Writing Components

Apache Camel is designed to make it very easy to drop in new components whether they be routing components, transformers, transports etc. The idea of a component is to be a factory and manager of Endpoints.

Here are the main steps to writing a component:

  • Write a POJO which implements the Component interface. The simplest approach is just to derive from DefaultComponent.

  • To support auto-discovery of your component add a file to META-INF/services/org/apache/camel/component/FOO where FOO is the URI scheme for your component and any related endpoints created on the fly. The latter file should contain the definition of the component class. For example if your component is implemented by the com.example.CustomComponent class, the service file should contain the following line — class=com.example.CustomComponent.

Users can then either explicitly create your component, configure it and register with a CamelContext or users can use a URI which auto-creates your component.

It is recommended to bootstrap your initial component using Camel Maven Archetypes, as it will give you all the necessary bits to start developing your component with ease. You will need as well to make sure to have Camel Component Maven Plugin included in your component’s pom.xml file, order to generate all the necessary metadata and Java files for your component.

Writing Endpoints

When implementing an Endpoint you typically may implement one or more of the following methods:

  • createProducer will create a producer for sending message exchanges to the endpoint

  • createConsumer implements the Event Driven Consumer pattern for consuming message exchanges from the endpoint.

Typically, you just derive from DefaultEndpoint

Annotating your Endpoint

If you want to benefit from the automatic generation of HTML documentation for all the parameters on your endpoint as part of the maven site reports, you need to annotate your Endpoint’s parameters.

So this means you add a @UriEndpoint annotation to your Endpoint class and then annotate each parameter you wish to be configured via the URI configuration mechanism with @UriParam (or @UriParams for nested configuration objects).

Refer to the Endpoint Annotations guide for details.

Options

If your component has options you can let it have public getters/setters and Camel will automatically set the properties when the endpoint is created.

If you however want to take the matter in your own hands, then you must remove the option from the given parameter list as Camel will validate that all options are used. If not Camel will throw a ResolveEndpointFailedException stating which options are unknown.

The parameters are provided by Camel in the createEndpoint method from DefaultComponent class:

protected abstract Endpoint<E> createEndpoint(String uri, String remaining, Map parameters)

The code is an example from the SEDA component that removes the size parameter:

    public BlockingQueue<Exchange> createQueue(String uri, Map parameters) {
        int size = 1000;
        Object value = parameters.remove("size");
        if (value != null) {
            Integer i = convertTo(Integer.class, value);
            if (i != null) {
                size = i;
            }
        }
        return new LinkedBlockingQueue<Exchange>(size);
    }
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