title: How extract all the json content as a attribute in NiFi
body: <p>I have some flowfiles and their contents are json like this:</p>
  <pre><code>{&quot;Message&quot;: &quot;...&quot;, &quot;Id&quot;:&quot;122&quot;, &quot;Size&quot;:&quot;123&quot;}
  </code></pre>
  <p>I would like to extract this whole json as an attribute in flowfile.</p>
  <p>How to achieve it?</p>