NMR

NMR Component

The nmr component is an adapter to the Normalized Message Router (NMR) in ServiceMix, which is intended for use by Apache Camel applications deployed directly into the OSGi container. By contrast, the JBI component is intended for use by Apache Camel applications deployed into the ServiceMix JBI container.

By contrast, the JBI component is intended for use by Camel applications deployed into the ServiceMix JBI container.

Installing in Apache Servicemix

The NMR component is provided with Apache ServiceMix. It is not distributed with Apache Camel. To install the NMR component in ServiceMix, enter the following command in the ServiceMix console window:

features install nmr

Installing in plain Apache Karaf

In plain Karaf the nmr component can also be installed using the servicemix artifacts:

features:chooseurl camel <version>
features:addurl mvn:org.apache.servicemix.nmr/apache-servicemix-nmr/1.5.0/xml/features
features:install camel-blueprint nmr camel-nmr
install -s mvn:org.apache.servicemix.camel/org.apache.servicemix.camel.component/4.4.2

Configuration

You also need to instantiate the NMR component. You can do this by editing your Spring configuration file, META-INF/spring/*.xml, and adding the following bean instance:

<beans xmlns:osgi="http://www.springframework.org/schema/osgi" ... >
    ...
    <bean id="nmr" class="org.apache.servicemix.camel.nmr.ServiceMixComponent">
        <property name="nmr">
            <osgi:reference interface="org.apache.servicemix.nmr.api.NMR" />
        </property>
    </bean>
    ...
</beans>

NMR consumer and producer endpoints

The following code:

from("nmr:MyServiceEndpoint")

Automatically exposes a new endpoint to the bus with endpoint name MyServiceEndpoint (see URI format).

When an NMR endpoint appears at the end of a route, for example:

to("nmr:MyServiceEndpoint")

the messages sent by this producer endpoint are sent to the already deployed NMR endpoint.

URI format

An NMR endpoint has this format:

nmr:endpointName

URI Options

An NMR endpoint supports these options:

Option Default Description
synchronous false When set to true on a consumer endpoint, an incoming, synchronous NMR Exchange is handled on the sender's thread, instead of on a new thread from the NMR endpoint's thread pool.
runAsSubject false Apache ServiceMix 4.4: When set to true on a consumer endpoint, the endpoint is invoked on behalf of the Subject and set on the Exchange (that is, the call to Subject.getSubject(AccessControlContext) returns the Subject instance).
timeout 0 Apache ServiceMix 4.4: When set to a value greater than 0, the producer endpoint times out if it doesn't receive a response from the NMR within the given timeout period (in milliseconds). Configuring a timeout value switches from the default asynchronous messaging to using synchronous interactions with the NMR.
throwExceptionOnFailure true Apache ServiceMix 4.5.2: When set to false, the NMR's exceptions (such as TimeoutException) are consumed silently.

Examples

Consumer:

// consume nmr exchanges asynchronously
from("nmr:MyServiceEndpoint") 
// consume nmr exchanges synchronously and use the same thread as  defined by NMR ThreadPool
from("nmr:MyServiceEndpoint?synchronous=true").to()  

Producer:

// produce nmr exchanges asynchronously
from()...to("nmr:MyServiceEndpoint") 
// produce nmr exchanges synchronously and wait till 10s to receive response
from()...to("nmr:MyServiceEndpoint?timeout=10000") 

Using Stream bodies

If you are using a stream type as the message body, be aware that a stream is capable of being read only once. So if you enable DEBUG logging, the body is usually logged and thus read. To deal with this, Camel has a streamCaching option that can cache the stream, enabling you to read it multiple times.

from("nmr:MyEndpoint").streamCaching().to("xslt:transform.xsl", "bean:doSomething");

From Apache Camel 1.5 onwards, stream caching is enabled by default, so you need not set the streamCaching() option. In Apache Camel 2.0 big input streams (by default, over 64K) are stored in a temp file, using CachedOutputStream. When you close the input stream, the temp file is deleted.

Testing

NMR camel routes can be tested using the Apache Camel unit test approach, even if they will be deployed next in different bundles in an OSGi runtime. With this aim in view, you will extend the ServiceMixNMR Mock class, org.apache.servicemix.camel.nmr.AbstractComponentTest, which will create an NMR bus, register the Apache Camel NMR Component and the endpoints defined into the Apache Camel routes.

public class ExchangeUsingNMRTest extends AbstractComponentTest {

    @Test
    public void testProcessing() throws InterruptedException {
        MockEndpoint mock = getMockEndpoint("mock:simple");
        mock.expectedBodiesReceived("Simple message body");

        template.sendBody("direct:simple", "Simple message body");

        assertMockEndpointsSatisfied();

    }

    @Override
    protected RouteBuilder createRouteBuilder() throws Exception {
        returnnew RouteBuilder() {

            @Override
            public void configure() throws Exception {
                from("direct:simple").to("nmr:simple");
                from("nmr:simple?synchronous=true").to("mock:simple");
            }
        };
    }
}