Spring

Apache Camel is designed to work nicely with the Spring Framework in a number of ways.

  • Camel uses Spring Transactions as the default transaction handling in components like JMS and JPA

  • Camel works with Spring 2 XML processing with the Xml Configuration

  • Camel provides powerful Bean Integration with any bean defined in a Spring ApplicationContext

  • Camel integrates with various Spring helper classes; such as providing Type Converter support for Spring Resources etc

  • Allows Spring to dependency inject Component instances or the CamelContext instance itself and auto-expose Spring beans as components and endpoints.

  • Allows you to reuse the Spring Testing framework to simplify your unit and integration testing using Enterprise Integration Patterns and Camel’s powerful Mock and Test endpoints Camel supports Spring Boot using the camel-spring-boot component.

Using Spring to configure the CamelContext

You can configure a CamelContext inside any spring.xml using the CamelContextFactoryBean. This will automatically start the CamelContext along with any referenced Routes along any referenced Component and Endpoint instances.

  • Adding Camel schema

  • Configure Routes in two ways:

    • Using Java Code

    • Using Spring XML

Adding Camel Schema

You need to add Camel to the schemaLocation declaration

http://camel.apache.org/schema/spring http://camel.apache.org/schema/spring/camel-spring.xsd

So the XML file looks like this:

<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="
          http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
          http://camel.apache.org/schema/spring http://camel.apache.org/schema/spring/camel-spring.xsd">

Using camel: namespace

Or you can refer to camel XSD in the XML declaration:

xmlns:camel="http://camel.apache.org/schema/spring"

  1. so the declaration is:

<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:camel="http://camel.apache.org/schema/spring"
       xsi:schemaLocation="
          http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
          http://camel.apache.org/schema/spring http://camel.apache.org/schema/spring/camel-spring.xsd">

  1. and then use the camel: namespace prefix, and you can omit the inline namespace declaration:

<camel:camelContext id="camel5">
  <camel:package>org.apache.camel.spring.example</camel:package>
</camel:camelContext>

Advanced configuration using Spring

See more details at Advanced configuration of CamelContext using Spring

$# Using Java Code

You can use Java Code to define your RouteBuilder implementations. These can be defined as beans in spring and then referenced in your camel context e.g.

Using <package>

Camel also provides a powerful feature that allows for the automatic discovery and initialization of routes in given packages. This is configured by adding tags to the camel context in your spring context definition, specifying the packages to be recursively searched for RouteBuilder implementations. To use this feature in 1.X, requires a <package></package> tag specifying a comma separated list of packages that should be searched e.g.

  <camelContext xmlns="http://camel.apache.org/schema/spring">
    <package>org.apache.camel.spring.config.scan.route</package>
  </camelContext>
Use caution when specifying the package name as org.apache.camel or a sub package of this. This causes Camel to search in its own packages for your routes which could cause problems.

Will ignore already instantiated classes

The <package> and <packageScan> will skip any classes which has already been created by Spring etc. So if you define a route builder as a spring bean tag then that class will be skipped. You can include those beans using <routeBuilder ref="theBeanId"/> or the <contextScan> feature.

Using <packageScan>

The component allows selective inclusion and exclusion of discovered route classes using Ant like path matching. In spring this is specified by adding a <packageScan/> tag. The tag must contain one or more 'package' elements, and optionally one or more 'includes' or 'excludes' elements specifying patterns to be applied to the fully qualified names of the discovered classes. e.g.

  <camelContext xmlns="http://camel.apache.org/schema/spring">
    <packageScan>
      <package>org.example.routes</package>
      <excludes>**.*Excluded*</excludes>
      <includes>**.*</includes>
    </packageScan>
  </camelContext>

Exclude patterns are applied before the include patterns. If no include or exclude patterns are defined then all the Route classes discovered in the packages will be returned.

In the above example, camel will scan all the 'org.example.routes' package and any subpackages for RouteBuilder classes. Say the scan finds two RouteBuilders, one in org.example.routes called 'MyRoute" and another 'MyExcludedRoute' in a subpackage 'excluded'. The fully qualified names of each of the classes are extracted (org.example.routes.MyRoute, org.example.routes.excluded.MyExcludedRoute) and the include and exclude patterns are applied.

The exclude pattern *.*Excluded is going to match the fqcn 'org.example.routes.excluded.MyExcludedRoute' and veto camel from initializing it.

Under the covers, this is using Spring’s AntPatternMatcher implementation, which matches as follows

? matches one character
* matches zero or more characters
** matches zero or more segments of a fully qualified name

For example:

*.*Excluded would match org.simple.Excluded, org.apache.camel.SomeExcludedRoute or org.example.RouteWhichIsExcluded

*.??cluded would match org.simple.IncludedRoute, org.simple.Excluded but not match org.simple.PrecludedRoute

Using contextScan

Available as of Camel 2.4

You can allow Camel to scan the container context, e.g. the Spring ApplicationContext for route builder instances. This allow you to use the Spring <component-scan> feature and have Camel pickup any RouteBuilder instances which was created by Spring in its scan process.

This allows you to just annotate your routes using the Spring @Component and have those routes included by Camel

@Component
public class MyRoute extends SpringRouteBuilder {

    @Override
    public void configure() throws Exception {
        from("direct:start").to("mock:result");
    }
}

You can also use the ANT style for inclusion and exclusion, as mentioned above in the <packageScan> documentation.

How do I import routes from other XML files

Available as of Camel 2.3

When defining routes in Camel using XML DSL you may want to define some routes in other XML files. For example you may have many routes and it may help to maintain the application if some of the routes are in separate XML files. You may also want to store common and reusable routes in other XML files, which you can simply import when needed.

It is possible to define routes outside <camelContext/> which you do in a new <routeContext/> tag.

Notice: When you use <routeContext> then they are separated, and cannot reuse existing <onException>, <intercept>, <dataFormats> and similar cross cutting functionality defined in the <camelContext>. In other words the <routeContext> is currently isolated.

For example we could have a file named myCoolRoutes.xml which contains a couple of routes as shown:

myCoolRoutes.xml

Then in your XML file which contains the CamelContext you can use Spring to import the myCoolRoute.xml file.

 And then inside `<camelContext/>` you can refer to the
`<routeContext/>` by its id as shown below:

Also notice that you can mix and match, having routes inside CamelContext and also externalized in RouteContext.

You can have as many <routeContextRef/> as you like.

Reusable routes

The routes defined in <routeContext/> can be reused by multiple <camelContext/>. However its only the definition which is reused. At runtime each CamelContext will create its own instance of the route based on the definition.

Test time exclusion.

At test time it is often desirable to be able to selectively exclude matching routes from being initalized that are not applicable or useful to the test scenario. For instance you might a spring context file routes-context.xml and three Route builders RouteA, RouteB and RouteC in the 'org.example.routes' package. The packageScan definition would discover all three of these routes and initialize them.

Say RouteC is not applicable to our test scenario and generates a lot of noise during test. It would be nice to be able to exclude this route from this specific test. The SpringTestSupport class has been modified to allow this. It provides two methods (excludedRoute and excludedRoutes) that may be overridden to exclude a single class or an array of classes.

public class RouteAandRouteBOnlyTest extends SpringTestSupport {
    @Override
    protected Class excludeRoute() {
        return RouteC.class;
    }
}

In order to hook into the camelContext initialization by spring to exclude the MyExcludedRouteBuilder.class we need to intercept the spring context creation. When overriding createApplicationContext to create the spring context, we call the getRouteExcludingApplicationContext() method to provide a special parent spring context that takes care of the exclusion.

@Override
protected AbstractXmlApplicationContext createApplicationContext() {
    return new ClassPathXmlApplicationContext(new String[] {"routes-context.xml"}, getRouteExcludingApplicationContext());
}

RouteC will now be excluded from initialization. Similarly, in another test that is testing only RouteC, we could exclude RouteB and RouteA by overriding

@Override
protected Class[] excludeRoutes() {
    return new Class[]{RouteA.class, RouteB.class};
}

Using Spring XML

You can use Spring 2.0 XML configuration to specify your Xml Configuration for Routes such as in the following example.

Configuring Components and Endpoints

You can configure your Component or Endpoint instances in your Spring XML as follows in this example.

Which allows you to configure a component using some name (activemq in the above example), then you can refer to the component using activemq:[queue:|topic:]destinationName. This works by the SpringCamelContext lazily fetching components from the spring context for the scheme name you use for Endpoint URIs.

For more detail see Configuring Endpoints and Components.

CamelContextAware

If you want to be injected with the CamelContext in your POJO just implement the CamelContextAware interface; then when Spring creates your POJO the CamelContext will be injected into your POJO. Also see the Bean Integration for further injections.

Integration Testing

To avoid a hung route when testing using Spring Transactions see the note about Spring Integration Testing under Transactional Client.

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