junlapong · January 28, 2022 10:32 · Jan 20, 2015 · Jan 20, 2015
diff --git a/DefaultListener → DefaultListener.java b/DefaultListener → DefaultListener.java
diff --git a/NotificationChannel → NotificationChannel.java b/NotificationChannel → NotificationChannel.java
diff --git a/NotificationEvent → NotificationEvent.java b/NotificationEvent → NotificationEvent.java
diff --git a/NotificationListener → NotificationListener.java b/NotificationListener → NotificationListener.java
diff --git a/DefaultListener b/DefaultListener
@@ -0,0 +1,3 @@
+public interface DefaultListener {
+	public void onNotification(NotificationEvent event);
+}
diff --git a/NotificationChannel b/NotificationChannel
@@ -0,0 +1,80 @@
+import java.io.IOException;
+import java.io.PrintWriter;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.ConcurrentMap;
+
+import javax.inject.Inject;
+import javax.servlet.AsyncContext;
+import javax.servlet.ServletException;
+import javax.servlet.annotation.WebServlet;
+import javax.servlet.http.HttpServlet;
+import javax.servlet.http.HttpServletRequest;
+import javax.servlet.http.HttpServletResponse;
+
+@WebServlet(urlPatterns = {"/notify"}, asyncSupported = true)
+public class NotificationChannel extends HttpServlet implements DefaultListener{
+	private static final long serialVersionUID = -2827663265593547983L;
+	private ConcurrentMap<String, AsyncContext> contexts = new ConcurrentHashMap<>();
+	@Inject
+	NotificationListener listener;
+
+	@Override
+	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException{
+		//initialize for server-sent events
+		response.setContentType("text/event-stream");
+		response.setCharacterEncoding("UTF-8");
+
+		final String userId = request.getParameter("userId"); //retrieve the user Id
+		if (userId == null){
+			response.sendError(HttpServletResponse.SC_BAD_REQUEST);
+			return;
+		}
+
+		//to clear threads and allow for asynchronous execution
+		final AsyncContext asyncContext = request.startAsync(request, response);
+		asyncContext.setTimeout(0); 
+
+		//add context to list for later use
+		if (contexts == null || contexts.isEmpty() || !contexts.containsKey(userId)){
+			if (contexts == null){
+				contexts = new ConcurrentHashMap<String, AsyncContext>();
+			}
+			contexts.put(userId, asyncContext);
+		}
+
+		listener.addListener(this);	
+		sendNotification(userId, "connected");
+	}
+
+	protected void sendNotification(String userId, String notification){
+		try{
+			if(contexts.containsKey(userId)){
+				AsyncContext asyncContext = contexts.get(userId);
+				PrintWriter writer = asyncContext.getResponse().getWriter();
+				writer.write("data: " + notification + "\n\n");
+				writer.flush();
+			}
+		}catch (Exception e){
+			e.printStackTrace();
+			//try again before disconnecting the user
+			try{
+				if(contexts.containsKey(userId)){
+					AsyncContext asyncContext = contexts.get(userId);
+					PrintWriter writer = asyncContext.getResponse().getWriter();
+					writer.write("data: " + notification + "\n\n");
+					writer.flush();
+				}
+			}catch (Exception e2){
+				e2.printStackTrace();
+				AsyncContext asyncContext = contexts.remove(userId);
+				asyncContext.complete();
+			}
+		}
+	}
+
+	@Override
+	public void onNotification(NotificationEvent event) {
+		this.sendNotification(event.getUserId(), event.getJSONEvent());
+	}
+
+}
diff --git a/NotificationEvent b/NotificationEvent
@@ -0,0 +1,44 @@
+import org.json.JSONException;
+import org.json.JSONObject;
+
+public class NotificationEvent {
+	private String type;
+	private String message;
+	private String toUserId;
+
+	public NotificationEvent(String type, String message, String toUserId){
+		this.type = type;
+		this.message = message;
+		this.toUserId = toUserId;
+	}
+
+	public NotificationEvent(String type, String toUserId){
+		this.type = type;
+		this.message = "";
+		this.toUserId = toUserId;
+	}
+
+	public String getType(){
+		return this.type;
+	}
+
+	public String getMessage(){
+		return this.message;
+	}
+
+	public String getUserId(){
+		return this.toUserId;
+	}
+
+	public String getJSONEvent(){
+		JSONObject obj = new JSONObject();
+		try {
+			obj.put("type", type);
+			obj.put("message", message);
+		} catch (JSONException e) {
+			e.printStackTrace();
+		}
+		return obj.toString();
+	}
+
+}
diff --git a/NotificationListener b/NotificationListener
@@ -0,0 +1,33 @@
+import java.util.ArrayList;
+import java.util.List;
+
+import javax.ejb.Asynchronous;
+import javax.ejb.Stateful;
+import javax.enterprise.context.ApplicationScoped;
+import javax.enterprise.event.Observes;
+
+@Stateful
+@ApplicationScoped
+public class NotificationListener {
+
+	List<DefaultListener> listeners = new ArrayList<>();
+
+	public void addListener(DefaultListener l){
+		listeners.add(l);
+	}
+
+	@Asynchronous
+	public void listenForNotifications(@Observes NotificationEvent event){
+		//this method is called by the container whenever a NotificationEvent is fired
+		for (DefaultListener l : listeners){
+			l.onNotification(event);
+		}
+	}
+
+	@Asynchronous
+	public void checkForUpdates(String userId){
+		//manually check the database for updates
+
+	}
+
+}
diff --git a/notify.js b/notify.js
@@ -0,0 +1,14 @@
+(function(){
+	console.log("notify.js");
+	var eventSource = new EventSource("notify?userId=123456");//need a way to access userId from server, then apply it here
+	eventSource.onopen = function(e){
+		console.log("Connection Opened");
+	};
+	eventSource.onmessage = function(e){
+		console.log("Message: " + e.data);
+	};
+	eventSource.onerror = function(e){
+		console.log("Error");
+	};
+
+})();
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