title: How to achieve this Map<String, List<>> structure
body: <p>I have data like below:</p>
  
  <pre><code> Key       value
  -----      ------
  car         toyota
  car         bmw
  car         honda
  
  fruit       apple
  fruit       banana
  
  computer    acer
  computer    asus
  computer    ibm 
  ...
  </code></pre>
  
  <p>(Each row of above data is an <strong>object</strong> with fields "key" and "value", all in one List <code>List&lt;DataObject&gt;</code>)</p>
  
  <p>I would like to construct the data to a <code>Map&lt;String, List&lt;String&gt;&gt;</code> like following:</p>
  
  <pre><code> "car"      : ["toyota", "bmw", "honda"]
   "fruit"    : ["apple","banana"]
   "computer" : ["acer","asus","ibm"]
  </code></pre>
  
  <p>How to achieve above <code>Map</code> structure from the data objects?</p>
  
  <p><em><strong></em>**<em>*</em>***</strong><em>Besides</em><strong><em>*</em>**<em>*</em>**</strong></p>
  
  <p>I am more interested in using pure JDK provided classes or interfaces to achieve the result instead of using external library. Any help?</p>