Java oauh2 google get access token

import org.apache.http.HttpResponse;
import org.apache.http.NameValuePair;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.message.BasicNameValuePair;
import org.json.JSONException;
import org.json.JSONObject;
import org.json.simple.JSONValue;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.URLEncoder;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

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

         
            DefaultHttpClient httpClient = new DefaultHttpClient();
            HttpPost postRequest = new HttpPost(
                    "https://www.googleapis.com/oauth2/v4/token");
           
            List<NameValuePair> urlParameters = new ArrayList<NameValuePair>();
            urlParameters.add(new BasicNameValuePair("grant_type", "authorization_code"));
            urlParameters.add(new BasicNameValuePair("client_id", clientId));
            urlParameters.add(new BasicNameValuePair("client_secret", clientSecret));
            urlParameters.add(new BasicNameValuePair("code", code));
            urlParameters.add(new BasicNameValuePair("redirect_uri", redirectUri));
           
            postRequest.setEntity(new UrlEncodedFormEntity(urlParameters));
           
            HttpResponse response = httpClient.execute(postRequest);

            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();
          
            JSONObject jsonObject = new JSONObject(sb.toString());
            accessToken = jsonObject.getString("access_token");

            httpClient.getConnectionManager().shutdown();

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