title: How to get value by key from JSON?
body: <p>JSON looks like:</p>
  
  <pre><code>{  
     "cover":"blabla.jpg",
     "content":[  
        {  
           "article":"article_text",
           "document":"document_text"
        }
     ]
  }
  </code></pre>
  
  <p>I know how to get <code>"cover"</code>:</p>
  
  <pre><code>JSONObject json = new JsonObject(jsonStr);
  json.get("cover");
  </code></pre>
  
  <p>But how can I get value by <code>"article"</code> key?</p>