payload transformations and testing. There is plenty of good stuff for experienced developers too as we work through parallel and asynchronous processing, error handling and compensation, transactions and idempotency, monitoring and debugging, as well as detailing Camel’s support for security – your company encrypts all traffic, right? No? Well, no more excuses.

The chapters cover:

  • Structuring routes – everything from how to integrate the framework through to route templating
  • Message routing – a coverage of the main routing patterns
  • Routing to your code – how Camel interacts with your Java Code (bean binding, processors etc.)
  • Transformation – moving between XML, JSON, CSVs etc.
  • Splitting and Aggregating – a deep dive into the related Splitter and Aggregator EIPs
  • Parallel Processing – outlines Camel’s support for scaling out processing
  • Error Handling and Compensation – dealing with failure, including capabilities for triggering compensating logic
  • Transactions and Idempotency – how to handle failure of transactional (JDBC, JMS) and non-transactional (web services) resources
  • Testing – how to verify your routes’ behavior without the need for backend systems
  • Monitoring and Debugging – describes Camel’s support for logging, tracing, and debugging
  • Security – encrypting communication between systems, hiding sensitive configuration information, non-repudiation using certificates, and applying authentication and authorization to your routes
  • Web Services – a deep dive into working with one of Camel’s main use cases: SOAP web services

Some of the juicier recipes include:

  • Working with asynchronous APIs
  • Defining completion actions dynamically
  • Testing routes with fixed endpoints using conditional events
  • Digitally signing and verifying messages
  • Enabling step-by-step tracing in code
  • Monitoring other systems using the Camel JMX Component
  • Idempotency inside transactions
  • Setting up XA transactions over multiple transactional resources (many thanks to the guys at Atomikos for their help on this one)

The book is right up to date, with coverage of Camel 2.12.2 and a bit of eye candy thrown in for the monitoring chapter thanks to the hawtio project.

One of the things that we agreed that bugged us about most technical books was that the code frequently did not work. So right at the start we decided that every single snippet of code had to be taken straight from a fully-functional unit test. Whenever we made a statement in the book about how something behaved, we wrote a test for it (and found lots of interesting undocumented corner cases and gotchas, which we subsequently wrote up). The result is a massive set of examples, with 450 supporting tests – all readily usable (I have used them myself with clients on site). If you are interested in taking a look, all of the code is available on github at CamelCookbook/camel-cookbook-examples.

From the feedback that we have received from our reviewers – both formal and informal – is that we hit the mark; something we are really thrilled about. We were really privileged to have a number of Camel committers reviewing the book as well as our own clients who had varying levels of expertise with the framework. Many thanks go out to Claus Ibsen, Christian Posta, Bilgin Ibryam and Phil Wilkins for going through it all with a fine-toothed comb.

We hope that the book proves useful to the entire Apache Camel community, and further popularizes this amazingly productive integration framework.

Deep testing of integrations with Camel

One of the things that often comes up in client conversations about developing integration code with Camel is what test support is available, and more to the point appropriate, for testing integrations. There is a spectrum of test types that can be performed, ranging from fully automated unit tests to full-blown multi-system, user-based “click and see the flow through effects” tests. Camel came with comprehensive test support baked in from it’s very inception, but the mechanisms that are available can be used to go way beyond the standard unit test.

Unit tests

Without wanting to get academic about it, let’s define a unit test as being one that tests the logic encapsulated within a block of code without external side effects. Unit testing straightforward classes is trivial. If you want to make use of external service classes, these can be mocked using your favourite mocking library and injected into the class under test. Camel routes are a little different, in that what they define isn’t executed directly, but rather builds up a set of instructions that are handed to the Camel runtime for execution.

Camel has extensive support for testing routes defined using both the Java DSL as well as the Spring/Blueprints XML DSL. In general the pattern is:

  1. instantiate a RouteBuilder or Spring context containing the routes with a CamelContext, and start the context (this is handled for you by CamelTestSupport or CamelSpringTestSupport – see Camel testing). These should contain direct: endpoints as the inputs to the routes (consumers) and mock: endpoints as the outputs (producers).
  2. get a hold of the mock endpoints, and outline the expectations. A MockEndpoint itself uses a directed builder DSL to allow tou to define a suite of comprehensive expectation, ranging from checking the number of messages received to the details of an individual message. You can make full use of Camel expressions in these tests as well.
  3. create messages that you want to feed in to the route and send them to the direct: endpoint at the top of the route under test using a ProducerTemplate.
  4. assert that the mock endpoints received the expected messages.

An example of this approach can be seen in the RssConsumerRouteBuilderTest in the horo-app I blogged about yesterday.

There are a couple of things that you need to employ this approach successfully. If using Java, the RouteBuilder class that defines your routes should have the ability to have the route endpoint URIs injected and any beans that touch external resources into it – see RssConsumerRouteBuilder. The external beans can easily be mocked as in a standard unit test.

Using the Spring DSL, we can still employ the same general approach, but we need to jump through a couple of hoops to do it. Consider what you would need to do the equivalent. A simple route might be defined via:

    <route id="fileCopyRoute">
        <from uri="file:///some/directory"/>
        <to uri="file:///some/other/directory"/>

You can externalise any URIs using Spring’s property support:

    <route id="fileCopyRoute">
        <from uri="${fileCopyRoute.input}"/>
        <to uri="${fileCopyRoute.output}"/>

You could then define a PropertyPlaceHolderConfigurer with a properties file that defines these properties as


The definition of this class should be in a Spring context file seperate to that of your route definitions. For testing you would run the routes with another test XML file that defines a PropertyPlaceHolderConfigurer that points to a test file with the test URIs:

This is usually why Spring DM/Blueprints based bundle projects split the config across (a minimum of) two context files. One (META-INF/spring/spring-context-osgi.xml) contains all of the beans that touch the OSGi runtime including the properties mechanism, and the other (META-INF/spring/spring-context.xml) contains your physical routes. When testing you can easily switch out the OSGi bits via another config file. This allows you to inject in other bits during a unit test of the XML-based routes, or when using the camel-maven-plugin in order to run those routes off the command line without an OSGi container like ServiceMix.

Embedded integration tests

Sometimes, testing just the route logic isn’t enough. When I was building out the horo-app, I happily coded up my routes, tested tham and deployed, only to have them blow up immediately. What happened? The objects that I was expecting to receive from the RSS component didn’t match those the component actually sent out. So I changed tact. To engage the component as part of the route I needed a web server to serve the file that fed the test.

Integration testing is usually pretty problematic in that you need an external system servicing your tests – and when you are in an environment where the service changes, you can break the code of the other people working against the same system. But there is a solution! Sun’s Java 6 comes with an embeddable web server that you can start up as part of your integration tests.

The approach that I used was to spin up this server at the start of my test, and configure it programatically to serve up a response suitable for my test when a certain resource was consumed. The server was started on port 0, which means that it’s up to the runtime to assign an available port on the machine when the test runs. This is very important as it enables multiple instances of the same test to run at the same time, as is often the case on CI servers. Without it, tests would trip over each other. Similar approaches are possible using other embeddable server types, such as LDAP via ApacheDS, messaging via ActiveMQ, or databases via H2 or Derby.

Tests that require an external resource often start failing on large projects without any changes on the programmer’s side due to this exact reason – the underlying system dependencies changing. By embedding the server to test your integration against, you decouple yourself from that dependency.

The routes in your test then inject the URI to the embedded resource. In my case, I whipped up an integration test version of the original unit test (RssConsumerRouteBuilderITCase) to do exactly this. Integration tests can be wired in to a seperate part of the Maven build lifecycle using the maven-failsafe-plugin and use a different naming convention (* as opposed to *

Usually the way the you structure your tests to avoid duplicating the lifecycle of these embedded backends ends up relying on a test class hierarchy, which may end up looking like:

  • CamelTestSupport
    • CamelTestSupportWithDatabase
    • CamelTestSupportWithWebserver

which I don’t really like, as you inevitably end up requiring two kinds of resource in a test. A much better option is to manage these extended resources using JUnit’s @Rule annotation. This treats any object that implements the org.junit.rules.ExternalResource interface as an aspect of the test, stopping and starting it as part of the test’s lifecycle. As such, you can compose your test of as many of these dependencies as you like – all without a rigid class hierarchy.

This approach allows you to test your integration code against a physical backend, without requiring that backend to be shared between developers. This decouples your development from the rest of the team and allows your integration tests to be run in a CI server. A huge win, as only tests which are deterministic end up being run and maintained in the long term.


Transactional persistence with MyBatis in ServiceMix

This post has been a long time coming. A while back I cooked up a sample application, kind of a pet store for integration, that demonstrates a bunch of things that you might want to do beyond the standard bootstrap examples. This app takes the form of a horoscope aggregator, which allows you to view the last x days worth of horoscopes for a starsign (perhaps for the purposes of checking how accurate, or not, they were). The project is available as usual on GitHub at FuseByExample/horo-app.

The app demonstrates a number of useful things that you would typically want to do in an integration:

  • MyBatis via Spring for persistence directly from Camel routes, as well as for use directly by a web app (seperate bundles)
  • database transactions via a Spring PlatformTransactionManager
  • testing of your MyBatis templates against an embedded database; the one I have used is H2, the one used by the real app is Postgres
  • templatize your Camel routes; the app consumes two seperate RSS feeds in exactly the same way, though with different endpoints
  • unit test your routes by dependency injecting your endpoints, and using the CamelTestSupport mechanisms
  • perform “semi-integration” tests via the @Rule annotation against an embedded server within your JUnit tests, in such a way that multiple integration tests can run at the same time on the same server. This plugs in to the integration test part of the Maven build lifecycle, via the maven-failsafe-plugin Incredibly useful for CI! In this case, the purpose was to test the behaviour of the camel-rss component as part of the route.
  • deploy CXF JAX-RS services alongside your Camel bundles to provide access to your data via XML and JSON using just the one mechanism
  • share expensive resources such as DataSources between bundles using metadata, such as the database name that they provide access to
  • idempotent consumption, so the same stuff doesn’t keep getting processed (saved to the database) over and over. This is saved to a JDBC IdempotentRepository in a live environment, and an in-memory one in tests.

Full documentation available in the README. Enjoy!

System Integrations as Plugins using Camel and ServiceMix

I recently had a client with a use case that I thought would be interesting to share (and they were happy for me to talk about – no names, industry changed). Sample code and full instructions for the solution available as always at FuseByExample on Github.

Imagine a system integration where the core logic is static, but the systems that participate in a particular process change over time. Take as an example, a travel booking system that accepts orders for buying flights. How do you go about adding new integration logic for a particular capability such as the booking of a flight with a new airline via its system? On top of this:

  • without changing any of the core logic around the main business process (the booking of a flight also includes taking payment)
  • with no application downtime (hot deployment)
  • enabling other development teams to define integrations for new airlines

Conceptually, these requirements could be satisfied via an application-level “plugin” solution. Your core flight booking application forms a platform alongside which you deploy capabilities specific to individual airlines. This may seem like a complicated set of requirements, but there is a set of tools that you can use to enable exactly this type of application.

Using Camel provides us with a way that to easily partition integration logic into a core process (flight bookings) and sub-processes (booking a ticket with a particular airline), and dynamically route to the right sub-process depending on the booking request. Routes can be connected within the one container by using the ServiceMix NMR to pass messages beteen bundles.

Deploying logic that is specific to an individual airline as an OSGi component enables the separation of code away from the core process, and provides the required dynamicity (and allows others to write that logic). The trick is in putting it all together.

Conceptual overview

OSGi bundles can be thought of as mini-applications. Basing a bundle on SpringDM/Blueprints (essentially defining a Spring-like config in a known location), we can embed a Camel context inside it and have routing logic start up when that bundle is deployed. This is a good candidate for our airline-specific booking code.

We then need to somehow advise the main application bundle that the new process is on-line and ready to do business by having messages routed to it. To achieve this part, we use of the OSGi service registry. To those unfamiliar with it, the registry acts as a conceptual whiteboard inside an OSGi container. Our plugin bundles can register beans inside the registry as implementors of an interface. The core application that wishes to use these services looks up the registry to get a handle on the implementations.

To advertise the availability of a sub-process and provide the name of the Camel endpoint that accepts bookings for a particular airline, we use an interface that indicates to the main application that a plugin bundle is available to take bookings. This is placed in its own bundle such that it could be implemented in the airline-specific bundles, and used in the main booking process.

public interface BookingProcessor {
        public String getAirlineCode();
        public String getBookingRouteUri();

Each airline bundle defines its own implementation that returns the airline code that it accepts booking messages for, and the URI for the endpoint of the Camel route that it would be listening for messages on.

Bundle dependencies

This object is then registered with the OSGi service registry:

<osgi:service ref="germanAirlinePlugin" 
        interface="" />

The main process bundle is then able to get a dynamic proxy to a set of BookingProcessors that may come and go:

<osgi:set id="bookingProcessors" 

This set can then be injected into a bean (BookingProcessorRegistry) that makes decisions such as:

  • Is this airline currently supported by the system?
  • What is the route that can be invoked to process this booking?

The Camel routing logic can then be really simple:

<route id="placeBooking">
	<from uri="jetty:" />
			<method bean="bookingProcessorRegistry" method="isAirlineSupported"/>
			<recipientList stopOnException="true" strategyRef="bookingResponseAggregationStrategy">
				<constant>direct:takePayment, direct:placeBookingWithAirline</constant>
				<simple>Unable to book flight for ${body} - unsupported airline</simple>

<route id="placeBookingWithAirline">
	<from uri="direct:placeBookingWithAirline" />
	<!-- work out who to send the message to -->
	<setHeader headerName="bookingProcessor">
		<method bean="bookingProcessorRegistry" method="getBookingProcessorUri"/>
	<log message="Calling out to ${headers.bookingProcessor}"/>

So to make a new airline available for bookings, you:

  1. create a new OSGi bundle
  2. register a BookingProcessor in the service registry that indicates the route that processes these bookings
  3. write the integration logic in a route that listens on that endpoint
  4. build the bundle and drop it into Servicemix alongside the main process.

Voila! An application-specific plugin system. You can then use the Karaf web console as a mechanism to make the bundle logic available via REST to a single container, or if you want to distribute it across a cluster – Fuse Fabric via Fuse ESB Enterprise.

Build-time integration testing OSGi bundles in ServiceMix

I have just added a new project to GitHub under FuseByExample/smx-integration-testing that you can use to verify at build time that your bundles and features will deploy and run as expected in a specific version of ServiceMix. The intention is that you can use it to kick start testing in your own projects.

To do this I hooked up the process described by Ioannis Canellos in Advanced integration testing with Pax Exam Karaf to start up and deploy your project artifacts into an embedded FuseSource distribution of ServiceMix (4.4.1-fuse-01.13 at time of writing), using the maven-failsafe-plugin for integration testing.

The result is a build that compiles and assembles your bundle or features project, unit tests it, packages it up for installation and then integration tests the binary using pax-exam-karaf and JUnit.

If your bundle fails either to install into the embedded ServiceMix container, or fails any of the criteria defined in your integration test, the build will fail and the build artifact won’t end up being installed to your Maven repo.

The sample demonstrates:

  • the wiring required to assemble this approach in Maven
  • the separation of test artifacts for a SpringDM bundle into both unit and integration tests; abstracting out the OSGi bits for unit testing while ensuring ${} placeholders work, and
  • shows a number of ways to exercise the code in your bundle via:
    • straight Camel route testing
    • using the OSGi BundleContext to verify that a bundle is installed and active
    • checking that a SpringDM OSGi service is deployed via the @Inject mechanism

The documentation in the README file goes into full detail as to how this is achieved.


Bootstrap Projects for Getting Started with ServiceMix 4

Over the Christmas break I cleaned up and published a set of Maven projects for getting started with ServiceMix 4.4.1+ into GitHub. I found myself reusing the same code for a number of activities, and figured it may be of broader use to others. You can find it under FuseByExample/smx-bootstraps.

smx-bootstraps contains within it a set of OSGI Blueprints (DI, based on the ideas behind Spring) bundles that exercise some of the core things that you will want to do with ServiceMix:

  • defining services in bundles that can be reused in other bundles
  • use Camel for writing integration code
  • use ActiveMQ for sending persistent messages between bundles, regardless of whether they are in the same container or in others
  • request-response over messaging
  • Update 20/02/2012: RESTful web services!!!
  • externalising your environment configuration
  • group bundles into features

The README document at the project root explains how to get started with ServiceMix, deploy bundles, change code and play with config.

Why would you want to use them?

ServiceMix went through a massive generational change between versions 3.X and 4.X, moving from JBI to an OSGi based model. While development work on it is proceeding at a huge rate, the documentation hasn’t kept up – although it is being brought up to date in the background. smx-bootstraps contains small artifacts that are hopefully easy to understand and play with, along with instructions on how to use them in the container.

The project may also be use of use as a starting starting point to further development. A fairly clean project layout exists that you can use as a reference point, which acts as a supplement to the Maven archetypes that are publicly available, such as:

  • org.apache.camel.archetypes:camel-archetype-blueprint for generating Blueprint bundles to run Camel routes; similar to smx-pinger and smx-ponger bundles in smx-bootstraps
  • org.apache.karaf.archetypes:karaf-blueprint-archetype for generating simple Blueprint bundles; such as the smx-ponger-service bundle

I have found these bundles to be a really handy way of exercising ServiceMix features, and working with various configurations. Not having to code up something new each time is a huge time saver. Hopefully you should find this as well.

I expect to expand this little project as time goes on and I find myself recreating other use cases, such as exposing web services – next on my “todo list”. Please drop me a line at “jakub dot korab at gmail” if you find this useful or have any ideas that would fit in well. Of course being GitHub, feel free to fork it or contribute back changes.