title: Create and Invert MultiMap w/ Java 8 Streams
body: <p>How can I convert a <code>Set&lt;Result&gt;</code> into a <code>Map&lt;Item, Set&lt;String&gt;&gt;</code> or <code>SetMultimap&lt;Item, String&gt;</code> using Java 8 streams or Multimaps, where <code>Result</code> is:</p>
  
  <pre><code>class Result {
      String name;
      Set&lt;Item&gt; items;
  }
  </code></pre>
  
  <p>For example, I start with:</p>
  
  <pre><code>result1:
      name: name1
      items:
          - item1
          - item2
  result2:
      name: name2
      items:
          - item2
          - item3
  </code></pre>
  
  <p>and end with:</p>
  
  <pre><code>item1:
      - name1
  item2:
      - name1
      - name2
  item3:
      - name2
  </code></pre>