Facebook Login with OAuth Authentication Using Java

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This Java tutorial is to help implement authentication in Java using Facebook OAuth Login API. We will be using Java and a JSON parser API and other than that we will not use any third-party component. Facebook is not providing any sdk for Java client.

Apart from Spring Social I couldn’t find any reputable Java SDK for Facebook integration. With a Json parser we can handle everything ourselves. In this tutorial, we will see how to use Facebook to implement an authentication in a custom Java application and get Facebook profile data like name, email and gender.

Facebook Web Application


We need to create a web application in Facebook. After logging in to https://developers.facebook.com/ under Apps menu click “Create a New App”


Create-Facebook-Application

Facebook Application Settings

We need to specify the application callback url in the FB settings. This will be used by the FB server on authentication to hand back control to our application.


Facebook-Application-Settings

There is a lot of discussion about how Facebook will directly call our “localhost” as it will not be visible to it. Facebook will never call the application URL directly. A request will be sent back as response to the client browser with the callback url. The browser does the request. A sequence diagram given below explains the flow of control in authentication using Facebook OAuth.

Facebook OAuth Authentication Sequence Flow




  • On access of an url or in welcome page the Facebook Login button is shown. The user will click the FB button to login into the Java web application. On click of that button a Facebook URL will be invoked.
  • Facebook will validate the application ID and then will redirect to its login page.
  • User will enter the FB login credentials and submit the form.
  • Facebook will validate the credentials and then redirect back to the browser with a request to forward to the redirect_url. Redirect_url is the URL in our application which will take care of further processing.
  • Browser will call the redirect url.
  • Redirect URL page will again call the Facebook to request for access_token.
  • Facebook on validation success will respond back with access_token.
  • Redirect URL page will again call the Facebook to request for user data by sending the access_token.
  • Facebook on validating the access_token will respond back with user data requested.
  • Redirect URL page will forward to a page showing user data in the client browser.
  • Facebook Login Page


Screen shot shown in the start of this tutorial is the login page in our application and following is the code.
<%@page import="com.s2ptech.java.social.facebook.FBConnection"%>
<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
pageEncoding="ISO-8859-1"%>
<%
FBConnection fbConnection = new FBConnection();
%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>Java Facebook Login</title>
</head>
<body style="text-align: center; margin: 0 auto;">
<div
style="margin: 0 auto; background-image: url(./img/fbloginbckgrnd.jpg); height: 360px; width: 610px;">
<a href="<%=fbConnection.getFBAuthUrl()%>"> <img
style="margin-top: 138px;" src="./img/facebookloginbutton.png" />
</a>
</div>
</body>
</html>

Application redirect URL


Following is the page the Facebook issues a redirect request to the browser.

package com.s2ptech.java.social.facebook;
import java.io.IOException;
import java.util.Map;
import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class MainMenu extends HttpServlet {
private static final long serialVersionUID = 1L;
private String code="";
public void service(HttpServletRequest req, HttpServletResponse res)
throws ServletException, IOException { code = req.getParameter("code");
if (code == null || code.equals("")) {
throw new RuntimeException(
"ERROR: Didn't get code parameter in callback.");
}
FBConnection fbConnection = new FBConnection();
String accessToken = fbConnection.getAccessToken(code);
FBGraph fbGraph = new FBGraph(accessToken);
String graph = fbGraph.getFBGraph();
Map<String, String> fbProfileData = fbGraph.getGraphData(graph);
ServletOutputStream out = res.getOutputStream();
out.println("<h1>Facebook Login using Java</h1>");
out.println("<h2>Application Main Menu</h2>");
out.println("<div>Welcome "+fbProfileData.get("first_name"));
out.println("<div>Your Email: "+fbProfileData.get("email"));
out.println("<div>You are "+fbProfileData.get("gender")); }
}

Facebook Get Access Token

package com.s2ptech.java.social.facebook;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.UnsupportedEncodingException;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLConnection;
import java.net.URLEncoder;
public class FBConnection {
public static final String FB_APP_ID = "234231262685378";
public static final String FB_APP_SECRET = "y2a73dede3n49uid13502f5ab8cdt390";
public static final String REDIRECT_URI = "http://localhost:8080/Facebook_Login/fbhome";
static String accessToken = "";
public String getFBAuthUrl() {
String fbLoginUrl = "";
try {
fbLoginUrl = "http://www.facebook.com/dialog/oauth?" + "client_id="
+ FBConnection.FB_APP_ID + "&redirect_uri="
+ URLEncoder.encode(FBConnection.REDIRECT_URI, "UTF-8")
+ "&scope=email";
} catch (UnsupportedEncodingException e) {
e.printStackTrace();
}
return fbLoginUrl;
}
public String getFBGraphUrl(String code) {
String fbGraphUrl = "";
try {
fbGraphUrl = "https://graph.facebook.com/oauth/access_token?"
+ "client_id=" + FBConnection.FB_APP_ID + "&redirect_uri="
+ URLEncoder.encode(FBConnection.REDIRECT_URI, "UTF-8")
+ "&client_secret=" + FB_APP_SECRET + "&code=" + code;
} catch (UnsupportedEncodingException e) {
e.printStackTrace();
}
return fbGraphUrl;
}
public String getAccessToken(String code) {
if ("".equals(accessToken)) {
URL fbGraphURL;
try {
fbGraphURL = new URL(getFBGraphUrl(code));
} catch (MalformedURLException e) {
e.printStackTrace();
throw new RuntimeException("Invalid code received " + e);
}
URLConnection fbConnection;
StringBuffer b = null;
try {
fbConnection = fbGraphURL.openConnection();
BufferedReader in;
in = new BufferedReader(new InputStreamReader(
fbConnection.getInputStream()));
String inputLine;
b = new StringBuffer();
while ((inputLine = in.readLine()) != null)
b.append(inputLine + "\n");
in.close();
} catch (IOException e) {
e.printStackTrace();
throw new RuntimeException("Unable to connect with Facebook "
+ e);
}
accessToken = b.toString();
if (accessToken.startsWith("{")) {
throw new RuntimeException("ERROR: Access Token Invalid: "
+ accessToken);
}
}
return accessToken;
}
}

Access Facebook Graph Profile Data

package com.s2ptech.java.social.facebook;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.URL;
import java.net.URLConnection;
import java.util.HashMap;
import java.util.Map;
import org.json.JSONException;
import org.json.JSONObject;
public class FBGraph {
private String accessToken;
public FBGraph(String accessToken) {
this.accessToken = accessToken;
}
public String getFBGraph() {
String graph = null;
try {
String g = "https://graph.facebook.com/me?" + accessToken;
URL u = new URL(g);
URLConnection c = u.openConnection();
BufferedReader in = new BufferedReader(new InputStreamReader(
c.getInputStream()));
String inputLine;
StringBuffer b = new StringBuffer();
while ((inputLine = in.readLine()) != null)
b.append(inputLine + "\n");
in.close();
graph = b.toString();
System.out.println(graph);
} catch (Exception e) {
e.printStackTrace();
throw new RuntimeException("ERROR in getting FB graph data. " + e);
}
return graph;
}
public Map getGraphData(String fbGraph) {
Map fbProfile = new HashMap();
try {
JSONObject json = new JSONObject(fbGraph);
fbProfile.put("id", json.getString("id"));
fbProfile.put("first_name", json.getString("first_name"));
if (json.has("email"))
fbProfile.put("email", json.getString("email"));
if (json.has("gender"))
fbProfile.put("gender", json.getString("gender"));
} catch (JSONException e) {
e.printStackTrace();
throw new RuntimeException("ERROR in parsing FB graph data. " + e);
}
return fbProfile;
}
}

Facebook Authentication Success and Profile Data


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