Spring Support

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 Spring XML Schema's is defined at Xml Reference
  • Camel supports a powerful version of Spring Remoting which can use powerful routing between the client and server side along with using all of the available Components for the transport
  • 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

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

For Camel 1.x you need to use the following namespace: 
http://activemq.apache.org/camel/schema/spring

with the following schema location:

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

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"

... 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">

... 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.

  <camelContext id="camel5" xmlns="http://camel.apache.org/schema/spring">
    <routeBuilder ref="myBuilder" />    
  </camelContext>
  
  <bean id="myBuilder" class="org.apache.camel.spring.example.test1.MyRouteBuilder"/>
  
</beans>

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>

In Camel 2.0 this has been extended to allow 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 (similar to 1.x), 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.

<!-- enable Spring @Component scan -->
<context:component-scan base-package="org.apache.camel.spring.issues.contextscan"/>

<camelContext xmlns="http://camel.apache.org/schema/spring">
    <!-- and then let Camel use those @Component scanned route builders -->
    <contextScan/>
</camelContext>

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.

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.

<camelContext id="camel-A" xmlns="http://camel.apache.org/schema/spring">
  <route>
    <from uri="seda:start"/>
    <to uri="mock:result"/>
  </route>
</camelContext>

Configuring Components and Endpoints

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

<camelContext id="camel" xmlns="http://camel.apache.org/schema/spring">
    <jmxAgent id="agent" disabled="true"/>
</camelContext>

<bean id="activemq" class="org.apache.activemq.camel.component.ActiveMQComponent">
  <property name="connectionFactory">
    <bean class="org.apache.activemq.ActiveMQConnectionFactory">
      <property name="brokerURL" value="vm://localhost?broker.persistent=false&amp;broker.useJmx=false"/>
    </bean>
  </property>
</bean>

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.

See also
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