title: Add or remove an entry from a List type attribute in a DynamoDB table item
body: <p>I have a very simple class, with a string type primary key and List type attributes. I want to write an API for adding and removing an item from the attribute list, and saving the changes back to DDB.</p>
  <p>The simplest solution I can think of is:</p>
  <ol>
  <li>Read the list (if it exists)</li>
  <li>If it exists, remove or add the item from the List type attribute</li>
  <li>Put the modified object back</li>
  </ol>
  <p><em>Is there a cleaner/simpler way to do this via DynamoDB java API?</em></p>