Introduction
Llama is a lightweight Clojure implementation of Apache Camel, a framework for integrating systems together. It currently provides a Clojure translation of the routing DSL and associated helper methods to work with elements of Camel.
Status of this work
Thanks to the .. macro, any expression of the form (route (x foo) (y) (bar z)) is directly translated to the method chain of applying first x then y and then z, meaning, it is equivalent to the Java call x(foo).y().bar(z). Since this happens to match exactly how the routing DSL works in Java, Llama effectively has full support for the DSL already, but see the next section.
Clojure conversions
Most methods like process in the Java DSL accept anynymous classes based on abstract classes. Llama tries to provide as many macros to make the DSL be more Clojure-like, e.g., process automatically converts its argument to a Processor if it the argument is a function. Similarly, from and to can be called with multiple args and this translated into a call with an Array argument of endpoints.
So, everything that is in the Java API already works, but their usage may be cumbersome, since Camel was written before Java 8 lambdas. Here is a list of the methods that are implemented by a Clojure macro, and their modification:
The rest of the work is ongoing. The additional benefit of having a macro behind is to provide a suitable doc on this page. For example, the aggregator pattern is not yet implemented, and its parameter is either an Expression or a AggregationStrategy, so you’d need to reify an instance of those classes to get them to work.
Contributions of macros for the routing DSL are welcome!
Other features
Besides the routing DSL, planned features are to have Consumers and Producers like in Akka Camel using core.async channels, so that you could do
(def ch (chan))
(defcontext ctx)
(consume-to ctx "activemq:foo:bar" ch)
;; now ch gets messages from activemq