Allow EventListeners to handle exceptions

Any uncaught exceptions on the EventStream's polling thread will be sent
to the EventStream listeners through the onException(Throwable e)
method. The exception will be sent to each listener (in the order in
which they were added) until one of them returns true, indicating that
the exception was handled.

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

@@ -2,4 +2,6 @@
 
 public interface EventListener {
     void onEvent(BoxEvent event);
+
+    boolean onException(Throwable e);
 }

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

@@ -54,7 +54,13 @@ public void start() {
         final long initialPosition = jsonObject.get("next_stream_position").asLong();
         this.poller = new Poller(initialPosition);
 
-        new Thread(this.poller).start();
+        Thread pollerThread = new Thread(this.poller);
+        pollerThread.setUncaughtExceptionHandler(new Thread.UncaughtExceptionHandler() {
+            public void uncaughtException(Thread t, Throwable e) {
+                EventStream.this.notifyException(e);
+            }
+        });
+        pollerThread.start();
 
         this.started = true;
     }
@@ -74,6 +80,17 @@ private void notifyListeners(BoxEvent event) {
         }
     }
 
+    private void notifyException(Throwable e) {
+        this.stop();
+        synchronized (this.listenerLock) {
+            for (EventListener listener : this.listeners) {
+                if (listener.onException(e)) {
+                    return;
+                }
+            }
+        }
+    }
+
     private class Poller implements Runnable {
         private final long initialPosition;
         private final Object setServerLock;

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

@@ -21,6 +21,10 @@ public void receiveEventsForFolderCreateAndFolderDelete() throws InterruptedExce
             public void onEvent(BoxEvent event) {
                 observedEvents.add(event);
             }
+
+            public boolean onException(Throwable e) {
+                return true;
+            }
         });
         stream.start();