In order to access Google API you to have an Application registered with <a href="https://code.google.com/apis/console" target="_blank" 

class="news_link" title="Google API console">Google API console</a>. The registration gives you client_id, client_secret, and an 

API key. You also have to define at least one redirect_url. 



Web server flow authentication is a two part process. Getting a code and requesting for an access_token in exchange for the code. 


<h3>
The Code
</h3>

The process starts by requesting an authorization URL from Google Authorization server. This is accomplished by using the following snippet.




<pre class="brush: java; highlight:7">
public String getCode() {

 final String scope = "https://www.googleapis.com/auth/latitude.current.best";
 final String redirect_url = "https://kahimyang.com/kauswagan/Latitude.xhtml";
 final String client_id = "YOUR_CLIENT_ID";

 authorizeUrl = new GoogleAuthorizationRequestUrl(client_id,
 redirect_url, scope).build();

 return authorizeUrl;

}

</pre>



The JSF markup that calls the bean method shown above.



<pre class="brush: xml">
&lt;h:outputLink value="#{myBean.code}">
 &lt;h:outputText value="Latitude" />
&lt;/h:outputLink>
</pre>



<ul>
<li>
redirect_url should be defined in the redirect URL of your Applications' API Access settings at the Google API console.
</li>
<li>
client_id is your Application client_id also from Google API console. 
</li>

<li>
scope for Google Latitude is <a href="http://code.google.com/apis/latitude/v1/using_rest.html#WorkingCurrentLocation" 

target="_blank" class="news_link" title="Google Latitude docs">well documented in this page</a>.
</li>



<li>
authorizeUrl will yield a screen like below. 
</li>
</ul>


If not already logged in, the user is presented with a login page before the authorization page like the one shown below is shown to the user.




<img loading="lazy" src="https://cdn.kahimyang.com/resources/gauth.png" />




User action takes us to the redirect_url. A code parameter is added to the request of the 

redirect_url if the user clicked on "Allow access" (granted permission) to your Application or an 

error if the user clicked on "No thanks". 


<h3>
The Access Token
</h3>


The following method is part of the backing bean of the redirect_url.



<pre class="brush: java; highlight:50">
String location;
String accessToken;
AccessTokenResponse authResponse;

public String getLocation() {
 return location;
}

@PostConstruct
void init () {
 FacesContext context = FacesContext.getCurrentInstance();
 HttpServletRequest request = 
 (HttpServletRequest) context.getExternalContext().getRequest(); 

 String error = request.getParameter("error");
 // do something about the error.

 final String authorizationCode = request.getParameter("code");


 final String redirect_url = "https://kahimyang.com/kauswagan/Latitude.xhtml";
 final String CLIENT_ID = "APP_CLIENT_ID";
 final String CLIENT_SECRET = "YOUR_APP_SECRET";

 HttpTransport transport = new NetHttpTransport();
 JsonFactory json_factory = new JacksonFactory();


 try {

 // Exchange for an access and refresh token
 GoogleAuthorizationCodeGrant authRequest = 
 new GoogleAuthorizationCodeGrant(transport,
 json_factory, CLIENT_ID, CLIENT_SECRET, 
 authorizationCode, redirect_url);

 authRequest.useBasicAuthorization = false;

 authResponse = authRequest.execute();
 accessToken = authResponse.accessToken;

 // At this point we already have an access Token

 GoogleAccessProtectedResource access = 
 new GoogleAccessProtectedResource(accessToken,
 transport, json_factory, CLIENT_ID, CLIENT_SECRET, 
 authResponse.refreshToken);
 HttpRequestFactory rf = transport.createRequestFactory(access);

 final String ep = "https://www.googleapis.com/latitude/v1/currentLocation";

 GenericUrl gurl = new GenericUrl(ep);

 HttpRequest lreq = rf.buildGetRequest(gurl);
 lreq.setEnableGZipContent(false);

 HttpResponse lresp = lreq.execute();
 BufferedReader instream = 
 new BufferedReader(new InputStreamReader(lresp.getContent()));

 StringBuilder respData = new StringBuilder();

 String line;
 while ((line = instream.readLine()) != null) {
 respData.append(line);
 }

 Map&lt;String, Map&lt;String, Object>> gsonData = new LinkedHashMap();
 com.google.gson.Gson gs = new com.google.gson.Gson();
 gsonData = gs.fromJson(respData.toString(), gsonData.getClass());
 Map&lt;String, Object> data = (Map&lt;String, Object>) gsonData.get("data");
 String kind = (String) data.get("kind");
 if (kind.contains("latitude")) {
 Double lat = (Double) data.get("latitude");
 Double longi = (Double) data.get("longitude");
 //String timestamp = (String)data.get("timestamp");
 location = lat.toString() + "," + longi.toString();
 }
 

 } catch (Exception e) {
 // Log error
 location = "not found";
 }
}
</pre>



Line 50 highlighted above is the end point URL which varies depending on the requested SCOPE. Please see the link that follows for more on latitude scopes. <a href="http://code.google.com/p/google-api-java-

client/wiki/APIs#Google_Latitude_API" target="_blank" class="news_link" title="API and can be found here">See downloads and documentation here</a>.



<a href="http://code.google.com/p/google-api-java-client/downloads/list" class="news_link" target="_blank" title="google-api-java-

client">google-api-java-client</a> is used this this blog. 




That's it. Good luck.

How to use Google implementation of OAuth 2.0 protocol to Access its APIs, Google Latitude example