Making Apache Camel work for you

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Making Apache
Camel
work for you

Intro to Camel

What’s Camel?
• Camel is an open source MOM language
developed by Apache and based on
Enterprise Integration Patterns
• Book by Gregor Hohpe and Bobby Woolf
• Centers around 60+ common patterns found
in Enterprise integration projects
• Defines these common patterns in a vendor
neutral way
• Camel aims to provide a language which
implements these patterns, in a style
modeled after the UNIX pipeline
• Camel is a very large topic, we will only
scrape the surface in this session

How does it work?
• Camel uses a repeatable, normalized concatenation of “Processor” and
”Message” objects in a group called an Exchange
• There is an ”In” message, a “Processor”, and an “Out” message
Processor
In Out

How does it work?
• And, you can chain these Exchanges together – just like piping commands
through UNIX – and form a Camel Route
• The “Out” message of a previous Exchange becomes the “In” message of
a new Exchange:
P
In Out
P
In Out
P
In Out

Camel magic
• Now here’s the magical part – a Processor can be anything you want it to
be
• Components in Camel work by creating Processors that perform various
business functions
• For instance, you can have an “FTP” processor that takes the In message
and initiates an FTP session
• Or you can have an “SMTP” processor that takes the In message and
sends an email with it
• This is in addition to Camel’s many built-in patterns, such as LoadBalance,
Multicast, DataSets, etc.
• And there are a lot of components:
http://camel.apache.org/components.html

Camel components
Uhm, yeah, the list isn’t gonna fit…
The point is there are a lot!

So Camel is pretty awesome…
• Camel provides many benefits for enterprise messaging applications
• It comes with a free library of over a hundred integration components, as
well as a powerful framework for creating your own components
• Camel routes can be visually debugged, similar to jBPM or BPEL
• Camel cuts down on boilerplate code enormously, by providing Spring-
based integration components for popular applications and frameworks
• Camel is FOSS under Apache 2.0 License
• As Camel improves its underlying Spring libraries, you can take advantage
of better functionality with very little if any development effort
• Camel’s syntax is very easy to understand and provides a low learning
curve for developers

A few common EIPs

Intro to Camel
• Dynamic Router
– Where a message is routed to disparate endpoints based on
message criteria

Intro to Camel
• Content Enricher
– In which a basic message enters the pattern, takes data from
another source, and then adds it to the message

Intro to Camel
• Recipient List
– A message is broadcast to n channels based on message criteria.
When this message is broadcast to all channels regardless, it
becomes a Multicast pattern

Intro to Camel
• Scatter-Gather
– In which messages are broadcast out to disparate endpoints and
results are aggregated into a single message

Let’s dive in

Coding in Camel
• Camel routes can be coded in Java POJO
• Or by using Camel Spring DSL XML files
from("activemq:foo").filter().
xquery("//foo").
to("activemq:bar")
<route xmlns="http://camel.apache.org/schema/spring" id="TimerClient">
<from uri="timer:AMQLoadTimer?repeatCount=10000&delay=10000"/>
<setBody id="TimerClientSetBody">
<constant>This is a test JMS message.</constant>
</setBody>
<to uri="activemq:Test_ActiveMQ_Route.inQueue" id="TimerClient.InQueueProducer"/>
</route>

Coding in Camel
<route xmlns="http://camel.apache.org/schema/spring" id="TimerClient">
<from uri="timer:AMQLoadTimer?repeatCount=10000&delay=10000"/>
<setBody id="TimerClientSetBody">
<constant>This is a test JMS message.</constant>
</setBody>
<to uri="activemq:Test_ActiveMQ_Route.inQueue" id="TimerClient.InQueueProducer"/>
</route>
Example Spring DSL Camel Route

Message anatomy
• The anatomy of a Camel message is very similar to the anatomy of a JMS
message
• This is unsurprising, as Camel is a Normalized Message Router
• The “Normalized” part comes from exchange patterns all acting according
to the same structure, i.e. In Message, Out Message, and Processor
• And the Message part comes from the fact that Messages are the payload
in an Exchange

Embedded processors
Camel also contains a number of embedded script languages that can be
used for various purposes
• Simple: The Simple query language can be used to introspect message
headers, payloads, and properties, and is useful when routing messages
based on their content
• Xpath: The XPath query language will let you traverse XML structures
and query for attribute and entity values, which is great for routing
messages based on their XML content
• JSONPath: Just like XPath, except for JSON-structured messages
• Groovy: The Groovy scripting language can be used for more advanced
data introspection and manipulation
• JavaScript: Yes, you can do entire processors in JavaScript

Demo – Content Based Router
• For this example, we will be using a very simple content based router
• In fact, we’ll be using the Simple query language to introspect a JMS
header in a message, and routing it to a destination based on the contents
of that header
• We will use Camel deployed directly into ActiveMQ, and we’ll write it from
scratch against a clean ActiveMQ install

Camel deployment
Camel can be deployed in a number of ways:
• It can be deployed as a Java Web App using Spring or POJO
• Standalone Camel routes can also be deployed using Maven and Camel
• Spring Boot can launch Camel routes
• Camel can be embedded within another Java application
• Or within a Java-based container such as Jetty, Tomcat, JBoss/Wildfly, and
others
• ActiveMQ contains the Camel core libraries and can launch and deploy
Camel routes
• And OSGI containers like Karaf or its Servicemix counterpart can launch
Camel routes

Camel development
• Major IDEs like Eclipse and IntelliJ can ease Camel development by
allowing routes to execute within the IDE
• As of Camel 2.16, comprehensive in-line tools are available which allow
autocompletion and even list every parameter of an available component

Camel development
• But HawtIO is my current favorite way to prototype with Camel
• HawtIO allows for visual debugging of routes, tracing of message lifecycle,
diagram driven development, as well as monitoring

Camel monitoring
• Camel has a robust set of JMX instrumentation beans which can be
looked at to gain more information on the route
• Any JMX-capable Enterprise Monitoring Solution will be a good fit for
Camel

Demo: HawtIO and Camel
• In this demo, we’ll visually debug our content based router using HawtIO
• We’ll demonstrate setting a breakpoint and introspecting a message at
that breakpoint
• And we’ll show off the truly neat Trace function

Conclusion
• Of course we have barely scraped the surface
• Camel contains powerful aggregation strategies for combining large, multi-
threaded or multi-processed data sets together
• It has indispensable capabilities for message transformation, from your
run-of-the-mill XSLT or Velocity/Freemarker to more advanced, format
conversion libraries like POI or PDFBox
• The best thing to do is just start playing with it! It has a low learning curve,
and can be deployed in a number of ways, making the barrier to entry very
low
• And the Camel community is active and friendly. Check out the Camel
IRC channel at #apache-camel in Freenode, or the Community page here:
http://camel.apache.org/community.html

Making Apache Camel work for you

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