Camel RX

The camel-rx library provides Camel support for the Reactive Extensions (RX) using the RxJava library so that:

• Camel users can use the RxJava API for processing messages on endpoints using a typesafe composable API
• RxJava users get to use all of the Camel transports and protocols from within the RxJava API

Background on RX

For a more in depth background on RX check out the RxJava wiki on Observable and the Reactive pattern or the Microsoft RX documentation.

You can think of RX as providing an API similar to Java 8 / Groovy / Scala collections (methods like filter, forEach, map, reduce, zip etc) - but which operates on an asynchronous stream of events rather than a collection. So you could think of RX as like working with asynchronous push based collections (rather than the traditional synchronous pull based collections).

In RX you work with an Observable<T> which behaves quite like a Collection<T> in Java 8 so you can filter/map/concat and so forth. The Observable<T> then acts as a typesafe composable API for working with asynchronous events in a collection-like way.

Once you have an Observable<T> you can then

• filter events
• transform events
• combine event streams
• other utility methods

Observing events on Camel endpoints

You can create an Observable<Message> from any endpoint using the ReactiveCamel helper class and the toObservable() method.

import org.apache.camel.rx.*;

ReactiveCamel rx = new ReactiveCamel(camelContext);
Observable<Message> observable = rx.toObservable("activemq:MyMessages");

// we can now call filter/map/concat etc
filtered = observable.filter(m -> m.getHeader("foo") != null).map(m -> "Hello " + m.getBody()); 

If you know the type of the message payload (its body), you can use an overloaded version of toObservable() to pass in the class and get a typesafe Observable<T> back:

import org.apache.camel.rx.*;

ReactiveCamel rx = new ReactiveCamel(camelContext);
Observable<Order> observable = rx.toObservable("seda:orders", Order.class);

// now lets filter and map using Java 7
Observable<String> largeOrderIds = observable.filter(new Func1<Order, Boolean>() {
    public Boolean call(Order order) {
        return order.getAmount() > 100.0;
    }
}).map(new Func1<Order, String>() {
    public String call(Order order) {
        return order.getId();
    }
});

Sending Observable<T> events to Camel endpoints

If you have an Observable<T> from some other library; or have created one from a Future<T> using RxJava and you wish to send the events on the observable to a Camel endpoint you can use the sendTo() method on ReactiveCamel:

import org.apache.camel.rx.*;

// take some observable from somewhere
Observable<T> observable = ...;
ReactiveCamel rx = new ReactiveCamel(camelContext);

// lets send the events to a message queue
rx.sendTo(observable, "activemq:MyQueue");