title: Multiple key map and partial query
body: <p>I search map implementation with multiple key. I know <a href="http://commons.apache.org/collections/apidocs/org/apache/commons/collections/map/MultiKeyMap.html" rel="nofollow">Apache Commons</a> but it dosen't satisfy me.</p>
  
  <p>I want to be able to pass one key and get all entries which contain the passed key, e.g.</p>
  
  <pre><code>MultiKeyMap mkm = new MultiKeyMap();
  mkm.put("key1", "key2", "key3", "1");
  mkm.put("key1", "key22", "key33", "2");
  mkm.put("key12", "key22", "key32", "3");
  
  mkm.get("key1");
  </code></pre>
  
  <p>returns null but in this case I want to get "1" and "2"
  My own implementation is not an option. I want to use something which I can trust.</p>