Camel development series 12

Hello and welcome to another Camel development series. From now on I will paste less code to the blog and instead refer to the github repo where the code is stored. It makes writing the blog easier and that helps to motivate me to write more often.

In this serie I will touch upon a frequent scenario. Our problem is that we want to expose a HTTP endpoint in order to allow the client to perform a HTTP GET operation. We then want to call the backend HTTP(s) and retrieve say a picture and allow this to be displayed via the browser. How can we accomplish this?

Well if you want to jump straight to the code go here:

As you can see we accomplish this in four lines of code. We first expose our undertow endpoint and ensure only HTTP GET operations can be performed.  Then we set the Exchange.HTTP_QUERY header to our query parameter. Finally we call the backend https service using the http4 component. The key here is to enable the parameter bridgeEndpoint=true so that Camel understands it is acting as a proxy and doesn’t mix up the endpoints. Finally we convert the payload to byte and return it to the original client. That’s all!

Camel development series 11

Hello and welcome to another Camel development series.

In this series I thought we’d go through some more hints and some tricks I learned after one year of working with Camel.

Avoid unnecessary object creation

Do not create unnecessary object models of your data. As a java developer you tend to think everything in terms of object. But should you always create objects? The whole point of integration is to remain stateless and act as an interface to transfer data. So I would say, where possible don’t create objects. This has nothing to do with performance since object creation is cheap but more to do with not having to write unnecessary code for an behaviour related functionality. Let us work with an example.

So you receive a json message, you need to do some content-based routing and then generate a SOAP message and send to some web service.

Now you could off course create an object model for the json message or write a bean and the same goes for the SOAP xml. But unless you are dealing with completed message structure or attachments you don’t need to write code that way when it comes to integration. Here is an approach to solve it in another way.


.when(PredicateBuilder.isEqualTo(ExpressionBuilder.languageExpression("jsonpath", "$.data.request"), constant("valueToMatch1")))
        .when(PredicateBuilder.isEqualTo(ExpressionBuilder.languageExpression("jsonpath", "$.data.request"), constant("valueToMatch2")))
  .throwException(IllegalArgumentException.class, "Unknown request command received!")

In the above you can see that I don’t create any objects. I simply use the excellent library of json path or the camel version of it camel-jsonpath and simply perform a lookup in the data and based on that I route to my individual routes. This allows for writing less code, simpler code and I stay within the Camel dsl. It makes it also easy to understand what the integration is doing. I avoid going from one class to another.

Now about creating a SOAP message. Again you could write jaxb code, or use some other xml processing or use CXF or some other framework. But if your SOAP messages are relatively simple and does not contain attachments then you skip all that and use freemarker to inject data into your SOAP message. Here is an example:


Here is my freemarker template file:

<?xml version="1.0" encoding="UTF-8"?>
<soapenv:Envelope xmlns:xsi="" xmlns:xsd="" xmlns:soapenv="" xmlns:lan="http://test">

As you can see I extract the data again using json path and insert it in a header. Then I route to a freemarker endpoint. In my freemarker template I have written a simple expression to where the data should be injected. That’s all! I don’t write any xml code or worry about name space creation and stuff like that. Exactly same thing goes for the opposite. You can see xpath to extract data from xml messages and use a template json freemarker template to insert a simple expression.

Creating environment variables in your tests

A lot of the times you need to access environment variables but you don’t want to use real values in your tests but simple some fake value but you don’t want to change your code. You still want to access that same environment variable but just change the value.

I use the excellent library called system-rules by Stefan Birkner. It works really well and is really use to use. If you work with maven add this to your pom


How do you use it?

In your JUNIT test class add the following:

  public final EnvironmentVariables environmentVariables = new EnvironmentVariables();

  public void setUp() throws Exception {
    environmentVariables.set("VAR1", "1");
    environmentVariables.set("VAR2", "2");
    environmentVariables.set("VAR3", "3");

As you can see we add the rule and create a variable of type EnvironmentVariables. Then in your setUp method you simply create the variables and add values. As easy as that!

Testing JSON messages in your route tests

So quit often when you write route tests you will need to check if the json you produce needs to match some expected json. To do complicated JSON matches or even simple ones I simply the excellent library alled jsonassert. Add this to your pom:


To use it:
In your @test method add this:

JSONAssert.assertEquals(expectedResponse, response, false);

There are way more complicated things you can do with JSONAssert but if you want a simple way of comparing json messages this is great.