title: Hex-encoded String to Byte Array
body: <pre><code>String str = "9B7D2C34A366BF890C730641E6CECF6F";
  </code></pre>
  
  <p>I want to convert <code>str</code> into byte array, but <code>str.getBytes()</code> returns 32 bytes instead of 16. </p>