code: public static boolean mayBeJSON( String string ) {
        return string != null
              && ("null".equals( string )
                    || (string.startsWith( "[" ) && string.endsWith( "]" )) || (string.startsWith( "{" ) && string.endsWith( "}" )));
     }
docs: Tests if the String possibly represents a valid JSON String.<br>
  Valid JSON strings are:
  <ul>
  <li>"null"</li>
  <li>starts with "[" and ends with "]"</li>
  <li>starts with "{" and ends with "}"</li>
  </ul>