title: How to use system environment variable as part of @PropertySource value?
body: <p>I want to launch my program with <code>java ... -Denv=prod ...</code>
  and have</p>
  
  <pre><code>@PropertySource("classpath:/settings/$idontknowwhat$/database.properties")`
  </code></pre>
  
  <p>read properties file: <code>/settings/prod/database.properties</code></p>
  
  <p>I have tried using <code>#{systemProperties['env']}</code> but it is not resolved with exception:</p>
  
  <pre><code>Could not open ServletContext resource ['classpath:/settings/#{systemProperties['env']}/database.properties]
  </code></pre>