One of the simples and quickest approaches to generating a response message is to use a velocity template. Figure 10 shows the outline of a general template-based route. At the start of the route is a Camel CXF endpoint in provider mode, which is the appropriate mode to use for processing the message as an XML document. After doing the work required to process the message and stashing some intermediate results in message headers, the route generates the response message using a Velocity template.

Figure 10. Response Generated by Velocity

For example, you could define a template-based route specifically for the getCustoemrStatus operation, as follows:

        ...
        <when>
          <simple>${in.header.operationName} == 'getCustomerStatus'</simple>
          <setHeader headerName="customerId">
            <xpath resultType="java.lang.String">/cus:getCustomerStatus/customerId</xpath>
          </setHeader>
          <to uri="getCustomerStatus"/>
          <to uri="velocity:getCustomerStatusResponse.vm"/>
          <convertBodyTo type="javax.xml.transform.sax.SAXSource"/>
        </when>
      </choice>
    </route>
  </camelContext
  ...
  <bean id="getCustomerStatus"
    class="com.fusesource.customerwscamelcxfpayload.GetCustomerStatus"/>

Given the preceding route definition, any message whose operation name matches getCustomerStatus would be processed as follows:

	Note
	A common pattern when implementing Apache Camel routes is to use message headers as a temporary stash to hold intermediate results (you could also use exchange properties in the same way).

XPath expressions can be applied directly to SAXSource objects. The XPath implementation has a pluggable architecture that supports a variety of XML parsers and when XPath encounters a SAXSource object, it automatically loads the plug-in required to support SAXSource parsing.

The getCustomerStatus processor bean is an instance of the GetCustomerStatus processor class, which is defined as follows:

// Java
package com.fusesource.customerwscamelcxfpayload;

import org.apache.camel.Exchange;
import org.apache.camel.Processor;

public class GetCustomerStatus implements Processor
{
    public void process(Exchange exchng) throws Exception {
        String id = exchng.getIn().getHeader("customerId", String.class);

        // Maybe do some kind of lookup here!
        //

        exchng.getIn().setHeader("status", "Away");
        exchng.getIn().setHeader("statusMessage", "Going to sleep.");
    }
}

The implementation shown here is just a placeholder. In a realistic application you would perform some sort of checks or database lookup to obtain the customer status. In the demonstration code, however, the status and statusMessage are simply set to constant values and stashed in message headers.

You can generate a response message very simply using a Velocity template. The Velocity template consists of a message in plain text, where specific pieces of data can be inserted using expressions—for example, the expression ${header.HeaderName} substitutes the value of a named header.

The Velocity template for generating the getCustomerStatus reponse is located in the customer-ws-camel-cxf-provider/src/main/resources directory and it contains the following template script:

<ns2:getCustomerStatusResponse xmlns:ns2="http://demo.fusesource.com/wsdl/CustomerService/">
   <status>${headers.status}</status>
   <statusMessage>${headers.statusMessage}</statusMessage>
</ns2:getCustomerStatusResponse>