initial entry caching implementation

src/main/java/com/commafeed/backend/cache/CacheService.java

@@ -0,0 +1,31 @@
+package com.commafeed.backend.cache;
+
+import java.util.concurrent.TimeUnit;
+
+import com.commafeed.backend.model.Feed;
+import com.commafeed.backend.model.FeedEntry;
+import com.google.common.cache.Cache;
+import com.google.common.cache.CacheBuilder;
+
+public class CacheService {
+
+	Cache<String, Marker> entryCache = CacheBuilder.newBuilder()
+			.maximumSize(1000000).expireAfterWrite(24, TimeUnit.HOURS).build();
+
+	private static enum Marker {
+		INSTANCE
+	}
+
+	public boolean hasFeedEntry(Feed feed, FeedEntry entry) {
+		return entryCache.getIfPresent(buildKey(feed, entry)) == Marker.INSTANCE;
+	}
+
+	public void putFeedEntry(Feed feed, FeedEntry entry) {
+		entryCache.put(buildKey(feed, entry), Marker.INSTANCE);
+	}
+
+	private String buildKey(Feed feed, FeedEntry entry) {
+		return String.format("%s:%s:%s", feed.getId(), entry.getGuid(),
+				entry.getUrl());
+	}
+}