title: how to externalize context-param values in web.xml
body: <p>I'm tryin to migrate some legacy (struts2-based) web application from Jboss to Open-Liberty server, and I'm wondering if there is a way to externalize the values of context-params (or filter init-params) from web.xml, like it is possible with the ${} syntax in server.xml or using mpConfig feature of eclipse microprofile.
  In the original project the param values were injected in web.xml at build time, using a placeholder substitution but, according to 12-factor 3rd recommendation, I would prefer to set this values outside software, in environment variables, for example.
  In my specific case I need to configure a servlet filter and a custom taglibrary with environment dependent param values.</p>
  
  <p>I already tried to use the ${} syntax in web.xml, but no luck: </p>
  
  <pre><code>...
    &lt;context-param&gt;
      &lt;param-name&gt;remincl.resource.provider&lt;/param-name&gt;
      &lt;param-value&gt;${remincl.resource.provider}&lt;/param-value&gt;
    &lt;/context-param&gt;
  ...
  </code></pre>
  
  <p>the runtime value of the context-param is: "${remincl.resource.provider}" instead of the actual value that is stored in an environment variable.</p>
  
  <p>I think JEE specs doesn't allow this behavior, but I would like to know if open-liberty offers some extra feature to solve this problem. Otherwise I must keep injecting values at build time (or change the configuration strategy of both filter and taglib).</p>