title: property-placeholder location from another property
body: <p>I need to load some properties into a Spring context from a location that I don't know until the program runs. </p>
  
  <p>So I thought that if I had a PropertyPlaceholderConfigurer with no locations it would read in <code>my.location</code> from the system properties and then I could use that location in a context:property-placeholder</p>
  
  <p>Like this</p>
  
  <pre><code>&lt;bean class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer"/&gt;    
  &lt;context:property-placeholder location="${my.location}"/&gt;
  </code></pre>
  
  <p>but this doesn't work and nor does <code>location="classpath:${my.location}"</code></p>
  
  <p>Paul</p>