title: spring rest controller with and without callable
body: <p>First I wrote simple spring REST controller</p>
  
  <pre><code> @RequestMapping(value = "/id", method = RequestMethod.GET)
      public String getDetails(@PathVariable("id") String id) {
         // wrote logic for JSON response....
  }
  </code></pre>
  
  <p>Second we need to improve the performance so I wrote controller using Callable like this</p>
  
  <pre><code>@RequestMapping(value = "/id", method = RequestMethod.GET)
          public String getDetails(@PathVariable("id") String id) {
            return new Callable&lt;String&gt;(){
            @Override
            public String call() throws Exception {
             // ...
            return "someJSONString";
           }
         }
      }
  </code></pre>
  
  <p>Now the problem is when I compare the performance using JMETER for both above methods I dont see any major differences.</p>
  
  <p>So do I miss anything while writing Callable controller?</p>