Best way to create a json

HI,
In my spring mvc application i am creating a json like :

 @RequestMapping(value = "/snippets", method = RequestMethod.POST)
    public void createSnippet(@RequestBody String jsonString, HttpServletResponse response, HttpServletRequest request) throws IOException {
        Snippet snippet = new ObjectMapper().readValue(jsonString, Snippet.class);
        String uuid = snippetDao.insertData(snippet);
        response.addHeader("Location", "http://" + request.getHeader("Host") + "/snippets/" + uuid);
        response.setStatus(201);
        response.setContentType("application/json");
        response.setCharacterEncoding("UTF-8");
        String snippetURL = snippetURL(uuid, "/raw");
        String filename = snippetFilename(snippet.getTitle(), snippet.getMode());
        int size = snippet.getText().length();
        String json = "{\"download\" : {\"URL\": \""+snippetURL+"\",\"filename\":\""+filename+"\",\"size\":"+size+"}}";
        response.getWriter().write(json);
    }

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In the above code this is the line i am talking about :        String json = "{\"download\" : {\"URL\": \""+snippetURL+"\",\"filename\":\""+filename+"\",\"size\":"+size+"}}";
Althouth its just one line... but wondering if there is a better way to write this ?
Also in the line        response.getWriter().write(json);
Now this json is referred in the ajax call in the javascript code... So i am passing it this way... Please
comment on this... if this is a correct way to do this ?
This code is in controller... Should this be better moved to service ?
Thanks