Java facebook oauth2 get access token

 private static final String ACCESS_TOKEN_URL = "https://graph.facebook.com/oauth/access_token?client_id=%s&redirect_uri=%s&client_secret=%s&code=%s";

private String getAccessToken(String code, String clientId, String clientSecret,  
                String redirectUri,
                HttpServletResponse hsr) throws Exception {
        String accessToken = "";
        try {

            DefaultHttpClient httpClient = new DefaultHttpClient();
            HttpGet getRequest = new HttpGet(String.format(ACCESS_TOKEN_URL, clientId,
                    URLEncoder.encode(redirectUri, "UTF-8"), clientSecret, code));
            getRequest.addHeader("oauth2_access_token", code);
            HttpResponse response = httpClient.execute(getRequest);

            if (response.getStatusLine().getStatusCode() != 200) {
                          throw new Exception("Failed : HTTP error code : " + response.getStatusLine().getStatusCode());
            }
            BufferedReader br = new BufferedReader(new InputStreamReader(response.getEntity().getContent()));

            StringBuilder sb = new StringBuilder();
            String output;

            while ((output = br.readLine()) != null) {
                sb.append(output);
            }
            br.close();
           
            accessToken = sb.toString();

            httpClient.getConnectionManager().shutdown();

        } catch (IOException e) {
                    }
        return accessToken;
    }