title: @Produces @Consumes meaning ... JSON or it is just a String
body: <p>Suppose we have some RESTful resource serving this POST:</p>
  
  <pre><code>@POST
  @Produces("application/json")
  @Consumes("application/json")
  public String doPostJson(String string) {
      ...
  }
  </code></pre>
  
  <p>( I was able to run the above in my server so I am assuming this is a valid implementation )</p>
  
  <p>Now I am thinking the doPostJson() gets String and returns String. This string could be something totally different than JSON valid string. Am I right? So what is the meaning of "application/json" if I can use any string here?</p>
  
  <p>MORE:
  In other hand, could I just use this?</p>
  
  <pre><code>@POST
  @Produces("text/plain")
  @Consumes("text/plain")
  public String doPostJson(String string) {
      ... /* read passed parameter as JSON valid string and return JSON string */
  }
  </code></pre>