Added event listener for stream position changes

Author: Tanooj Luthra

src/main/java/com/box/sdk/EventListener.java

@@ -10,6 +10,12 @@ public interface EventListener {
      */
     void onEvent(BoxEvent event);
 
+    /**
+     * Invoked when an updated stream position is received from the API.
+     * @param position of the stream.
+     */
+    void onNextPosition(long position);
+
     /**
      * Invoked when an error occurs while waiting for events to be received.
      *

src/main/java/com/box/sdk/EventStream.java

@@ -131,6 +131,14 @@ protected boolean isDuplicate(String eventID) {
         return !this.receivedEvents.add(eventID);
     }
 
+    private void notifyNextPosition(long position) {
+        synchronized (this.listenerLock) {
+            for (EventListener listener : this.listeners) {
+                listener.onNextPosition(position);
+            }
+        }
+    }
+
     private void notifyEvent(BoxEvent event) {
         synchronized (this.listenerLock) {
             boolean isDuplicate = this.isDuplicate(event.getID());
@@ -184,12 +192,13 @@ public void run() {
                         EVENT_URL.build(EventStream.this.api.getBaseURL(), position), "GET");
                     BoxJSONResponse response = (BoxJSONResponse) request.send();
                     JsonObject jsonObject = JsonObject.readFrom(response.getJSON());
-                    position = jsonObject.get("next_stream_position").asLong();
                     JsonArray entriesArray = jsonObject.get("entries").asArray();
                     for (JsonValue entry : entriesArray) {
                         BoxEvent event = new BoxEvent(EventStream.this.api, entry.asObject());
                         EventStream.this.notifyEvent(event);
                     }
+                    position = jsonObject.get("next_stream_position").asLong();
+                    EventStream.this.notifyNextPosition(position);
                 }
             }
         }

src/test/java/com/box/sdk/EventStreamTest.java

@@ -33,10 +33,17 @@ public void receiveEventsForFolderCreateAndFolderDelete() throws InterruptedExce
         BoxAPIConnection api = new BoxAPIConnection(TestConfig.getAccessToken());
         EventStream stream = new EventStream(api);
         stream.addListener(new EventListener() {
+            @Override
             public void onEvent(BoxEvent event) {
                 observedEvents.add(event);
             }
 
+            @Override
+            public void onNextPosition(long position) {
+                return;
+            }
+
+            @Override
             public boolean onException(Throwable e) {
                 return true;
             }