ResponsEntity, how to obtain the body in html

I want to show in browser the body of a ResponsEntity returned by a Controller (using Spring):

return new ResponseEntity<>(l.getReachableDate(), HttpStatus.NOT_FOUND);

l.getReachableDate() returns a Date type, and I want to show it in a way like:

<header> <h1><span>Url is not reachable from</span> <!-- body --> </h1> </header>

How can I get it shown?