There now follows the documentation on camel tutorialsWe have a number of tutorials as listed below. The tutorials often comes with source code which is either available in the Camel Download or attached to the wiki page.
These tutorials listed below, is hosted at Apache. We offer the Articles page where we have a link collection for 3rd party Camel material, such as tutorials, blog posts, published articles, videos, pod casts, presentations, and so forth.
If you have written a Camel related article, then we are happy to provide a link to it. You can contact the Camel Team, for example using the Mailing Lists, (or post a tweet with the word Apache Camel).
Tutorial on Spring Remoting with JMS
This tutorial was kindly donated to Apache Camel by Martin Gilday.
This tutorial aims to guide the reader through the stages of creating a project which uses Camel to facilitate the routing of messages from a JMS queue to a Spring service. The route works in a synchronous fashion returning a response to the client.
This tutorial uses Maven to setup the Camel project and for dependencies for artifacts.
This sample is distributed with the Camel distribution as
This tutorial is a simple example that demonstrates more the fact how well Camel is seamless integrated with Spring to leverage the best of both worlds. This sample is client server solution using JMS messaging as the transport. The sample has two flavors of servers and also for clients demonstrating different techniques for easy communication.
The Server is a JMS message broker that routes incoming messages to a business service that does computations on the received message and returns a response.
We use the following Camel components:
Create the Camel Project
For the purposes of the tutorial a single Maven project will be used for both the client and server. Ideally you would break your application down into the appropriate components.
Update the POM with Dependencies
First we need to have dependencies for the core Camel jars, spring, jms components, and finally ActiveMQ as the message broker.As we use spring xml configuration for the ActiveMQ JMS broker we need this dependency:
Writing the Server
Create the Spring Service
For this example the Spring service (our business service) on the server will be a simple multiplier which trebles in the received value.And the implementation of this service is: Notice that this class has been annotated with the @Service spring annotation. This ensures that this class is registered as a bean in the registry with the given name multiplier.
Define the Camel RoutesThis defines a Camel route from the JMS queue named numbers to the Spring bean named multiplier. Camel will create a consumer to the JMS queue which forwards all received messages onto the the Spring bean, using the method named multiply.
The Spring config file is placed under
Notice that we also have enabled the JMXAgent so we will be able to introspect the Camel Server with a JMX Console. The ActiveMQ JMS broker is also configured in this xml file. We set it up to listen on TCP port 61610. As this examples uses JMS then Camel needs a JMS component that is connected with the ActiveMQ broker. This is configured as shown below: Notice: The JMS component is configured in standard Spring beans, but the gem is that the bean id can be referenced from Camel routes - meaning we can do routing using the JMS Component by just using jms: prefix in the route URI. What happens is that Camel will find in the Spring Registry for a bean with the id="jms". Since the bean id can have arbitrary name you could have named it id="jmsbroker" and then referenced to it in the routing as
We use the vm protocol to connect to the ActiveMQ server as its embedded in this application.
Run the Server
The Server is started using the
In this sample as there are two servers (with and without AOP) we have prepared some profiles in maven to start the Server of your choice.
Writing The Clients
This sample has three clients demonstrating different Camel techniques for communication
Client Using The ProducerTemplate
We will initially create a client by directly using
And the CamelClient source code:The
Before running the client be sure that both the ActiveMQ broker and the
Client Using Spring Remoting
Spring Remoting "eases the development of remote-enabled services". It does this by allowing you to invoke remote services through your regular Java interface, masking that a remote service is being called.The snippet above only illustrates the different and how Camel easily can setup and use Spring Remoting in one line configurations.
The proxy will create a proxy service bean for you to use to make the remote invocations. The serviceInterface property details which Java interface is to be implemented by the proxy. The serviceUrl defines where messages sent to this proxy bean will be directed. Here we define the JMS endpoint with the "numbers" queue we used when working with Camel template directly. The value of the id property is the name that will be the given to the bean when it is exposed through the Spring
And the Java client source code:Again, the client is similar to the original client, but with some important differences.
Client Using Message Endpoint EIP Pattern
This client uses the Message Endpoint EIP pattern to hide the complexity to communicate to the Server. The Client uses the same simple API to get hold of the endpoint, create an exchange that holds the message, set the payload and create a producer that does the send and receive. All done using the same neutral Camel API for all the components in Camel. So if the communication was socket TCP based you just get hold of a different endpoint and all the java code stays the same. That is really powerful.
Okay enough talk, show me the code!Switching to a different component is just a matter of using the correct endpoint. So if we had defined a TCP endpoint as:
Run the Clients
The Clients is started using their main class respectively.
In this sample we start the clients using maven:
Also see the Maven
Using the Camel Maven Plugin
The Camel Maven Plugin allows you to run your Camel routes directly from Maven. This negates the need to create a host application, as we did with Camel server, simply to start up the container. This can be very useful during development to get Camel routes running quickly.
All that is required is a new plugin definition in your Maven POM. As we have already placed our Camel config in the default location (camel-server.xml has been placed in META-INF/spring/) we do not need to tell the plugin where the route definitions are located. Simply run
Using Camel JMX
Camel has extensive support for JMX and allows us to inspect the Camel Server at runtime. As we have enabled the JMXAgent in our tutorial we can fire up the jconsole and connect to the following service URI:
In the screenshot below we can see the route and its performance metrics:
Tutorial - camel-example-reportincident
Creating this tutorial was inspired by a real life use-case I discussed over the phone with a colleague. He was working at a client whom uses a heavy-weight integration platform from a very large vendor. He was in talks with developer shops to implement a new integration on this platform. His trouble was the shop tripled the price when they realized the platform of choice. So I was wondering how we could do this integration with Camel. Can it be done, without tripling the cost .
This tutorial is written during the development of the integration. I have decided to start off with a sample that isn't Camel's but standard Java and then plugin Camel as we goes. Just as when people needed to learn Spring you could consume it piece by piece, the same goes with Camel.
The target reader is person whom hasn't experience or just started using Camel.
Motivation for this tutorial
I wrote this tutorial motivated as Camel lacked an example application that was based on the web application deployment model. The entire world hasn't moved to pure OSGi deployments yet.
The full source code for this tutorial as complete is part of the Apache Camel distribution in the
The goal is to allow staff to report incidents into a central administration. For that they use client software where they report the incident and submit it to the central administration. As this is an integration in a transition phase the administration should get these incidents by email whereas they are manually added to the database. The client software should gather the incident and submit the information to the integration platform that in term will transform the report into an email and send it to the central administrator for manual processing.
The figure below illustrates this process. The end users reports the incidents using the client applications. The incident is sent to the central integration platform as webservice. The integration platform will process the incident and send an OK acknowledgment back to the client. Then the integration will transform the message to an email and send it to the administration mail server. The users in the administration will receive the emails and take it from there.
In EIP patterns
We distill the use case as EIP patterns:
This tutorial is divided into sections and parts:
Section A: Existing Solution, how to slowly use Camel
Part 1 - This first part explain how to setup the project and get a webservice exposed using Apache CXF. In fact we don't touch Camel yet.
Part 2 - Now we are ready to introduce Camel piece by piece (without using Spring or any XML configuration file) and create the full feature integration. This part will introduce different Camel's concepts and How we can build our solution using them like :
Part 3 - Continued from part 2 where we implement that last part of the solution with the event driven consumer and how to send the email through the Mail component.
Section B: The Camel Solution
Part 4 - We now turn into the path of Camel where it excels - the routing.
Using Axis 2
This tutorial uses the following frameworks:
Note: The sample project can be downloaded, see the resources section.
Initial Project Setup
We want the integration to be a standard .war application that can be deployed in any web container such as Tomcat, Jetty or even heavy weight application servers such as WebLogic or WebSphere. There fore we start off with the standard Maven webapp project that is created with the following long archetype command:
Notice that the groupId etc. doens't have to be org.apache.camel it can be com.mycompany.whatever. But I have used these package names as the example is an official part of the Camel distribution.
Then we have the basic maven folder layout. We start out with the webservice part where we want to use Apache CXF for the webservice stuff. So we add this to the pom.xml
Developing the WebService
As we want to develop webservice with the contract first approach we create our .wsdl file. As this is a example we have simplified the model of the incident to only include 8 fields. In real life the model would be a bit more complex, but not to much.
We put the wsdl file in the folder
Then we integration the CXF wsdl2java generator in the pom.xml so we have CXF generate the needed POJO classes for our webservice contract.
And then we can add the CXF wsdl2java code generator that will hook into the compile goal so its automatic run all the time:
You are now setup and should be able to compile the project. So running the
Configuration of the web.xml
Next up is to configure the web.xml to be ready to use CXF so we can expose the webservice.
And then we have the CXF part where we define the CXF servlet and its URI mappings to which we have chosen that all our webservices should be in the path
Then the last piece of the puzzle is to configure CXF, this is done in a spring XML that we link to fron the web.xml by the standard Spring
We have named our CXF configuration file
Getting rid of the old jsp world
The maven archetype that created the basic folder structure also created a sample .jsp file index.jsp. This file
Configuration of CXF
The cxf-config.xml is as follows:
The 3 import elements is needed by CXF and they must be in the file.
Noticed that we have a spring bean reportIncidentEndpoint that is the implementation of the webservice endpoint we let CXF expose.
Implementing the ReportIncidentEndpoint
Phew after all these meta files its time for some java code so we should code the implementor of the webservice. So we fire up
You can use
As we want to quickly see our webservice we implement just a quick and dirty as it can get. At first beware that since its jaxws and Java 1.5 we get annotations for the money, but they reside on the interface so we can remove them from our implementations so its a nice plain POJO again:
We just output the person that invokes this webservice and returns a OK response. This class should be in the maven source root folder
To test if we are home free we run
Running our webservice
Now that the code compiles we would like to run it inside a web container, for this purpose we make use of Jetty which we will bootstrap using it's plugin
Notice: We make use of the Jetty version being defined inside the Camel's Parent POM.
So to see if everything is in order we fire up jetty with
So where is the damn webservice then? Well as we did configure the web.xml to instruct the CXF servlet to accept the pattern
Hitting the webservice
Now we have the webservice running in a standard .war application in a standard web container such as Jetty we would like to invoke the webservice and see if we get our code executed. Unfortunately this isn't the easiest task in the world - its not so easy as a REST URL, so we need tools for this. So we fire up our trusty webservice tool SoapUI and let it be the one to fire the webservice request and see the response.
Using SoapUI we sent a request to our webservice and we got the expected OK response and the console outputs the System.out so we are ready to code.
Okay a little sidestep but wouldn't it be cool to be able to debug your code when its fired up under Jetty? As Jetty is started from maven, we need to instruct maven to use debug mode.
Then you need to restart Jetty so its stopped with ctrl + c. Remember to start a new shell to pickup the new environment settings. And start jetty again.
Then we can from our IDE attach a remote debugger and debug as we want.
Then we set a breakpoint in our code
Adding a unit test
Oh so much hard work just to hit a webservice, why can't we just use an unit test to invoke our webservice? Yes of course we can do this, and that's the next step.
Here we have a plain old JUnit class. As we want to test webservices we need to start and expose our webservice in the unit test before we can test it. And JAXWS has pretty decent methods to help us here, the code is simple as:
The Endpoint class is the
Next up is to create a webservice client so we can invoke our webservice. For this we actually use the CXF framework directly as its a bit more easier to create a client using this framework than using the JAXWS style. We could have done the same for the server part, and you should do this if you need more power and access more advanced features.
So now we are ready for creating a unit test. We have the server and the client. So we just create a plain simple unit test method as the usual junit style:
Now we are nearly there. But if you run the unit test with
Well what is that, CXF also uses Jetty for unit test - well its just shows how agile, embedable and popular Jetty is.
So lets run our junit test with, and it reports:
Yep thats it for now. We have a basic project setup.
End of part 1
Thanks for being patient and reading all this more or less standard Maven, Spring, JAXWS and Apache CXF stuff. Its stuff that is well covered on the net, but I wanted a full fledged tutorial on a maven project setup that is web service ready with Apache CXF. We will use this as a base for the next part where we demonstrate how Camel can be digested slowly and piece by piece just as it was back in the times when was introduced and was learning the Spring framework that we take for granted today.
In this part we will introduce Camel so we start by adding Camel to our pom.xml:
That's it, only one dependency for now.
If you continue from part 1, remember to update your editor project settings since we have introduce new .jar files. For instance IDEA has a feature to synchronize with Maven projects.
Now we turn towards our webservice endpoint implementation where we want to let Camel have a go at the input we receive. As Camel is very non invasive its basically a .jar file then we can just grap Camel but creating a new instance of
In fact we create a constructor in our webservice and add this code:
Logging the "Hello World"
Here at first we want Camel to log the givenName and familyName parameters we receive, so we add the
Then we change the code in the method that is invoked by Apache CXF when a webservice request arrives. We get the name and let Camel have a go at it in the new method we create sendToCamel:
Next is the Camel code. At first it looks like there are many code lines to do a simple task of logging the name - yes it is. But later you will in fact realize this is one of Camels true power. Its concise API. Hint: The same code can be used for any component in Camel.
Okay there are code comments in the code block above that should explain what is happening. We run the code by invoking our unit test with maven
Write to file - easy with the same code style
Okay that isn't to impressive, Camel can log Well I promised that the above code style can be used for any component, so let's store the payload in a file. We do this by adding the file component to the Camel context
And then we let camel write the payload to the file after we have logged, by creating a new method sendToCamelFile. We want to store the payload in filename with the incident id so we need this parameter also:
And then the code that is 99% identical. We have change the URI configuration when we create the endpoint as we pass in configuration parameters to the file component.
After running our unit test again with
Fully java based configuration of endpoints
In the file example above the configuration was URI based. What if you want 100% java setter based style, well this is of course also possible. We just need to cast to the component specific endpoint and then we have all the setters available:
That's it. Now we have used the setters to configure the
Okay I wanted to demonstrate how you can be in 100% control of the configuration and usage of Camel based on plain Java code with no hidden magic or special XML or other configuration files. Just add the camel-core.jar and you are ready to go.
You must have noticed that the code for sending a message to a given endpoint is the same for both the log and file, in fact any Camel endpoint. You as the client shouldn't bother with component specific code such as file stuff for file components, jms stuff for JMS messaging etc. This is what the Message Endpoint EIP pattern is all about and Camel solves this very very nice - a key pattern in Camel.
Reducing code lines
Now that you have been introduced to Camel and one of its masterpiece patterns solved elegantly with the Message Endpoint its time to give productive and show a solution in fewer code lines, in fact we can get it down to 5, 4, 3, 2 .. yes only 1 line of code.
The key is the ProducerTemplate that is a Spring'ish xxxTemplate based producer. Meaning that it has methods to send messages to any Camel endpoints. First of all we need to get hold of such a template and this is done from the CamelContext
Now we can use template for sending payloads to any endpoint in Camel. So all the logging gabble can be reduced to:
And the same goes for the file, but we must also send the header to instruct what the output filename should be:
Reducing even more code lines
Well we got the Camel code down to 1-2 lines for sending the message to the component that does all the heavy work of wring the message to a file etc. But we still got 5 lines to initialize Camel.
This can also be reduced. All the standard components in Camel is auto discovered on-the-fly so we can remove these code lines and we are down to 3 lines.
Component auto discovery
When an endpoint is requested with a scheme that Camel hasn't seen before it will try to look for it in the classpath. It will do so by looking for special Camel component marker files that reside in the folder
The class property defines the component implementation.
Tip: End-users can create their 3rd party components using the same technique and have them been auto discovered on-the-fly.
Okay back to the 3 code lines:
Later will we see how we can reduce this to ... in fact 0 java code lines. But the 3 lines will do for now.
Okay lets head back to the over goal of the integration. Looking at the EIP diagrams at the introduction page we need to be able to translate the incoming webservice to an email. Doing so we need to create the email body. When doing the message translation we could put up our sleeves and do it manually in pure java with a StringBuilder such as:
But as always it is a hardcoded template for the mail body and the code gets kinda ugly if the mail message has to be a bit more advanced. But of course it just works out-of-the-box with just classes already in the JDK.
Lets use a template language instead such as Apache Velocity. As Camel have a component for Velocity integration we will use this component. Looking at the Component List overview we can see that camel-velocity component uses the artifactId camel-velocity so therefore we need to add this to the pom.xml
And now we have a Spring conflict as Apache CXF is dependent on Spring 2.0.8 and camel-velocity is dependent on Spring 2.5.5. To remedy this we could wrestle with the pom.xml with excludes settings in the dependencies or just bring in another dependency camel-spring:
In fact camel-spring is such a vital part of Camel that you will end up using it in nearly all situations - we will look into how well Camel is seamless integration with Spring in part 3. For now its just another dependency.
We create the mail body with the Velocity template and create the file
Letting Camel creating the mail body and storing it as a file is as easy as the following 3 code lines:
What is impressive is that we can just pass in our POJO object we got from Apache CXF to Velocity and it will be able to generate the mail body with this object in its context. Thus we don't need to prepare anything before we let Velocity loose and generate our mail body. Notice that the template method returns a object with out response. This object contains the mail body as a String object. We can cast to String if needed.
If we run our unit test with
First part of the solution
What we have seen here is actually what it takes to build the first part of the integration flow. Receiving a request from a webservice, transform it to a mail body and store it to a file, and return an OK response to the webservice. All possible within 10 lines of code. So lets wrap it up here is what it takes:
Okay I missed by one, its in fact only 9 lines of java code and 2 fields.
End of part 2
I know this is a bit different introduction to Camel to how you can start using it in your projects just as a plain java .jar framework that isn't invasive at all. I took you through the coding parts that requires 6 - 10 lines to send a message to an endpoint, buts it's important to show the Message Endpoint EIP pattern in action and how its implemented in Camel. Yes of course Camel also has to one liners that you can use, and will use in your projects for sending messages to endpoints. This part has been about good old plain java, nothing fancy with Spring, XML files, auto discovery, OGSi or other new technologies. I wanted to demonstrate the basic building blocks in Camel and how its setup in pure god old fashioned Java. There are plenty of eye catcher examples with one liners that does more than you can imagine - we will come there in the later parts.
Okay part 3 is about building the last pieces of the solution and now it gets interesting since we have to wrestle with the event driven consumer.
Lets just recap on the solution we have now:
This completes the first part of the solution: receiving the message using webservice, transform it to a mail body and store it as a text file.
Adding the Event Driven Consumer
We want to add the consumer to our integration that listen for new files, we do this by creating a private method where the consumer code lives. We must register our consumer in Camel before its started so we need to add, and there fore we call the method addMailSenderConsumer in the constructor below:
The consumer needs to be consuming from an endpoint so we grab the endpoint from Camel we want to consume. It's
The URL configuration in Camel endpoints is just like regular URL we know from the Internet. You use ? and & to set the options.
When we have the endpoint we can create the consumer (just as in part 1 where we created a producer}. Creating the consumer requires a Processor where we implement the java code what should happen when a message arrives. To get the mail body as a String object we can use the getBody method where we can provide the type we want in return.
Camel Type Converter
Why don't we just cast it as we always do in Java? Well the biggest advantage when you provide the type as a parameter you tell Camel what type you want and Camel can automatically convert it for you, using its flexible Type Converter mechanism. This is a great advantage, and you should try to use this instead of regular type casting.
Sending the email is still left to be implemented, we will do this later. And finally we must remember to start the consumer otherwise its not active and won't listen for new files.
Before we test it we need to be aware that our unit test is only catering for the first part of the solution, receiving the message with webservice, transforming it using Velocity and then storing it as a file - it doesn't test the Event Driven Consumer we just added. As we are eager to see it in action, we just do a common trick adding some sleep in our unit test, that gives our Event Driven Consumer time to react and print to System.out. We will later refine the test:
We run the test with
Sending the email
Sending the email requires access to a SMTP mail server, but the implementation code is very simple:
And just invoke the method from our consumer:
Unit testing mail
For unit testing the consumer part we will use a mock mail framework, so we add this to our pom.xml:
Then we prepare our integration to run with or without the consumer enabled. We do this to separate the route into the two parts:
So we change the constructor code a bit:
Then remember to change the ReportIncidentEndpointTest to pass in false in the
Adding new unit test
We are now ready to add a new unit test that tests the consumer part so we create a new test class that has the following code structure:
As we want to test the consumer that it can listen for files, read the file content and send it as an email to our mailbox we will test it by asserting that we receive 1 mail in our mailbox and that the mail is the one we expect. To do so we need to grab the mailbox with the mockmail API. This is done as simple as:
How do we trigger the consumer? Well by creating a file in the folder it listen for. So we could use plain java.io.File API to create the file, but wait isn't there an smarter solution? ... yes Camel of course. Camel can do amazing stuff in one liner codes with its ProducerTemplate, so we need to get a hold of this baby. We expose this template in our ReportIncidentEndpointImpl but adding this getter:
Then we can use the template to create the file in one code line:
Then we just need to wait a little for the consumer to kick in and do its work and then we should assert that we got the new mail. Easy as just:
The final class for the unit test is:
End of part 3
Okay we have reached the end of part 3. For now we have only scratched the surface of what Camel is and what it can do. We have introduced Camel into our integration piece by piece and slowly added more and more along the way. And the most important is: you as the developer never lost control. We hit a sweet spot in the webservice implementation where we could write our java code. Adding Camel to the mix is just to use it as a regular java code, nothing magic. We were in control of the flow, we decided when it was time to translate the input to a mail body, we decided when the content should be written to a file. This is very important to not lose control, that the bigger and heavier frameworks tend to do. No names mentioned, but boy do developers from time to time dislike these elephants. And Camel is no elephant.
I suggest you download the samples from part 1 to 3 and try them out. It is great basic knowledge to have in mind when we look at some of the features where Camel really excel - the routing domain language.
From part 1 to 3 we touched concepts such as::
This section is about regular Camel. The examples presented here in this section is much more in common of all the examples we have in the Camel documentation.
If you have been reading the previous 3 parts then, this quote applies:
So we start all over again!
Camel is particular strong as a light-weight and agile routing and mediation framework. In this part we will introduce the routing concept and how we can introduce this into our solution.
Before we jump into it, we want to state that this tutorial is about Developers not loosing control. In my humble experience one of the key fears of developers is that they are forced into a tool/framework where they loose control and/or power, and the possible is now impossible. So in this part we stay clear with this vision and our starting point is as follows:
So the starting point is:
Yes we have a simple plain Java class where we have the implementation of the webservice. The cursor is blinking at the WE ARE HERE block and this is where we feel home. More or less any Java Developers have implemented webservices using a stack such as: Apache AXIS, Apache CXF or some other quite popular framework. They all allow the developer to be in control and implement the code logic as plain Java code. Camel of course doesn't enforce this to be any different. Okay the boss told us to implement the solution from the figure in the Introduction page and we are now ready to code.
RouteBuilder is the hearth in Camel of the Java DSL routing. This class does all the heavy lifting of supporting EIP verbs for end-users to express the routing. It does take a little while to get settled and used to, but when you have worked with it for a while you will enjoy its power and realize it is in fact a little language inside Java itself. Camel is the only integration framework we are aware of that has Java DSL, all the others are usually only XML based.
As an end-user you usually use the RouteBuilder as of follows:
So we create a new class ReportIncidentRoutes and implement the first part of the routing:
What to notice here is the configure method. Here is where all the action is. Here we have the Java DSL langauge, that is expressed using the fluent builder syntax that is also known from Hibernate when you build the dynamic queries etc. What you do is that you can stack methods separating with the dot.
In the example above we have a very common routing, that can be distilled from pseudo verbs to actual code with:
from("direct:start") is the consumer that is kick-starting our routing flow. It will wait for messages to arrive on the direct queue and then dispatch the message.
So what we have implemented so far with our ReportIncidentRoutes RouteBuilder is this part of the picture:
Adding the RouteBuilder
Now we have our RouteBuilder we need to add/connect it to our CamelContext that is the hearth of Camel. So turning back to our webservice implementation class ReportIncidentEndpointImpl we add this constructor to the code, to create the CamelContext and add the routes from our route builder and finally to start it.
Okay how do you use the routes then? Well its just as before we use a ProducerTemplate to send messages to Endpoints, so we just send to the direct:start endpoint and it will take it from there.
Notice that we get the producer template using the createProducerTemplate method on the CamelContext. Then we send the input parameters to the direct:start endpoint and it will route it to the velocity endpoint that will generate the mail body. Since we use direct as the consumer endpoint (=from) and its a synchronous exchange we will get the response back from the route. And the response is of course the output from the velocity endpoint.
About creating ProducerTemplate
In the example above we create a new
We have now completed this part of the picture:
Now is the time we would like to unit test what we got now. So we call for camel and its great test kit. For this to work we need to add it to the pom.xml
After adding it to the pom.xml you should refresh your Java Editor so it pickups the new jar. Then we are ready to create out unit test class.
That is easy just return an instance of our route builder and this unit test will use our routes.
It is quite common in Camel itself to unit test using routes defined as an anonymous inner class, such as illustrated below:
The same technique is of course also possible for end-users of Camel to create parts of your routes and test them separately in many test classes.
We then code our unit test method that sends a message to the route and assert that its transformed to the mail body using the Velocity template.
Adding the File Backup
The next piece of puzzle that is missing is to store the mail body as a backup file. So we turn back to our route and the EIP patterns. We use the Pipes and Filters pattern here to chain the routing as:
Notice that we just add a 2nd .to on the newline. Camel will default use the Pipes and Filters pattern here when there are multi endpoints chained liked this. We could have used the pipeline verb to let out stand out that its the Pipes and Filters pattern such as:
But most people are using the multi .to style instead.
We re-run out unit test and verifies that it still passes:
But hey we have added the file producer endpoint and thus a file should also be created as the backup file. If we look in the
Setting the filename
For starters we show the simple solution and build from there. We start by setting a constant filename, just to verify that we are on the right path, to instruct the file producer what filename to use. The file producer uses a special header
What we do is to send the header when we "kick-start" the routing as the header will be propagated from the direct queue to the file producer. What we need to do is to use the
However we could also have used the route builder itself to configure the constant filename as shown below:
But Camel can be smarter and we want to dynamic set the filename based on some of the input parameters, how can we do this?
Using Bean Language to compute the filename
First we create our plain java class that computes the filename, and it has 100% no dependencies to Camel what so ever.
The class is very simple and we could easily create unit tests for it to verify that it works as expected. So what we want now is to let Camel invoke this class and its generateFilename with the input parameters and use the output as the filename. Pheeeww is this really possible out-of-the-box in Camel? Yes it is. So lets get on with the show. We have the code that computes the filename, we just need to call it from our route using the Bean Language:
Notice that we use the bean language where we supply the class with our bean to invoke. Camel will instantiate an instance of the class and invoke the suited method. For completeness and ease of code readability we add the method name as the 2nd parameter
Then other developers can understand what the parameter is, instead of
Now we have a nice solution, but as a sidetrack I want to demonstrate the Camel has other languages out-of-the-box, and that scripting language is a first class citizen in Camel where it etc. can be used in content based routing. However we want it to be used for the filename generation.
Using a script language to set the filename
We could do as in the previous parts where we send the computed filename as a message header when we "kick-start" the route. But we want to learn new stuff so we look for a different solution using some of Camels many Languages. As OGNL is a favorite language of mine (used by WebWork) so we pick this baby for a Camel ride. For starters we must add it to our pom.xml:
And remember to refresh your editor so you got the new .jars.
In OGNL glory this is done as:
Now we got the expression to dynamic compute the filename on the fly we need to set it on our route so we turn back to our route, where we can add the OGNL expression:
And since we are on Java 1.5 we can use the static import of ognl so we have:
Notice the import static also applies for all the other languages, such as the Bean Language we used previously.
Whatever worked for you we have now implemented the backup of the data files:
Sending the email
What we need to do before the solution is completed is to actually send the email with the mail body we generated and stored as a file. In the previous part we did this with a File consumer, that we manually added to the CamelContext. We can do this quite easily with the routing.
The last 3 lines of code does all this. It adds a file consumer from("file://target/subfolder"), sets the mail subject, and finally send it as an email.
The DSL is really powerful where you can express your routing integration logic.
We have now completed the integration:
We have just briefly touched the routing in Camel and shown how to implement them using the fluent builder syntax in Java. There is much more to the routing in Camel than shown here, but we are learning step by step. We continue in part 5. See you there.
Better JMS Transport for CXF Webservice using Apache Camel
Configuring JMS in Apache CXF before Version 2.1.3 is possible but not really easy or nice. This article shows how to use Apache Camel to provide a better JMS Transport for CXF.
Update: Since CXF 2.1.3 there is a new way of configuring JMS (Using the JMSConfigFeature). It makes JMS config for CXF as easy as with Camel. Using Camel for JMS is still a good idea if you want to use the rich feature of Camel for routing and other Integration Scenarios that CXF does not support.
So how to connect Apache Camel and CXF
The best way to connect Camel and CXF is using the Camel transport for CXF. This is a camel module that registers with cxf as a new transport. It is quite easy to configure.
This bean registers with CXF and provides a new transport prefix camel:// that can be used in CXF address configurations. The bean references a bean cxf which will be already present in your config. The other refrenceis a camel context. We will later define this bean to provide the routing config.
How is JMS configured in Camel
In camel you need two things to configure JMS. A ConnectionFactory and a JMSComponent. As ConnectionFactory you can simply set up the normal Factory your JMS provider offers or bind a JNDI ConnectionFactory. In this example we use the ConnectionFactory provided by ActiveMQ.
Then we set up the JMSComponent. It offers a new transport prefix to camel that we simply call jms. If we need several JMSComponents we can differentiate them by their name.
You can find more details about the JMSComponent at the Camel Wiki. For example you find the complete configuration options and a JNDI sample there.
Setting up the CXF client
We will configure a simple CXF webservice client. It will use stub code generated from a wsdl. The webservice client will be configured to use JMS directly. You can also use a direct: Endpoint and do the routing to JMS in the Camel Context.
We explicitly configure serviceName and endpointName so they are not read from the wsdl. The names we use are arbitrary and have no further function but we set them to look nice. The serviceclass points to the service interface that was generated from the wsdl. Now the important thing is address. Here we tell cxf to use the camel transport, use the JmsComponent who registered the prefix "jms" and use the queue "CustomerService".
Setting up the CamelContext
As we do not need additional routing an empty CamelContext bean will suffice.
Running the Example
As you have seen in this example you can use Camel to connect services to JMS easily while being able to also use the rich integration features of Apache Camel.
Tutorial using Axis 1.4 with Apache Camel
Removed from distribution
This example has been removed from Camel 2.9 onwards. Apache Axis 1.4 is a very old and unsupported framework. We encourage users to use CXF instead of Axis.
This tutorial uses Maven 2 to setup the Camel project and for dependencies for artifacts.
This sample is distributed with the Camel 1.5 distribution as
Apache Axis is/was widely used as a webservice framework. So in line with some of the other tutorials to demonstrate how Camel is not an invasive framework but is flexible and integrates well with existing solution.
We have an existing solution that exposes a webservice using Axis 1.4 deployed as web applications. This is a common solution. We use contract first so we have Axis generated source code from an existing wsdl file. Then we show how we introduce Spring and Camel to integrate with Axis.
This tutorial uses the following frameworks:
Setting up the project to run Axis
This first part is about getting the project up to speed with Axis. We are not touching Camel or Spring at this time.
Axis dependencies is available for maven 2 so we configure our pom.xml as:
Then we need to configure maven to use Java 1.5 and the Axis maven plugin that generates the source code based on the wsdl file:
We use the same .wsdl file as the Tutorial-Example-ReportIncident and copy it to
Okay we are now setup for the contract first development and can generate the source file. For now we are still only using standard Axis and not Spring nor Camel. We still need to setup Axis as a web application so we configure the web.xml in
The web.xml just registers Axis servlet that is handling the incoming web requests to its servlet mapping. We still need to configure Axis itself and this is done using its special configuration file
The tool will generate the source code based on the wsdl and save the files to the following folder:
This is standard Axis and so far no Camel or Spring has been touched. To implement our webservice we will add our code, so we create a new class
Now we need to configure Axis itself and this is done using its
The globalConfiguration and transport is not in the deploy.wsdd file so you gotta write that yourself. The service is a 100% copy from deploy.wsdd. Axis has more configuration to it than shown here, but then you should check the Axis documentation.
What we need to do now is important, as we need to modify the above configuration to use our webservice class than the default one, so we change the classname parameter to our class AxisReportIncidentService:
Running the Example
Now we are ready to run our example for the first time, so we use Jetty as the quick web container using its maven command:
Then we can hit the web browser and enter this URL:
Clicking on the .wsdl link shows the wsdl file, but what. It's an auto generated one and not our original .wsdl file. So we need to fix this ASAP and this is done by configuring Axis in the server-config.wsdd file:
We do this by adding the wsdlFile tag in the service element where we can point to the real .wsdl file.
First we need to add its dependencies to the pom.xml.
Spring is integrated just as it would like to, we add its listener to the web.xml and a context parameter to be able to configure precisely what spring xml files to use:
Next is to add a plain spring XML file named axis-example-context.xml in the src/main/resources folder.
The spring XML file is currently empty. We hit jetty again with
We would like to be able to get hold of the Spring ApplicationContext from our webservice so we can get access to the glory spring, but how do we do this? And our webservice class AxisReportIncidentService is created and managed by Axis we want to let Spring do this. So we have two problems.
We solve these problems by creating a delegate class that Axis creates, and this delegate class gets hold on Spring and then gets our real webservice as a spring bean and invoke the service.
First we create a new class that is 100% independent from Axis and just a plain POJO. This is our real service.
So now we need to get from AxisReportIncidentService to this one ReportIncidentService using Spring. Well first of all we add our real service to spring XML configuration file so Spring can handle its lifecycle:
And then we need to modify AxisReportIncidentService to use Spring to lookup the spring bean id="incidentservice" and delegate the call. We do this by extending the spring class
To see if everything is okay we run
In the code above we get hold of our service at each request by looking up in the application context. However Spring also supports an init method where we can do this once. So we change the code to:
So now we have integrated Axis with Spring and we are ready for Camel.
Again the first step is to add the dependencies to the maven pom.xml file:
Now that we have integrated with Spring then we easily integrate with Camel as Camel works well with Spring.
Camel does not require Spring
Camel does not require Spring, we could easily have used Camel without Spring, but most users prefer to use Spring also.
We choose to integrate Camel in the Spring XML file so we add the camel namespace and the schema location:
Store a file backup
We want to store the web service request as a file before we return a response. To do this we want to send the file content as a message to an endpoint that produces the file. So we need to do two steps:
The endpoint is configured in spring XML so we just add it as:
In the CamelContext we have defined our endpoint with the id
Next up is to be able to send a message to this endpoint. The easiest way is to use a ProducerTemplate. A ProducerTemplate is inspired by Spring template pattern with for instance JmsTemplate or JdbcTemplate in mind. The template that all the grunt work and exposes a simple interface to the end-user where he/she can set the payload to send. Then the template will do proper resource handling and all related issues in that regard. But how do we get hold of such a template? Well the CamelContext is able to provide one. This is done by configuring the template on the camel context in the spring XML as:
Then we can expose a ProducerTemplate property on our service with a setter in the Java code as:
And then let Spring handle the dependency inject as below:
Now we are ready to use the producer template in our service to send the payload to the endpoint. The template has many sendXXX methods for this purpose. But before we send the payload to the file endpoint we must also specify what filename to store the file as. This is done by sending meta data with the payload. In Camel metadata is sent as headers. Headers is just a plain
The template in the code above uses 4 parameters:
Running the example
We start our integration with maven using
You can then test it using a web service test tools such as SoapUI.
And there should be a file in the target subfolder.
We would like to be able to unit test our ReportIncidentService class. So we add junit to the maven dependency:
And then we create a plain junit testcase for our service class.
Then we can run the test with maven using:
What is the problem? Well our service uses a CamelProducer (the template) to send a message to the file endpoint so the message will be stored in a file. What we need is to get hold of such a producer and inject it on our service, by calling the setter.
Since Camel is very light weight and embedable we are able to create a CamelContext and add the endpoint in our unit test code directly. We do this to show how this is possible:
So now we are ready to set the ProducerTemplate on our service, and we get a hold of that baby from the CamelContext as:
And this time when we run the unit test its a success:
We would like to test that the file exists so we add these two lines to our test method:
Smarter Unit Testing with Spring
The unit test above requires us to assemble the Camel pieces manually in java code. What if we would like our unit test to use our spring configuration file axis-example-context.xml where we already have setup the endpoint. And of course we would like to test using this configuration file as this is the real file we will use. Well hey presto the xml file is a spring ApplicationContext file and spring is able to load it, so we go the spring path for unit testing. First we add the spring-test jar to our maven dependency:
And then we refactor our unit test to be a standard spring unit class. What we need to do is to extend
What we must remember to add is the classpath: prefix as our xml file is located in
The last change is to get hold of the producer template and now we can just refer to the bean id it has in the spring xml file:
So we get hold of it by just getting it from the spring ApplicationContext as all spring users is used to do:
Now our unit test is much better, and a real power of Camel is that is fits nicely with Spring and you can use standard Spring'ish unit test to test your Camel applications as well.
Unit Test calling WebService
What if you would like to execute a unit test where you send a webservice request to the AxisReportIncidentService how do we unit test this one? Well first of all the code is merely just a delegate to our real service that we have just tested, but nevertheless its a good question and we would like to know how. Well the answer is that we can exploit that fact that Jetty is also a slim web container that can be embedded anywhere just as Camel can. So we add this to our pom.xml:
Then we can create a new class AxisReportIncidentServiceTest to unit test with Jetty. The code to setup Jetty is shown below with code comments:
Now we just need to send the incident as a webservice request using Axis. So we add the following code:
And now we have an unittest that sends a webservice request using good old Axis.
Both Camel and Spring has annotations that can be used to configure and wire trivial settings more elegantly. Camel has the endpoint annotation
Camel is smart as
Running the unit test with
And since we use the
And the final touch we can do is that since the endpoint is injected with concrete endpoint to use we can remove the
To without the name:
Then we avoid to duplicate the name and if we rename the endpoint name then we don't forget to change it in the code also.
This tutorial hasn't really touched the one of the key concept of Camel as a powerful routing and mediation framework. But we wanted to demonstrate its flexibility and that it integrates well with even older frameworks such as Apache Axis 1.4.
Check out the other tutorials on Camel and the other examples.
Note that the code shown here also applies to Camel 1.4 so actually you can get started right away with the released version of Camel. As this time of writing Camel 1.5 is work in progress.
Tutorial on using Camel in a Web Application
Camel has been designed to work great with the Spring framework; so if you are already a Spring user you can think of Camel as just a framework for adding to your Spring XML files.
So you can follow the usual Spring approach to working with web applications; namely to add the standard Spring hook to load a /WEB-INF/applicationContext.xml file. In that file you can include your usual Camel XML configuration.
Step1: Edit your web.xml
To enable spring add a context loader listener to your /WEB-INF/web.xml file
This will cause Spring to boot up and look for the /WEB-INF/applicationContext.xml file.
Step 2: Create a /WEB-INF/applicationContext.xml file
Now you just need to create your Spring XML file and add your camel routes or configuration.
Then boot up your web application and you're good to go!
Hints and Tips
If you use Maven to build your application your directory tree will look like this...
You should update your Maven pom.xml to enable WAR packaging/naming like this...
To enable more rapid development we highly recommend the jetty:run maven plugin.
Please refer to the help for more information on using jetty:run - but briefly if you add the following to your pom.xml
Then you can run your web application as follows
Then Jetty will also monitor your target/classes directory and your src/main/webapp directory so that if you modify your spring XML, your web.xml or your java code the web application will be restarted, re-creating your Camel routes.
If your unit tests take a while to run, you could miss them out when running your web application via
Tutorial Business Partners
This tutorial is a work in progress.
Background and Introduction
So there's a company, which we'll call Acme. Acme sells widgets, in a fairly unusual way. Their customers are responsible for telling Acme what they purchased. The customer enters into their own systems (ERP or whatever) which widgets they bought from Acme. Then at some point, their systems emit a record of the sale which needs to go to Acme so Acme can bill them for it. Obviously, everyone wants this to be as automated as possible, so there needs to be integration between the customer's system and Acme.
Sadly, Acme's sales people are, technically speaking, doormats. They tell all their prospects, "you can send us the data in whatever format, using whatever protocols, whatever. You just can't change once it's up and running."
The result is pretty much what you'd expect. Taking a random sample of 3 customers:
Now on the Acme side, all this has to be converted to a canonical XML format and submitted to the Acme accounting system via JMS. Then the Acme accounting system does its stuff and sends an XML reply via JMS, with a summary of what it processed (e.g. 3 line items accepted, line item #2 in error, total invoice $123.45). Finally, that data needs to be formatted into an e-mail, and sent to a contact at the customer in question ("Dear Joyce, we received an invoice on 1/2/08. We accepted 3 line items totaling $123.45, though there was an error with line items #2 [invalid quantity ordered]. Thank you for your business. Love, Acme.").
So it turns out Camel can handle all this:
This tutorial will cover all that, plus setting up tests along the way.
Before starting, you should be familiar with:
You may choose to treat this as a hands-on tutorial, and work through building the code and configuration files yourself. Each of the sections gives detailed descriptions of the steps that need to be taken to get the components and routes working in Camel, and takes you through tests to make sure they are working as expected.
But each section also links to working copies of the source and configuration files, so if you don't want the hands-on approach, you can simply review and/or download the finished files.
Here's more or less what the integration process looks like.
First, the input from the customers to Acme:
And then, the output from Acme to the customers:
To get through this scenario, we're going to break it down into smaller pieces, implement and test those, and then try to assemble the big scenario and test that.
Here's what we'll try to accomplish:
Let's Get Started!
Step 1: Initial Maven build
We'll use Maven for this project as there will eventually be quite a few dependencies and it's nice to have Maven handle them for us. You should have a current version of Maven (e.g. 2.0.9) installed.
You can start with a pretty empty project directory and a Maven POM file, or use a simple JAR archetype to create one.
Here's a sample POM. We've added a dependency on camel-core, and set the compile version to 1.5 (so we can use annotations):
Step 2: Get Sample Files
You can make up your own if you like, but here are the "off the shelf" ones. You can save yourself some time by downloading these to
If you look at these files, you'll see that the different input formats use different field names and/or ordering, because of course the sales guys were totally OK with that. Sigh.
Step 3: XSD and JAXB Beans for the Canonical XML Format
Here's the sample of the canonical XML file:
If you're ambitions, you can write your own XSD (XML Schema) for files that look like this, and save it to
Solution: If not, you can download mine, and save that to save it to
Generating JAXB Beans
Down the road we'll want to deal with the XML as Java POJOs. We'll take a moment now to set up those XML binding POJOs. So we'll update the Maven POM to generate JAXB beans from the XSD file.
We need a dependency:
And a plugin configured:
That should do it (it automatically looks for XML Schemas in
Step 4: Initial Work on Customer 1 Input (XML over FTP)
To get a start on Customer 1, we'll create an XSLT template to convert the Customer 1 sample file into the canonical XML format, write a small Camel route to test it, and build that into a unit test. If we get through this, we can be pretty sure that the XSLT template is valid and can be run safely in Camel.
Create an XSLT template
Start with the Customer 1 sample input. You want to create an XSLT template to generate XML like the canonical XML sample above – an
Solution: My sample XSLT template isn't that smart, but it'll get you going if you don't want to write one of your own.
Create a unit test
Here's where we get to some meaty Camel work. We need to:
The easiest way to do this is to set up a Spring context that defines the Camel stuff, and then use a base unit test class from Spring that knows how to load a Spring context to run tests against. So, the procedure is:
Set Up a Skeletal Camel/Spring Unit Test
Test it by running mvn install and make sure there are no build errors. So far it doesn't test much; just that your project and test and source files are all organized correctly, and the one empty test method completes successfully.
Solution: Your test class might look something like this:
Flesh Out the Unit Test
So now we're going to write a Camel route that applies the XSLT to the sample Customer 1 input file, and makes sure that some XML output comes out:
Solution: Your finished test might look something like this:
Test Base Class
Once your test class is working, you might want to extract things like the @Autowired CamelContext, the ProducerTemplate, and the setUp method to a custom base class that you extend with your other tests.
Step 5: Initial Work on Customer 2 Input (CSV over HTTP)
To get a start on Customer 2, we'll create a POJO to convert the Customer 2 sample CSV data into the JAXB POJOs representing the canonical XML format, write a small Camel route to test it, and build that into a unit test. If we get through this, we can be pretty sure that the CSV conversion and JAXB handling is valid and can be run safely in Camel.
Create a CSV-handling POJO
To begin with, CSV is a known data format in Camel. Camel can convert a CSV file to a List (representing rows in the CSV) of Lists (representing cells in the row) of Strings (the data for each cell). That means our POJO can just assume the data coming in is of type
Looking at the JAXB code in
So to implement the CSV-to-JAXB POJO, we need to do something like this:
Solution: Here's an example of what the CSVConverterBean might look like.
Create a unit test
Start with a simple test class and test Spring context like last time, perhaps based on the name
Now the meaty part is to flesh out the test class and write the Camel routes.
Solution: Your finished test might look something like this:
Step 6: Initial Work on Customer 3 Input (Excel over e-mail)
To get a start on Customer 3, we'll create a POJO to convert the Customer 3 sample Excel data into the JAXB POJOs representing the canonical XML format, write a small Camel route to test it, and build that into a unit test. If we get through this, we can be pretty sure that the Excel conversion and JAXB handling is valid and can be run safely in Camel.
Create an Excel-handling POJO
Camel does not have a data format handler for Excel by default. We have two options – create an Excel DataFormat (so Camel can convert Excel spreadsheets to something like the CSV
So, we need a POJO with a method that takes something like an
Solution: Here's an example of what the ExcelConverterBean might look like.
Create a unit test
The unit tests should be pretty familiar now. The test class and context for the Excel bean should be quite similar to the CSV bean.
You may notice that your tests emit a lot less output all of a sudden. The dependency on POI brought in Log4J and configured commons-logging to use it, so now we need a log4j.properties file to configure log output. You can use the attached one (snarfed from ActiveMQ) or write your own; either way save it to
Solution: Your finished test might look something like this:
Step 7: Put this all together into Camel routes for the Customer Input
With all the data type conversions working, the next step is to write the real routes that listen for HTTP, FTP, or e-mail input, and write the final XML output to an ActiveMQ queue. Along the way these routes will use the data conversions we've developed above.
So we'll create 3 routes to start with, as shown in the diagram back at the beginning:
Step 8: Create a unit test for the Customer Input Routes