title: how to make camel simple expression work with property placeholder in spring xml
body: <p>I am trying to using property placeholder in camel route.
  I have test.properties which define property: MQ.queuename1=TESTQUEUE.
  In camel context, i define placeholder:</p>
  
  <pre><code>&lt;camel:camelContext xmlns="http://camel.apache.org/schema/spring" &gt;
    &lt;propertyPlaceholder id="camel-properties"  location="file:${web.external.propdir}/test.properties"/&gt;
  </code></pre>
  
  <p>In the route, i use simple expresion to evaluate the property:</p>
  
  <pre><code>&lt;choice&gt;
             &lt;when&gt;
                  &lt;simple&gt;${in.header.queuename} == '{{MQ.queuename1}}'&lt;/simple&gt;
              &lt;bean ref="ExtractOrderContent" method="extractContent"/&gt;
                  &lt;to uri="websphere-mq:queue:TESTQUEUE" pattern="InOnly"/&gt;
              &lt;/when&gt; 
          &lt;/choice&gt;
  </code></pre>
  
  <p>When i run camel, the property file is recognized by camel but it looks like the simple expression doesn't work. Do i miss anything?</p>