Java DSL
Apache Camel offers a Java based DSL using the fluent builder style. The
Java DSL is available by extending the
RouteBuilder class, and implement the
configure
method.
This is best illustrate by an example. In the code below we create a new
class called MyRouteBuilder
that extends the
org.apache.camel.builder.RouteBuilder
from Camel.
In the configure
method the Java DSL is at our disposal.
import org.apache.camel.builder.RouteBuilder;
/**
* A Camel Java DSL Router
*/
public class MyRouteBuilder extends RouteBuilder {
/**
* Let's configure the Camel routing rules using Java code...
*/
public void configure() {
// here is a sample which processes the input files
// (leaving them in place - see the 'noop' flag)
// then performs content based routing on the message using XPath
from("file:src/data?noop=true")
.choice()
.when(xpath("/person/city = 'London'"))
.to("file:target/messages/uk")
.otherwise()
.to("file:target/messages/others");
}
}
In the configure
method we can define Camel Routes.
In the example above we have a single route, which pickup files,
(eg the from).
from("file:src/data?noop=true")
Then we use the Content Based Router
(for ex:
the choice) to route the message depending if the person is from London
or not.
.choice()
.when(xpath("/person/city = 'London'"))
.to("file:target/messages/uk")
.otherwise()
.to("file:target/messages/others");
Routes
Camel supports the definition of routing rules using a Java DSL (domain specific language) which avoids the need for cumbersome XML using a RouteBuilder.
For example a simple route can be created as follows.
RouteBuilder builder = new RouteBuilder() {
public void configure() {
errorHandler(deadLetterChannel("mock:error"));
from("direct:a").to("direct:b");
}
};
As you can see from the above Camel uses URIs to wire endpoints together.
URI String formatting
Since Camel 2.0
If you have endpoint URIs that accept options and you want to be able to
substitute the value, e.g. build the URI by concat the strings together,
then you can use the java.lang.String.format
method. But in Camel 2.0
we have added two convenient methods in the Java DSL so you can do
fromF
and toF
that uses String formatting to build the URI.
from("direct:start").toF("file://%s?fileName=%s", path, name);
fromF("file://%s?include=%s", path, pattern).toF("mock:%s", result);
Filters
You can combine simple routes with filters which can be arbitrary Predicate implementations.
RouteBuilder builder = new RouteBuilder() {
public void configure() {
errorHandler(deadLetterChannel("mock:error"));
from("direct:a")
.filter(header("foo").isEqualTo("bar"))
.to("direct:b");
}
};
Choices
With a choice you provide a list of predicates and outcomes along with an optional default otherwise clause which is invoked if none of the conditions are met.
RouteBuilder builder = new RouteBuilder() {
public void configure() {
errorHandler(deadLetterChannel("mock:error"));
from("direct:a")
.choice()
.when(header("foo").isEqualTo("bar"))
.to("direct:b")
.when(header("foo").isEqualTo("cheese"))
.to("direct:c")
.otherwise()
.to("direct:d");
}
};
Using a custom processor
Here is an example of using a custom Processor
myProcessor = new Processor() {
public void process(Exchange exchange) {
log.debug("Called with exchange: " + exchange);
}
};
RouteBuilder builder = new RouteBuilder() {
public void configure() {
errorHandler(deadLetterChannel("mock:error"));
from("direct:a")
.process(myProcessor);
}
};
You can mix and match custom processors with filters and choices.
RouteBuilder builder = new RouteBuilder() {
public void configure() {
errorHandler(deadLetterChannel("mock:error"));
from("direct:a")
.filter(header("foo").isEqualTo("bar"))
.process(myProcessor);
}
};