title: map entry key reference to constant value
body: <p>By default I initialize map using <code>entry</code> for <code>Map</code> in xml like this</p>
  
  <pre><code>&lt;entry key="key"&gt;
      &lt;bean class="org.test.SimpleClass"/&gt;
  &lt;/entry&gt;
  </code></pre>
  
  <p>However I've got several constants in my another class</p>
  
  <pre><code>class MyClass {
       public static String KEY_VAL = "String";
  }
  </code></pre>
  
  <p>How to reference value <code>KEY_VAL</code> as <code>key</code> value for xml configuration?
  I know about <code>util</code> </p>
  
  <pre><code>&lt;util:constant static-field="org.test.MyClass.KEY_VAL" /&gt;
  </code></pre>
  
  <p>But how to apply it for <code>Map</code> entries?</p>