title: JSON File - Java: editing/updating fields values
body: <p>I have some JSONObject(s) in my workflow, and the same JSONObjects are stored by writting them into a json file.</p>
  
  <p>I would like an efficient way to update the json file, <strong>only fields where is needed</strong>, with the content of newer JSONObjects instances.</p>
  
  <p>Eg:</p>
  
  <p>On file I have</p>
  
  <pre><code>ObjectOnFile = {key1:val1, key2:val2,...}
  </code></pre>
  
  <p>In memory I have </p>
  
  <pre><code>ObjectInMemory = {key1:val1_newer, key2:val2_newer,...}
  </code></pre>
  
  <p>The update will be like: </p>
  
  <pre><code> if (!(ObjectInMemory.get(key1).equals(ObjectOnFile.get(key1)))
         // update file field value &lt;--- how to?
  </code></pre>
  
  <p>In general I would like to update the value of every key where its content is newer (different).</p>
  
  <p>Actually my code is:</p>
  
  <pre><code>import org.json.JSONObject;
  import com.fasterxml.jackson.databind.ObjectMapper;
  
  ObjectMapper mapper = new ObjectMapper();
  Sting key = "key1"; //whatever
  JSONObject jo = new JSONObject("{key1:\"val1\", key2:\"val2\"}");
  JSONObject root = mapper.readValue(new File(json_file), JSONObject.class);
  JSONObject val_newer = jo.getJSONObject(key);
  JSONObject val_older = root.getJSObject(key);
  if(!val_newer.equals(val_older)){
     root.put(key,val_newer);
  /*write back root to the json file...how? */
  }
  </code></pre>