• Illustrates using Facebook API within a Java Servlet
  
• Uses Facebook client class (FacebookJsonRestClient)
• Handles logon
• Uses Facebook Query Language (FQL) to get user name
• Add the application
• Download Source
• SocialJava Home

• Check to see whether the user is logged on.
• The presence of a session key parameter indicates whether or not the user is logged in.
• If the sessionKey is null, then the user is NOT logged in.
• If the user is not logged in, redirect to the login page. That is done by using an FBML redirect.
  

• Add Facebook Developer and create application See Hello Social Java World
• Get Most recent Project Jar Files (Open Source Facebook Client) Current facebook-java-api
• Facebook Java Client Library
• JSON Library
• Check Additional Requirements if using Java 5
• Get Background on REST client in Facebook (Blog Entry)

public class SocialJavaAPIIntroApp extends HttpServlet {

	//Application API Key and application secret from creating app in FB
	String appapikey = new String("00b0049fc7cf0d1e4a4ba2ea3e55b269"); //api key obtained after creating Facebook app
	String appsecret = new String("8ad8...api secret here..."); // api secret obtained after creating Facebook app

	//Facebook loginPage to this application.  Parameter canvas=true shows the result in Facebook canvas
	String loginPage = "http://www.facebook.com/login.php?api_key="+"00b0049fc7cf0d1e4a4ba2ea3e55b269"+"&v=1.0&canvas=true";
	FacebookJsonRestClient facebook;  // the facebook client, talks to REST Server
	PrintWriter servletOutput;  // output of servlet. HTML or FBML out

	public void doGet( HttpServletRequest req, HttpServletResponse res ) throws ServletException, IOException{
		servletOutput = res.getWriter(); // response is sent to ServletOutput
		res.setContentType( "text/html" );
		servletOutput.println("This is the doGet method");
	}

	public void doPost(HttpServletRequest req, 
			HttpServletResponse res) 
	throws ServletException, IOException {

		servletOutput = res.getWriter(); // response is sent to ServletOutput
		res.setContentType( "text/html" );
		servletOutput.println("This is the doPost method");
		servletOutput.println("<br>");

		String user =null;
		String sessionKey=null;
		sessionKey = req.getParameter(FacebookParam.SESSION_KEY.toString());  // Session Key passed as request parameter
		if (sessionKey==null) { // If there is not session key, they user not logged in
			servletOutput.println("");  // Facebook Redirect to login page
		}
		else{
			user = req.getParameter("fb_sig_user");  // get user as a string.  User info passed as request parameter
			servletOutput.println("User is " + user);  // displays numeric value
			servletOutput.println("<br>");
			facebook = new FacebookJsonRestClient(appapikey, appsecret,sessionKey);  // create Facebook Json Rest Client
			servletOutput.println("Facebook Client created");
			servletOutput.println("<br>");
			// with Facebook client created, now Facebook API calls can be made
			// In this case, a call to FQL to get username
			try{
				String query = "SELECT name FROM user WHERE uid=" + user;
				org.json.JSONArray resultArray = (org.json.JSONArray)facebook.fql_query(query); // query return an object.  Casting it as a String
				servletOutput.println("User Name is " + resultArray); 
			}
			catch( FacebookException ex )
			{
				servletOutput.println(">Error: Couldn't talk to Facebook> "  + ex );
			}
		} //else user is logged in
		servletOutput.close();
	}  // end doPost()
}