title: JSON Representation of Map with Complex Key
body: <p>I want to serialize to JSON the following (java) data structure:</p>
  
  <pre><code>class Machine {
    String name;
    Map&lt;PartDescriptor, Part&gt; parts;
  }
  
  class PartDescriptor {
    String group;
    String id;
  
    hashCode()
    equals()
  }
  
  class Part {
    String group;
    String id;
    String description;
    String compat;
    ...
    ...
  }
  </code></pre>
  
  <p>What would be JSON representation of one <code>Machine</code>?</p>
  
  <p>Also (<em>optional</em>), point me to a JSON to Java serializer/deserializer that will support your representation</p>