Fix bug when EventStream max LRU size is hit

Also fix an issue where re-added items aren't made newer in the LRU
cache.

Fixes #48.

Author: gcurtis

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

@@ -2,7 +2,6 @@
 
 import java.util.ArrayList;
 import java.util.Collection;
-import java.util.LinkedHashSet;
 
 import com.eclipsesource.json.JsonArray;
 import com.eclipsesource.json.JsonObject;
@@ -19,7 +18,6 @@
  */
 public class EventStream {
     private static final int LIMIT = 800;
-    private static final int LRU_SIZE = 512;
     private static final URLTemplate EVENT_URL = new URLTemplate("events?limit=" + LIMIT + "&stream_position=%s");
     private static final int STREAM_POSITION_NOW = -1;
 
@@ -28,7 +26,7 @@ public class EventStream {
     private final Collection<EventListener> listeners;
     private final Object listenerLock;
 
-    private LinkedHashSet<String> receivedEvents;
+    private LRUCache<String> receivedEvents;
     private boolean started;
     private Poller poller;
     private Thread pollerThread;
@@ -127,15 +125,10 @@ public void uncaughtException(Thread t, Throwable e) {
      */
     protected boolean isDuplicate(String eventID) {
         if (this.receivedEvents == null) {
-            this.receivedEvents = new LinkedHashSet<String>(LRU_SIZE);
+            this.receivedEvents = new LRUCache<String>();
         }
 
-        boolean newEvent = this.receivedEvents.add(eventID);
-        if (newEvent && this.receivedEvents.size() > LRU_SIZE) {
-            this.receivedEvents.iterator().remove();
-        }
-
-        return !newEvent;
+        return !this.receivedEvents.add(eventID);
     }
 
     private void notifyEvent(BoxEvent event) {

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

@@ -0,0 +1,29 @@
+package com.box.sdk;
+
+import java.util.Iterator;
+import java.util.LinkedHashSet;
+
+class LRUCache<E> {
+    static final int MAX_SIZE = 512;
+
+    private final LinkedHashSet<E> linkedHashSet;
+
+    public LRUCache() {
+        this.linkedHashSet = new LinkedHashSet<E>(MAX_SIZE);
+    }
+
+    boolean add(E item) {
+        boolean newItem = !this.linkedHashSet.remove(item);
+        if (newItem) {
+            this.linkedHashSet.add(item);
+        }
+
+        if (this.linkedHashSet.size() >= MAX_SIZE) {
+            Iterator<E> it = this.linkedHashSet.iterator();
+            it.next();
+            it.remove();
+        }
+
+        return newItem;
+    }
+}

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

@@ -0,0 +1,56 @@
+package com.box.sdk;
+
+import static org.hamcrest.Matchers.is;
+import static org.junit.Assert.assertThat;
+
+import org.junit.Test;
+import org.junit.experimental.categories.Category;
+
+public class LRUCacheTest {
+    @Test
+    @Category(UnitTest.class)
+    public void addReturnsTrueForNewItem() {
+        LRUCache<Integer> lru = new LRUCache<Integer>();
+        boolean added = lru.add(1);
+
+        assertThat(added, is(true));
+    }
+
+    @Test
+    @Category(UnitTest.class)
+    public void addReturnsFalseForExistingItem() {
+        LRUCache<Integer> lru = new LRUCache<Integer>();
+        lru.add(1);
+        boolean added = lru.add(1);
+
+        assertThat(added, is(false));
+    }
+
+    @Test
+    @Category(UnitTest.class)
+    public void addRemovesOldestItemWhenMaxSizeIsReached() {
+        LRUCache<Integer> lru = new LRUCache<Integer>();
+
+        for (int i = 0; i < LRUCache.MAX_SIZE + 1; i++) {
+            lru.add(i);
+        }
+
+        boolean added = lru.add(0);
+        assertThat(added, is(true));
+    }
+
+    @Test
+    @Category(UnitTest.class)
+    public void addMakesExistingItemNewer() {
+        LRUCache<Integer> lru = new LRUCache<Integer>();
+
+        for (int i = 0; i < LRUCache.MAX_SIZE; i++) {
+            lru.add(i);
+        }
+
+        lru.add(0);
+        lru.add(LRUCache.MAX_SIZE + 1);
+        boolean added = lru.add(1);
+        assertThat(added, is(true));
+    }
+}