title: Return JSON for ResponseEntity<String>
body: <p>I have a method in my controller that should returns a String in JSON. It returns JSON for non primitive types:</p>
  
  <pre class="lang-java prettyprint-override"><code>@RequestMapping(value = "so", method = RequestMethod.GET, produces = MediaType.APPLICATION_JSON_VALUE)
  ResponseEntity&lt;String&gt; so() {
      return new ResponseEntity&lt;String&gt;("This is a String", HttpStatus.OK);
  }
  </code></pre>
  
  <p>The curl response is:</p>
  
  <pre><code>This is a String
  </code></pre>