Chapter 1. Building Blocks for Route Definitions

Abstract

Apache Camel supports two alternative Domain Specific Languages (DSL) for defining routes: a Java DSL and a Spring XML DSL. The basic building blocks for defining routes are endpoints and processors, where the behavior of a processor is typically modified by expressions or logical predicates. Apache Camel enables you to define expressions and predicates using a variety of different languages.

1.1. Implementing a RouteBuilder Class

Overview

To use the Domain Specific Language (DSL), you extend the RouteBuilder class and override its configure() method (where you define your routing rules).
You can define as many RouteBuilder classes as necessary. Each class is instantiated once and is registered with the CamelContext object. Normally, the lifecycle of each RouteBuilder object is managed automatically by the container in which you deploy the router.

RouteBuilder classes

As a router developer, your core task is to implement one or more RouteBuilder classes. There are two alternative RouteBuilder classes that you can inherit from:
  • org.apache.camel.builder.RouteBuilder—this is the generic RouteBuilder base class that is suitable for deploying into any container type. It is provided in the camel-core artifact.
  • org.apache.camel.spring.SpringRouteBuilder—this base class is specially adapted to the Spring container. In particular, it provides extra support for the following Spring specific features: looking up beans in the Spring registry (using the beanRef() Java DSL command) and transactions (see the Transactions Guide for details). It is provided in the camel-spring artifact.
The RouteBuilder class defines methods used to initiate your routing rules (for example, from(), intercept(), and exception()).

Implementing a RouteBuilder

Example 1.1, “Implementation of a RouteBuilder Class” shows a minimal RouteBuilder implementation. The configure() method body contains a routing rule; each rule is a single Java statement.

Example 1.1. Implementation of a RouteBuilder Class

import org.apache.camel.builder.RouteBuilder;

public class MyRouteBuilder extends RouteBuilder {

public void configure() {
  // Define routing rules here:
  from("file:src/data?noop=true").to("file:target/messages");

  // More rules can be included, in you like.
  // ...
}
}
The form of the rule from(URL1).to(URL2) instructs the router to read files from the directory src/data and send them to the directory target/messages. The option ?noop=true instructs the router to retain (not delete) the source files in the src/data directory.
Note
When you use the contextScan with Spring or Blueprint to filter RouteBuilder classes, by default Apache Camel will look for singleton beans. However, you can turn on the old behavior to include prototype scoped with the new option includeNonSingletons.