A Look Inside FUSE ESB 4: An OSGi-Based Integration Platform

In the first two examples we focused on the Camel functionality available in FUSE ESB. But FUSE ESB also provides an easy to use definition for web services with Apache CXF. But to communicate between Camel routes and these web services we need an interaction layer. So we need a bus inside the ESB, which is named the NMR in FUSE ESB 4.

Introducing the NMR

The NMR project enables the interaction between different components in the OSGi container. This is quite similar to the normalized message router which is defined in the JBI specification, but it’s more flexible and not only dedicated to JBI. The main purpose of the NMR is to mediate between service consumers and service providers. In the example shown in figure 5, you can see that the NMR can be used to communicate between a Camel route definition and a JAX-WS endpoint. This example is provided with FUSE ESB 4 with the name cxf-camel-nmr.

Figure 5 An overview of the cxf-camel-nmr example provided with FUSE ESB 4. This example shows the use of a NMR to mediate between a Camel route and a JAX-WS endpoint.

For a change we don’t trigger the integration logic with a file or a JMS message in the cxf-camel-nmr example, but with a timer. The timer is defined as part of the Camel route definition. Then a Spring bean, MyTransform, is invoked with its transform method, which basically returns the message that can be sent as a request to the web service. Then the web service is invoked via the NMR and the result is passed on, again to the MyTransform Spring bean, which logs the web service response with the display method. Now let’s take a look at the XML configuration in listing 5.

Listing 5 The XML configuration for the Camel route and JAX-WS endpoint definition.

<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:osgi="http://www.springframework.org/schema/osgi"
xmlns:camel-osgi="http://activemq.apache.org/camel/schema/osgi"
xmlns:jaxws="http://cxf.apache.org/jaxws"
xsi:schemaLocation="
http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-2.0.xsd
http://www.springframework.org/schema/osgi
http://www.springframework.org/schema/osgi/spring-osgi.xsd
http://activemq.apache.org/camel/schema/spring
http://activemq.apache.org/camel/schema/spring/camel-spring.xsd
http://activemq.apache.org/camel/schema/osgi
http://activemq.apache.org/camel/schema/osgi/camel-osgi.xsd
http://cxf.apache.org/jaxws
http://cxf.apache.org/schemas/jaxws.xsd">
<import resource="classpath:META-INF/cxf/cxf.xml" />
<import resource="classpath:META-INF/cxf/cxf-extension-soap.xml" />
<import resource="classpath:META-INF/cxf/transport/nmr/cxf-transport-nmr.xml" />
<import resource="classpath:org/apache/servicemix/camel/nmr/camel-nmr.xml" />
<camel-osgi:camelContext xmlns="http://activemq.apache.org/camel/schema/spring">
<!-- Route periodically sent events into the NMR -->
<route>
<from
uri="timer://myTimer?fixedRate=true&period=5000&exchangePattern=InOut" />
<bean ref="myTransform" method="transform"/>
<to uri="nmr:{http://cxfcamel.examples.servicemix.apache.org/}HelloWorldImplPort"/>
<bean ref="myTransform" method="display" />
</route>
</camel-osgi:camelContext>
<bean id="myTransform" class="org.apache.servicemix.examples.cxfcamel.MyTransform">
<property name="value">
<value><![CDATA[
<soap:Envelope xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/">
<soap:Body>
<ns1:sayHi xmlns:ns1="http://cxf.examples.servicemix.apache.org/">
<arg0>Guillaume</arg0>
</ns1:sayHi>
</soap:Body>
</soap:Envelope>]
]></value></property>
</bean>
<jaxws:endpoint id="helloWorld"
implementor="org.apache.servicemix.examples.cxfcamel.HelloWorldImpl"
address="nmr:HelloWorld" />
</beans>

We’ll start with the timer definition in the Camel route. The timer triggers the Camel route at a fixed rate of 5 seconds and produces an InOut exchange pattern. We need this InOut exchange pattern to communicate with the web service, because we need to send a request (In) and receive a response (Out). In the next step the transform method of the MyTransform Spring bean is invoked. In listing 6 we’ll look at the implementation of the MyTransform class in detail, but this method returns the SOAP envelope as configured with the value property of the myTransform Spring bean definition. So this produces a message with an element of sayHi and a value of Guillaume.

Then the hello world web service is invoked which is configured with the jaxws:endpoint. We’ll look at the implementation of the HelloWorldImpl in listing 7, but this method returns the obvious “hello” message. Then the MyTransform bean is called again, but now with the display method, which logs the web service response. Notice that we need to import several XML files at the top of the XML configuration file, to initialize Apache CXF and the NMR.The implementation of the MyTransform class is shown in listing 6, but this will not be too complex.

Listing 6 The MyTransform implementation which produces the web service request and logs the response.

package org.apache.servicemix.examples.cxfcamel;
import java.util.logging.Logger;
import javax.xml.transform.Source;
import org.apache.camel.converter.jaxp.StringSource;
import org.apache.camel.converter.jaxp.XmlConverter;
public class MyTransform {
private static final transient Logger LOG = Logger.getLogger(MyTransform.class);
private String value;
public Object transform(Object body) {
LOG.info(">>>> " + value);
return new StringSource(value);
}
public void display(Source body) throws Exception {
String str = new XmlConverter().toString(body);
LOG.info("<<<< " + str);
}
// omitted the getter and setter for the value property
}

The HelloWorldImpl class is very simple and is annotated with the @WebService annotation which sets the web service interface class, which just defines the sayHi method in this example.