from("java7:anonymousClasses").to("java8:lambda")

With Camel 2.18 we have introduced a few functional APIs in RouteBuilder so you can leverage lambdas to easily build your routes.

Note

this is just the beginning so you should expect more and better functional APIs in the coming versions.

Let’s start writing a simple and intentionally verbose Java 7 route that logs if a number is even or odd.

from("timer:simple?period=503")
    .setBody(exchangeProperty(Exchange.TIMER_FIRED_TIME))
    .transform(new ExpressionAdapter() {
        @Override
        public Object evaluate(Exchange exchange) {
            return exchange.getIn().getBody(Date.class).getTime();
        }
    })
    .choice()
        .when(new Predicate() {
                @Override
                public boolean matches(Exchange exchange) {
                    long number = exchange.getIn().getBody(Long.class);
                    return (number & 1) == 0;
                }
            })
            .to("Received even number")
        .when(new Predicate() {
                @Override
                public boolean matches(Exchange exchange) {
                    long number = exchange.getIn().getBody(Long.class);
                    return (number & 1) != 0;
                }
            })
            .to("Received odd number")
    .endChoice();

You can now switch to Java 8 and start using new constructs to implement EIP:

  • Message Translator

    You have a number of options to translate messages and among them you may think to use an Expression but unfortunately you can’t use a lambda to implement such interface as this interface is generic so you may think to use a method reference but that is not really an improvement over using a bean.

    Here is where Camel 2.18 can help so you can implement the patter as below:

        .transform()
        .body(Date.class, Date::getTime)

  • Content Based Router

    A Predicate can be easily implemented using lambda, like:

        .when(exchange -> (exchange.getIn().getBody(Integer.class) & 1) != 0)
        .to("Received odd number")

    However in Camel 2.18 we can make it even easier

        .when()
        .body(Long.class, b -> (b & 1) == 0)
        .to("Received odd number")

We are now ready to apply the new APIs to our route and rewrite it as follow:

from("timer:simple?period=503")
    .setBody(exchangeProperty(Exchange.TIMER_FIRED_TIME))
    .transform()
        .body(Date.class, Date::getTime)
    .choice()
        .when()
            .body(Long.class, b -> (b & 1) == 0)
            .log("Received even number ${body}")
        .when()
            .body(Long.class, b -> (b & 1) != 0)
            .log("Received odd number ${body}")
    .endChoice();
Tip

The new Java 8 APIs introduced in RouteBuilder helps to reduce the amount of code but it also helps to make it clear which is the target of a Predicate/Processor/Expression, i.e. in the example above you can easily spot that the routing is based on the content of the body.

As Java 8 API refinement is ongoing here an updated list of EIP that have been enanced to be Java 8 friendly:

From Camel 2.18.1

  • Aggregator

    you can implement your aggregation policy/aggregation strategy as lambda:

    from("direct:aggregate")
    .aggregate()
        .body(Long.class, b -> (b & 1) == 0)
        .strategy()
            .body(Long.class, (o, n) -> o != null ? o + n : n)
        .completion()
            .body(Long.class, b -> b >= 10)
    .to("mock:result");

  • Content Enricher

    You can enrich content using data from an external service and merge it with a lambda expression:

    fom("direct:start")
    .enrichWith("direct:resource")
        .body(String.class, (o, n) -> n + o)
    .to("mock:enriched");

From Camel 2.19

  • Dynamic Router

    class MyRouteBuilder extends RouteBuilder {
    @Override
    public void configure() throws Exception {
        from("direct:start-1")
            .dynamicRouter()
                .exchange(this::slip);
    }

    private String slip(Exchange exchange) {
        String previous = ExchangeHelper.getHeaderOrProperty(
            exchange,
            Exchange.SLIP_ENDPOINT,
            String.class);

        if (previous == null) {
            return "mock:a,mock:b";
        } else if ("mock://b".equals(previous)) {
            return "mock:c";
        }

        // no more so return null
        return null;
    }
}

  • Idempotent Consumer

    from("direct:start")
    .idempotentConsumer()
        .message(m -> m.getHeader("MessageId"))
        .messageIdRepository(new MemoryIdempotentRepository())
    .to("mock:result")

  • Loop

    You can express the do/while end condition as lamda

    from("direct:start")
    .loopDoWhile()
        .body(String.class, b -> b.length() <= 5)
        .transform()
            .body(String.class, b -> b += "A")
        .to("mock:loop")
    .end()
    .to("mock:result");

  • Multicast

    You can implement your custom onPrepare function using lambda as well as the aggregation strategy used to assemble the replies from the multicasts.

    from("direct:start")
    .multicast()
        .onPrepare()
            .message(m -> m.setHeader("onPrepare", true))
        .aggregationStrategy()
            .body(Integer.class, (o, n) -> o != null ? o + n : n)
        .to("direct:do-something-1", "direct:do-something-2")
        .end()
    .to("mock:result");

  • Routing Slip

    from("direct:start")
    .routingSlip()
        .message(m -> m.getHeader("RecipientListHeader", String.class).split(","))
    .end();