title: How does Spring interpolate ${x} inside a string?
body: <p>I have a java class in a Spring project that looks (edited) like:</p>
  <pre><code>@Component
  public class X
  {
  private static final ApplicationContext CTX = new FileSystemXmlApplicationContext(&quot;file:${PATH}/ApplicationContext.xml&quot;);
  ...
  </code></pre>
  <p>I am looking for the reference explaining how the ${PATH} is interpolated in the string parameter. The PATH is passed as a system property ( java -DPATH=...) so I assume it takes it from there but I can't find an explanation describing the mechanism. Is it a Spring related feature similar to the syntax  used in @Value?</p>