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 on the fly
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.
Writing Endpoints
An Endpoint is an object which can have message Exchange objects sent to it via a Producer or can have message exchanges consumed via either
- Event Driven Consumer via the Consumer interface
- Polling Consumer via the PollingConsumer interface
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 creating a Consumer
- createPollingConsumer() implements the Polling Consumer pattern implementing a PollingConsumer
Typically you just derive from DefaultEndpoint and implement the
- createProducer() and / or createConsumer() methods. The createPollingConsumer() method will be created by default for you in the DefaultEndpoint class.
If your endpoint is a polling-centric component you can derive from DefaultPollingEndpoint and then implement createPollingConsumer(); the createConsumer() method will be created for you which avoids you having to write any polling code.
Dependency injection and auto-discovery
When using auto-discovery the CamelContext will default to its Injector implementation to inject any required or optional dependencies on the component. This allows you to use auto-discovery of components via URIs while still getting the benefits of dependency injection.
For example your component can depend on a JDBC DataSource or JMS ConnectionFactory which can be provided in the ApplicationContext in Spring or Module in Guice.
So you can if you prefer configure your Component using an IoC framework like Spring or Guice; then add it to the CamelContext. Or you can let the Component auto-inject itself as the endpoints are auto-discovered.