title: How to group List<Map<String,Object>> to Map<String,List<Map<String,Object>> in Java8
body: <p>I have a <code>List&lt;Map&lt;String,Object&gt;&gt;</code></p>
  
  <pre><code>[ {key1: object1a, key2: object2a, key3: object3a}, 
    {key1: object1a, key2: object2a, key3: object3a}, 
    {key1: object1b, key2: object2b, key3: object3b}, 
    {key1: object1b, key2: object2b, key3: object3b}, 
    ...
  ]
  </code></pre>
  
  <p>and I would like to group it by the third value, to obtain a <code>Map&lt;String,List&lt;Map&lt;String,Object&gt;&gt;&gt;</code>:</p>
  
  <pre><code>{ object3a: [ {key1: object1a, key2: object2a}, 
                {key1: object1a, key2: object2a}
              ],
    object3b: [ {key1: object1b, key2: object2b}, 
                {key1: object1b, key2: object2b}
              ],
    ...
  }
  </code></pre>
  
  <p>Is it possible by using the <a href="http://docs.oracle.com/javase/8/docs/api/java/util/stream/Collectors.html#groupingBy-java.util.function.Function-" rel="nofollow"><code>Collectors.groupingBy?</code></a> method, and how ?</p>